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Published for SISSA by Springer

Received: February 11, 2013

Accepted: March 21, 2013

Published: April 11, 2013

Study of the underlying event at forward rapidity in

pp collisions at
√
s = 0.9, 2.76, and 7TeV

The CMS collaboration

E-mail: cms-publication-committee-chair@cern.ch

Abstract: The underlying event activity in proton-proton collisions at forward pseudo-

rapidity (−6.6 < η < −5.2) is studied with the CMS detector at the LHC, using a novel

observable: the ratio of the forward energy density, dE/dη, for events with a charged-

particle jet produced at central pseudorapidity (|ηjet| < 2) to the forward energy density

for inclusive events. This forward energy density ratio is measured as a function of the cen-

tral jet transverse momentum, pT, at three different pp centre-of-mass energies (
√
s = 0.9,

2.76, and 7 TeV). In addition, the
√
s evolution of the forward energy density is studied

in inclusive events and in events with a central jet. The results are compared to those of

Monte Carlo event generators for pp collisions and are discussed in terms of the underly-

ing event. Whereas the dependence of the forward energy density ratio on jet pT at each√
s separately can be well reproduced by some models, all models fail to simultaneously

describe the increase of the forward energy density with
√
s in both inclusive events and

in events with a central jet.

Keywords: Hadron-Hadron Scattering

ArXiv ePrint: 1302.2394

Open Access, Copyright CERN,

for the benefit of the CMS collaboration

doi:10.1007/JHEP04(2013)072

mailto:cms-publication-committee-chair@cern.ch
http://arxiv.org/abs/1302.2394
http://dx.doi.org/10.1007/JHEP04(2013)072


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Contents

1 Introduction 1

2 Phenomenology of the underlying event 2

3 Monte Carlo models 4

4 The CMS detector 5

5 Event selection and reconstruction 6

6 Data correction 7

7 Systematic uncertainties 8

8 Results 10

9 Summary 14

The CMS collaboration 19

1 Introduction

Particle production in soft, nondiffractive inelastic collisions between hadrons is character-

ized by a particle density that is uniform in rapidity within a rapidity range proportional to

ln s, where
√
s is the centre-of-mass energy of the collision (see, e.g. [1, 2]). The particle den-

sity and the average momentum per particle slowly increase with s, and, as a consequence,

the energy density per unit of rapidity is expected to show an approximately logarith-

mic increase with s [3].

This picture changes when a hard scattering occurs in the collision, resulting in two

back-to-back, large transverse-momentum (pT) jets. These are accompanied by hadronic

activity due to initial- and final-state parton showers. In the commonly used DGLAP

approach [4–7], the transverse momentum kT of these parton showers increases as their

rapidity approaches the rapidity of the partons emerging from the hard interaction. Al-

ternative models for parton dynamics, such as BFKL [8–10] or CCFM [11–14], however,

also allow large-kT parton emissions far away from the hard scatter, thus yielding a larger

energy density at rapidities well separated from the high-pT jets. Additionally, the incom-

ing particle remnants may re-scatter and fragment, thereby producing a final state similar

to that of soft collisions. Parton showers and remnant interactions form the so-called

underlying event.

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Previous studies [15–19] typically separate hadronic activity due to the underlying

event from activity resulting from the hard scattering by dividing the azimuthal plane

into the so-called toward, transverse, and away regions with respect to the direction of

the highest-pT jet. The hadronic activity in the transverse region is then assumed to be

dominated by the underlying event, while the toward and away regions are also populated

by the jets. A complementary method, followed in this paper, consists of studying the

hadronic activity in a region far away in rapidity from the hard-scattering products. The

toward, transverse, and away regions are then all dominated by the underlying event.

In the present paper, the underlying event activity is studied at forward pseudorapidity

(−6.6 < η < −5.2) in a novel way by measuring the ratio of the forward energy density per

unit of pseudorapidity for events with a charged-particle jet produced at central pseudo-

rapidity (|ηjet| < 2) to the forward energy density for inclusive, dominantly nondiffractive,

events. This energy density ratio is measured as a function of the jet transverse momen-

tum at three different proton-proton centre-of-mass energies (
√
s = 0.9, 2.76, and 7 TeV).

In addition, the relative increase of the forward energy density as a function of centre-of-

mass energy is presented for inclusive events and for events with a central charged-particle

jet. This extends the study of the forward energy density in the pseudorapidity range

3 < |η| < 5 published in [20] to a previously unexplored region.

The paper is structured as follows. A discussion of the phenomenology of the underly-

ing event is given in section 2. Monte Carlo (MC) simulation programs used to correct data

for detector effects and to compare models to corrected data are discussed in section 3.

Section 4 gives a short description of the CMS detector. The analysis is discussed in sec-

tions 5 and 6. Section 7 describes the investigation of systematic uncertainties. Results

are discussed in section 8 and a summary is given in section 9.

2 Phenomenology of the underlying event

One theoretical framework used to describe the underlying event is the multiple-parton

interaction (MPI) model, which assumes that parton interactions occur in addition to the

primary hard scattering. These additional interactions are softer than the primary one,

but still perturbatively calculable.

The requirement of jets in the final state selects, on average, collisions with a smaller

impact parameter [21, 22]. In the MPI model as implemented in pythia 6 [23], this

correlation is realised by a suppression factor of low-pT parton interactions at small impact

parameter. Such central collisions have a larger overlap of the matter distributions of the

colliding hadrons and are therefore more likely to have many parton interactions. The

comparison of particle and energy densities between events with hard jets in the final

state and inclusive events thus yields information on underlying events with many parton

interactions relative to those with few of them.

Figure 1 shows the result of a simulation based on the D6T underlying event tune [24,

25] of the pythia 6 generator. Although it is not the best tune to describe early measure-

ments of the underlying event activity at the Large Hadron Collider (LHC), this tune is

used here because it yields a large number of MPIs, which results in an enhanced effect

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­1

 [
G

e
V

]
η

 /
 d

 i
n

c
l

d
E

200

400

600

(a)CMS Simulation

PYTHIA6 D6T

PYTHIA6 D6T no MPI

 < −5.2η−6.6 < 

­1

 [
G

e
V

]
η

 /
 d

 h
a

rd
d

E

200

400

600

(b)

>10 GeV/c
T

pPYTHIA6 D6T, 

>10 GeV/c
T

pPYTHIA6 D6T no MPI, 

>25 GeV/c
T

pPYTHIA6 D6T, 

 [TeV]s

0.7 1 2 3 4 5 6 7 8 9 10

)
η

 /
 d

 i
n

c
l

)/
(d

E
η

 /
 d

 h
a
rd

(d
E

0

0.5

1

1.5

2

(c)
>10 GeV/c

T
pPYTHIA6 D6T, 

>10 GeV/c
T

pPYTHIA6 D6T no MPI, 

>25 GeV/c
T

pPYTHIA6 D6T, 

Figure 1. The energy density dE/dη in the pseudorapidity region −6.6 < η < −5.2, obtained with

pythia 6 D6T, is plotted as a function of
√
s, for inclusive, nondiffractive events (a) and for events

with a central (|η| < 2) hard parton interaction with transverse momentum transfer, p̂T, above a

given threshold (b). The ratios of the plots in (a) and (b) are shown in (c).

on the forward energy density. Other tunes show a similar, albeit somewhat reduced, be-

haviour. Figure 1a shows the energy density, dE/dη, for −6.6 < η < −5.2, as a function

of
√
s for inclusive events. Figure 1b shows the energy density for events with a central

(|η| < 2) hard parton interaction with transverse momentum transfer, p̂T, above 10 or

25 GeV/c. Finally, figure 1c shows the ratio of these two distributions, henceforward called

the “hard-to-inclusive forward energy ratio”.

It can be seen that the energy density in inclusive events is only slightly affected by the

presence of MPIs. This is not the case in events with a hard parton interaction at large
√
s,

where a large increase of the energy density is predicted when including MPIs. Moreover,

this increase is roughly independent of p̂T, indicating that collisions are already central for

p̂T > 10 GeV/c. Finally, the hard-to-inclusive forward energy ratio would be close to unity

in the absence of MPIs. With MPIs, however, the ratio is substantially higher than 1 at

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large
√
s, while it drops below 1 at small

√
s. This last observation points to a depletion of

the energy of the proton remnant in events with hard central jets. Indeed, at
√
s = 0.9TeV,

the proton remnant has a rapidity y = ln (
√
s/mp) ≈ 7 where mp is the proton rest mass.

At this centre-of-mass energy, the energy density in the considered pseudorapidity range is

thus sensitive to the details of remnant fragmentation.

3 Monte Carlo models

In this section, the main features of the Monte Carlo models used in the analysis are

presented, with emphasis on the implementation and tuning of the underlying event.

Several tunes of the pythia 6 (version 6.424) [23] and pythia 8 (version 8.145) [26]

event generators are used, each providing a different description of the underlying event

in nondiffractive interactions: D6T [24, 25], Z2 [18] and Z2* for pythia 6 and 4C [27] for

pythia 8. The parameter settings in D6T were determined from the Tevatron data, while

the other tunes were determined from the LHC data on inclusive and underlying event

properties at central pseudorapidity. The more recent pythia 6 Z2 and Z2* tunes, as well

as pythia 8, use a new model [28] where multiple-parton interactions are interleaved with

parton showering. The Z2 and Z2* tunes are derived from the Z1 tune [29], which uses the

CTEQ5L parton distribution set, whereas Z2 and Z2* adopt CTEQ6L. The Z2* tune is

the result of retuning the pythia 6 parameters PARP(82) and PARP(90) by means of the

automated Professor tool [30], yielding PARP(82)=1.921 and PARP(90)=0.227. The re-

sults of this study are also compared to predictions obtained with pythia 6, tune Z2*, with

multiple-parton interactions switched off. pythia 8 is used with tune 4C, based on the early

LHC data. Parton showers in pythia are modelled according to the DGLAP prescription.

The herwig++ (version 2.5) [31] MC event generator, with a recent tune to LHC data

(UE-EE-3C [32]), is used for comparison to data. The evolution of the parton distribution

functions with momentum scale in herwig++ is also driven by the DGLAP equations.

In contrast to pythia and herwig++, cascade [33, 34] is based on the CCFM

evolution equation for the initial-state cascade, supplemented with off-shell matrix elements

for the hard scattering. Multiple-parton interactions are not implemented in cascade.

The dipsy generator [35] is based on a dipole picture of BFKL evolution. It includes

multiple dipole interactions, with parameters tuned as described in [35], and can be used

to predict nondiffractive final states. In the present implementation, however, quarks are

not included in the evolution. The treatment of the proton remnant and valence quark

structure is therefore simplistic, and predictions for the structure of the final state in the

very forward region are somewhat uncertain.

Finally, data are also compared to the predictions of Monte Carlo pp event generators

used in cosmic-ray physics [36]. The generators epos1.99 [37] , QGSJetII [38], and sybill

2.1 [39] are considered (for an overview, see [40]). In general, these models describe the soft

component in terms of the exchange of virtual quasi-particle states, as in Gribov’s reggeon

field theory [41], with multi-pomeron exchanges accounting for MPI effects. At higher

energies and scales, the interaction is described by perturbative Quantum Chromodynamics

(QCD) (with DGLAP evolution). These models also include non-linear parton effects,

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either by including pomeron-pomeron interactions, as in QGSJet and EPOS, or by means

of a parton saturation approach, as in sybill. These cosmic ray models were not tuned to

LHC data.

4 The CMS detector

The central feature of the Compact Muon Solenoid (CMS) apparatus is a superconducting

solenoid of 6 m internal diameter. Within the field volume are a silicon pixel and strip

tracker, a crystal electromagnetic calorimeter and a brass/scintillator hadron calorimeter.

Muons are measured in gas-ionization detectors embedded in the steel flux return yoke. In

addition to the barrel and endcap detectors, CMS has extensive forward calorimetry.

The CMS experiment uses a right-handed coordinate system, with the origin at the

nominal interaction point, the x-axis pointing to the center of the LHC ring, the y-

axis pointing up (perpendicular to the plane of the LHC ring), and the z-axis along the

anticlockwise-beam direction. The polar angle θ is measured from the positive z-axis

and the azimuthal angle φ is measured in the x-y plane. Pseudorapidity is defined as

η = − ln tan(θ/2) and approximates true rapidity y = ln E+pz
E−pz . Pseudorapidity equals

rapidity for massless particles.

The tracker measures charged particles within the pseudorapidity range |η| < 2.5. It

consists of 1 440 silicon pixel and 15 148 silicon strip detector modules and is located in the

3.8 T field of the superconducting solenoid. It provides an impact parameter resolution of

∼15µm and a transverse momentum resolution of about 1.5% for 100 GeV/c particles.

The hadronic forward (HF) calorimeters cover the region 2.9 < |η| < 5.2. They consist

of iron absorbers and embedded radiation-hard quartz fibres read out by radiation-hard

photomultiplier tubes (PMTs). Calorimeter cells are formed by grouping bundles of fibres.

Clusters of these cells form a calorimeter tower. There are 13 towers in η, each with a size

∆η ≈ 0.175, except for the lowest- and highest-|η| towers with ∆η ≈ 0.1 and ∆η ≈ 0.3,

respectively. The azimuthal segmentation ∆φ of all towers is 10◦, except for the ones at

highest-|η|, which have ∆φ = 20◦.

More forward angles, −6.6 < η < −5.2, are covered by the Centauro And Strange

Object Research (CASTOR) calorimeter, which is located only on the negative-z side

of CMS, at 14.37 m from the interaction point. The calorimeter is segmented in 16 φ-

sectors and 14 z-modules, corresponding to a total of 224 cells. Each cell consists of 5

quartz plates of 4 mm thickness (2 mm for the electromagnetic modules) embedded in 5

tungsten absorber plates of 10 mm thickness (5 mm for the electromagnetic modules), with

45◦ inclination with respect to the beam axis. Air core light guides provide a fast collection

of the Čerenkov light to fine-mesh PMTs [42], which can operate in magnetic fields up to

0.5 T if the field direction is within ±45◦ with respect to the PMT axis [43]. The first

two modules, which have an absorber thickness half of that of the other modules, are used

to detect electromagnetic showers. The full calorimeter has a depth of 10.5 interaction

lengths. However, the responses of PMTs reading out modules 6 to 8 are affected by the

fringe field of the CMS solenoid. Therefore, only the 5 front modules in a φ sector are used,

with the signals from the cells in a φ sector grouped into a so-called tower. These 5 modules

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correspond to 3.23 interaction lengths and detect 80% of the hadronic showers in inclusive

events, on average. Test beam measurements with a full-length CASTOR prototype [43]

were used to validate the simulation of the detector response.

