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Published for SISSA by Springer

Received: July 1, 2011

Accepted: August 31, 2011

Published: September 23, 2011

Measurement of the underlying event activity at the

LHC with
√

s = 7 TeV and comparison with√
s = 0.9 TeV

The CMS collaboration

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

Abstract: A measurement of the underlying activity in events with a jet of transverse
momentum in the several GeV region is performed in proton-proton collisions at

√
s = 0.9

and 7 TeV, using data collected by the CMS experiment at the LHC. The production of
charged particles with pseudorapidity |η|<2 and transverse momentum pT >0.5 GeV/c is
studied in the azimuthal region transverse to that of the leading set of charged particles
forming a track-jet. A significant growth of the average multiplicity and scalar-pT sum of
the particles in the transverse region is observed with increasing pT of the leading track-
jet, followed by a much slower rise above a few GeV/c. For track-jet pT larger than a
few GeV/c, the activity in the transverse region is approximately doubled with a centre-
of-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as
implemented in pythia are compared to the data.

Keywords: Hadron-Hadron Scattering

Open Access, Copyright CERN,

for the benefit of the CMS collaboration

doi:10.1007/JHEP09(2011)109

mailto:cms-publication-committee-chair@cern.ch
http://dx.doi.org/10.1007/JHEP09(2011)109


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Contents

1 Introduction 1

2 Experimental details 3

3 Underlying event in the transverse region 5
3.1 Hard-scale dependence 5
3.2 Multiplicity and transverse momentum distributions 7
3.3 Centre-of-mass energy dependence 8

4 Summary and conclusions 11

The CMS collaboration 14

1 Introduction

In hadron-hadron scatterings, the “underlying event” (UE) is defined, in the presence of a
hard parton-parton scattering with large transverse momentum transfer, as any hadronic
activity that is additional to what can be attributed to the hadronization of partons in-
volved in the hard scatter and to related initial and final state QCD radiation. The UE
activity is thus attributed to the hadronization of partonic constituents that have under-
gone multiple parton interactions (MPI), as well as to beam-beam remnants, concentrated
along the beam direction. Good understanding of UE properties is important for precision
measurements of standard model processes and the search for new physics at high energy.
Examples are the determination of the losses of events due to isolation criteria in lepton
identification, or the computation of reconstruction efficiency for processes like H→ γγ

where the vertex is given by the underlying event.
The first measurement of UE activity at the LHC, with proton-proton centre-of-mass

energy
√
s = 0.9 TeV, has been published by CMS [1]. The present paper, which follows

the same analysis procedure, reports on a measurement at
√
s = 7 TeV; new measurements

at 0.9 TeV are also reported, with an event sample 30 times larger than that in ref. [1]. In
this paper all measurements are fully corrected for detector effects. Details are given below.
The ATLAS collaboration has reported on measurements at

√
s = 0.9 and 7 TeV [2], using

slightly different analysis procedures.
The UE activity in jet production at a given centre-of-mass energy is expected to in-

crease with the hard scale in the interaction, as defined by the transverse momentum of the
jet. Events with a harder scale are indeed expected to correspond, on average, to interac-
tions with a smaller impact parameter, a feature which in turn should enhance MPI [3, 4].
This increased activity is observed to reach a plateau for high scales, corresponding to

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an MPI “saturation” effect for impact parameters selected by a sufficiently hard leading
interaction. Conversely, for events with the same hard scale but taken at different values of
the centre-of-mass energy, MPI activity is expected to increase with

√
s [3, 4]. The present

analysis is focused on measurements that can contribute to the understanding of the UE
dynamics, through the comparison of events at the same

√
s but with different hard scales,

and the comparison of data with the same hard scale but with different values of
√
s.

To study the UE, it is convenient to refer to the difference in azimuthal angle, ∆φ, be-
tween the projections onto the plane perpendicular to the beam of the directions of the hard
scatter and of any hadron in the event. With this method, the UE activity is made manifest
in the “transverse” region with 60◦ < |∆φ|< 120◦, even though it cannot in principle be
uniquely separated from initial and final state radiation. In this paper, the direction of the
hard scatter is identified with that of the leading “track-jet”, i.e. the object with largest
transverse momentum, pT , formed using a jet algorithm applied to reconstructed tracks of
particles above some minimum pT value in the event. The leading track-jet pT is taken as
defining the hard scale in the event. An advantage of using a track-jet as a reference is that
it is an experimentally well-defined object, essentially free from pileup effects. No attempt
is made to refer to the corresponding parton-level objects, as this would result in additional
model uncertainties. However, the track-jet is much closer to the parton-level object than
the leading track. Finally, in the few GeV/c region, the value of the track-jet pT is better
defined and more stable than for calorimeter based jets, which suffer from large fluctuations.

The UE dynamics are studied through the comparison with data of models imple-
mented in Monte Carlo (MC) simulations adopting MPI. The predictions of the models
without MPI fail to reproduce the evolution of the UE observables with the scale of the
interaction and with the centre-of-mass energy [5]. The predictions for inelastic events are
provided here by several tunes of the pythia program, versions 6.420 [3, 6] and 8.145 [7, 8].
The pre-LHC D6T tune [9, 10] of pythia6, which describes the lower energy UA5 and Teva-
tron data, is a widely used reference that will also be used for the present analysis. The
tunes DW [10] and CW [1], which were found to describe best the data at 0.9 TeV [1],
will be discussed for the present 7 TeV data. The new pythia6 tune, Z1 [11], includes
pT ordering of parton showers and the new pythia MPI model [12]. It implements the
results of the Professor tunes [13] considering the fragmentation and the coulor reconnec-
tion parameters of the AMBT1 tune [14]; preliminary CMS UE results at 7 TeV have been
used to tune the parameters governing the value and the

√
s dependence of the transverse

momentum cutoff that in pythia regularizes the divergence of the leading order scatter-
ing amplitude as the final state parton transverse momentum p̂T approaches 0. The tune
Z2 is similar to Z1, except for the transverse momentum cutoff at the nominal energy of
√
s0 = 1.8 TeV which is decreased by 0.1 GeV/c. pythia8 also uses the new pythia MPI

model, which is interleaved with parton showering. The new pythia8 version 4C [15]
has also been tuned to the early LHC data. The pythia8 model includes soft and hard
diffraction [16], whereas only soft diffraction is included in pythia6; the precise descrip-
tion of diffraction is, however, of little relevance for the present analyses since it has been
checked that the diffractive contributions are strongly suppressed by the trigger and event
selection requirements, especially for large pT values of the leading track-jet. The parton

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distribution functions (PDF) used to describe the protons are the CTEQ6L1 set [17] for
D6T, Z2 and 4C, and CTEQ5L [18] for the other simulations.

The outline of the paper is as follows. Section 2 presents experimental details: brief
detector description, data samples, event and track selection, track-jet reconstruction, un-
folding procedure and systematic uncertainties. Section 3 presents results on the transverse
region dynamics: hard-scale dependence and particle spectra at

√
s = 7 TeV, and centre-

of-mass energy dependence of the transverse region dynamics. Section 4 summarizes the
main results of the study and draws conclusions.

2 Experimental details

A description of the CMS detector can be found in ref. [19]. The coordinate system has
the origin at the nominal interaction point. The z axis is parallel to the anticlockwise
beam direction; it defines the polar angle θ and the pseudorapidity η = − ln(tan(θ/2)).
The azimuthal angle φ is measured in the plane transverse to the beam, from the direction
pointing to the centre of the LHC ring toward the upward direction. The pixel and silicon
strip tracker, immersed in the uniform 3.8 T magnetic field provided by a 6 m diameter su-
perconducting solenoid, measures charged particle trajectories in the pseudorapidity range
|η|< 2.5. The pT resolution for 1 GeV/c charged particles is between 0.7% at η = 0 and
2% at |η| = 2.5.

For this analysis, the same selection conditions apply to events and tracks at 0.9 and
7 TeV; these conditions are very similar to those at 0.9 TeV in ref. [1]. Minimum bias events
are triggered by requiring activity in both Beam Scintillator Counters (BSC) [19, 20], in
coincidence with signals from both beams in the Beam Pick-up Timing for eXperiments
(BPTX) devices [19, 21]; low-pT track-jets are recorded with a prescaled minimum bias
trigger. At 7 TeV, in order to enhance the acquisition of events with a harder scale and
reduce statistical fluctuations, the analysis also uses single-jet triggers.

Selected events are required to contain one and only one primary vertex, reconstructed
in fits with more than four degrees of freedom, with a z coordinate within 10 cm of the cen-
tre of the 4 cm-wide beam collision region. Rejecting events with more than one primary
vertex does not bias the final results, as was checked by comparing data with different
pileup conditions, taken at low and high instantaneous luminosities.

Selected events are also required to contain a track-jet with pT >1 GeV/c, reconstructed
with pseudorapidity |η|<2. Track-jets are defined using the SISCone algorithm [22] as im-
plemented in the FastJet package [23] with a clustering radius R =

√
(∆φ)2 + (∆η)2 = 0.5.

Charged particles reconstructed in the tracker with pT > 0.5 GeV/c and |η|< 2.5 are used
to define the track-jet; this η range is wider than that used for the UE analysis (|η|<2) in
order to avoid a kinematic bias.