Including the HF and CASTOR forward calorimeters, the CMS detector covers the

range −6.6 < η < +5.2.

For the online selection of events, the CMS trigger system is used, together with two

elements of the CMS detector monitoring system: the beam scintillation counters (BSC)

and the Beam Pick-up Timing for the eXperiments (BPTX). The BSCs cover the region

3.23 < |η| < 4.65. The BPTX devices are located around the beampipe at a distance

of ±175 m on both side of the IP and are designed to provide precise information on the

bunch structure and timing of the incoming beam.

A more detailed description of the CMS detector can be found in [44].

5 Event selection and reconstruction

This analysis is based on data collected in 2010 and 2011 at
√
s = 0.9, 2.76, and 7 TeV, cor-

responding to integrated luminosities of 0.19 nb−1, 0.30 nb−1, and 0.12 nb−1, respectively.

Runs are selected by requiring that the relevant components of the CMS detector were

fully functional. The average number of collisions per bunch crossing, inferred from the

instantaneous luminosity and the total inelastic cross section, in each of the runs considered

for this analysis is 0.017, 0.22, and 0.12 at
√
s = 0.9, 2.76, and 7 TeV, respectively.

The CMS data acquisition was triggered by the presence of hits in both BSC detectors,

for the 0.9 and 7 TeV data sample, or hits in either of the BSC detectors, for the 2.76 TeV

data sample. Standard CMS algorithms to remove beam halo events are applied.

A sample of inclusive nondiffractive events is selected offline, with minimal bias, by

requiring exactly one primary vertex, at least one HF tower with energy larger than 4 GeV

in the pseudorapidity range of each BSC detector, and at least one CASTOR tower with

energy above 1.5 GeV. The numbers of selected minimum-bias events are 4.7, 9.8, and 4.6

million at
√
s = 0.9, 2.76, and 7 TeV, respectively.

Track jets are reconstructed with the anti-kT algorithm [45] with a size parameter

of 0.5, applied to tracks fitted to a primary vertex and with transverse momentum of at

least 0.3 GeV/c. The leading track jet with pT > 1 GeV/c and |ηjet| < 2 defines the hard

scale in the event. An advantage of using track jets is that they are experimentally well-

defined objects. No attempt is made to correct to the corresponding parton-level objects,

as this would result in additional model uncertainties. Moreover, track jets are much better

correlated in energy and direction to partons than the highest-pT track. Finally, in the few

GeV/c region, the pT of a track jet is better determined than the pT of calorimeter-based

jets, which suffer from poor energy resolution at low pT.

The total charge collected by the PMTs of the 5 front z-modules of the CASTOR

calorimeter is used to measure the energy deposited in the CASTOR η range. The response

of individual CASTOR cells is equalized by using a sample of beam halo muon events. An

absolute calibration factor of 0.015 GeV/fC, with an uncertainty of ±20%, is obtained

from an extrapolation of the η dependence of the energy density in HF to the CASTOR

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acceptance region and is found to be consistent with the results of test beam measurements.

The energy ratios presented in this analysis, however, do not depend on the absolute

calibration and are only marginally affected by the relative inter-calibration of channels.

6 Data correction

In order to be able to compare to theoretical predictions, the data are corrected for various

detector effects, including trigger efficiency, event selection efficiency, energy reconstruction

efficiency in CASTOR and smearing effects in track jet pT. Except for the trigger efficiency

correction, which is extracted directly from data, corrected results are obtained by means

of a simulation of the CMS detector based on Geant4 [46, 47].

The trigger conditions and event selection criteria outlined in section 5 are chosen

to select a sample of dominantly nondiffractive events. However, high-mass diffractive

dissociation events, covering the full detector and having a large rapidity gap outside the

acceptance, remain in the data sample. A precise definition of the phase space, at the level

of stable particles, for which corrected results are presented is obtained as follows.

The collection of stable (lifetime τ > 10−12 s) final-state particles is divided into two

systems, X and Y , based on the mean rapidity of the two particles separated by the largest

rapidity gap in the event. All particles on the negative side of the largest gap are assigned to

the system X, while the particles on the positive side are assigned to the system Y [48]. The

invariant masses, MX and MY, of each system are calculated by using the four-momenta

of the individual particles; their ratios to the centre-of-mass energy, ξX, ξY, and ξDD, are

defined as follows:

ξX =
M2

X

s
, ξY =

M2
Y

s
, ξDD =

M2
XM

2
Y

m2
p s

, (6.1)

where mp is the proton rest mass and the subscript DD refers to double diffractive dissoci-

ation. These Lorentz-invariant variables are well-defined for any type of events. In the case

of large rapidity gap events, they are related to the size of the rapidity gap via ∆y ' ln 1/ξ.

The phase space remaining for events with a large rapidity gap, after applying detector-

level selection criteria, can then be quantified at the stable-particle level by appropriate

limits on ξX, ξY, and ξDD. These acceptance limits are obtained from a dedicated study

based on pythia 6 (tune Z2*) using fully simulated events and are tabulated in table 1.

An event is selected at the stable-particle level if any of ξX, ξY, or ξDD is larger than the

respective limit. Because the detector acceptance changes with centre-of-mass energy, dif-

ferent thresholds are used at
√
s = 0.9, 2.76, and 7 TeV. In all cases, however, the selection

applied ensures that there are no large gaps inside the detector acceptance. Adapting the

selected phase space dynamically to the detector acceptance results in a smaller correction

of the data, and thus also in a smaller model dependence of the correction factors.

Similarly to reconstructed track jets, jets at the stable-particle level are obtained by

running an anti-kT algorithm, with a size parameter of 0.5, on stable charged particles with

pT > 0.3 GeV/c and |η| < 2.5. Particle level jets are selected by requiring pjetT > 1 GeV/c

and |ηjet| < 2.

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√
s (TeV) ξmin

X ξmin
Y ξmin

DD

0.9 0.1 0.4 0.5

2.76 0.07 0.2 0.5

7 0.04 0.1 0.5

Table 1. Acceptance limits on ξX, ξY, and ξDD used to define the phase space domain for which

corrected results are presented. These limits at the stable-particle level correspond to the phase

space selected by detector level criteria.

The trigger efficiency is determined from a sample of zero bias events. Zero bias

events are triggered by the BPTX devices, which require to have filled bunches crossing

each other in the CMS interaction point. The efficiency of the trigger used for the collection

of minimum-bias events is determined as the fraction of events that have been triggered

in a sample of offline selected zero bias events. The overall efficiency for triggering on

the coincidence of a hit in both BSCs is 96.5% (98.4%) at
√
s = 0.9 (7) TeV. For

√
s =

2.76 TeV, where a trigger based on a hit in either BSC is used, the overall trigger efficiency

is 99.9% and no further correction is applied. The efficiency at
√
s = 0.9 and 7 TeV is

parameterized as a function of the energy measured by the HF calorimeters in the BSC

pseudorapidity range. To correct for the trigger inefficiency, a weight equal to the inverse

of this parameterized efficiency is applied to each observed event.

The results presented in section 8 are all based on ratios of energies reconstructed in

CASTOR. By measuring energy ratios, many systematic uncertainties, and, in particular,

the absolute calibration uncertainty, cancel. However, because of the noncompensating

nature of the CASTOR calorimeter, the response may still vary with changing particle

composition and energy spectrum. The measured energy ratio is therefore corrected by

a factor that depends on the measured central track jet pT. This correction, of at most

5%, is obtained from the pythia 6 Z2 MC, reweighted as a function of the particle jet

pT and of the total energy in CASTOR in order to maximize the agreement between data

and simulation.

A further bin-by-bin correction is applied to account for migrations in track jet pT. The

final correction factor applied to the data is the product of the two above-mentioned factors:

dEtrue/dη(pT
true
jet )

dEdet/dη(pTdet
jet )

=
dEtrue/dη(pT

true
jet )

dEtrue/dη(pTdet
jet )
×

dEtrue/dη(pT
det
jet )

dEdet/dη(pTdet
jet )

, (6.2)

with the superscripts “true” and “det” referring to variables estimated at stable-particle

level and detector level, respectively. The first ratio on the right-hand-side of eq. (6.2)

corrects for migration in track jet pT, while the second ratio is the correction factor ap-

plied to the energy measured in CASTOR. The overall correction factor varies between

0.96 and 1.06.

7 Systematic uncertainties

Several sources of systematic uncertainties are investigated. For each systematic effect, the

full analysis is repeated and the deviations from the nominal result are added in quadrature

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Source of uncertainty
√
s = 0.9 TeV

√
s = 2.76 TeV

√
s = 7 TeV

CASTOR alignment 1.5% 2.9% 3.1%

Noncompensation 1.1% 0.4% 0.6%

Model dependence 3.0% 2.3% 1.3%

Shower containment 1.2% 1.4% 1.0%

Noise suppression 0.3% 0.2% 0.2%

Total uncertainty 3.7% 4.0% 3.6%

Table 2. Systematic uncertainties on the hard-to-inclusive forward energy ratio for track jet

pT > 10 GeV/c at different centre-of-mass energies.

Source of uncertainty 0.9 TeV (incl.) 0.9 TeV (hard) 7 TeV (incl.) 7 TeV (hard)

CASTOR alignment 8.0% 7.0% 2.5% 2.7%

Non-compensation 0.5% 1.1% 0.1% 1.0%

Model dependence 2.4% 3.6% 2.0% 2.2%

Shower containment 1.2% 1.0% 1.3% 0.9%

Noise suppression 0.6% 0.8% 0.6% 1.0%

Total uncertainty 8.5% 8.0% 3.5% 3.9%

Table 3. Systematic uncertainties on the relative energy density vs.
√
s in inclusive events (incl.)

and in events with a central charged-particle jet with pT > 10 GeV/c (hard).

to obtain the total systematic uncertainty. The following sources are considered and the

corresponding uncertainties are summarized in tables 2 and 3:

• CASTOR alignment. Sensors monitoring the position of CASTOR indicate that the

detector moves by ∼1 cm in the transverse plane when the CMS solenoid is switched

on or off. The CASTOR alignment is therefore run period dependent. Some φ sec-

tors move towards more central pseudorapidity and the range they cover changes to

approximately −6.3 < η < −5.13, while corrected results are presented for the range

−6.6 < η < −5.2. A new correction factor is obtained by assuming a shift between

the pseudorapidity range at the detector and the stable-particle level in the MC sim-

ulation equal to the displacement of the most affected sectors in data. Corrected

results are obtained as the average between the correction factors based on the nomi-

nal and the shifted position of CASTOR, with half the difference taken as systematic

uncertainty. In addition, for the study of the centre-of-mass energy dependence, a

second systematic uncertainty is included in order to account for possible changes in

the CASTOR position in runs at different
√
s. This is obtained from dedicated MC

samples with CASTOR appropriately shifted.

• Non-compensation. The CASTOR detector is a noncompensating calorimeter. Mea-

surements with a test beam setup [43] have shown that the response to pions rel-

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2
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ative to that to electrons is ≈50%. This ratio slowly increases with incoming par-

ticle energy, a behaviour described by the simulation. The systematic uncertainty

is obtained by scaling the response to hadronic showers in the simulation by the

uncertainty (±5%) on the pion-to-electron response ratio obtained from the test

beam measurement.

• Model dependence. Correction factors are obtained from MC simulation and may

be model dependent. The correction of the CASTOR energy ratio in particular

is sensitive to the charged- to neutral-pion production ratio. Therefore, different

response factors are obtained from a generator level study based on the models used

in the comparison with corrected results. The response factors are defined as the

sum of the electromagnetic energy and 50% of the hadonic energy divided by the

total energy deposited in CASTOR. The largest relative variation in the response

factors is taken as a systematic uncertainty on the correction factor. In addition,

fully simulated samples of pythia 6 tune Z2 and pythia 8 tune 4C are used to

directly compute the model uncertainty on the correction factor.

• Shower containment. In this analysis only the 5 front modules of the CASTOR

calorimeter are used. In order to assess the systematic uncertainty due to the partial

containment of the hadronic shower, the difference in the observed energy ratios

obtained from simulations based on all 14 modules and those based on only the front

5 modules is taken as a contribution to the systematic uncertainty.

• Noise suppression. The noise threshold applied to CASTOR towers is varied by

±20%, reflecting the uncertainty in the absolute calibration factor.

The systematic uncertainty due to the effect of event overlays in one bunch crossing was

found to be negligible. Similarly, the systematic uncertainty resulting from the description

of dead material in the detector model used in the simulation was found to be negligible

for the relative measurements presented in this paper.

8 Results

All the data are fully corrected for detector effects as described in section 6. In particular,

results are obtained for a sample of events dominated by nondiffractive collisions so that the

energy density ratios are not biased by rapidity gaps in the CASTOR pseudorapidity range.

Figures 2 and 3 show the hard-to-inclusive forward energy ratios, defined as the energy

deposited in the pseudorapidity range −6.6 < η < −5.2 in events with a charged-particle

jet with |ηjet| < 2 divided by the energy deposited in inclusive, dominantly nondiffractive

events, as a function of the jet transverse momentum pT. Both figures show the same data

points, but compared to different models.

At
√
s = 7 TeV, a fast increase is seen at low pT followed by a plateau above pT =

8 GeV/c. In the framework of the MPI model for the underlying event, this can be under-

stood from the relation between the impact parameter and the scale of the event, quantified

– 10 –



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 (GeV/c)
T

Leading charged jet p
5 10 15 20 25

) η
/d

in
cl

)/
(d

E
η

/d
h

ar
d

(d
E

0.6

0.8

1

1.2

1.4

1.6

1.8

2

 = 0.9 TeVs < -5.2     ηCMS    -6.6 < 
| < 2jetηLeading charged jet |

Data
PYTHIA6 D6T
PYTHIA6 Z2*
PYTHIA6 Z2* no MPI
PYTHIA8 4C
HERWIG++ 2.5

5 10 15 20 25

M
C

/d
at

a

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0.9

1
1.1
1.2

 (GeV/c)
T

Leading charged jet p
5 10 15 20 25

) η
/d

in
cl

)/
(d

E
η

/d
h

ar
d

(d
E

0.6

0.8

1

1.2

1.4

1.6

1.8

2

 = 2.76 TeVs

5 10 15 20 25

M
C

/d
at

a
0.8

0.9

1

1.1

1.2
 (GeV/c)

T
Leading charged jet p

5 10 15 20 25

) η
/d

in
cl

)/
(d

E
η

/d
h

ar
d

(d
E

0.6

0.8

1

1.2

1.4

1.6

1.8

2

 = 7 TeVs

 (GeV/c)
T

Leading charged jet p
5 10 15 20 25

M
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/d
at

a

0.8

0.9

1

1.1

1.2

Figure 2. Ratio of the energy deposited in the pseudorapidity range −6.6 < η < −5.2 for events

with a charged-particle jet with |ηjet| < 2 with respect to the energy in inclusive events, as a

function of the jet transverse momentum pT for
√
s = 0.9 (left), 2.76 (middle), and 7 TeV (right).

Corrected results are compared to the pythia and herwig++ MC models. Error bars indicate

the statistical uncertainty on the data points, while the grey band represents the statistical and

systematic uncertainties added in quadrature.

 (GeV/c)
T

Leading charged jet p
5 10 15 20 25

) η
/d

in
cl

)/
(d

E
η

/d
h

ar
d

(d
E

0.6

0.8

1

1.2

1.4

1.6

1.8

2

 = 0.9 TeVs < -5.2     ηCMS    -6.6 < 
| < 2jetηLeading charged jet |

Data
EPOS 1.99
QGSJETII-03
SIBYLL 2.1
CASCADE 2
DIPSY

5 10 15 20 25

M
C

/d
at

a

0.8
0.9

1
1.1
1.2

 (GeV/c)
T

Leading charged jet p
5 10 15 20 25

) η
/d

in
cl

)/
(d

E
η

/d
h

ar
d

(d
E

0.6

0.8

1

1.2

1.4

1.6

1.8

2

 = 2.76 TeVs

5 10 15 20 25

M
C

/d
at

a

0.8

0.9

1

1.1

1.2
 (GeV/c)

T
Leading charged jet p

5 10 15 20 25

) η
/d

in
cl

)/
(d

E
η

/d
h

ar
d

(d
E

0.6

0.8

1

1.2

1.4

1.6

1.8

2

 = 7 TeVs

 (GeV/c)
T

Leading charged jet p
5 10 15 20 25

M
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/d
at

a

0.8

0.9

1

1.1

1.2

Figure 3. Ratio of the energy deposited in the pseudorapidity range −6.6 < η < −5.2 for events

with a charged-particle jet with |ηjet| < 2 with respect to the energy in inclusive events, as a function

of the jet transverse momentum pT for
√
s = 0.9 (left), 2.76 (middle), and 7 TeV (right). Corrected

results are compared to MC models used in cosmic ray physics and to cascade and dipsy. Error

bars indicate the statistical uncertainty on the data points, while the grey band represents the

statistical and systematic uncertainties added in quadrature.

by pT. As pT increases, the collisions become more central and the number of parton inter-

actions increases. Above pT = 10 GeV/c, the collision is central and the underlying event

activity saturates. The pre-LHC pythia 6 tune D6T fails to describe the data, while

pythia 6 and pythia 8 tunes fitted to LHC data on the underlying event at central ra-

pidity agree with the data at forward rapidity within ±5%. As expected, when MPIs are

switched off, pythia predicts a forward energy density that is independent of the central

– 11 –



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jet pT. The herwig++ 2.5 simulation with tune UE-EE-3C gives a slightly worse descrip-

tion of the data in the turn-on region, but is still within ±10% of the measured points. The

cascade model, which does not simulate multiple-parton interactions, does not describe

the data. The discrepancy shows that the features observed in the data cannot be explained

by the CCFM parton dynamics as implemented in this model. The dipsy model, based on

the BFKL dipole picture, and supplemented with multiple interactions between dipoles,

however, also fails to describe the data. Models used in cosmic ray physics, on the other

hand, do describe the increase of the energy ratio as a function of pT reasonably well. The

QGSJetII-03 generator yields a ratio that is too low in the plateau region, while Sibyll

2.1, and Epos 1.99 overestimate the turn-on but converge on a very good description at

large pT.

At
√
s = 2.76 TeV, the increase of the energy ratio with pT is much reduced. This

tendency is consistent with the result at
√
s = 0.9 TeV, where the ratio becomes less than

unity. Here, the energy density in events with a central jet is thus lower than the energy

density in inclusive events. As discussed in section 2, this can be understood as a kinematic

effect: the production of central hard jets, accompanied by higher underlying event activity

(as seen in studies at central rapidity [18]), depletes the energy of the proton remnant, which

at
√
s = 0.9 TeV fragments within the pseudorapidity region covered by CASTOR. This

feature is roughly described by the models. Again, the pythia 6 D6T tune exhibits too

strong an underlying event activity, even at
√
s = 0.9 TeV. Other pythia tunes describe the

data at
√
s = 2.76 TeV and 0.9 TeV rather well. The herwig++ 2.5 predictions lie slightly

below the data at
√
s = 0.9 TeV, which indicates too strong an underlying event activity.

The cascade generator does not reproduce the data, while dipsy yields a reasonable

description at these lower centre-of-mass energies. Most of the cosmic ray models describe

the data well, with QGSJetII-03 again yielding slightly too low underlying event activity.

Overall, in this study, both the pythia 6 Z2* and pythia 8 4C tunes give a good

description of all data. This is in contrast with studies of the underlying event in the

central region [18], where pythia 6 Z2* gives an excellent description of the underlying

event activity in the region transverse to the jet in azimuth (to which it was tuned), while

pythia 8 4C is too low.

Figures 4 and 5 present the increase of the energy density deposited in the range −6.6 <

η < −5.2 as a function of
√
s, normalized to the energy density at

√
s = 2.76 TeV, for both

inclusive events and for events with a central charged-particle jet. The
√
s = 2.76 TeV data

are taken as a normalization point because this minimizes the statistical and systematic

uncertainties. The pT threshold for jets is 10 GeV/c at all centre-of-mass energies. Since

this is well within the plateau region, the energy density does not change significantly as

a function of the actual value of the threshold. Both figures again show the same data

points, but compared to different models.

None of the pythia or herwig++ models describe the increase with
√
s seen in data.

For inclusive events the predictions differ little and they all underestimate the increase

from
√
s = 2.76 to 7 TeV (by up to ∼20% for herwig++ 2.5). In this event class, the

contribution of the underlying event is expected to be small. For events with central

charged-particle jets, the predictions vary more widely. Indeed, for this event class the

description of the underlying event in various tunes is expected to differ. None of the tunes

– 12 –



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6 
Te

V
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Inclusive events
Data
PYTHIA6 D6T
PYTHIA6 Z2*
PYTHIA6 Z2* no MPI
PYTHIA8 4C
HERWIG++ 2.5

0.9 TeV 2.76 TeV 7 TeV

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at

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1.2 s
0.9 TeV 2.76 TeV 7 TeV

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n

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Te

V
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d

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/d

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1.5

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3

Leading charged jet
| < 2jetη > 10 GeV/c, |

T
p

s
0.9 TeV 2.76 TeV 7 TeV

M
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/d
at

a

0.8

1

1.2

Figure 4. Energy density in the pseudorapidity range −6.6 < η < −5.2 in inclusive events (left) and

in events with a charged-particle jet in the range |ηjet| < 2 (right) as a function of
√
s, normalized to

the energy density at
√
s = 2.76 TeV. The pT threshold used for jets is 10 GeV/c at all centre-of-mass

energies. Corrected results are compared to the pythia and herwig++ MC models. Statistical

uncertainties are smaller than the marker size, while the grey band represents the statistical and

systematic uncertainties added in quadrature.

s
0.9 TeV 2.76 TeV 7 TeV

 (
n

o
rm

 t
o

 2
.7

6 
Te

V
)

η
d

E
/d

0

0.5

1

1.5

2

2.5

3
 < -5.2ηCMS    -6.6 < 

Inclusive events
Data
EPOS 1.99
QGSJETII-03
SIBYLL 2.1
CASCADE 2
DIPSY

0.9 TeV 2.76 TeV 7 TeV

M
C

/d
at

a

0.8

1

1.2 s
0.9 TeV 2.76 TeV 7 TeV

 (
n

o
rm

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o

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.7

6 
Te

V
)

η
d

E
/d

0

0.5

1

1.5

2

2.5

3

Leading charged jet
| < 2jetη > 10 GeV/c, |

T
p

s
0.9 TeV 2.76 TeV 7 TeV

M
C

/d
at

a

0.8

1

1.2

Figure 5. Energy density in the pseudorapidity range −6.6 < η < −5.2 in inclusive events (left) and

in events with a charged-particle jet in the range |ηjet| < 2 (right) as a function of
√
s, normalized

to the energy density at
√
s = 2.76 TeV. The pT threshold used for jets is 10 GeV/c at all centre-

of-mass energies. Corrected results are compared to MC models used in cosmic ray physics and

to cascade and dipsy. Statistical uncertainties are smaller than the marker size, while the grey

band represents the statistical and systematic uncertainties added in quadrature.

give a satisfactory description, with pythia 6 D6T and pythia 8 4C being closest to the

data and herwig++ 2.5 underestimating the increase from 2.76 to 7 TeV by ∼ 25%. The

cascade and dipsy generators also show a slower increase of the forward energy density

with
√
s than observed in data. Of the cosmic ray models, QGSJetII-03 gives a good

– 13 –



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description of data. The EPOS and sybill generators yield an increase with centre-of-

mass energy that is lower than that in the data by 10–15%.

The results presented in this paper show that the MPI model, as implemented in

pythia, and tuned to central inclusive and underlying event data, is capable of describing

the pT dependence of the forward energy density. This is an important consistency check

of the MPI model. Models inspired by BFKL or CCFM parton dynamics do not describe

the pT dependence of the data. Hence, contributions which go beyond what is presently

implemented in the models seem to be mandatory. Models used for cosmic rays studies,

which include MPI and saturation effects via multi-pomeron interactions work well. The

pythia 6 model with tune D6T describes the
√
s dependence well, but only by invoking

too large an amount of MPIs, as can be concluded from the pT dependence.

9 Summary

A study of the underlying event at forward pseudorapidity (−6.6 < η < −5.2) has been

performed with a novel observable. The energy density per unit of pseudorapidity has

been measured at
√
s = 0.9, 2.76, and 7 TeV, for events with a central charged-particle jet,

relative to the energy density for inclusive events. This hard-to-inclusive forward energy

ratio has been studied as a function of the jet transverse momentum pT. In addition,

the relative increase of the energy density as a function of the centre-of-mass energy has

been measured for both inclusive events and events with a central charged-particle jet. All

results have been corrected to stable-particle level.

These results complement those obtained from studies of the underlying event at cen-

tral rapidity [15–18] because the large η separation from the central hard scattering system

yields a different sensitivity to the relative contributions of parton showers and multiple-

parton interactions. These data can thus be used to tune the underlying event parameters

in a way which is complementary to that possible with central-rapidity data.

The data exhibit the typical underlying event behaviour characterized by a rapid

change of the energy density at small charged-particle jet pT, followed by a plateau at

larger pT. At
√
s = 7 TeV, the relative energy density increases with jet pT, while at√

s = 0.9 TeV, the energy density decreases with increasing jet pT. At this center-of-mass

energy, the hard-to-inclusive forward energy ratio drops below 1, which suggests that the

energy of the proton remnant is depleted in events with a central charged-particle jet.

Data at
√
s = 2.76 TeV exhibit an intermediate behaviour and are characterized by an

approximately constant energy density as a function of the jet pT.

Models based on multiple-parton interactions suggest that the latter only make a

limited contribution to the forward energy density in inclusive events. In contrast, collisions

with a small impact parameter, characterized by the presence of a charged-particle jet,

appear to give rise to a significant number of multiple-parton interactions. Above pT =

8 GeV/c, the hard-to-inclusive forward energy ratio is roughly independent of pT, indicating

that the collisions are already central for this value of the jet pT. Some Monte Carlo models

are able to describe the hard-to-inclusive forward energy ratio as a function of pT; however,

all models fail to reproduce the dependence on the centre-of-mass energy simultaneously

for inclusive events and for events with a central charged-particle jet.

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Acknowledgments

We would like to thank Leif Lönnblad for making the dipsy predictions available to the

CMS collaboration.

We congratulate our colleagues in the CERN accelerator departments for the excellent

performance of the LHC and thank the technical and administrative staffs at CERN and at

other CMS institutes for their contributions to the success of the CMS effort. In addition,

we gratefully acknowledge the computing centres and personnel of the Worldwide LHC

Computing Grid for delivering so effectively the computing infrastructure essential to our

analyses. Finally, we acknowledge the enduring support for the construction and operation

of the LHC and the CMS detector provided by the following funding agencies: BMWF

and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP

(Brazil); MEYS (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS

(Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09 and ERDF (Estonia);

Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF,

DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and

DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Republic of Ko-

rea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI

(New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Ar-

menia, Belarus, Georgia, Ukraine, Uzbekistan); MON, RosAtom, RAS and RFBR (Russia);

MSTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC

(Taipei); ThEPCenter, IPST and NSTDA (Thailand); TUBITAK and TAEK (Turkey);

NASU (Ukraine); STFC (United Kingdom); DOE and NSF (USA). Individuals have re-

ceived support from the A.G. Leventis Foundation, the Helmholtz Association, the Russian

Foundation for Basic Research, the Russian Federation Presidential Grants N1456.2008.2,

N4142.2010.2 and N3920.2012.2, the Russian Ministry of Education and Science, and the

Belgian Federal Science Policy Office.

Open Access. This article is distributed under the terms of the Creative Commons

Attribution License which permits any use, distribution and reproduction in any medium,

provided the original author(s) and source are credited.

References

[1] CMS collaboration, Transverse momentum and pseudorapidity distributions of charged

hadrons in pp collisions at
√
s = 0.9 and 2.36 TeV, JHEP 02 (2010) 041 [arXiv:1002.0621]

[INSPIRE].

[2] CMS collaboration, Transverse-momentum and pseudorapidity distributions of charged

hadrons in pp collisions at
√
s = 7 TeV, Phys. Rev. Lett. 105 (2010) 022002

[arXiv:1005.3299] [INSPIRE].

[3] W. Kittel and E. De Wolf, Soft multihadron dynamics, World Scientific, Singapore (2005).

[4] V. Gribov and L. Lipatov, Deep inelastic ep scattering in perturbation theory, Sov. J. Nucl.

Phys. 15 (1972) 438 [INSPIRE].

– 15 –

http://dx.doi.org/10.1007/JHEP02(2010)041
http://arxiv.org/abs/1002.0621
http://inspirehep.net/search?p=find+EPRINT+arXiv:1002.0621
http://dx.doi.org/10.1103/PhysRevLett.105.022002
http://arxiv.org/abs/1005.3299
http://inspirehep.net/search?p=find+EPRINT+arXiv:1005.3299
http://inspirehep.net/search?p=find+J+Sov.J.Nucl.Phys.,15,438


J
H
E
P
0
4
(
2
0
1
3
)
0
7
2

[5] L.N. Lipatov, The parton model and perturbation theory, Sov. J. Nucl. Phys. 20 (1975) 94

[INSPIRE].