A track is selected for the UE analysis if it is consistent with the primary vertex
and is reconstructed in the pixel and silicon strip tracker with transverse momentum
pT > 0.5 GeV/c and pseudorapidity |η| < 2. A high-purity reconstruction algorithm is
used, which keeps low levels of misreconstructed and poorly reconstructed tracks [24]. To
decrease contamination by secondary tracks from decays of long-lived particles and photon

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√
s = 7 TeV

√
s = 0.9 TeV

leading track-jet pT > 1 GeV/c 3 GeV/c 20 GeV/c 1 GeV/c 3 GeV/c 20 GeV/c

No. selected events (×103) 18 543 6 674 19 5 140 783 0.25

No. selected tracks (×103) 202 952 120 945 638 33 743 9 001 5.8

Table 1. Number of selected events and corresponding number of selected tracks, for three values
of minimum track-jet pT and for both

√
s = 0.9 and 7 TeV.

conversions, the distance of closest approach between the track and the primary vertex is
required to be less than three times its (significantly non-Gaussian) estimated uncertainty,
both in the transverse plane and along the z-axis; the uncertainty in the vertex position is
also taken into account. Poorly measured tracks are removed by requiring σ(pT )/pT <5%,
where σ(pT ) is the uncertainty on the pT measurement. In the selected track sample with
|η| < 2, these selections result in a background level of 3%: 1% from K0

S and Λ0 decay
products and 2% from combinatorial background, as estimated using MC simulations. The
number of selected events at both centre-of-mass energies, for track-jet pT > 1, 3, and
20 GeV/c, and the corresponding number of selected tracks are given in table 1.

The distributions presented below are fully corrected for detector effects. An iterative
unfolding technique [25] is used, except for some cases that will be detailed below. The
pythia6 MC with Z2 tune was used to correct the experimental distributions, while Z1,
D6T and the default configuration of pythia 8.135 (“tune 1”) were used for cross-checks
and systematic uncertainty estimates. The detector response was simulated in detail using
the GEANT4 package [26], and simulated events were processed and reconstructed in the
same manner as collision data. The simulations were found to give a very good description
of all features related to detector performance that are relevant to this analysis. The unfold-
ing procedure was tested using MC events, by comparing the genuine distributions for gen-
erated hadrons with the distributions obtained, after unfolding, from reconstructed tracks.

Systematic uncertainties on the corrected data have been studied in detail. They cor-
respond essentially to the uncertainties described in [1] taking into account the progress
reported in ref. [24]. They include the implementation in the simulation of vertex and track
selection criteria, tracker alignment and tracker material content, background contamina-
tion from K0

S and Λ0 production, trigger conditions, run-to-run variations of tracker and
beam conditions, including the effect of pileup, and the effect of limited samples.

Using as MC input the Z1 simulation, which gives the best description of data, un-
folding procedures were performed using both the Z2 and tune 1 models; the maximum
discrepancies with the MC input were taken as systematic uncertainties.

Systematic uncertainties are largely independent of one another, but they are corre-
lated among data points in each experimental distribution. They are added in quadrature
to statistical uncertainties and represented in all figures.

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0

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Data
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
charged particles

)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |
T

(p

 = 7 TeVsCMS  

 [GeV/c]
T

Leading track-jet p
0 20 40 60 80 100

>
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Data
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PYTHIA-6 D6T
charged particles

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T

(p

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T

Leading track-jet p
0 20 40 60 80 100

>
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eV
/c

]
ch

>
 / 

<
N

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0

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1

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1.6

1.8

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Data
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
charged particles

)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |
T

(p

 = 7 TeVsCMS  

Figure 1. Fully corrected measurements of charged particles with pT > 0.5 GeV/c and |η|< 2 in
the transverse region, 60◦ < |∆φ| < 120◦, as a function of the pT of the leading track-jet: (left)
average multiplicity per unit of pseudorapidity and per radian; (centre) average scalar

∑
pT per

unit of pseudorapidity and per radian; (right) ratio of the average scalar
∑
pT and the average

multiplicity. Predictions of three pythia tunes are compared to the data.

3 Underlying event in the transverse region

The hadronic activity at 7 TeV in the transverse region, for charged particles with pT >

0.5 GeV/c, |η|<2, and 60◦< |∆φ|<120◦, is first presented as a function of the leading track-
jet pT (section 3.1). Multiplicity and transverse momentum distributions are then reported
for two minimal values, 3 and 20 GeV/c, of the leading track-jet pT (section 3.2). Results
at the two centre-of-mass energies,

√
s = 0.9 and 7 TeV, are finally compared (section 3.3).

Predictions from the various pythia models are compared to the corrected data.

3.1 Hard-scale dependence

Figure 1 presents the average multiplicity and the average scalar momentum sum in the
transverse region, as a function of the leading track-jet pT . For these distributions, full
unfolding was performed in both the track-jet pT and the studied variable, for leading
track-jet pT up to 20 GeV/c. Bin-by-bin corrections were used at higher values of the
leading track-jet pT where the pT dependence of the studied variables is small.

The horizontal error bars indicate the bin size; the vertical inner error bars indicate
the statistical uncertainties affecting the measurements; the outer error bars represent the
statistical and systematic uncertainties added in quadrature; statistical uncertainties dom-
inate at large values of the hard scale. The same conventions and considerations apply
throughout this paper.

Two regions are visible for both observables in figure 1: a fast rise for pT . 8 GeV/c,
attributed mainly to the increase of MPI activity, followed by a plateau-like region with
nearly constant average number of selected particles and a slow increase of ΣpT . A similar
structure is observed at 0.9 TeV (see ref. [1] and figure 5 below), the fast rise being limited
in that case to the region with leading track-jet pT . 4 GeV/c. All pythia models predict
such a distinct change of the amount of activity in the transverse region as a function of
the leading track-jet pT .

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PYTHIA-6 Z1
PYTHIA-8 4C
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syst.
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charged particles
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T
(p

 = 7 TeVsCMS  

 [GeV/c]
T

Leading track-jet p
0 20 40 60 80 100

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TpΣ

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C
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0.5

0.75

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1.25

1.5
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
syst.
syst. + stat.

 = 7 TeVsCMS  

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

Leading track-jet p
0 20 40 60 80 100

>
ch

>
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<
N

TpΣ
M

C
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D
at

a 
 <

0.5

0.75

1

1.25

1.5
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
syst.
syst. + stat.

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 = 7 TeVsCMS  

Figure 2. Ratios, as a function of the leading track-jet pT , of three MC predictions to the fully
corrected measurements of charged particles with pT > 0.5 GeV/c and |η| < 2 in the transverse
region, 60◦ < |∆φ|< 120◦ (cf. figure 1): (left) average multiplicity; (centre) average scalar

∑
pT ;

(right) ratio of the average scalar
∑
pT and the average multiplicity. The inner bands correspond to

the systematic uncertainties and the outer bands to the total experimental uncertainties (statistical
and systematic uncertainties added in quadrature).

These evolutions result in a slow but continuous increase of the average pT of the se-
lected particles for leading track-jet pT above a few GeV/c. This is observed in figure 1
(right plot), which is obtained from the ratio of the two profile distributions, with the
relative uncertainties conservatively summed in quadrature. (A similar behaviour of the
ratio can be deduced at 0.9 TeV).

The information on the quality of the data description by the different models is
summarized in figure 2, which presents the ratio of the MC predictions to the measurements
for the observables shown in figure 1. Statistical fluctuations in the data induce correlated
fluctuations for the various MC/data ratios. Variations in the error bands are related to
the unfolding procedures, and to the different sets of data collected with different triggers.

The description provided by Z1 is very good for both the average multiplicity and the
average scalar momentum sum, over the full leading track-jet pT range. For the pythia8 4C
tune, in the region with track-jet pT < 20 GeV/c the predictions are below the data by 5%
(10%) for the average charged multiplicity (average scalar

∑
pT ); for larger track-jet pT val-

ues, the average charged multiplicity is well described but the average
∑
pT is increasingly

underestimated, by up to 20%. This confirms observations reported in ref. [27]. The predic-
tions of the Z2 tune (not shown in this paper) reveal similar trends as for pythia8 4C with,
however, a more uniform and more limited underestimate ( . 10%) of the average

∑
pT .

As illustrated by D6T, the predictions of older pythia6 tunes are significantly be-
low the data in the region characterized by the fast rise of the observables (track-jet
pT . 8 GeV/c); in the “saturation” region, tune D6T provides a good description of
the average multiplicity but the average

∑
pT is largely underestimated for track-jet pT

> 40 GeV/c. In this region, DW predictions are lower than for D6T, and CW even lower,
which reflects the different values of the cutoff transverse momentum and its

√
s depen-

dence [1] (CW and the DW predictions are not shown in this paper).

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The comparison with data of the MC predictions for the ratio of the average
∑
pT

and the average multiplicity is shown in figure 2 (right). The absolute value is described
within 5% and the hard-scale dependence is well described by Z1. The pythia8 4C and Z2
predictions agree with Z1 in the rising region, but the normalization is up to 10% and 20%
lower in the “saturation” region, respectively. For D6T, the ratio is overestimated below
30 GeV/c, and underestimated above 30 GeV/c.

3.2 Multiplicity and transverse momentum distributions

Figure 3 presents, for charged particles in the transverse region, the normalized multiplicity
distribution, the normalized

∑
pT distribution, and the particle pT spectrum. Events are

selected with two minimal values of the leading track-jet pT : pT > 3 GeV/c (upper row)
and pT >20 GeV/c (central row). For the charged multiplicity and

∑
pT distributions, full

unfolding was performed for leading track-jet pT > 3 GeV/c, whereas for leading track-jet
pT >20 GeV/c, in the “saturation” region, simpler unfolding is performed, which does not
take into account the hard-scale dependence. In the latter case the unfolding procedure
is found to occasionally introduce correlations between adjacent bins, which arise from
statistical fluctuations in the uncorrected distributions. For the pT spectra presented in
the right column of figure 3 bin-by-bin corrections were applied. The correction factors are
found to be mostly independent of the track-jet pT and from the centre-of-mass energy.

The distributions in figure 3 are presented for a range of the variables for which the
total relative uncertainty, after unfolding, does not exceed 30%. It is remarkable that the
charged particle spectra extend to pT > 10 GeV/c, indicating the presence of a hard com-
ponent in particle production in the transverse region. The distributions for the two scale
selections pT >3 GeV/c and pT >20 GeV/c are directly compared in the lower-row plots of
figure 3. Growth of the UE activity with increasing hard scale is observed both through
multiplicity increase and single-particle pT spectra hardening, consistent with the increase
of particle average pT shown in figure 1 (right). The three distributions are overall rather
well described by the selected MC models over several orders of magnitude (more than 6
for the pT spectrum).

Detailed comparisons are provided in figure 4, which presents the ratio of the MC
predictions to the measurements in figure 3. In the presence of a hard scale, characterized
by a leading track-jet with pT >20 GeV/c (lower plots in figure 4), the Z1, Z2, and pythia8

4C tunes describe the data well in view of the steeply falling character of the distributions.
They do indeed describe all three distributions within 10− 15% over most of the domain,
except for pythia8 4C for very small values of Nch and

∑
pT , and for pT > 4 GeV/c. Data

description by D6T is worse, especially the
∑
pT distribution and the pT spectrum.

The description of the data in the region with leading track-jet pT >3 GeV/c (figure 3
upper plots), dominated by interactions with a soft scale, is not so good. In this domain,
all tunes overestimate the contributions of events with very low multiplicity and

∑
pT

(Nch . 4,
∑
pT . 4 GeV/c); the discrepancies are largest for D6T. For larger values of the

observables, the predictions of Z1, Z2, and pythia8 4C are reasonably close to the data, the
weak points being the description by Z1 of multiplicities between 10 and 20, and the descrip-

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Data
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PYTHIA-8 4C
PYTHIA-6 D6T

 = 7 TeVsCMS  

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leading track-jet p

charged particles
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charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

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(p

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 = 7 TeVsCMS  

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leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

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(p

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T

pΣ
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d

ev
) 

 d
N

ev
(1

/N

-510

-410

-310

-210

-110

Data
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T

 = 7 TeVsCMS  

 > 20 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

p
0 2 4 6 8 10 12 14

]
-1

 [(
G

eV
/c

)
T

 / 
dp

ch
dN

-810

-710

-610

-510

-410

-310

-210

-110

1

10

Data
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T

 = 7 TeVsCMS  

 > 20 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

chN
0 5 10 15 20 25 30

ch
 / 

dN
ev

) 
 d

N
ev

(1
/N

-710

-610

-510

-410

-310

-210

-110

1

 > 20 GeV/c
T

Data, p

 > 3 GeV/c
T

Data, p

 > 20 GeV/c
T

PYTHIA Z1, p

 > 3 GeV/c
T

PYTHIA Z1, p

 = 7 TeVsCMS   = 7 TeVsCMS  

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

pΣ
0 5 10 15 20 25 30 35

]
-1

 [(
G

eV
/c

)
TpΣ

 / 
d

ev
) 

 d
N

ev
(1

/N

-510

-410

-310

-210

-110

 > 20 GeV/c
T

Data, p

 > 3 GeV/c
T

Data, p

 > 20 GeV/c
T

PYTHIA Z1, p

 > 3 GeV/c
T

PYTHIA Z1, p

 = 7 TeVsCMS  

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

p
0 2 4 6 8 10 12 14

]
-1

 [(
G

eV
/c

)
T

 / 
dp

ch
dN

-810

-710

-610

-510

-410

-310

-210

-110

1

10

 > 20 GeV/c
T

Data, p

 > 3 GeV/c
T

Data, p

 > 20 GeV/c
T

PYTHIA Z1, p

 > 3 GeV/c
T

PYTHIA Z1, p

 = 7 TeVsCMS  

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

Figure 3. Fully corrected measurements of charged particles with pT >0.5 GeV/c and |η|<2 in the
transverse region, 60◦< |∆φ|< 120◦: (left) normalized multiplicity distributions; (centre) normal-
ized scalar

∑
pT distributions; (right) particle pT spectra. The leading track-jet is required to have

|η|<2 and (upper row) pT >3 GeV/c, or (central row) pT >20 GeV/c. The plots in the lower row
provide a direct comparison of the distributions for pT >3 GeV/c and pT >20 GeV/c. Predictions
of three pythia tunes are compared to the data.

tion by all tunes of the pT spectrum in the region 3−8 GeV/c. For D6T, as well as for DW
and CW, the descriptions of the

∑
pT distribution and of the particle pT spectrum are poor.

3.3 Centre-of-mass energy dependence

The centre-of-mass energy dependence of the hadronic activity in the transverse region is
presented in figure 5 (upper plots) as a function of the leading track-jet pT , for

√
s = 0.9

and 7 TeV. The same unfolding methodology as for figure 1 was applied for the data at√
s = 0.9 TeV, in this case with a separation between the two correction procedures at

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C

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D

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a

ch
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dN
ev

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N
ev

(1
/N

0

0.5

1

1.5

2

2.5
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
syst.
syst. + stat.

 = 7 TeVsCMS  

 > 3 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

pΣ
0 5 10 15 20 25 30 35

  M
C

 / 
D

at
a

TpΣ
 / 

d
ev

) 
 d

N
ev

(1
/N

0

0.5

1

1.5

2

2.5
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
syst.
syst. + stat.

 = 7 TeVsCMS  

 > 3 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

p
0 2 4 6 8 10 12 14

  M
C

 / 
D

at
a

T
 / 

dp
ch

dN

0

0.5

1

1.5

2

2.5
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
syst.
syst. + stat.

 = 7 TeVsCMS  

 > 3 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

p
0 2 4 6 8 10 12 14

  M
C

 / 
D

at
a

T
 / 

dp
ch

dN

0

0.5

1

1.5

2

2.5

chN
0 5 10 15 20 25 30

  M
C

 / 
D

at
a

ch
 / 

dN
ev

) 
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N
ev

(1
/N

0

0.5

1

1.5

2

2.5
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
syst.
syst. + stat.

 = 7 TeVsCMS  

 > 20 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

pΣ
0 5 10 15 20 25 30 35

  M
C

 / 
D

at
a

TpΣ
 / 

d
ev

) 
 d

N
ev

(1
/N

0

0.5

1

1.5

2

2.5
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
syst.
syst. + stat.

 = 7 TeVsCMS  

 > 20 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

p
0 2 4 6 8 10 12 14

  M
C

 / 
D

at
a

T
 / 

dp
ch

dN

0

0.5

1

1.5

2

2.5
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T
syst.
syst. + stat.

 = 7 TeVsCMS  

 > 20 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

Figure 4. Ratios of three MC predictions to the fully corrected measurements of charged particles
with pT >0.5 GeV/c and |η|<2 in the transverse region, 60◦< |∆φ|<120◦ (cf. figure 3): (left) mul-
tiplicity distributions; (centre) scalar

∑
pT distributions; (right) particle pT spectra. The leading

track-jet is required to have |η|<2 and (upper plots) pT >3 GeV/c, or (lower plots) pT >20 GeV/c.
The inner bands correspond to the systematic uncertainties and the outer bands to the total ex-
perimental uncertainties (statistical and systematic uncertainties added in quadrature).

10 GeV/c reflecting the narrower rising region. The large increase with
√
s of the hadronic

activity in the transverse region and its hard-scale dependence is shown in the lower plots
of figure 5, in the form of the ratio of the 7 TeV to the 0.9 TeV results. Here the systematic
uncertainties at 0.9 and 7 TeV were conservatively combined quadratically, thus neglecting
cancellation effects. The ratios, which are close to one for leading track-jet pT = 1.5 GeV/c,
reach a factor of two for pT & 6− 8 GeV/c.

The evolution with the hard scale of the ratio of the UE activity at 7 TeV and 0.9 TeV
is described by the Z1 MC. The trend is also reproduced by pythia8 4C. The evolution is
much too strong for D6T. The Z2 predictions at

√
s = 0.9 TeV (not shown here) agree with

Z1 in shape but the normalization is 5-10% too high for both observables; this trend is
opposite to that observed at 7 TeV, which indicates that a less pronounced

√
s dependence

of the transverse momentum cutoff should be adopted for tunes using the CTEQ6L1 PDF
set than for tunes optimized for CTEQ5L. The pythia8 tune 4C [15] already implements
such a prescription.

The strong growth of UE activity with
√
s is also striking in the comparison of the

normalized distributions of charged particle multiplicity and of scalar
∑
pT as well as in

the pT spectra, which are presented in figure 6 for events at
√
s = 7 TeV and 0.9 TeV with

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 [GeV/c]
T

Leading track-jet p
0 20 40 60 80 100

>
ch

) 
<

N
φ∆(∆ η∆

1 
/  

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Data, 7 TeV
Data, 0.9 TeV
PYTHIA-6 Z1, 7 TeV
PYTHIA-6 Z1, 0.9 TeV
PYTHIA-8 4C, 7 TeV
PYTHIA-8 4C, 0.9 TeV

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

CMS

 [GeV/c]
T

Leading track-jet p
0 20 40 60 80 100

>
 [G

eV
/c

]
TpΣ

) 
 <

φ∆(∆ η∆
1 

/ 

0

0.5

1

1.5

2

2.5

Data, 7 TeV
Data, 0.9 TeV
PYTHIA-6 Z1, 7 TeV
PYTHIA-6 Z1, 0.9 TeV
PYTHIA-8 4C, 7 TeV
PYTHIA-8 4C, 0.9 TeV

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

CMS

 [GeV/c]
T

Leading track-jet p
0 5 10 15 20 25

0.
9 

T
eV

>
ch

 / 
 <

N
7 

T
eV

>
ch

<
N

0

0.5

1

1.5

2

2.5

3

3.5
Data
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

CMS

 [GeV/c]
T

Leading track-jet p
0 5 10 15 20 25

0.
9 

T
eV

>
TpΣ

 / 
<

7T
eV

>
TpΣ<

0

0.5

1

1.5

2

2.5

3

3.5

4
Data
PYTHIA-6 Z1
PYTHIA-8 4C
PYTHIA-6 D6T

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

CMS

Figure 5. Fully corrected measurements of charged particles with pT > 0.5 GeV/c and |η|< 2 in
the transverse region, 60◦< |∆φ|<120◦: (left plots) average multiplicity, and (right plots) average
scalar