[6] G. Altarelli and G. Parisi, Asymptotic freedom in parton language, Nucl. Phys. B 126 (1977)

298 [INSPIRE].

[7] Y.L. Dokshitzer, Calculation of the structure functions for deep inelastic scattering and e+e−

annihilation by perturbation theory in quantum chromodynamics., Sov. Phys. JETP 46

(1977) 641 [INSPIRE].

[8] E. Kuraev, L. Lipatov and V.S. Fadin, Multi-Reggeon processes in the Yang-Mills theory,

Sov. Phys. JETP 44 (1976) 443 [INSPIRE].

[9] E. Kuraev, L. Lipatov and V.S. Fadin, The Pomeranchuk singularity in nonabelian gauge

theories, Sov. Phys. JETP 45 (1977) 199 [INSPIRE].

[10] I. Balitsky and L. Lipatov, The Pomeranchuk singularity in quantum chromodynamics, Sov.

J. Nucl. Phys. 28 (1978) 822 [INSPIRE].

[11] M. Ciafaloni, Coherence effects in initial jets at small Q2/s, Nucl. Phys. B 296 (1988) 49

[INSPIRE].

[12] S. Catani, F. Fiorani and G. Marchesini, QCD coherence in initial state radiation, Phys.

Lett. B 234 (1990) 339 [INSPIRE].

[13] C. Burgess, C. Lütken and F. Quevedo, Bosonization in higher dimensions, Phys. Lett. B

336 (1994) 18 [hep-th/9407078] [INSPIRE].

[14] G. Marchesini, QCD coherence in the structure function and associated distributions at small

x, Nucl. Phys. B 445 (1995) 49 [hep-ph/9412327] [INSPIRE].

[15] CMS collaboration, First measurement of the underlying event activity at the LHC with√
s = 0.9 TeV, Eur. Phys. J. C 70 (2010) 555 [arXiv:1006.2083] [INSPIRE].

[16] ATLAS collaboration, Measurement of underlying event characteristics using charged

particles in pp collisions at
√
s = 900GeV and 7 TeV with the ATLAS detector, Phys. Rev.

D 83 (2011) 112001 [arXiv:1012.0791] [INSPIRE].

[17] ATLAS collaboration, Measurements of underlying-event properties using neutral and

charged particles in pp collisions at 900 GeV and 7 TeV with the ATLAS detector at the

LHC, Eur. Phys. J. C 71 (2011) 1636 [arXiv:1103.1816] [INSPIRE].

[18] CMS collaboration, Measurement of the underlying event activity at the LHC with
√
s = 7

TeV and comparison with
√
s = 0.9 TeV, JHEP 09 (2011) 109 [arXiv:1107.0330] [INSPIRE].

[19] ALICE collaboration, Underlying event measurements in pp collisions at
√
s = 0.9 and 7

TeV with the ALICE experiment at the LHC, JHEP 07 (2012) 116 [arXiv:1112.2082]

[INSPIRE].

[20] CMS collaboration, Measurement of energy flow at large pseudorapidities in pp collisions at√
s = 0.9 and 7 TeV, JHEP 11 (2011) 148 [Erratum ibid. 1202 (2012) 055]

[arXiv:1110.0211] [INSPIRE].

[21] T. Sjöstrand and M. van Zijl, Multiple parton-parton interactions in an impact parameter

picture, Phys. Lett. B 188 (1987) 149 [INSPIRE].

[22] L. Frankfurt, M. Strikman and C. Weiss, Transverse nucleon structure and diagnostics of

hard parton-parton processes at LHC, Phys. Rev. D 83 (2011) 054012 [arXiv:1009.2559]

[INSPIRE].

– 16 –

http://inspirehep.net/search?p=find+J+Sov.J.Nucl.Phys.,20,94
http://dx.doi.org/10.1016/0550-3213(77)90384-4
http://dx.doi.org/10.1016/0550-3213(77)90384-4
http://inspirehep.net/search?p=find+J+Nucl.Phys.,B126,298
http://inspirehep.net/search?p=find+J+Sov.Phys.JETP,46,641
http://inspirehep.net/search?p=find+J+Sov.Phys.JETP,44,443
http://inspirehep.net/search?p=find+J+Sov.Phys.JETP,45,199
http://inspirehep.net/search?p=find+J+Sov.J.Nucl.Phys.,28,822
http://dx.doi.org/10.1016/0550-3213(88)90380-X
http://inspirehep.net/search?p=find+J+Nucl.Phys.,B296,49
http://dx.doi.org/10.1016/0370-2693(90)91938-8
http://dx.doi.org/10.1016/0370-2693(90)91938-8
http://inspirehep.net/search?p=find+J+Phys.Lett.,B234,339
http://dx.doi.org/10.1016/0370-2693(94)00963-5
http://dx.doi.org/10.1016/0370-2693(94)00963-5
http://arxiv.org/abs/hep-th/9407078
http://inspirehep.net/search?p=find+J+Phys.Lett.,B336,18
http://dx.doi.org/10.1016/0550-3213(95)00149-M
http://arxiv.org/abs/hep-ph/9412327
http://inspirehep.net/search?p=find+EPRINT+hep-ph/9412327
http://dx.doi.org/10.1140/epjc/s10052-010-1453-9
http://arxiv.org/abs/1006.2083
http://inspirehep.net/search?p=find+EPRINT+arXiv:1006.2083
http://dx.doi.org/10.1103/PhysRevD.83.112001
http://dx.doi.org/10.1103/PhysRevD.83.112001
http://arxiv.org/abs/1012.0791
http://inspirehep.net/search?p=find+EPRINT+arXiv:1012.0791
http://dx.doi.org/10.1140/epjc/s10052-011-1636-z
http://arxiv.org/abs/1103.1816
http://inspirehep.net/search?p=find+EPRINT+arXiv:1103.1816
http://dx.doi.org/10.1007/JHEP09(2011)109
http://arxiv.org/abs/1107.0330
http://inspirehep.net/search?p=find+EPRINT+arXiv:1107.0330
http://dx.doi.org/10.1007/JHEP07(2012)116
http://arxiv.org/abs/1112.2082
http://inspirehep.net/search?p=find+EPRINT+arXiv:1112.2082
http://dx.doi.org/10.1007/JHEP11(2011)148
http://arxiv.org/abs/1110.0211
http://inspirehep.net/search?p=find+EPRINT+arXiv:1110.0211
http://dx.doi.org/10.1016/0370-2693(87)90722-2
http://inspirehep.net/search?p=find+J+Phys.Lett.,B188,149
http://dx.doi.org/10.1103/PhysRevD.83.054012
http://arxiv.org/abs/1009.2559
http://inspirehep.net/search?p=find+EPRINT+arXiv:1009.2559


J
H
E
P
0
4
(
2
0
1
3
)
0
7
2

[23] T. Sjöstrand, S. Mrenna and P.Z. Skands, PYTHIA 6.4 physics and manual, JHEP 05

(2006) 026 [hep-ph/0603175] [INSPIRE].

[24] R. Field, Physics at the Tevatron, Acta Phys. Polon. B 39 (2008) 2611 [INSPIRE].

[25] R. Field, Studying the underlying event at CDF and the LHC, in the proceedings of the First

International Workshop on Multiple Partonic Interactions at the LHC, October 27–31,

Perugia, Italy (2009).

[26] T. Sjöstrand, S. Mrenna and P.Z. Skands, A brief introduction to PYTHIA 8.1, Comput.

Phys. Commun. 178 (2008) 852 [arXiv:0710.3820] [INSPIRE].

[27] R. Corke and T. Sjöstrand, Interleaved parton showers and tuning prospects, JHEP 03

(2011) 032 [arXiv:1011.1759] [INSPIRE].

[28] P.Z. Skands and D. Wicke, Non-perturbative QCD effects and the top mass at the Tevatron,

Eur. Phys. J. C 52 (2007) 133 [hep-ph/0703081] [INSPIRE].

[29] R. Field, Early LHC underlying event data — Findings and surprises, in the proceedings of

Hadron Collider Physics Symposium 2010 (HCP2010), August 23–27, Toronto, Canada

(2010), arXiv:1010.3558 [INSPIRE].

[30] A. Buckley, H. Hoeth, H. Lacker, H. Schulz and J.E. von Seggern, Systematic event generator

tuning for the LHC, Eur. Phys. J. C 65 (2010) 331 [arXiv:0907.2973] [INSPIRE].

[31] M. Bahr et al., HERWIG++ physics and manual, Eur. Phys. J. C 58 (2008) 639

[arXiv:0803.0883] [INSPIRE].

[32] S. Gieseke, D. Grellscheid, K. Hamilton, A. Papaefstathiou, S. Platzer, et al., HERWIG++

2.5 release note, arXiv:1102.1672 [INSPIRE].

[33] H. Jung and G. Salam, Hadronic final state predictions from CCFM: the hadron level Monte

Carlo generator CASCADE, Eur. Phys. J. C 19 (2001) 351 [hep-ph/0012143] [INSPIRE].

[34] H. Jung et al., The CCFM Monte Carlo generator CASCADE version 2.2.03, Eur. Phys. J.

C 70 (2010) 1237 [arXiv:1008.0152] [INSPIRE].

[35] C. Flensburg, G. Gustafson and L. Lönnblad, Inclusive and exclusive observables from

dipoles in high energy collisions, JHEP 08 (2011) 103 [arXiv:1103.4321] [INSPIRE].

[36] D. d’Enterria, R. Engel, T. Pierog, S. Ostapchenko and K. Werner, Constraints from the first

LHC data on hadronic event generators for ultra-high energy cosmic-ray physics, Astropart.

Phys. 35 (2011) 98 [arXiv:1101.5596] [INSPIRE].

[37] K. Werner, F.-M. Liu and T. Pierog, Parton ladder splitting and the rapidity dependence of

transverse momentum spectra in deuteron-gold collisions at RHIC, Phys. Rev. C 74 (2006)

044902 [hep-ph/0506232] [INSPIRE].

[38] S. Ostapchenko, Monte Carlo treatment of hadronic interactions in enhanced Pomeron

scheme: I. QGSJET-II model, Phys. Rev. D 83 (2011) 014018 [arXiv:1010.1869] [INSPIRE].

[39] E.-J. Ahn, R. Engel, T.K. Gaisser, P. Lipari and T. Stanev, Cosmic ray interaction event

generator SIBYLL 2.1, Phys. Rev. D 80 (2009) 094003 [arXiv:0906.4113] [INSPIRE].

[40] S. Ostapchenko, High energy cosmic ray interactions: an overview, J. Phys. Conf. Ser. 60

(2007) 167 [astro-ph/0610788] [INSPIRE].

[41] V.N. Gribov, A reggeon diagram technique, Sov. Phys. JETP 26 (1968) 414 [INSPIRE].

– 17 –

http://dx.doi.org/10.1088/1126-6708/2006/05/026
http://dx.doi.org/10.1088/1126-6708/2006/05/026
http://arxiv.org/abs/hep-ph/0603175
http://inspirehep.net/search?p=find+EPRINT+hep-ph/0603175
http://inspirehep.net/search?p=find+J+ActaPhys.Polon.,B39,2611
http://dx.doi.org/10.1016/j.cpc.2008.01.036
http://dx.doi.org/10.1016/j.cpc.2008.01.036
http://arxiv.org/abs/0710.3820
http://inspirehep.net/search?p=find+EPRINT+arXiv:0710.3820
http://dx.doi.org/10.1007/JHEP03(2011)032
http://dx.doi.org/10.1007/JHEP03(2011)032
http://arxiv.org/abs/1011.1759
http://inspirehep.net/search?p=find+EPRINT+arXiv:1011.1759
http://dx.doi.org/10.1140/epjc/s10052-007-0352-1
http://arxiv.org/abs/hep-ph/0703081
http://inspirehep.net/search?p=find+EPRINT+hep-ph/0703081
http://arxiv.org/abs/1010.3558
http://inspirehep.net/search?p=find+EPRINT+arXiv:1010.3558
http://dx.doi.org/10.1140/epjc/s10052-009-1196-7
http://arxiv.org/abs/0907.2973
http://inspirehep.net/search?p=find+EPRINT+arXiv:0907.2973
http://dx.doi.org/10.1140/epjc/s10052-008-0798-9
http://arxiv.org/abs/0803.0883
http://inspirehep.net/search?p=find+EPRINT+arXiv:0803.0883
http://arxiv.org/abs/1102.1672
http://inspirehep.net/search?p=find+EPRINT+arXiv:1102.1672
http://dx.doi.org/10.1007/s100520100604
http://arxiv.org/abs/hep-ph/0012143
http://inspirehep.net/search?p=find+EPRINT+hep-ph/0012143
http://dx.doi.org/10.1140/epjc/s10052-010-1507-z
http://dx.doi.org/10.1140/epjc/s10052-010-1507-z
http://arxiv.org/abs/1008.0152
http://inspirehep.net/search?p=find+EPRINT+arXiv:1008.0152
http://dx.doi.org/10.1007/JHEP08(2011)103
http://arxiv.org/abs/1103.4321
http://inspirehep.net/search?p=find+EPRINT+arXiv:1103.4321
http://dx.doi.org/10.1016/j.astropartphys.2011.05.002
http://dx.doi.org/10.1016/j.astropartphys.2011.05.002
http://arxiv.org/abs/1101.5596
http://inspirehep.net/search?p=find+EPRINT+arXiv:1101.5596
http://dx.doi.org/10.1103/PhysRevC.74.044902
http://dx.doi.org/10.1103/PhysRevC.74.044902
http://arxiv.org/abs/hep-ph/0506232
http://inspirehep.net/search?p=find+EPRINT+hep-ph/0506232
http://dx.doi.org/10.1103/PhysRevD.83.014018
http://arxiv.org/abs/1010.1869
http://inspirehep.net/search?p=find+EPRINT+arXiv:1010.1869
http://dx.doi.org/10.1103/PhysRevD.80.094003
http://arxiv.org/abs/0906.4113
http://inspirehep.net/search?p=find+EPRINT+arXiv:0906.4113
http://dx.doi.org/10.1088/1742-6596/60/1/033
http://dx.doi.org/10.1088/1742-6596/60/1/033
http://arxiv.org/abs/astro-ph/0610788
http://inspirehep.net/search?p=find+EPRINT+astro-ph/0610788
http://inspirehep.net/search?p=find+J+Sov.Phys.JETP,26,414


J
H
E
P
0
4
(
2
0
1
3
)
0
7
2

[42] H1 SpaCal Group collaboration, R. Appuhn et al., Series tests of fine mesh photomultiplier

tubes in magnetic fields of up to 1.2 Tesla, Nucl. Instrum. Meth. A 404 (1998) 265 [INSPIRE].