∑
pT , per unit of pseudorapidity and per radian, as a function of the leading track-jet pT , for

(upper row) data at
√
s = 0.9 TeV and

√
s = 7 TeV; (lower row) ratio of the average values at 7 TeV

to the average values at 0.9 TeV. Predictions of three pythia tunes are compared to the data.

chN
0 5 10 15 20 25 30

ch
 / 

dN
ev

) 
 d

N
ev

(1
/N

-810

-710

-610

-510

-410

-310

-210

-110

1

Data 7 TeV

Data 0.9 TeV

PYTHIA-6 Z1, 7 TeV

PYTHIA-6 Z1, 0.9 TeV

CMS

 > 3 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

pΣ
0 5 10 15 20 25 30 35

]
-1

 [(
G

eV
/c

)
TpΣ

 / 
d

ev
) 

 d
N

ev
(1

/N

-810

-710

-610

-510

-410

-310

-210

-110

Data 7 TeV

Data 0.9 TeV

PYTHIA-6 Z1, 7 TeV

PYTHIA-6 Z1, 0.9 TeV

CMS

 > 3 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

 [GeV/c]
T

p
0 2 4 6 8 10 12 14

]
-1

 [(
G

eV
/c

)
T

 / 
dp

ch
dN

-910

-810

-710

-610

-510

-410

-310

-210

-110

1

10
CMS

 > 3 GeV/c
T

leading track-jet p

charged particles
)°| < 120φ∆ < |°| < 2, 60η > 0.5 GeV/c, |

T
(p

Data 7 TeV

Data 0.9 TeV

PYTHIA-6 Z1, 7 TeV

PYTHIA-6 Z1, 0.9 TeV

Figure 6. For charged particles with pT > 0.5 GeV/c and |η| < 2 in the transverse region,
60◦ < |∆φ| < 120◦, (left) normalized multiplicity distributions; (centre) normalized scalar

∑
pT

distributions; (right) pT spectra, at
√
s = 7 TeV and at

√
s = 0.9 TeV. Events with leading track-

jet pT >3 GeV/c are selected. Predictions from tune Z1 are compared to the data.

leading track-jet pT > 3 GeV/c. The same unfolding methodology as for figure 3 (upper
row) was applied at

√
s = 0.9 TeV.

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4 Summary and conclusions

This paper presents a study of the production of charged particles with pT > 0.5 GeV/c
and |η|<2 at the LHC with the CMS detector in proton-proton collisions at

√
s = 0.9 and

7 TeV. Events were selected according to the hard scale of the process, provided by the
transverse momentum of the leading track-jet, which extends up to 100 GeV/c. The study
was done in the transverse region, defined by the difference in azimuthal angle between the
leading track-jet and charged particle directions, 60◦< |∆φ|<120◦, which is appropriate for
the study of the underlying event. All distributions were fully corrected for detector effects.

A strong increase of the UE activity, quantified through the average multiplicity and
the average scalar transverse momentum sum of charged particles in the transverse region,
is observed with increasing leading track-jet pT . At

√
s = 7 TeV this fast rise is followed

above ∼ 8 GeV/c by a “saturation” region with nearly constant multiplicity and small∑
pT increase. The large increase of activity in the transverse region is observed in the

multiplicity distribution, in the
∑
pT distribution and in the charged particle pT spectrum,

which were studied, respectively, up to Nch = 30,
∑
pT = 35 GeV/c, and pT = 14 GeV/c.

The events at the right end of the distributions indicate the presence of a hard component
in the transverse region.

By comparing data taken at
√
s = 0.9 and 7 TeV, a strong growth with increasing

centre-of-mass energy of the hadronic activity in the transverse region is also observed for
the same value of the leading track-jet pT .

The predictions of several tunes of the pythia program version 6, in particular the
new tunes Z1 and Z2, and of the new version pythia8 with tune 4C have been compared
to the measurements. A good description of most distributions at

√
s = 7 TeV and of the√

s dependence from 0.9 to 7 TeV is provided by the Z1 tune. The predictions of the Z2
and pythia8 4C tunes are also in reasonable agreement with the data.

Acknowledgments

We thank Mark Strikman (Penn State University) and Torbjorn Sjöstrand (Lund Univer-
sity) for useful discussions and for assistance in simulating theoretical models.

We wish to congratulate our colleagues in the CERN accelerator departments for the
excellent performance of the LHC machine. We thank the technical and administrative
staff at CERN and other CMS institutes, and acknowledge support from: FMSR (Aus-
tria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES
(Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES
(Croatia); RPF (Cyprus); Academy of Sciences and NICPB (Estonia); Academy of Fin-
land, 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 (Korea); LAS (Lithuania); CINVES-
TAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pakistan);
SCSR (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan);
MST and MAE (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss Funding

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Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United
Kingdom); DOE and NSF (USA).

Individuals have received support from the Marie-Curie programme and the European
Research Council (European Union); the Leventis Foundation; the A. P. Sloan Foundation;
the Alexander von Humboldt Foundation; the Associazione per lo Sviluppo Scientifico e
Tecnologico del Piemonte (Italy); the Belgian Federal Science Policy Office; the Fonds pour
la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); and
the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium).

Open Access. This article is distributed under the terms of the Creative Commons
Attribution Noncommercial License which permits any noncommercial use, distribution,
and reproduction in any medium, provided the original author(s) and source are credited.

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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, T. Bergauer, M. Dragicevic, J. Erö, C. Fabjan, M. Friedl, R. Frühwirth,
V.M. Ghete, J. Hammer1, S. Hänsel, M. Hoch, N. Hörmann, J. Hrubec, M. Jeitler,
W. Kiesenhofer, M. Krammer, D. Liko, I. Mikulec, M. Pernicka, H. Rohringer,
R. Schöfbeck, J. Strauss, A. Taurok, F. Teischinger, P. Wagner, W. Waltenberger,
G. Walzel, E. Widl, C.-E. Wulz

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

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

Universiteit Antwerpen, Antwerpen, Belgium

S. Bansal, L. Benucci, E.A. De Wolf, X. Janssen, J. Maes, T. Maes, L. Mucibello,
S. Ochesanu, B. Roland, R. Rougny, M. Selvaggi, H. Van Haevermaet, P. Van Mechelen,
N. Van Remortel

Vrije Universiteit Brussel, Brussel, Belgium

F. Blekman, S. Blyweert, J. D’Hondt, O. Devroede, R. Gonzalez Suarez, A. Kalogeropoulos,
M. Maes, W. Van Doninck, P. Van Mulders, G.P. Van Onsem, I. Villella

Université Libre de Bruxelles, Bruxelles, Belgium

O. Charaf, B. Clerbaux, G. De Lentdecker, V. Dero, A.P.R. Gay, G.H. Hammad, T. Hreus,
P.E. Marage, L. Thomas, C. Vander Velde, P. Vanlaer

Ghent University, Ghent, Belgium

V. Adler, A. Cimmino, S. Costantini, M. Grunewald, B. Klein, J. Lellouch, A. Marinov,
J. Mccartin, D. Ryckbosch, F. Thyssen, M. Tytgat, L. Vanelderen, P. Verwilligen, S. Walsh,
N. Zaganidis

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

S. Basegmez, G. Bruno, J. Caudron, L. Ceard, E. Cortina Gil, J. De Favereau De Jeneret,
C. Delaere1, D. Favart, A. Giammanco, G. Grégoire, J. Hollar, V. Lemaitre, J. Liao,
O. Militaru, S. Ovyn, D. Pagano, A. Pin, K. Piotrzkowski, N. Schul

Université de Mons, Mons, Belgium

N. Beliy, T. Caebergs, E. Daubie

Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil

G.A. Alves, D. De Jesus Damiao, M.E. Pol, M.H.G. Souza

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

W. Carvalho, E.M. Da Costa, C. De Oliveira Martins, S. Fonseca De Souza, L. Mundim,
H. Nogima, V. Oguri, W.L. Prado Da Silva, A. Santoro, S.M. Silva Do Amaral, A. Sznajder

– 14 –



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Instituto de Fisica Teorica, Universidade Estadual Paulista, Sao Paulo, Brazil
C.A. Bernardes2, F.A. Dias, T.R. Fernandez Perez Tomei, E. M. Gregores2, C. Lagana,
F. Marinho, P.G. Mercadante2, S.F. Novaes, Sandra S. Padula

Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
N. Darmenov1, V. Genchev1, P. Iaydjiev1, S. Piperov, M. Rodozov, S. Stoykova, G. Sul-
tanov, V. Tcholakov, R. Trayanov

University of Sofia, Sofia, Bulgaria
A. Dimitrov, R. Hadjiiska, A. Karadzhinova, V. Kozhuharov, L. Litov, M. Mateev,
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, J. Wang, X. Wang, Z. Wang, H. Xiao, M. Xu, J. Zang, Z. Zhang

State Key Lab. of Nucl. Phys. and Tech., Peking University, Beijing, China
Y. Ban, S. Guo, Y. Guo, W. Li, Y. Mao, S.J. Qian, H. Teng, B. Zhu, W. Zou

Universidad de Los Andes, Bogota, Colombia
A. Cabrera, B. Gomez Moreno, A.A. Ocampo Rios, A.F. Osorio Oliveros, J.C. Sanabria

Technical University of Split, Split, Croatia
N. Godinovic, D. Lelas, K. Lelas, R. Plestina3, D. Polic, I. Puljak

University of Split, Split, Croatia
Z. Antunovic, M. Dzelalija

Institute Rudjer Boskovic, Zagreb, Croatia
V. Brigljevic, S. Duric, K. Kadija, S. Morovic

University of Cyprus, Nicosia, Cyprus
A. Attikis, M. Galanti, 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. Assran4, S. Khalil5, M.A. Mahmoud6

National Institute of Chemical Physics and Biophysics, Tallinn, Estonia
A. Hektor, M. Kadastik, M. Müntel, M. Raidal, L. Rebane

Department of Physics, University of Helsinki, Helsinki, Finland
V. Azzolini, P. Eerola, G. Fedi

Helsinki Institute of Physics, Helsinki, Finland
S. Czellar, J. Härkönen, A. Heikkinen, V. Karimäki, R. Kinnunen, M.J. Kortelainen,
T. Lampén, K. Lassila-Perini, S. Lehti, T. Lindén, P. Luukka, T. Mäenpää, E. Tuominen,
J. Tuominiemi, E. Tuovinen, D. Ungaro, L. Wendland

– 15 –



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Lappeenranta University of Technology, Lappeenranta, Finland

K. Banzuzi, A. Korpela, T. Tuuva

Laboratoire d’Annecy-le-Vieux de Physique des Particules, IN2P3-CNRS,
Annecy-le-Vieux, France

D. Sillou

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

M. Besancon, S. Choudhury, M. Dejardin, D. Denegri, B. Fabbro, J.L. Faure, F. Ferri,
S. Ganjour, F.X. Gentit, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry,
E. Locci, J. Malcles, M. Marionneau, L. Millischer, J. Rander, A. Rosowsky, I. Shreyber,
M. Titov, P. Verrecchia

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

S. Baffioni, F. Beaudette, L. Benhabib, L. Bianchini, M. Bluj7, C. Broutin, P. Busson,
C. Charlot, T. Dahms, L. Dobrzynski, S. Elgammal, R. Granier de Cassagnac, M. Hague-
nauer, P. Miné, C. Mironov, C. Ochando, P. Paganini, D. Sabes, R. Salerno, Y. Sirois,
C. Thiebaux, B. Wyslouch8, A. Zabi

Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Univer-
sité de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France

J.-L. Agram9, J. Andrea, D. Bloch, D. Bodin, J.-M. Brom, M. Cardaci, E.C. Chabert,
C. Collard, E. Conte9, F. Drouhin9, C. Ferro, J.-C. Fontaine9, D. Gelé, U. Goerlach,
S. Greder, P. Juillot, M. Karim9, A.-C. Le Bihan, Y. Mikami, P. Van Hove

Centre de Calcul de l’Institut National de Physique Nucleaire et de Physique
des Particules (IN2P3), Villeurbanne, France

F. Fassi, D. Mercier

Université de Lyon, Université Claude Bernard Lyon 1, CNRS-IN2P3, Institut
de Physique Nucléaire de Lyon, Villeurbanne, France

C. Baty, S. Beauceron, N. Beaupere, M. Bedjidian, O. Bondu, G. Boudoul, D. Boumediene,
H. Brun, J. Chasserat, R. Chierici, D. Contardo, P. Depasse, H. El Mamouni, J. Fay,
S. Gascon, B. Ille, T. Kurca, T. Le Grand, M. Lethuillier, L. Mirabito, S. Perries, V. Sordini,
S. Tosi, Y. Tschudi, P. Verdier

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

D. Lomidze

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

G. Anagnostou, M. Edelhoff, L. Feld, N. Heracleous, O. Hindrichs, R. Jussen, K. Klein,
J. Merz, N. Mohr, A. Ostapchuk, A. Perieanu, F. Raupach, J. Sammet, S. Schael,
D. Sprenger, H. Weber, M. Weber, B. Wittmer

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RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany
M. Ata, W. Bender, E. Dietz-Laursonn, M. Erdmann, J. Frangenheim, T. Hebbeker,
A. Hinzmann, K. Hoepfner, T. Klimkovich, D. Klingebiel, P. Kreuzer, D. Lanske†,
C. Magass, M. Merschmeyer, A. Meyer, P. Papacz, H. Pieta, H. Reithler, S.A. Schmitz,
L. Sonnenschein, J. Steggemann, D. Teyssier

RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany
M. Bontenackels, M. Davids, M. Duda, G. Flügge, H. Geenen, M. Giffels, W. Haj Ahmad,
D. Heydhausen, T. Kress, Y. Kuessel, A. Linn, A. Nowack, L. Perchalla, O. Pooth,
J. Rennefeld, P. Sauerland, A. Stahl, M. Thomas, D. Tornier, M.H. Zoeller

Deutsches Elektronen-Synchrotron, Hamburg, Germany
M. Aldaya Martin, W. Behrenhoff, U. Behrens, M. Bergholz10, A. Bethani, K. Borras,
A. Cakir, A. Campbell, E. Castro, D. Dammann, G. Eckerlin, D. Eckstein, A. Floss-
dorf, G. Flucke, A. Geiser, J. Hauk, H. Jung1, M. Kasemann, I. Katkov11, P. Katsas,
C. Kleinwort, H. Kluge, A. Knutsson, M. Krämer, D. Krücker, E. Kuznetsova, W. Lange,
W. Lohmann10, R. Mankel, M. Marienfeld, I.-A. Melzer-Pellmann, A.B. Meyer, J. Mnich,
A. Mussgiller, J. Olzem, A. Petrukhin, D. Pitzl, A. Raspereza, A. Raval, M. Rosin,
R. Schmidt10, T. Schoerner-Sadenius, N. Sen, A. Spiridonov, M. Stein, J. Tomaszewska,
R. Walsh, C. Wissing

University of Hamburg, Hamburg, Germany
C. Autermann, V. Blobel, S. Bobrovskyi, J. Draeger, H. Enderle, U. Gebbert, K. Kaschube,
G. Kaussen, R. Klanner, J. Lange, B. Mura, S. Naumann-Emme, F. Nowak, N. Pietsch,
C. Sander, H. Schettler, P. Schleper, M. Schröder, T. Schum, J. Schwandt, H. Stadie,
G. Steinbrück, J. Thomsen

Institut für Experimentelle Kernphysik, Karlsruhe, Germany
C. Barth, J. Bauer, J. Berger, V. Buege, T. Chwalek, W. De Boer, A. Dierlamm, G. Dirkes,
M. Feindt, J. Gruschke, C. Hackstein, F. Hartmann, M. Heinrich, H. Held, K.H. Hoffmann,
S. Honc, J.R. Komaragiri, T. Kuhr, D. Martschei, S. Mueller, Th. Müller, M. Niegel,
O. Oberst, A. Oehler, J. Ott, T. Peiffer, G. Quast, K. Rabbertz, F. Ratnikov, N. Ratnikova,
M. Renz, C. Saout, A. Scheurer, P. Schieferdecker, F.-P. Schilling, G. Schott, H.J. Simonis,
F.M. Stober, D. Troendle, J. Wagner-Kuhr, T. Weiler, M. Zeise, V. Zhukov11, E.B. Ziebarth

Institute of Nuclear Physics ”Demokritos”, Aghia Paraskevi, Greece
G. Daskalakis, T. Geralis, S. Kesisoglou, A. Kyriakis, D. Loukas, I. Manolakos, A. Markou,
C. Markou, C. Mavrommatis, E. Ntomari, E. Petrakou

University of Athens, Athens, Greece
L. Gouskos, T.J. Mertzimekis, A. Panagiotou, E. Stiliaris

University of Ioánnina, Ioánnina, Greece
I. Evangelou, C. Foudas, P. Kokkas, N. Manthos, I. Papadopoulos, V. Patras, F.A. Triantis

KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary
A. Aranyi, G. Bencze, L. Boldizsar, C. Hajdu1, P. Hidas, D. Horvath12, A. Kapusi,
K. Krajczar13, F. Sikler1, G.I. Veres13, G. Vesztergombi13

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Institute of Nuclear Research ATOMKI, Debrecen, Hungary
N. Beni, J. Molnar, J. Palinkas, Z. Szillasi, V. Veszpremi

University of Debrecen, Debrecen, Hungary
P. Raics, Z.L. Trocsanyi, B. Ujvari

Panjab University, Chandigarh, India
S.B. Beri, V. Bhatnagar, N. Dhingra, R. Gupta, M. Jindal, M. Kaur, J.M. Kohli,
M.Z. Mehta, N. Nishu, L.K. Saini, A. Sharma, A.P. Singh, J. Singh, S.P. Singh

University of Delhi, Delhi, India
S. Ahuja, S. Bhattacharya, B.C. Choudhary, B. Gomber, P. Gupta, S. Jain, S. Jain,
R. Khurana, A. Kumar, M. Naimuddin, K. Ranjan, R.K. Shivpuri

Saha Institute of Nuclear Physics, Kolkata, India
S. Sarkar

Bhabha Atomic Research Centre, Mumbai, India
R.K. Choudhury, D. Dutta, S. Kailas, V. Kumar, P. Mehta, A.K. Mohanty1, L.M. Pant,
P. Shukla

Tata Institute of Fundamental Research - EHEP, Mumbai, India
T. Aziz, M. Guchait14, A. Gurtu, M. Maity15, D. Majumder, G. Majumder, K. Mazumdar,
G.B. Mohanty, A. Saha, K. Sudhakar, N. Wickramage

Tata Institute of Fundamental Research - HECR, Mumbai, India
S. Banerjee, S. Dugad, N.K. Mondal

Institute for Research and Fundamental Sciences (IPM), Tehran, Iran
H. Arfaei, H. Bakhshiansohi16, S.M. Etesami, A. Fahim16, M. Hashemi, A. Jafari16,
M. Khakzad, A. Mohammadi17, M. Mohammadi Najafabadi, S. Paktinat Mehdiabadi,
B. Safarzadeh, M. Zeinali18