[43] CMS-CASTOR collaboration, P. Gottlicher, Design and test beam studies for the CASTOR

calorimeter of the CMS experiment, Nucl. Instrum. Meth. A 623 (2010) 225 [INSPIRE].

[44] CMS collaboration, The CMS experiment at the CERN LHC, 2008 JINST 3 S08004

[INSPIRE].

[45] M. Cacciari, G.P. Salam and G. Soyez, The anti-kt jet clustering algorithm, JHEP 04 (2008)

063 [arXiv:0802.1189] [INSPIRE].

[46] GEANT4 collaboration, S. Agostinelli et al., GEANT4: a simulation toolkit, Nucl. Instrum.

Meth. A 506 (2003) 250 [INSPIRE].

[47] GEANT4 collaboration, GEANT4 developments and applications, IEEE Trans. Nucl. Sci. 53

(2006) 270.

[48] H1 collaboration, C. Adloff et al., Diffraction dissociation in photoproduction at HERA, Z.

Phys. C 74 (1997) 221 [hep-ex/9702003] [INSPIRE].

– 18 –

http://dx.doi.org/10.1016/S0168-9002(97)01092-9
http://inspirehep.net/search?p=find+J+Nucl.Instrum.Meth.,A404,265
http://dx.doi.org/10.1016/j.nima.2010.02.203
http://inspirehep.net/search?p=find+J+Nucl.Instrum.Meth.,A623,225
http://dx.doi.org/10.1088/1748-0221/3/08/S08004
http://inspirehep.net/search?p=find+J+JINST,3,S08004
http://dx.doi.org/10.1088/1126-6708/2008/04/063
http://dx.doi.org/10.1088/1126-6708/2008/04/063
http://arxiv.org/abs/0802.1189
http://inspirehep.net/search?p=find+EPRINT+arXiv:0802.1189
http://dx.doi.org/10.1016/S0168-9002(03)01368-8
http://dx.doi.org/10.1016/S0168-9002(03)01368-8
http://inspirehep.net/search?p=find+J+Nucl.Instrum.Meth.,A506,250
http://dx.doi.org/10.1109/TNS.2006.869826
http://dx.doi.org/10.1109/TNS.2006.869826
http://dx.doi.org/10.1007/s002880050385
http://dx.doi.org/10.1007/s002880050385
http://arxiv.org/abs/hep-ex/9702003
http://inspirehep.net/search?p=find+EPRINT+hep-ex/9702003


J
H
E
P
0
4
(
2
0
1
3
)
0
7
2

The CMS collaboration

Yerevan Physics Institute, Yerevan, Armenia

S. Chatrchyan, V. Khachatryan, A.M. Sirunyan, A. Tumasyan

Institut für Hochenergiephysik der OeAW, Wien, Austria

W. Adam, E. Aguilo, T. Bergauer, M. Dragicevic, J. Erö, C. Fabjan1, M. Friedl,

R. Frühwirth1, V.M. Ghete, N. Hörmann, J. Hrubec, M. Jeitler1, W. Kiesenhofer,

V. Knünz, M. Krammer1, I. Krätschmer, D. Liko, I. Mikulec, M. Pernicka†, D. Rabady2,

B. Rahbaran, C. Rohringer, H. Rohringer, R. Schöfbeck, J. Strauss, A. Taurok, W. Wal-

tenberger, C.-E. Wulz1

National Centre for Particle and High Energy Physics, Minsk, Belarus

V. Mossolov, N. Shumeiko, J. Suarez Gonzalez

Universiteit Antwerpen, Antwerpen, Belgium

S. Alderweireldt, M. Bansal, S. Bansal, T. Cornelis, E.A. De Wolf, X. Janssen, S. Luyckx,

L. Mucibello, S. Ochesanu, B. Roland, R. Rougny, H. Van Haevermaet, P. Van Mechelen,

N. Van Remortel, A. Van Spilbeeck

Vrije Universiteit Brussel, Brussel, Belgium

F. Blekman, S. Blyweert, J. D’Hondt, R. Gonzalez Suarez, A. Kalogeropoulos, M. Maes,

A. Olbrechts, S. Tavernier, W. Van Doninck, P. Van Mulders, G.P. Van Onsem, I. Villella

Université Libre de Bruxelles, Bruxelles, Belgium

B. Clerbaux, G. De Lentdecker, V. Dero, A.P.R. Gay, T. Hreus, A. Léonard, P.E. Marage,

A. Mohammadi, T. Reis, L. Thomas, C. Vander Velde, P. Vanlaer, J. Wang

Ghent University, Ghent, Belgium

V. Adler, K. Beernaert, A. Cimmino, S. Costantini, G. Garcia, M. Grunewald, B. Klein,

J. Lellouch, A. Marinov, J. Mccartin, A.A. Ocampo Rios, D. Ryckbosch, M. Sigamani,

N. Strobbe, F. Thyssen, M. Tytgat, S. Walsh, E. Yazgan, N. Zaganidis

Université Catholique de Louvain, Louvain-la-Neuve, Belgium

S. Basegmez, G. Bruno, R. Castello, L. Ceard, C. Delaere, T. du Pree, D. Favart,

L. Forthomme, A. Giammanco3, J. Hollar, V. Lemaitre, J. Liao, O. Militaru, C. Nuttens,

D. Pagano, A. Pin, K. Piotrzkowski, M. Selvaggi, J.M. Vizan Garcia

Université de Mons, Mons, Belgium

N. Beliy, T. Caebergs, E. Daubie, G.H. Hammad

Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil

G.A. Alves, M. Correa Martins Junior, T. Martins, M.E. Pol, M.H.G. Souza

Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil

W.L. Aldá Júnior, W. Carvalho, J. Chinellato4, A. Custódio, E.M. Da Costa, D. De Jesus

Damiao, C. De Oliveira Martins, S. Fonseca De Souza, H. Malbouisson, M. Malek, D. Matos

Figueiredo, L. Mundim, H. Nogima, W.L. Prado Da Silva, A. Santoro, L. Soares Jorge,

A. Sznajder, E.J. Tonelli Manganote4, A. Vilela Pereira

– 19 –



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Universidade Estadual Paulista a, Universidade Federal do ABC b, São Paulo,

Brazil

T.S. Anjosb, C.A. Bernardesb, F.A. Diasa,5, T.R. Fernandez Perez Tomeia, E.M. Gregoresb,

C. Laganaa, F. Marinhoa, P.G. Mercadanteb, S.F. Novaesa, Sandra S. Padulaa

Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria

V. Genchev2, P. Iaydjiev2, S. Piperov, M. Rodozov, S. Stoykova, G. Sultanov, V. Tcholakov,

R. Trayanov, M. Vutova

University of Sofia, Sofia, Bulgaria

A. Dimitrov, R. Hadjiiska, V. Kozhuharov, L. Litov, B. Pavlov, P. Petkov

Institute of High Energy Physics, Beijing, China

J.G. Bian, G.M. Chen, H.S. Chen, C.H. Jiang, D. Liang, S. Liang, X. Meng, J. Tao,

J. Wang, X. Wang, Z. Wang, H. Xiao, M. Xu, J. Zang, Z. Zhang

State Key Laboratory of Nuclear Physics and Technology, Peking University,

Beijing, China

C. Asawatangtrakuldee, Y. Ban, Y. Guo, W. Li, S. Liu, Y. Mao, S.J. Qian, H. Teng,

D. Wang, L. Zhang, W. Zou

Universidad de Los Andes, Bogota, Colombia

C. Avila, C.A. Carrillo Montoya, J.P. Gomez, B. Gomez Moreno, A.F. Osorio Oliveros,

J.C. Sanabria

Technical University of Split, Split, Croatia

N. Godinovic, D. Lelas, R. Plestina6, D. Polic, I. Puljak

University of Split, Split, Croatia

Z. Antunovic, M. Kovac

Institute Rudjer Boskovic, Zagreb, Croatia

V. Brigljevic, S. Duric, K. Kadija, J. Luetic, D. Mekterovic, S. Morovic, L. Tikvica

University of Cyprus, Nicosia, Cyprus

A. Attikis, G. Mavromanolakis, J. Mousa, C. Nicolaou, F. Ptochos, P.A. Razis

Charles University, Prague, Czech Republic

M. Finger, M. Finger Jr.

Academy of Scientific Research and Technology of the Arab Republic of Egypt,

Egyptian Network of High Energy Physics, Cairo, Egypt

Y. Assran7, S. Elgammal8, A. Ellithi Kamel9, A.M. Kuotb Awad10, M.A. Mahmoud10,

A. Radi11,12

National Institute of Chemical Physics and Biophysics, Tallinn, Estonia

M. Kadastik, M. Müntel, M. Murumaa, M. Raidal, L. Rebane, A. Tiko

Department of Physics, University of Helsinki, Helsinki, Finland

P. Eerola, G. Fedi, M. Voutilainen

– 20 –



J
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0
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2
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1
3
)
0
7
2

Helsinki Institute of Physics, Helsinki, Finland

J. Härkönen, A. Heikkinen, V. Karimäki, R. Kinnunen, M.J. Kortelainen, T. Lampén,

K. Lassila-Perini, S. Lehti, T. Lindén, P. Luukka, T. Mäenpää, T. Peltola, E. Tuominen,

J. Tuominiemi, E. Tuovinen, D. Ungaro, L. Wendland

Lappeenranta University of Technology, Lappeenranta, Finland

A. Korpela, T. Tuuva

DSM/IRFU, CEA/Saclay, Gif-sur-Yvette, France

M. Besancon, S. Choudhury, F. Couderc, M. Dejardin, D. Denegri, B. Fabbro, J.L. Faure,

F. Ferri, S. Ganjour, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry, E. Locci,

J. Malcles, L. Millischer, A. Nayak, J. Rander, A. Rosowsky, M. Titov

Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau,

France

S. Baffioni, F. Beaudette, L. Benhabib, L. Bianchini, M. Bluj13, P. Busson, C. Charlot,

N. Daci, T. Dahms, M. Dalchenko, L. Dobrzynski, A. Florent, R. Granier de Cassagnac,

M. Haguenauer, P. Miné, C. Mironov, I.N. Naranjo, M. Nguyen, C. Ochando, P. Paganini,

D. Sabes, R. Salerno, Y. Sirois, C. Veelken, A. Zabi

Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Univer-

sité de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France

J.-L. Agram14, J. Andrea, D. Bloch, D. Bodin, J.-M. Brom, E.C. Chabert, C. Collard,

E. Conte14, F. Drouhin14, J.-C. Fontaine14, D. Gelé, U. Goerlach, P. Juillot, A.-C. Le

Bihan, P. Van Hove

Université de Lyon, Université Claude Bernard Lyon 1, CNRS-IN2P3, Institut

de Physique Nucléaire de Lyon, Villeurbanne, France

S. Beauceron, N. Beaupere, O. Bondu, G. Boudoul, S. Brochet, J. Chasserat, R. Chierici2,

D. Contardo, P. Depasse, H. El Mamouni, J. Fay, S. Gascon, M. Gouzevitch, B. Ille,

T. Kurca, M. Lethuillier, L. Mirabito, S. Perries, L. Sgandurra, V. Sordini, Y. Tschudi,

P. Verdier, S. Viret

Institute of High Energy Physics and Informatization, Tbilisi State University,

Tbilisi, Georgia

Z. Tsamalaidze15

RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany

C. Autermann, S. Beranek, B. Calpas, M. Edelhoff, L. Feld, N. Heracleous, O. Hindrichs,

R. Jussen, K. Klein, J. Merz, A. Ostapchuk, A. Perieanu, F. Raupach, J. Sammet, S. Schael,

D. Sprenger, H. Weber, B. Wittmer, V. Zhukov16

RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany

M. Ata, J. Caudron, E. Dietz-Laursonn, D. Duchardt, M. Erdmann, R. Fischer, A. Güth,

T. Hebbeker, C. Heidemann, K. Hoepfner, D. Klingebiel, P. Kreuzer, M. Merschmeyer,

A. Meyer, M. Olschewski, K. Padeken, P. Papacz, H. Pieta, H. Reithler, S.A. Schmitz,

L. Sonnenschein, J. Steggemann, D. Teyssier, S. Thüer, M. Weber

– 21 –



J
H
E
P
0
4
(
2
0
1
3
)
0
7
2

RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany

M. Bontenackels, V. Cherepanov, Y. Erdogan, G. Flügge, H. Geenen, M. Geisler, W. Haj

Ahmad, F. Hoehle, B. Kargoll, T. Kress, Y. Kuessel, J. Lingemann2, A. Nowack, I.M. Nu-

gent, L. Perchalla, O. Pooth, P. Sauerland, A. Stahl

Deutsches Elektronen-Synchrotron, Hamburg, Germany

M. Aldaya Martin, I. Asin, N. Bartosik, J. Behr, W. Behrenhoff, U. Behrens, M. Bergholz17,

A. Bethani, K. Borras, A. Burgmeier, A. Cakir, L. Calligaris, A. Campbell, E. Castro,

F. Costanza, D. Dammann, C. Diez Pardos, T. Dorland, G. Eckerlin, D. Eckstein,

G. Flucke, A. Geiser, I. Glushkov, P. Gunnellini, S. Habib, J. Hauk, G. Hellwig,

H. Jung, M. Kasemann, P. Katsas, C. Kleinwort, H. Kluge, A. Knutsson, M. Krämer,

D. Krücker, E. Kuznetsova, W. Lange, J. Leonard, W. Lohmann17, B. Lutz, R. Mankel,

I. Marfin, M. Marienfeld, I.-A. Melzer-Pellmann, A.B. Meyer, J. Mnich, A. Mussgiller,

S. Naumann-Emme, O. Novgorodova, F. Nowak, J. Olzem, H. Perrey, A. Petrukhin,

D. Pitzl, A. Raspereza, P.M. Ribeiro Cipriano, C. Riedl, E. Ron, M. Rosin, J. Salfeld-

Nebgen, R. Schmidt17, T. Schoerner-Sadenius, N. Sen, A. Spiridonov, M. Stein, R. Walsh,

C. Wissing

University of Hamburg, Hamburg, Germany

V. Blobel, H. Enderle, J. Erfle, U. Gebbert, M. Görner, M. Gosselink, J. Haller,

T. Hermanns, R.S. Höing, K. Kaschube, G. Kaussen, H. Kirschenmann, R. Klanner,

J. Lange, T. Peiffer, N. Pietsch, D. Rathjens, C. Sander, H. Schettler, P. Schleper,

E. Schlieckau, A. Schmidt, M. Schröder, T. Schum, M. Seidel, J. Sibille18, V. Sola,

H. Stadie, G. Steinbrück, J. Thomsen, L. Vanelderen

Institut für Experimentelle Kernphysik, Karlsruhe, Germany

C. Barth, C. Baus, J. Berger, C. Böser, T. Chwalek, W. De Boer, A. Descroix, A. Dier-

lamm, M. Feindt, M. Guthoff2, C. Hackstein, F. Hartmann2, T. Hauth2, M. Heinrich,

H. Held, K.H. Hoffmann, U. Husemann, I. Katkov16, J.R. Komaragiri, P. Lobelle Pardo,

D. Martschei, S. Mueller, Th. Müller, M. Niegel, A. Nürnberg, O. Oberst, A. Oehler, J. Ott,

G. Quast, K. Rabbertz, F. Ratnikov, N. Ratnikova, S. Röcker, F.-P. Schilling, G. Schott,

H.J. Simonis, F.M. Stober, D. Troendle, R. Ulrich, J. Wagner-Kuhr, S. Wayand, T. Weiler,

M. Zeise

Institute of Nuclear Physics ”Demokritos”, Aghia Paraskevi, Greece

G. Anagnostou, G. Daskalakis, T. Geralis, S. Kesisoglou, A. Kyriakis, D. Loukas,

A. Markou, C. Markou, E. Ntomari

University of Athens, Athens, Greece

L. Gouskos, T.J. Mertzimekis, A. Panagiotou, N. Saoulidou

University of Ioánnina, Ioánnina, Greece

I. Evangelou, C. Foudas, P. Kokkas, N. Manthos, I. Papadopoulos

KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary

G. Bencze, C. Hajdu, P. Hidas, D. Horvath19, F. Sikler, V. Veszpremi, G. Vesztergombi20,

A.J. Zsigmond

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Institute of Nuclear Research ATOMKI, Debrecen, Hungary

N. Beni, S. Czellar, J. Molnar, J. Palinkas, Z. Szillasi

University of Debrecen, Debrecen, Hungary

J. Karancsi, P. Raics, Z.L. Trocsanyi, B. Ujvari

Panjab University, Chandigarh, India

S.B. Beri, V. Bhatnagar, N. Dhingra, R. Gupta, M. Kaur, M.Z. Mehta, M. Mittal, N. Nishu,

L.K. Saini, A. Sharma, J.B. Singh

University of Delhi, Delhi, India

Ashok Kumar, Arun Kumar, S. Ahuja, A. Bhardwaj, B.C. Choudhary, S. Malhotra,

M. Naimuddin, K. Ranjan, P. Saxena, V. Sharma, R.K. Shivpuri

Saha Institute of Nuclear Physics, Kolkata, India

S. Banerjee, S. Bhattacharya, K. Chatterjee, S. Dutta, B. Gomber, Sa. Jain, Sh. Jain,

R. Khurana, A. Modak, S. Mukherjee, D. Roy, S. Sarkar, M. Sharan

Bhabha Atomic Research Centre, Mumbai, India

A. Abdulsalam, D. Dutta, S. Kailas, V. Kumar, A.K. Mohanty2, L.M. Pant, P. Shukla

Tata Institute of Fundamental Research - EHEP, Mumbai, India

T. Aziz, R.M. Chatterjee, S. Ganguly, M. Guchait21, A. Gurtu22, M. Maity23, G. Ma-

jumder, K. Mazumdar, G.B. Mohanty, B. Parida, K. Sudhakar, N. Wickramage

Tata Institute of Fundamental Research - HECR, Mumbai, India

S. Banerjee, S. Dugad

Institute for Research in Fundamental Sciences (IPM), Tehran, Iran

H. Arfaei24, H. Bakhshiansohi, S.M. Etesami25, A. Fahim24, M. Hashemi26, H. Hesari,

A. Jafari, M. Khakzad, M. Mohammadi Najafabadi, S. Paktinat Mehdiabadi,

B. Safarzadeh27, M. Zeinali

INFN Sezione di Bari a, Università di Bari b, Politecnico di Bari c, Bari, Italy

M. Abbresciaa,b, L. Barbonea,b, C. Calabriaa,b,2, S.S. Chhibraa,b, A. Colaleoa,

D. Creanzaa,c, N. De Filippisa,c,2, M. De Palmaa,b, L. Fiorea, G. Iasellia,c, G. Maggia,c,

M. Maggia, B. Marangellia,b, S. Mya,c, S. Nuzzoa,b, N. Pacificoa, A. Pompilia,b,

G. Pugliesea,c, G. Selvaggia,b, L. Silvestrisa, G. Singha,b, R. Vendittia,b, P. Verwilligena,

G. Zitoa

INFN Sezione di Bologna a, Università di Bologna b, Bologna, Italy

G. Abbiendia, A.C. Benvenutia, D. Bonacorsia,b, S. Braibant-Giacomellia,b,

L. Brigliadoria,b, P. Capiluppia,b, A. Castroa,b, F.R. Cavalloa, M. Cuffiania,b,

G.M. Dallavallea, F. Fabbria, A. Fanfania,b, D. Fasanellaa,b, P. Giacomellia, C. Grandia,

L. Guiduccia,b, S. Marcellinia, G. Masettia, M. Meneghellia,b,2, A. Montanaria,

F.L. Navarriaa,b, F. Odoricia, A. Perrottaa, F. Primaveraa,b, A.M. Rossia,b, T. Rovellia,b,

G.P. Sirolia,b, N. Tosi, R. Travaglinia,b

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INFN Sezione di Catania a, Università di Catania b, Catania, Italy

S. Albergoa,b, G. Cappelloa,b, M. Chiorbolia,b, S. Costaa,b, R. Potenzaa,b, A. Tricomia,b,

C. Tuvea,b

INFN Sezione di Firenze a, Università di Firenze b, Firenze, Italy

G. Barbaglia, V. Ciullia,b, C. Civininia, R. D’Alessandroa,b, E. Focardia,b, S. Frosalia,b,

E. Galloa, S. Gonzia,b, M. Meschinia, S. Paolettia, G. Sguazzonia, A. Tropianoa,b

INFN Laboratori Nazionali di Frascati, Frascati, Italy

L. Benussi, S. Bianco, S. Colafranceschi28, F. Fabbri, D. Piccolo

INFN Sezione di Genova a, Università di Genova b, Genova, Italy

P. Fabbricatorea, R. Musenicha, S. Tosia,b

INFN Sezione di Milano-Bicocca a, Università di Milano-Bicocca b, Milano,

Italy

A. Benagliaa, F. De Guioa,b, L. Di Matteoa,b,2, S. Fiorendia,b, S. Gennaia,2, A. Ghezzia,b,

M.T. Lucchini2, S. Malvezzia, R.A. Manzonia,b, A. Martellia,b, A. Massironia,b,

D. Menascea, L. Moronia, M. Paganonia,b, D. Pedrinia, S. Ragazzia,b, N. Redaellia,

T. Tabarelli de Fatisa,b

INFN Sezione di Napoli a, Università di Napoli ’Federico II’ b, Università della

Basilicata (Potenza) c, Università G. Marconi (Roma) d, Napoli, Italy

S. Buontempoa, N. Cavalloa,c, A. De Cosaa,b,2, O. Doganguna,b, F. Fabozzia,c,

A.O.M. Iorioa,b, L. Listaa, S. Meolaa,d,2, M. Merolaa, P. Paoluccia,2

INFN Sezione di Padova a, Università di Padova b, Università di

Trento (Trento) c, Padova, Italy

P. Azzia, N. Bacchettaa,2, D. Biselloa,b, A. Brancaa,b,2, R. Carlina,b, P. Checchiaa,

T. Dorigoa, M. Galantia,b, F. Gasparinia,b, U. Gasparinia,b, A. Gozzelinoa,

K. Kanishcheva,c, S. Lacapraraa, I. Lazzizzeraa,c, M. Margonia,b, A.T. Meneguzzoa,b,

J. Pazzinia,b, M. Pegoraroa, N. Pozzobona,b, P. Ronchesea,b, F. Simonettoa,b, E. Torassaa,

M. Tosia,b, S. Vaninia,b, P. Zottoa,b, G. Zumerlea,b

INFN Sezione di Pavia a, Università di Pavia b, Pavia, Italy

M. Gabusia,b, S.P. Rattia,b, C. Riccardia,b, P. Torrea,b, P. Vituloa,b

INFN Sezione di Perugia a, Università di Perugia b, Perugia, Italy

M. Biasinia,b, G.M. Bileia, L. Fanòa,b, P. Laricciaa,b, G. Mantovania,b, M. Menichellia,

A. Nappia,b†, F. Romeoa,b, A. Sahaa, A. Santocchiaa,b, A. Spieziaa,b, S. Taronia,b

INFN Sezione di Pisa a, Università di Pisa b, Scuola Normale Superiore di

Pisa c, Pisa, Italy

P. Azzurria,c, G. Bagliesia, J. Bernardinia, T. Boccalia, G. Broccoloa,c, R. Castaldia,

R.T. D’Agnoloa,c,2, R. Dell’Orsoa, F. Fioria,b,2, L. Foàa,c, A. Giassia, A. Kraana,

F. Ligabuea,c, T. Lomtadzea, L. Martinia,29, A. Messineoa,b, F. Pallaa, A. Rizzia,b,

A.T. Serbana,30, P. Spagnoloa, P. Squillaciotia,2, R. Tenchinia, G. Tonellia,b, A. Venturia,

P.G. Verdinia

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INFN Sezione di Roma a, Università di Roma b, Roma, Italy

L. Baronea,b, F. Cavallaria, D. Del Rea,b, M. Diemoza, C. Fanellia,b, M. Grassia,b,2,

E. Longoa,b, P. Meridiania,2, F. Michelia,b, S. Nourbakhsha,b, G. Organtinia,b,

R. Paramattia, S. Rahatloua,b, L. Soffia,b

INFN Sezione di Torino a, Università di Torino b, Università del Piemonte

Orientale (Novara) c, Torino, Italy

N. Amapanea,b, R. Arcidiaconoa,c, S. Argiroa,b, M. Arneodoa,c, C. Biinoa, N. Cartigliaa,

S. Casassoa,b, M. Costaa,b, N. Demariaa, C. Mariottia,2, S. Masellia, E. Migliorea,b,

V. Monacoa,b, M. Musicha,2, M.M. Obertinoa,c, N. Pastronea, M. Pelliccionia,

A. Potenzaa,b, A. Romeroa,b, M. Ruspaa,c, R. Sacchia,b, A. Solanoa,b, A. Staianoa

INFN Sezione di Trieste a, Università di Trieste b, Trieste, Italy

S. Belfortea, V. Candelisea,b, M. Casarsaa, F. Cossuttia,2, G. Della Riccaa,b, B. Gobboa,

M. Maronea,b,2, D. Montaninoa,b, A. Penzoa, A. Schizzia,b

Kangwon National University, Chunchon, Korea

T.Y. Kim, S.K. Nam

Kyungpook National University, Daegu, Korea

S. Chang, D.H. Kim, G.N. Kim, D.J. Kong, H. Park, D.C. Son

Chonnam National University, Institute for Universe and Elementary Particles,

Kwangju, Korea

J.Y. Kim, Zero J. Kim, S. Song

Korea University, Seoul, Korea

S. Choi, D. Gyun, B. Hong, M. Jo, H. Kim, T.J. Kim, K.S. Lee, D.H. Moon, S.K. Park,

Y. Roh

University of Seoul, Seoul, Korea

M. Choi, J.H. Kim, C. Park, I.C. Park, S. Park, G. Ryu

Sungkyunkwan University, Suwon, Korea

Y. Choi, Y.K. Choi, J. Goh, M.S. Kim, E. Kwon, B. Lee, J. Lee, S. Lee, H. Seo, I. Yu

Vilnius University, Vilnius, Lithuania

M.J. Bilinskas, I. Grigelionis, M. Janulis, A. Juodagalvis

Centro de Investigacion y de Estudios Avanzados del IPN, Mexico City, Mexico

H. Castilla-Valdez, E. De La Cruz-Burelo, I. Heredia-de La Cruz, R. Lopez-Fernandez,

J. Mart́ınez-Ortega, A. Sanchez-Hernandez, L.M. Villasenor-Cendejas

Universidad Iberoamericana, Mexico City, Mexico

S. Carrillo Moreno, F. Vazquez Valencia

Benemerita Universidad Autonoma de Puebla, Puebla, Mexico

H.A. Salazar Ibarguen

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Universidad Autónoma de San Luis Potośı, San Luis Potośı, Mexico

E. Casimiro Linares, A. Morelos Pineda, M.A. Reyes-Santos

University of Auckland, Auckland, New Zealand

D. Krofcheck

University of Canterbury, Christchurch, New Zealand

A.J. Bell, P.H. Butler, R. Doesburg, S. Reucroft, H. Silverwood

National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan

M. Ahmad, M.I. Asghar, J. Butt, H.R. Hoorani, S. Khalid, W.A. Khan, T. Khurshid,

S. Qazi, M.A. Shah, M. Shoaib

National Centre for Nuclear Research, Swierk, Poland

H. Bialkowska, B. Boimska, T. Frueboes, M. Górski, M. Kazana, K. Nawrocki,

K. Romanowska-Rybinska, M. Szleper, G. Wrochna, P. Zalewski

Institute of Experimental Physics, Faculty of Physics, University of Warsaw,

Warsaw, Poland

G. Brona, K. Bunkowski, M. Cwiok, W. Dominik, K. Doroba, A. Kalinowski, M. Konecki,

J. Krolikowski, M. Misiura, W. Wolszczak

Laboratório de Instrumentação e F́ısica Experimental de Part́ıculas, Lisboa,

Portugal

N. Almeida, P. Bargassa, A. David, P. Faccioli, P.G. Ferreira Parracho, M. Gallinaro,

J. Seixas2, J. Varela, P. Vischia

Joint Institute for Nuclear Research, Dubna, Russia

I. Belotelov, P. Bunin, M. Gavrilenko, I. Golutvin, I. Gorbunov, A. Kamenev, V. Karjavin,

G. Kozlov, A. Lanev, A. Malakhov, P. Moisenz, V. Palichik, V. Perelygin, S. Shmatov,

V. Smirnov, A. Volodko, A. Zarubin

Petersburg Nuclear Physics Institute, Gatchina (St. Petersburg), Russia

S. Evstyukhin, V. Golovtsov, Y. Ivanov, V. Kim, P. Levchenko, V. Murzin, V. Oreshkin,

I. Smirnov, V. Sulimov, L. Uvarov, S. Vavilov, A. Vorobyev, An. Vorobyev

Institute for Nuclear Research, Moscow, Russia

Yu. Andreev, A. Dermenev, S. Gninenko, N. Golubev, M. Kirsanov, N. Krasnikov,

V. Matveev, A. Pashenkov, D. Tlisov, A. Toropin

Institute for Theoretical and Experimental Physics, Moscow, Russia

V. Epshteyn, M. Erofeeva, V. Gavrilov, M. Kossov, N. Lychkovskaya, V. Popov,

G. Safronov, S. Semenov, I. Shreyber, V. Stolin, E. Vlasov, A. Zhokin

P.N. Lebedev Physical Institute, Moscow, Russia

V. Andreev, M. Azarkin, I. Dremin, M. Kirakosyan, A. Leonidov, G. Mesyats,

S.V. Rusakov, A. Vinogradov

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Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University,