INFN Sezione di Bari a, Università di Bari b, Politecnico di Bari c, Bari, Italy
M. Abbresciaa,b, L. Barbonea,b, C. Calabriaa,b, A. Colaleoa, D. Creanzaa,c, N. De
Filippisa,c,1, M. De Palmaa,b, L. Fiorea, G. Iasellia,c, L. Lusitoa,b, G. Maggia,c, M. Maggia,
N. Mannaa,b, B. Marangellia,b, S. Mya,c, S. Nuzzoa,b, N. Pacificoa,b, G.A. Pierroa,
A. Pompilia,b, G. Pugliesea,c, F. Romanoa,c, G. Rosellia,b, G. Selvaggia,b, L. Silvestrisa,
R. Trentaduea, S. Tupputia,b, G. Zitoa

INFN Sezione di Bologna a, Università di Bologna b, Bologna, Italy
G. Abbiendia, A.C. Benvenutia, D. Bonacorsia, S. Braibant-Giacomellia,b, L. Brigliadoria,
P. Capiluppia,b, A. Castroa,b, F.R. Cavalloa, M. Cuffiania,b, G.M. Dallavallea, F. Fabbria,
A. Fanfania,b, D. Fasanellaa, P. Giacomellia, M. Giuntaa, C. Grandia, S. Marcellinia,
G. Masettib, M. Meneghellia,b, A. Montanaria, F.L. Navarriaa,b, F. Odoricia, A. Perrottaa,
F. Primaveraa, A.M. Rossia,b, T. Rovellia,b, G. Sirolia,b, R. Travaglinia,b

INFN Sezione di Catania a, Università di Catania b, Catania, Italy
S. Albergoa,b, G. Cappelloa,b, M. Chiorbolia,b,1, S. Costaa,b, A. Tricomia,b, C. Tuvea,b

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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, P. Lenzia,b, M. Meschinia, S. Paolettia, G. Sguazzonia,
A. Tropianoa,1

INFN Laboratori Nazionali di Frascati, Frascati, Italy
L. Benussi, S. Bianco, S. Colafranceschi19, F. Fabbri, D. Piccolo

INFN Sezione di Genova, Genova, Italy
P. Fabbricatore, R. Musenich

INFN Sezione di Milano-Bicocca a, Università di Milano-Bicocca b, Milano,
Italy
A. Benagliaa,b, F. De Guioa,b,1, L. Di Matteoa,b, S. Gennai1, A. Ghezzia,b, S. Malvezzia,
A. Martellia,b, A. Massironia,b, D. Menascea, L. Moronia, M. Paganonia,b, D. Pedrinia,
S. Ragazzia,b, N. Redaellia, S. Salaa, T. Tabarelli de Fatisa,b

INFN Sezione di Napoli a, Università di Napoli ”Federico II” b, Napoli, Italy
S. Buontempoa, C.A. Carrillo Montoyaa,1, N. Cavalloa,20, A. De Cosaa,b, F. Fabozzia,20,
A.O.M. Iorioa,1, L. Listaa, M. Merolaa,b, P. Paoluccia

INFN Sezione di Padova a, Università di Padova b, Università di
Trento (Trento) c, Padova, Italy
P. Azzia, N. Bacchettaa, P. Bellana,b, D. Biselloa,b, A. Brancaa, R. Carlina,b, P. Checchiaa,
M. De Mattiaa,b, T. Dorigoa, U. Dossellia, F. Fanzagoa, F. Gasparinia,b, U. Gasparinia,b,
A. Gozzelino, S. Lacapraraa,21, I. Lazzizzeraa,c, M. Margonia,b, M. Mazzucatoa,
A.T. Meneguzzoa,b, M. Nespoloa,1, L. Perrozzia,1, 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
P. Baessoa,b, U. Berzanoa, S.P. Rattia,b, C. Riccardia,b, P. Torrea,b, P. Vituloa,b,
C. Viviania,b

INFN Sezione di Perugia a, Università di Perugia b, Perugia, Italy
M. Biasinia,b, G.M. Bileia, B. Caponeria,b, L. Fanòa,b, P. Laricciaa,b, A. Lucaronia,b,1,
G. Mantovania,b, M. Menichellia, A. Nappia,b, F. Romeoa,b, A. Santocchiaa,b, S. Taronia,b,1,
M. Valdataa,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,b, T. Boccalia,1, G. Broccoloa,c, R. Castaldia,
R.T. D’Agnoloa,c, R. Dell’Orsoa, F. Fioria,b, L. Foàa,c, A. Giassia, A. Kraana,
F. Ligabuea,c, T. Lomtadzea, L. Martinia,22, A. Messineoa,b, F. Pallaa, G. Segneria,
A.T. Serbana, P. Spagnoloa, R. Tenchinia, G. Tonellia,b,1, A. Venturia,1, P.G. Verdinia

INFN Sezione di Roma a, Università di Roma ”La Sapienza” b, Roma, Italy
L. Baronea,b, F. Cavallaria, D. Del Rea,b, E. Di Marcoa,b, M. Diemoza, D. Francia,b,
M. Grassia,1, E. Longoa,b, S. Nourbakhsha, G. Organtinia,b, F. Pandolfia,b,1, R. Paramattia,
S. Rahatloua,b, C. Rovelli1

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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, C. Bottaa,b,1,
N. Cartigliaa, R. Castelloa,b, M. Costaa,b, N. Demariaa, A. Grazianoa,b,1, C. Mariottia,
M. Maronea,b, S. Masellia, E. Migliorea,b, G. Milaa,b, V. Monacoa,b, M. Musicha,b,
M.M. Obertinoa,c, N. Pastronea, M. Pelliccionia,b, A. Romeroa,b, M. Ruspaa,c, R. Sacchia,b,
V. Solaa,b, A. Solanoa,b, A. Staianoa, A. Vilela Pereiraa

INFN Sezione di Trieste a, Università di Trieste b, Trieste, Italy
S. Belfortea, F. Cossuttia, G. Della Riccaa,b, B. Gobboa, D. Montaninoa,b, A. Penzoa

Kangwon National University, Chunchon, Korea
S.G. Heo, S.K. Nam

Kyungpook National University, Daegu, Korea
S. Chang, J. Chung, D.H. Kim, G.N. Kim, J.E. Kim, D.J. Kong, H. Park, S.R. Ro, D. Son,
D.C. Son, T. Son

Chonnam National University, Institute for Universe and Elementary Particles,
Kwangju, Korea
Zero Kim, J.Y. Kim, S. Song

Korea University, Seoul, Korea
S. Choi, B. Hong, M.S. Jeong, M. Jo, H. Kim, J.H. Kim, T.J. Kim, K.S. Lee, D.H. Moon,
S.K. Park, H.B. Rhee, E. Seo, S. Shin, K.S. Sim

University of Seoul, Seoul, Korea
M. Choi, S. Kang, 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, J. Lee, S. Lee, H. Seo, I. Yu

Vilnius University, Vilnius, Lithuania
M.J. Bilinskas, I. Grigelionis, M. Janulis, D. Martisiute, P. Petrov, T. Sabonis

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,
R. Magaña Villalba, A. Sánchez-Hernández, 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

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, J. Tam

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University of Canterbury, Christchurch, New Zealand
P.H. Butler, R. Doesburg, H. Silverwood

National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan
M. Ahmad, I. Ahmed, M.I. Asghar, H.R. Hoorani, W.A. Khan, T. Khurshid, S. Qazi

Institute of Experimental Physics, Faculty of Physics, University of Warsaw,
Warsaw, Poland
G. Brona, M. Cwiok, W. Dominik, K. Doroba, A. Kalinowski, M. Konecki, J. Krolikowski

Soltan Institute for Nuclear Studies, Warsaw, Poland
T. Frueboes, R. Gokieli, M. Górski, M. Kazana, K. Nawrocki, K. Romanowska-Rybinska,
M. Szleper, G. Wrochna, P. Zalewski

Laboratório de Instrumentação e F́ısica Experimental de Part́ıculas, Lisboa,
Portugal
N. Almeida, P. Bargassa, A. David, P. Faccioli, P.G. Ferreira Parracho, M. Gallinaro,
P. Musella, A. Nayak, P.Q. Ribeiro, J. Seixas, J. Varela

Joint Institute for Nuclear Research, Dubna, Russia
I. Belotelov, P. Bunin, I. Golutvin, A. Kamenev, V. Karjavin, V. Konoplyanikov, G. Kozlov,
A. Lanev, P. Moisenz, V. Palichik, V. Perelygin, S. Shmatov, V. Smirnov, A. Volodko,
A. Zarubin

Petersburg Nuclear Physics Institute, Gatchina (St Petersburg), Russia
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, A. Toropin, S. Troitsky

Institute for Theoretical and Experimental Physics, Moscow, Russia
V. Epshteyn, V. Gavrilov, V. Kaftanov†, M. Kossov1, A. Krokhotin, N. Lychkovskaya,
V. Popov, G. Safronov, S. Semenov, V. Stolin, E. Vlasov, A. Zhokin

Moscow State University, Moscow, Russia
E. Boos, M. Dubinin23, L. Dudko, A. Ershov, A. Gribushin, O. Kodolova, I. Lokhtin,
A. Markina, S. Obraztsov, M. Perfilov, S. Petrushanko, L. Sarycheva, V. Savrin, A. Snigirev

P.N. Lebedev Physical Institute, Moscow, Russia
V. Andreev, M. Azarkin, I. Dremin, M. Kirakosyan, A. Leonidov, S.V. Rusakov, A. Vino-
gradov

State Research Center of Russian Federation, Institute for High Energy
Physics, Protvino, Russia
I. Azhgirey, S. Bitioukov, V. Grishin1, V. Kachanov, D. Konstantinov, A. Korablev,
V. Krychkine, V. Petrov, R. Ryutin, S. Slabospitsky, A. Sobol, L. Tourtchanovitch,
S. Troshin, N. Tyurin, A. Uzunian, A. Volkov

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

P. Adzic24, M. Djordjevic, D. Krpic24, 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. Cepeda,
M. Cerrada, M. Chamizo Llatas, N. Colino, B. De La Cruz, A. Delgado Peris, C. Diez
Pardos, 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, 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