Moscow, Russia

A. Belyaev, G. Bogdanova, E. Boos, L. Khein, V. Klyukhin, O. Kodolova, I. Lokhtin,

O. Lukina, A. Markina, S. Obraztsov, M. Perfilov, S. Petrushanko, A. Popov,

A. Proskuryakov, L. Sarycheva†, V. Savrin, V. Volkov

State Research Center of Russian Federation, Institute for High Energy

Physics, Protvino, Russia

I. Azhgirey, I. Bayshev, S. Bitioukov, V. Grishin2, V. Kachanov, D. Konstantinov,

V. Krychkine, V. Petrov, R. Ryutin, A. Sobol, L. Tourtchanovitch, S. Troshin, N. Tyurin,

A. Uzunian, A. Volkov

University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear

Sciences, Belgrade, Serbia

P. Adzic31, M. Djordjevic, M. Ekmedzic, D. Krpic31, J. Milosevic

Centro de Investigaciones Energéticas Medioambientales y Tec-

nológicas (CIEMAT), Madrid, Spain

M. Aguilar-Benitez, J. Alcaraz Maestre, P. Arce, C. Battilana, E. Calvo, M. Cerrada,

M. Chamizo Llatas, N. Colino, B. De La Cruz, A. Delgado Peris, D. Domı́nguez Vázquez,

C. Fernandez Bedoya, J.P. Fernández Ramos, A. Ferrando, J. Flix, M.C. Fouz, P. Garcia-

Abia, O. Gonzalez Lopez, S. Goy Lopez, J.M. Hernandez, M.I. Josa, G. Merino, J. Puerta

Pelayo, A. Quintario Olmeda, I. Redondo, L. Romero, J. Santaolalla, M.S. Soares,

C. Willmott

Universidad Autónoma de Madrid, Madrid, Spain

C. Albajar, G. Codispoti, J.F. de Trocóniz

Universidad de Oviedo, Oviedo, Spain

H. Brun, J. Cuevas, J. Fernandez Menendez, S. Folgueras, I. Gonzalez Caballero, L. Lloret

Iglesias, J. Piedra Gomez

Instituto de F́ısica de Cantabria (IFCA), CSIC-Universidad de Cantabria,

Santander, Spain

J.A. Brochero Cifuentes, I.J. Cabrillo, A. Calderon, S.H. Chuang, J. Duarte Campderros,

M. Felcini32, M. Fernandez, G. Gomez, J. Gonzalez Sanchez, A. Graziano, C. Jorda,

A. Lopez Virto, J. Marco, R. Marco, C. Martinez Rivero, F. Matorras, F.J. Munoz Sanchez,

T. Rodrigo, A.Y. Rodŕıguez-Marrero, A. Ruiz-Jimeno, L. Scodellaro, I. Vila, R. Vilar

Cortabitarte

CERN, European Organization for Nuclear Research, Geneva, Switzerland

D. Abbaneo, E. Auffray, G. Auzinger, M. Bachtis, P. Baillon, A.H. Ball, D. Barney,

J. Bendavid, J.F. Benitez, C. Bernet6, G. Bianchi, P. Bloch, A. Bocci, A. Bonato,

C. Botta, H. Breuker, T. Camporesi, G. Cerminara, T. Christiansen, J.A. Coarasa Perez,

D. d’Enterria, A. Dabrowski, A. De Roeck, S. De Visscher, S. Di Guida, M. Dobson,

N. Dupont-Sagorin, A. Elliott-Peisert, J. Eugster, B. Frisch, W. Funk, G. Georgiou,

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M. Giffels, D. Gigi, K. Gill, D. Giordano, M. Girone, M. Giunta, F. Glege, R. Gomez-

Reino Garrido, P. Govoni, S. Gowdy, R. Guida, J. Hammer, M. Hansen, P. Harris,

C. Hartl, J. Harvey, B. Hegner, A. Hinzmann, V. Innocente, P. Janot, K. Kaadze,

E. Karavakis, K. Kousouris, K. Krajczar, P. Lecoq, Y.-J. Lee, P. Lenzi, C. Lourenço,

N. Magini, T. Mäki, M. Malberti, L. Malgeri, M. Mannelli, L. Masetti, F. Meijers, S. Mersi,

E. Meschi, R. Moser, M. Mulders, P. Musella, E. Nesvold, L. Orsini, E. Palencia Cortezon,

E. Perez, L. Perrozzi, A. Petrilli, A. Pfeiffer, M. Pierini, M. Pimiä, D. Piparo, G. Polese,

L. Quertenmont, A. Racz, W. Reece, J. Rodrigues Antunes, G. Rolandi33, C. Rovelli34,

M. Rovere, H. Sakulin, F. Santanastasio, C. Schäfer, C. Schwick, I. Segoni, S. Sekmen,

A. Sharma, P. Siegrist, P. Silva, M. Simon, P. Sphicas35, D. Spiga, A. Tsirou, G.I. Veres20,

J.R. Vlimant, H.K. Wöhri, S.D. Worm36, W.D. Zeuner

Paul Scherrer Institut, Villigen, Switzerland

W. Bertl, K. Deiters, W. Erdmann, K. Gabathuler, R. Horisberger, Q. Ingram,

H.C. Kaestli, S. König, D. Kotlinski, U. Langenegger, F. Meier, D. Renker, T. Rohe

Institute for Particle Physics, ETH Zurich, Zurich, Switzerland

F. Bachmair, L. Bäni, P. Bortignon, M.A. Buchmann, B. Casal, N. Chanon, A. Deisher,

G. Dissertori, M. Dittmar, M. Donegà, M. Dünser, P. Eller, K. Freudenreich, C. Grab,

D. Hits, P. Lecomte, W. Lustermann, A.C. Marini, P. Martinez Ruiz del Arbol, N. Mohr,

F. Moortgat, C. Nägeli37, P. Nef, F. Nessi-Tedaldi, F. Pandolfi, L. Pape, F. Pauss,

M. Peruzzi, F.J. Ronga, M. Rossini, L. Sala, A.K. Sanchez, A. Starodumov38, B. Stieger,

M. Takahashi, L. Tauscher†, A. Thea, K. Theofilatos, D. Treille, C. Urscheler, R. Wallny,

H.A. Weber, L. Wehrli

Universität Zürich, Zurich, Switzerland

C. Amsler39, V. Chiochia, C. Favaro, M. Ivova Rikova, B. Kilminster, B. Millan Mejias,

P. Otiougova, P. Robmann, H. Snoek, S. Tupputi, M. Verzetti

National Central University, Chung-Li, Taiwan

M. Cardaci, Y.H. Chang, K.H. Chen, C. Ferro, C.M. Kuo, S.W. Li, W. Lin, Y.J. Lu,

A.P. Singh, R. Volpe, S.S. Yu

National Taiwan University (NTU), Taipei, Taiwan

P. Bartalini, P. Chang, Y.H. Chang, Y.W. Chang, Y. Chao, K.F. Chen, C. Dietz,

U. Grundler, W.-S. Hou, Y. Hsiung, K.Y. Kao, Y.J. Lei, R.-S. Lu, D. Majumder,

E. Petrakou, X. Shi, J.G. Shiu, Y.M. Tzeng, X. Wan, M. Wang

Chulalongkorn University, Bangkok, Thailand

B. Asavapibhop, E. Simili, N. Srimanobhas, N. Suwonjandee

Cukurova University, Adana, Turkey

A. Adiguzel, M.N. Bakirci40, S. Cerci41, C. Dozen, I. Dumanoglu, E. Eskut, S. Girgis,

G. Gokbulut, E. Gurpinar, I. Hos, E.E. Kangal, T. Karaman, G. Karapinar42, A. Kayis

Topaksu, G. Onengut, K. Ozdemir, S. Ozturk43, A. Polatoz, K. Sogut44, D. Sunar Cerci41,

B. Tali41, H. Topakli40, M. Vergili

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Middle East Technical University, Physics Department, Ankara, Turkey

I.V. Akin, T. Aliev, B. Bilin, S. Bilmis, M. Deniz, H. Gamsizkan, A.M. Guler, K. Ocalan,

A. Ozpineci, M. Serin, R. Sever, U.E. Surat, M. Yalvac, M. Zeyrek

Bogazici University, Istanbul, Turkey

E. Gülmez, B. Isildak45, M. Kaya46, O. Kaya46, S. Ozkorucuklu47, N. Sonmez48

Istanbul Technical University, Istanbul, Turkey

H. Bahtiyar49, E. Barlas, K. Cankocak, Y.O. Günaydin50, F.I. Vardarlı, M. Yücel

National Scientific Center, Kharkov Institute of Physics and Technology,

Kharkov, Ukraine

L. Levchuk

University of Bristol, Bristol, United Kingdom

J.J. Brooke, E. Clement, D. Cussans, H. Flacher, R. Frazier, J. Goldstein, M. Grimes,

G.P. Heath, H.F. Heath, L. Kreczko, S. Metson, D.M. Newbold36, K. Nirunpong, A. Poll,

S. Senkin, V.J. Smith, T. Williams

Rutherford Appleton Laboratory, Didcot, United Kingdom

L. Basso51, K.W. Bell, A. Belyaev51, C. Brew, R.M. Brown, D.J.A. Cockerill, J.A. Cough-

lan, K. Harder, S. Harper, J. Jackson, B.W. Kennedy, E. Olaiya, D. Petyt, B.C. Radburn-

Smith, C.H. Shepherd-Themistocleous, I.R. Tomalin, W.J. Womersley

Imperial College, London, United Kingdom

R. Bainbridge, G. Ball, R. Beuselinck, O. Buchmuller, D. Colling, N. Cripps, M. Cutajar,

P. Dauncey, G. Davies, M. Della Negra, W. Ferguson, J. Fulcher, D. Futyan, A. Gilbert,

A. Guneratne Bryer, G. Hall, Z. Hatherell, J. Hays, G. Iles, M. Jarvis, G. Karapostoli,

M. Kenzie, L. Lyons, A.-M. Magnan, J. Marrouche, B. Mathias, R. Nandi, J. Nash,

A. Nikitenko38, J. Pela, M. Pesaresi, K. Petridis, M. Pioppi52, D.M. Raymond, S. Rogerson,

A. Rose, C. Seez, P. Sharp†, A. Sparrow, M. Stoye, A. Tapper, M. Vazquez Acosta,

T. Virdee, S. Wakefield, N. Wardle, T. Whyntie

Brunel University, Uxbridge, United Kingdom

M. Chadwick, J.E. Cole, P.R. Hobson, A. Khan, P. Kyberd, D. Leggat, D. Leslie,

W. Martin, I.D. Reid, P. Symonds, L. Teodorescu, M. Turner

Baylor University, Waco, USA

K. Hatakeyama, H. Liu, T. Scarborough

The University of Alabama, Tuscaloosa, USA

O. Charaf, S.I. Cooper, C. Henderson, P. Rumerio

Boston University, Boston, USA

A. Avetisyan, T. Bose, C. Fantasia, A. Heister, P. Lawson, D. Lazic, J. Rohlf, D. Sperka,

J. St. John, L. Sulak

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Brown University, Providence, USA

J. Alimena, S. Bhattacharya, G. Christopher, D. Cutts, Z. Demiragli, A. Ferapontov,

A. Garabedian, U. Heintz, S. Jabeen, G. Kukartsev, E. Laird, G. Landsberg, M. Luk,

M. Narain, M. Segala, T. Sinthuprasith, T. Speer

University of California, Davis, Davis, USA

R. Breedon, G. Breto, M. Calderon De La Barca Sanchez, M. Caulfield, S. Chauhan,

M. Chertok, J. Conway, R. Conway, P.T. Cox, J. Dolen, R. Erbacher, M. Gardner,

R. Houtz, W. Ko, A. Kopecky, R. Lander, O. Mall, T. Miceli, R. Nelson, D. Pellett,

F. Ricci-Tam, B. Rutherford, M. Searle, J. Smith, M. Squires, M. Tripathi, R. Vasquez

Sierra, R. Yohay

University of California, Los Angeles, USA

V. Andreev, D. Cline, R. Cousins, J. Duris, S. Erhan, P. Everaerts, C. Farrell, J. Hauser,

M. Ignatenko, C. Jarvis, G. Rakness, P. Schlein†, P. Traczyk, V. Valuev, M. Weber

University of California, Riverside, Riverside, USA

J. Babb, R. Clare, M.E. Dinardo, J. Ellison, J.W. Gary, F. Giordano, G. Hanson, H. Liu,

O.R. Long, A. Luthra, H. Nguyen, S. Paramesvaran, J. Sturdy, S. Sumowidagdo, R. Wilken,

S. Wimpenny

University of California, San Diego, La Jolla, USA

W. Andrews, J.G. Branson, G.B. Cerati, S. Cittolin, D. Evans, A. Holzner, R. Kelley,

M. Lebourgeois, J. Letts, I. Macneill, B. Mangano, S. Padhi, C. Palmer, G. Petrucciani,

M. Pieri, M. Sani, V. Sharma, S. Simon, E. Sudano, M. Tadel, Y. Tu, A. Vartak,

S. Wasserbaech53, F. Würthwein, A. Yagil, J. Yoo

University of California, Santa Barbara, Santa Barbara, USA

D. Barge, R. Bellan, C. Campagnari, M. D’Alfonso, T. Danielson, K. Flowers, P. Geffert,

C. George, F. Golf, J. Incandela, C. Justus, P. Kalavase, D. Kovalskyi, V. Krutelyov,

S. Lowette, R. Magaña Villalba, N. Mccoll, V. Pavlunin, J. Ribnik, J. Richman, R. Rossin,

D. Stuart, W. To, C. West

California Institute of Technology, Pasadena, USA

A. Apresyan, A. Bornheim, J. Bunn, Y. Chen, E. Di Marco, J. Duarte, M. Gataullin,

D. Kcira, Y. Ma, A. Mott, H.B. Newman, C. Rogan, M. Spiropulu, V. Timciuc, J. Veverka,

R. Wilkinson, S. Xie, Y. Yang, R.Y. Zhu

Carnegie Mellon University, Pittsburgh, USA

V. Azzolini, A. Calamba, R. Carroll, T. Ferguson, Y. Iiyama, D.W. Jang, Y.F. Liu,

M. Paulini, H. Vogel, I. Vorobiev

University of Colorado at Boulder, Boulder, USA

J.P. Cumalat, B.R. Drell, W.T. Ford, A. Gaz, E. Luiggi Lopez, J.G. Smith, K. Stenson,

K.A. Ulmer, S.R. Wagner

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Cornell University, Ithaca, USA

J. Alexander, A. Chatterjee, N. Eggert, L.K. Gibbons, B. Heltsley, W. Hopkins, A. Khukhu-

naishvili, B. Kreis, N. Mirman, G. Nicolas Kaufman, J.R. Patterson, A. Ryd, E. Salvati,

W. Sun, W.D. Teo, J. Thom, J. Thompson, J. Tucker, Y. Weng, L. Winstrom, P. Wittich

Fairfield University, Fairfield, USA

D. Winn

Fermi National Accelerator Laboratory, Batavia, USA

S. Abdullin, M. Albrow, J. Anderson, L.A.T. Bauerdick, A. Beretvas, J. Berryhill,

P.C. Bhat, K. Burkett, J.N. Butler, V. Chetluru, H.W.K. Cheung, F. Chlebana, S. Ci-

hangir, V.D. Elvira, I. Fisk, J. Freeman, Y. Gao, D. Green, O. Gutsche, J. Hanlon,

R.M. Harris, J. Hirschauer, B. Hooberman, S. Jindariani, M. Johnson, U. Joshi, B. Klima,

S. Kunori, S. Kwan, C. Leonidopoulos54, J. Linacre, D. Lincoln, R. Lipton, J. Lykken,

K. Maeshima, J.M. Marraffino, V.I. Martinez Outschoorn, S. Maruyama, D. Mason,

P. McBride, K. Mishra, S. Mrenna, Y. Musienko55, C. Newman-Holmes, V. O’Dell,

O. Prokofyev, E. Sexton-Kennedy, S. Sharma, W.J. Spalding, L. Spiegel, L. Taylor,

S. Tkaczyk, N.V. Tran, L. Uplegger, E.W. Vaandering, R. Vidal, J. Whitmore, W. Wu,

F. Yang, J.C. Yun

University of Florida, Gainesville, USA

D. Acosta, P. Avery, D. Bourilkov, M. Chen, T. Cheng, S. Das, M. De Gruttola, G.P. Di

Giovanni, D. Dobur, A. Drozdetskiy, R.D. Field, M. Fisher, Y. Fu, I.K. Furic, J. Gartner,

J. Hugon, B. Kim, J. Konigsberg, A. Korytov, A. Kropivnitskaya, T. Kypreos, J.F. Low,

K. Matchev, P. Milenovic56, G. Mitselmakher, L. Muniz, R. Remington, A. Rinkevicius,

N. Skhirtladze, M. Snowball, J. Yelton, M. Zakaria

Florida International University, Miami, USA

V. Gaultney, S. Hewamanage, L.M. Lebolo, S. Linn, P. Markowitz, G. Martinez, J.L. Ro-

driguez

Florida State University, Tallahassee, USA

T. Adams, A. Askew, J. Bochenek, J. Chen, B. Diamond, S.V. Gleyzer, J. Haas,

S. Hagopian, V. Hagopian, M. Jenkins, K.F. Johnson, H. Prosper, V. Veeraraghavan,

M. Weinberg

Florida Institute of Technology, Melbourne, USA

M.M. Baarmand, B. Dorney, M. Hohlmann, H. Kalakhety, I. Vodopiyanov, F. Yumiceva

University of Illinois at Chicago (UIC), Chicago, USA

M.R. Adams, L. Apanasevich, Y. Bai, V.E. Bazterra, R.R. Betts, I. Bucinskaite, J. Callner,

R. Cavanaugh, O. Evdokimov, L. Gauthier, C.E. Gerber, D.J. Hofman, S. Khalatyan,

F. Lacroix, C. O’Brien, C. Silkworth, D. Strom, P. Turner, N. Varelas

The University of Iowa, Iowa City, USA

U. Akgun, E.A. Albayrak, B. Bilki57, W. Clarida, K. Dilsiz, F. Duru, S. Griffiths, J.-

P. Merlo, H. Mermerkaya58, A. Mestvirishvili, A. Moeller, J. Nachtman, C.R. Newsom,

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E. Norbeck, H. Ogul, Y. Onel, F. Ozok49, S. Sen, P. Tan, E. Tiras, J. Wetzel, T. Yetkin,

K. Yi

Johns Hopkins University, Baltimore, USA

B.A. Barnett, B. Blumenfeld, S. Bolognesi, D. Fehling, G. Giurgiu, A.V. Gritsan, Z.J. Guo,

G. Hu, P. Maksimovic, M. Swartz, A. Whitbeck

The University of Kansas, Lawrence, USA

P. Baringer, A. Bean, G. Benelli, R.P. Kenny Iii, M. Murray, D. Noonan, S. Sanders,

R. Stringer, G. Tinti, J.S. Wood

Kansas State University, Manhattan, USA

A.F. Barfuss, T. Bolton, I. Chakaberia, A. Ivanov, S. Khalil, M. Makouski, Y. Maravin,

S. Shrestha, I. Svintradze

Lawrence Livermore National Laboratory, Livermore, USA

J. Gronberg, D. Lange, F. Rebassoo, D. Wright

University of Maryland, College Park, USA

A. Baden, B. Calvert, S.C. Eno, J.A. Gomez, N.J. Hadley, R.G. Kellogg, M. Kirn,

T. Kolberg, Y. Lu, M. Marionneau, A.C. Mignerey, K. Pedro, A. Peterman, A. Skuja,

J. Temple, M.B. Tonjes, S.C. Tonwar

Massachusetts Institute of Technology, Cambridge, USA

A. Apyan, G. Bauer, W. Busza, E. Butz, I.A. Cali, M. Chan, V. Dutta, G. Gomez

Ceballos, M. Goncharov, Y. Kim, M. Klute, A. Levin, P.D. Luckey, T. Ma, S. Nahn,

C. Paus, D. Ralph, C. Roland, G. Roland, G.S.F. Stephans, F. Stöckli, K. Sumorok,

K. Sung, D. Velicanu, E.A. Wenger, R. Wolf, B. Wyslouch, M. Yang, Y. Yilmaz, A.S. Yoon,

M. Zanetti, V. Zhukova

University of Minnesota, Minneapolis, USA

B. Dahmes, A. De Benedetti, G. Franzoni, A. Gude, S.C. Kao, K. Klapoetke, Y. Kubota,

J. Mans, N. Pastika, R. Rusack, M. Sasseville, A. Singovsky, N. Tambe, J. Turkewitz

University of Mississippi, Oxford, USA

L.M. Cremaldi, R. Kroeger, L. Perera, R. Rahmat, D.A. Sanders

University of Nebraska-Lincoln, Lincoln, USA

E. Avdeeva, K. Bloom, S. Bose, D.R. Claes, A. Dominguez, M. Eads, J. Keller,

I. Kravchenko, J. Lazo-Flores, S. Malik, G.R. Snow

State University of New York at Buffalo, Buffalo, USA

A. Godshalk, I. Iashvili, S. Jain, A. Kharchilava, A. Kumar, S. Rappoccio, Z. Wan

Northeastern University, Boston, USA

G. Alverson, E. Barberis, D. Baumgartel, M. Chasco, J. Haley, D. Nash, T. Orimoto,

D. Trocino, D. Wood, J. Zhang

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Northwestern University, Evanston, USA

A. Anastassov, K.A. Hahn, A. Kubik, L. Lusito, N. Mucia, N. Odell, R.A. Ofierzynski,

B. Pollack, A. Pozdnyakov, M. Schmitt, S. Stoynev, M. Velasco, S. Won

University of Notre Dame, Notre Dame, USA

D. Berry, A. Brinkerhoff, K.M. Chan, M. Hildreth, C. Jessop, D.J. Karmgard, J. Kolb,

K. Lannon, W. Luo, S. Lynch, N. Marinelli, D.M. Morse, T. Pearson, M. Planer, R. Ruchti,

J. Slaunwhite, N. Valls, M. Wayne, M. Wolf

The Ohio State University, Columbus, USA

L. Antonelli, B. Bylsma, L.S. Durkin, C. Hill, R. Hughes, K. Kotov, T.Y. Ling, D. Puigh,

M. Rodenburg, G. Smith, C. Vuosalo, G. Williams, B.L. Winer

Princeton University, Princeton, USA

E. Berry, P. Elmer, V. Halyo, P. Hebda, J. Hegeman, A. Hunt, P. Jindal, S.A. Koay,

D. Lopes Pegna, P. Lujan, D. Marlow, T. Medvedeva, M. Mooney, J. Olsen, P. Piroué,

X. Quan, A. Raval, H. Saka, D. Stickland, C. Tully, J.S. Werner, S.C. Zenz, A. Zuranski

University of Puerto Rico, Mayaguez, USA

E. Brownson, A. Lopez, H. Mendez, J.E. Ramirez Vargas

Purdue University, West Lafayette, USA

E. Alagoz, V.E. Barnes, D. Benedetti, G. Bolla, D. Bortoletto, M. De Mattia, A. Everett,

Z. Hu, M. Jones, O. Koybasi, M. Kress, A.T. Laasanen, N. Leonardo, V. Maroussov,

P. Merkel, D.H. Miller, N. Neumeister, I. Shipsey, D. Silvers, A. Svyatkovskiy, M. Vidal

Marono, H.D. Yoo, J. Zablocki, Y. Zheng

Purdue University Calumet, Hammond, USA

S. Guragain, N. Parashar

Rice University, Houston, USA

A. Adair, B. Akgun, C. Boulahouache, K.M. Ecklund, F.J.M. Geurts, W. Li, B.P. Padley,

R. Redjimi, J. Roberts, J. Zabel

University of Rochester, Rochester, USA

B. Betchart, A. Bodek, Y.S. Chung, R. Covarelli, P. de Barbaro, R. Demina, Y. Eshaq,

T. Ferbel, A. Garcia-Bellido, P. Goldenzweig, J. Han, A. Harel, D.C. Miner, D. Vishnevskiy,

M. Zielinski

The Rockefeller University, New York, USA

A. Bhatti, R. Ciesielski, L. Demortier, K. Goulianos, G. Lungu, S. Malik, C. Mesropian

Rutgers, The State University of New Jersey, Piscataway, USA

S. Arora, A. Barker, J.P. Chou, C. Contreras-Campana, E. Contreras-Campana, D. Dug-

gan, D. Ferencek, Y. Gershtein, R. Gray, E. Halkiadakis, D. Hidas, A. Lath, S. Panwalkar,

M. Park, R. Patel, V. Rekovic, J. Robles, K. Rose, S. Salur, S. Schnetzer, C. Seitz,

S. Somalwar, R. Stone, S. Thomas, M. Walker

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University of Tennessee, Knoxville, USA

G. Cerizza, M. Hollingsworth, S. Spanier, Z.C. Yang, A. York

Texas A&M University, College Station, USA

R. Eusebi, W. Flanagan, J. Gilmore, T. Kamon59, V. Khotilovich, R. Montalvo, I. Os-

ipenkov, Y. Pakhotin, A. Perloff, J. Roe, A. Safonov, T. Sakuma, S. Sengupta, I. Suarez,

A. Tatarinov, D. Toback

Texas Tech University, Lubbock, USA

N. Akchurin, J. Damgov, C. Dragoiu, P.R. Dudero, C. Jeong, K. Kovitanggoon, S.W. Lee,

T. Libeiro, I. Volobouev

Vanderbilt University, Nashville, USA

E. Appelt, A.G. Delannoy, C. Florez, S. Greene, A. Gurrola, W. Johns, P. Kurt, C. Maguire,

A. Melo, M. Sharma, P. Sheldon, B. Snook, S. Tuo, J. Velkovska

University of Virginia, Charlottesville, USA

M.W. Arenton, M. Balazs, S. Boutle, B. Cox, B. Francis, J. Goodell, R. Hirosky,

A. Ledovskoy, C. Lin, C. Neu, J. Wood

Wayne State University, Detroit, USA

S. Gollapinni, R. Harr, P.E. Karchin, C. Kottachchi Kankanamge Don, P. Lamichhane,

A. Sakharov

University of Wisconsin, Madison, USA

M. Anderson, D.A. Belknap, L. Borrello, D. Carlsmith, M. Cepeda, S. Dasu, E. Friis,

L. Gray, K.S. Grogg, M. Grothe, R. Hall-Wilton, M. Herndon, A. Hervé, P. Klabbers,

J. Klukas, A. Lanaro, C. Lazaridis, R. Loveless, A. Mohapatra, M.U. Mozer, I. Ojalvo,

F. Palmonari, G.A. Pierro, I. Ross, A. Savin, W.H. Smith, J. Swanson

†: Deceased

1: Also at Vienna University of Technology, Vienna, Austria

2: Also at CERN, European Organization for Nuclear Research, Geneva, Switzerland

3: Also at National Institute of Chemical Physics and Biophysics, Tallinn, Estonia

4: Also at Universidade Estadual de Campinas, Campinas, Brazil

5: Also at California Institute of Technology, Pasadena, USA

6: Also at Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France

7: Also at Suez Canal University, Suez, Egypt

8: Also at Zewail City of Science and Technology, Zewail, Egypt

9: Also at Cairo University, Cairo, Egypt

10: Also at Fayoum University, El-Fayoum, Egypt

11: Also at British University in Egypt, Cairo, Egypt

12: Now at Ain Shams University, Cairo, Egypt

13: Also at National Centre for Nuclear Research, Swierk, Poland

14: Also at Université de Haute Alsace, Mulhouse, France

15: Also at Joint Institute for Nuclear Research, Dubna, Russia

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16: Also at Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University,

Moscow, Russia

17: Also at Brandenburg University of Technology, Cottbus, Germany

18: Also at The University of Kansas, Lawrence, USA

19: Also at Institute of Nuclear Research ATOMKI, Debrecen, Hungary

20: Also at Eötvös Loránd University, Budapest, Hungary

21: Also at Tata Institute of Fundamental Research - HECR, Mumbai, India

22: Now at King Abdulaziz University, Jeddah, Saudi Arabia

23: Also at University of Visva-Bharati, Santiniketan, India

24: Also at Sharif Un