J. Cuevas, J. Fernandez Menendez, S. Folgueras, I. Gonzalez Caballero, L. Lloret Iglesias,
J.M. Vizan Garcia

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. Felcini25, M. Fernandez, G. Gomez, J. Gonzalez Sanchez, C. Jorda, P. Lobelle Pardo,
A. Lopez Virto, J. Marco, R. Marco, C. Martinez Rivero, F. Matorras, F.J. Munoz Sanchez,
J. Piedra Gomez26, T. Rodrigo, A.Y. Rodŕıguez-Marrero, A. Ruiz-Jimeno, L. Scodellaro,
M. Sobron Sanudo, I. Vila, R. Vilar Cortabitarte

CERN, European Organization for Nuclear Research, Geneva, Switzerland

D. Abbaneo, E. Auffray, G. Auzinger, P. Baillon, A.H. Ball, D. Barney, A.J. Bell27,
D. Benedetti, C. Bernet3, W. Bialas, P. Bloch, A. Bocci, S. Bolognesi, M. Bona, H. Breuker,
K. Bunkowski, T. Camporesi, G. Cerminara, T. Christiansen, J.A. Coarasa Perez, B. Curé,
D. D’Enterria, A. De Roeck, S. Di Guida, N. Dupont-Sagorin, A. Elliott-Peisert, B. Frisch,
W. Funk, A. Gaddi, G. Georgiou, H. Gerwig, D. Gigi, K. Gill, D. Giordano, F. Glege,
R. Gomez-Reino Garrido, M. Gouzevitch, P. Govoni, S. Gowdy, L. Guiducci, M. Hansen,
C. Hartl, J. Harvey, J. Hegeman, B. Hegner, H.F. Hoffmann, A. Honma, V. Innocente,
P. Janot, K. Kaadze, E. Karavakis, P. Lecoq, C. Lourenço, T. Mäki, M. Malberti, L. Mal-
geri, M. Mannelli, L. Masetti, A. Maurisset, F. Meijers, S. Mersi, E. Meschi, R. Moser,
M.U. Mozer, M. Mulders, E. Nesvold1, M. Nguyen, T. Orimoto, L. Orsini, E. Perez,
A. Petrilli, A. Pfeiffer, M. Pierini, M. Pimiä, D. Piparo, G. Polese, A. Racz, J. Rodrigues
Antunes, G. Rolandi28, T. Rommerskirchen, M. Rovere, H. Sakulin, C. Schäfer, C. Schwick,
I. Segoni, A. Sharma, P. Siegrist, P. Silva, M. Simon, P. Sphicas29, M. Spiropulu23,
M. Stoye, M. Tadel, P. Tropea, A. Tsirou, P. Vichoudis, M. Voutilainen, W.D. Zeuner

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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,
J. Sibille30, A. Starodumov31

Institute for Particle Physics, ETH Zurich, Zurich, Switzerland

L. Bäni, P. Bortignon, L. Caminada32, N. Chanon, Z. Chen, S. Cittolin, G. Dissertori,
M. Dittmar, J. Eugster, K. Freudenreich, C. Grab, W. Hintz, P. Lecomte, W. Lustermann,
C. Marchica32, P. Martinez Ruiz del Arbol, P. Meridiani, P. Milenovic33, F. Moortgat,
C. Nägeli32, P. Nef, F. Nessi-Tedaldi, L. Pape, F. Pauss, T. Punz, A. Rizzi, F.J. Ronga,
M. Rossini, L. Sala, A.K. Sanchez, M.-C. Sawley, B. Stieger, L. Tauscher†, A. Thea,
K. Theofilatos, D. Treille, C. Urscheler, R. Wallny, M. Weber, L. Wehrli, J. Weng

Universität Zürich, Zurich, Switzerland

E. Aguilo, C. Amsler, V. Chiochia, S. De Visscher, C. Favaro, M. Ivova Rikova, B. Millan
Mejias, P. Otiougova, C. Regenfus, P. Robmann, A. Schmidt, H. Snoek

National Central University, Chung-Li, Taiwan

Y.H. Chang, K.H. Chen, S. Dutta, C.M. Kuo, S.W. Li, W. Lin, Z.K. Liu, Y.J. Lu,
D. Mekterovic, R. Volpe, J.H. Wu, S.S. Yu

National Taiwan University (NTU), Taipei, Taiwan

P. Bartalini, P. Chang, Y.H. Chang, Y.W. Chang, Y. Chao, K.F. Chen, W.-S. Hou,
Y. Hsiung, K.Y. Kao, Y.J. Lei, R.-S. Lu, J.G. Shiu, Y.M. Tzeng, M. Wang

Cukurova University, Adana, Turkey

A. Adiguzel, M.N. Bakirci34, S. Cerci35, C. Dozen, I. Dumanoglu, E. Eskut, S. Girgis,
G. Gokbulut, I. Hos, E.E. Kangal, A. Kayis Topaksu, G. Onengut, K. Ozdemir, S. Ozturk36,
A. Polatoz, K. Sogut37, D. Sunar Cerci35, B. Tali35, H. Topakli34, D. Uzun, L.N. Vergili,
M. Vergili

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, E. Yildirim, M. Zeyrek

Bogazici University, Istanbul, Turkey

M. Deliomeroglu, D. Demir38, E. Gülmez, B. Isildak, M. Kaya39, O. Kaya39, M. Özbek,
S. Ozkorucuklu40, N. Sonmez41

National Scientific Center, Kharkov Institute of Physics and Technology,
Kharkov, Ukraine

L. Levchuk

University of Bristol, Bristol, United Kingdom

F. Bostock, J.J. Brooke, T.L. Cheng, E. Clement, D. Cussans, R. Frazier, J. Goldstein,
M. Grimes, M. Hansen, D. Hartley, G.P. Heath, H.F. Heath, L. Kreczko, S. Metson,
D.M. Newbold42, K. Nirunpong, A. Poll, S. Senkin, V.J. Smith, S. Ward

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Rutherford Appleton Laboratory, Didcot, United Kingdom

L. Basso43, K.W. Bell, A. Belyaev43, C. Brew, R.M. Brown, B. Camanzi, D.J.A. Cockerill,
J.A. Coughlan, 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,
S.D. Worm

Imperial College, London, United Kingdom

R. Bainbridge, G. Ball, J. Ballin, R. Beuselinck, O. Buchmuller, D. Colling, N. Cripps,
M. Cutajar, 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,
L. Lyons, B.C. MacEvoy, A.-M. Magnan, J. Marrouche, B. Mathias, R. Nandi, J. Nash,
A. Nikitenko31, A. Papageorgiou, M. Pesaresi, K. Petridis, M. Pioppi44, D.M. Raymond,
S. Rogerson, N. Rompotis, A. Rose, M.J. Ryan, C. Seez, P. Sharp, A. Sparrow, A. Tapper,
S. Tourneur, M. Vazquez Acosta, T. Virdee, S. Wakefield, N. Wardle, D. Wardrope,
T. Whyntie

Brunel University, Uxbridge, United Kingdom

M. Barrett, M. Chadwick, J.E. Cole, P.R. Hobson, A. Khan, P. Kyberd, D. Leslie,
W. Martin, I.D. Reid, L. Teodorescu

Baylor University, Waco, USA

K. Hatakeyama, H. Liu

Boston University, Boston, USA

T. Bose, E. Carrera Jarrin, C. Fantasia, A. Heister, J. St. John, P. Lawson, D. Lazic,
J. Rohlf, D. Sperka, L. Sulak

Brown University, Providence, USA

A. Avetisyan, S. Bhattacharya, J.P. Chou, D. Cutts, A. Ferapontov, U. Heintz, S. Jabeen,
G. Kukartsev, G. Landsberg, M. Luk, M. Narain, D. Nguyen, M. Segala, T. Sinthuprasith,
T. Speer, K.V. Tsang

University of California, Davis, Davis, USA

R. Breedon, M. Calderon De La Barca Sanchez, S. Chauhan, M. Chertok, J. Conway,
P.T. Cox, J. Dolen, R. Erbacher, E. Friis, W. Ko, A. Kopecky, R. Lander, H. Liu,
S. Maruyama, T. Miceli, M. Nikolic, D. Pellett, J. Robles, S. Salur, T. Schwarz, M. Searle,
J. Smith, M. Squires, M. Tripathi, R. Vasquez Sierra, C. Veelken

University of California, Los Angeles, Los Angeles, USA

V. Andreev, K. Arisaka, D. Cline, R. Cousins, A. Deisher, J. Duris, S. Erhan, C. Farrell,
J. Hauser, M. Ignatenko, C. Jarvis, C. Plager, G. Rakness, P. Schlein†, J. Tucker, V. Valuev

University of California, Riverside, Riverside, USA

J. Babb, A. Chandra, R. Clare, J. Ellison, J.W. Gary, F. Giordano, G. Hanson, G.Y. Jeng,
S.C. Kao, F. Liu, H. Liu, O.R. Long, A. Luthra, H. Nguyen, B.C. Shen†, R. Stringer,
J. Sturdy, S. Sumowidagdo, R. Wilken, S. Wimpenny

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University of California, San Diego, La Jolla, USA
W. Andrews, J.G. Branson, G.B. Cerati, D. Evans, F. Golf, A. Holzner, R. Kelley,
M. Lebourgeois, J. Letts, B. Mangano, S. Padhi, C. Palmer, G. Petrucciani, H. Pi, M. Pieri,
R. Ranieri, M. Sani, V. Sharma, S. Simon, E. Sudano, Y. Tu, A. Vartak, S. Wasserbaech45,
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,
J. Incandela, C. Justus, P. Kalavase, S.A. Koay, D. Kovalskyi, V. Krutelyov, S. Lowette,
N. Mccoll, V. Pavlunin, F. Rebassoo, J. Ribnik, J. Richman, R. Rossin, D. Stuart, W. To,
J.R. Vlimant

California Institute of Technology, Pasadena, USA
A. Apresyan, A. Bornheim, J. Bunn, Y. Chen, M. Gataullin, Y. Ma, A. Mott, H.B. New-
man, C. Rogan, K. Shin, V. Timciuc, P. Traczyk, J. Veverka, R. Wilkinson, Y. Yang,
R.Y. Zhu

Carnegie Mellon University, Pittsburgh, USA
B. Akgun, R. Carroll, T. Ferguson, Y. Iiyama, D.W. Jang, S.Y. Jun, Y.F. Liu, M. Paulini,
J. Russ, H. Vogel, I. Vorobiev

University of Colorado at Boulder, Boulder, USA
J.P. Cumalat, M.E. Dinardo, B.R. Drell, C.J. Edelmaier, W.T. Ford, A. Gaz, B. Heyburn,
E. Luiggi Lopez, U. Nauenberg, J.G. Smith, K. Stenson, K.A. Ulmer, S.R. Wagner,
S.L. Zang

Cornell University, Ithaca, USA
L. Agostino, J. Alexander, D. Cassel, A. Chatterjee, S. Das, N. Eggert, L.K. Gibbons,
B. Heltsley, W. Hopkins, A. Khukhunaishvili, B. Kreis, G. Nicolas Kaufman, J.R. Patter-
son, D. Puigh, A. Ryd, E. Salvati, X. Shi, W. Sun, W.D. Teo, J. Thom, J. Thompson,
J. Vaughan, Y. Weng, L. Winstrom, P. Wittich

Fairfield University, Fairfield, USA
A. Biselli, G. Cirino, D. Winn

Fermi National Accelerator Laboratory, Batavia, USA
S. Abdullin, M. Albrow, J. Anderson, G. Apollinari, M. Atac, J.A. Bakken, S. Banerjee,
L.A.T. Bauerdick, A. Beretvas, J. Berryhill, P.C. Bhat, I. Bloch, F. Borcherding, K. Bur-
kett, J.N. Butler, V. Chetluru, H.W.K. Cheung, F. Chlebana, S. Cihangir, W. Cooper,
D.P. Eartly, V.D. Elvira, S. Esen, I. Fisk, J. Freeman, Y. Gao, E. Gottschalk, D. Green,
K. Gunthoti, O. Gutsche, J. Hanlon, R.M. Harris, J. Hirschauer, B. Hooberman, H. Jensen,
M. Johnson, U. Joshi, R. Khatiwada, B. Klima, K. Kousouris, S. Kunori, S. Kwan,
C. Leonidopoulos, P. Limon, D. Lincoln, R. Lipton, J. Lykken, K. Maeshima, J.M. Marraf-
fino, D. Mason, P. McBride, T. Miao, K. Mishra, S. Mrenna, Y. Musienko46, C. Newman-
Holmes, V. O’Dell, R. Pordes, O. Prokofyev, N. Saoulidou, E. Sexton-Kennedy, S. Sharma,
W.J. Spalding, L. Spiegel, P. Tan, L. Taylor, S. Tkaczyk, L. Uplegger, E.W. Vaandering,
R. Vidal, J. Whitmore, W. Wu, F. Yang, F. Yumiceva, J.C. Yun

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University of Florida, Gainesville, USA

D. Acosta, P. Avery, D. Bourilkov, M. Chen, M. De Gruttola, G.P. Di Giovanni, D. Dobur,
A. Drozdetskiy, R.D. Field, M. Fisher, Y. Fu, I.K. Furic, J. Gartner, B. Kim, J. Konigsberg,
A. Korytov, A. Kropivnitskaya, T. Kypreos, K. Matchev, G. Mitselmakher, L. Muniz,
C. Prescott, R. Remington, M. Schmitt, B. Scurlock, P. Sellers, N. Skhirtladze, M. Snow-
ball, D. Wang, J. Yelton, M. Zakaria

Florida International University, Miami, USA

C. Ceron, V. Gaultney, L. Kramer, L.M. Lebolo, S. Linn, P. Markowitz, G. Martinez,
D. Mesa, J.L. Rodriguez

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, L. Quertenmont,
S. Sekmen, V. Veeraraghavan

Florida Institute of Technology, Melbourne, USA

M.M. Baarmand, B. Dorney, S. Guragain, M. Hohlmann, H. Kalakhety, R. Ralich,
I. Vodopiyanov

University of Illinois at Chicago (UIC), Chicago, USA

M.R. Adams, I.M. Anghel, L. Apanasevich, Y. Bai, V.E. Bazterra, R.R. Betts, J. Callner,
R. Cavanaugh, C. Dragoiu, L. Gauthier, C.E. Gerber, S. Hamdan, D.J. Hofman, S. Kha-
latyan, G.J. Kunde47, F. Lacroix, M. Malek, C. O’Brien, C. Silvestre, A. Smoron, D. Strom,
N. Varelas

The University of Iowa, Iowa City, USA

U. Akgun, E.A. Albayrak, B. Bilki, W. Clarida, F. Duru, C.K. Lae, E. McCliment, J.-
P. Merlo, H. Mermerkaya48, A. Mestvirishvili, A. Moeller, J. Nachtman, C.R. Newsom,
E. Norbeck, J. Olson, Y. Onel, F. Ozok, S. Sen, J. Wetzel, T. Yetkin, K. Yi

Johns Hopkins University, Baltimore, USA

B.A. Barnett, B. Blumenfeld, A. Bonato, C. Eskew, D. Fehling, G. Giurgiu, A.V. Gritsan,
Z.J. Guo, G. Hu, P. Maksimovic, S. Rappoccio, M. Swartz, N.V. Tran, A. Whitbeck

The University of Kansas, Lawrence, USA

P. Baringer, A. Bean, G. Benelli, O. Grachov, R.P. Kenny Iii, M. Murray, D. Noonan,
S. Sanders, J.S. Wood, V. Zhukova

Kansas State University, Manhattan, USA

A.F. Barfuss, T. Bolton, I. Chakaberia, A. Ivanov, S. Khalil, M. Makouski, Y. Maravin,
S. Shrestha, I. Svintradze, Z. Wan

Lawrence Livermore National Laboratory, Livermore, USA

J. Gronberg, D. Lange, D. Wright

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University of Maryland, College Park, USA
A. Baden, M. Boutemeur, S.C. Eno, D. Ferencek, J.A. Gomez, N.J. Hadley, R.G. Kellogg,
M. Kirn, Y. Lu, A.C. Mignerey, K. Rossato, P. Rumerio, F. Santanastasio, A. Skuja,
J. Temple, M.B. Tonjes, S.C. Tonwar, E. Twedt

Massachusetts Institute of Technology, Cambridge, USA
B. Alver, G. Bauer, J. Bendavid, W. Busza, E. Butz, I.A. Cali, M. Chan, V. Dutta,
P. Everaerts, G. Gomez Ceballos, M. Goncharov, K.A. Hahn, P. Harris, Y. Kim, M. Klute,
Y.-J. Lee, W. Li, C. Loizides, P.D. Luckey, T. Ma, S. Nahn, C. Paus, D. Ralph, C. Roland,
G. Roland, M. Rudolph, G.S.F. Stephans, F. Stöckli, K. Sumorok, K. Sung, E.A. Wenger,
R. Wolf, S. Xie, M. Yang, Y. Yilmaz, A.S. Yoon, M. Zanetti

University of Minnesota, Minneapolis, USA
S.I. Cooper, P. Cushman, B. Dahmes, A. De Benedetti, P.R. Dudero, G. Franzoni, J. Haupt,
K. Klapoetke, Y. Kubota, J. Mans, V. Rekovic, R. Rusack, M. Sasseville, A. Singovsky,
N. Tambe

University of Mississippi, University, USA
L.M. Cremaldi, R. Godang, R. Kroeger, L. Perera, R. Rahmat, D.A. Sanders, D. Summers

University of Nebraska-Lincoln, Lincoln, USA
K. Bloom, S. Bose, J. Butt, D.R. Claes, A. Dominguez, M. Eads, J. Keller, T. Kelly,
I. Kravchenko, J. Lazo-Flores, H. Malbouisson, S. Malik, G.R. Snow

State University of New York at Buffalo, Buffalo, USA
U. Baur, A. Godshalk, I. Iashvili, S. Jain, A. Kharchilava, A. Kumar, S.P. Shipkowski,
K. Smith

Northeastern University, Boston, USA
G. Alverson, E. Barberis, D. Baumgartel, O. Boeriu, M. Chasco, S. Reucroft, J. Swain,
D. Trocino, D. Wood, J. Zhang

Northwestern University, Evanston, USA
A. Anastassov, A. Kubik, N. Odell, R.A. Ofierzynski, B. Pollack, A. Pozdnyakov,
M. Schmitt, S. Stoynev, M. Velasco, S. Won

University of Notre Dame, Notre Dame, USA
L. Antonelli, D. Berry, A. Brinkerhoff, M. Hildreth, C. Jessop, D.J. Karmgard, J. Kolb,
T. Kolberg, K. Lannon, W. Luo, S. Lynch, N. Marinelli, D.M. Morse, T. Pearson, R. Ruchti,
J. Slaunwhite, N. Valls, M. Wayne, J. Ziegler

The Ohio State University, Columbus, USA
B. Bylsma, L.S. Durkin, J. Gu, C. Hill, P. Killewald, K. Kotov, T.Y. Ling, M. Rodenburg,
G. Williams

Princeton University, Princeton, USA
N. Adam, E. Berry, P. Elmer, D. Gerbaudo, V. Halyo, P. Hebda, A. Hunt, J. Jones,
E. Laird, D. Lopes Pegna, D. Marlow, T. Medvedeva, M. Mooney, J. Olsen, P. Piroué,
X. Quan, H. Saka, D. Stickland, C. Tully, J.S. Werner, A. Zuranski

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University of Puerto Rico, Mayaguez, USA

J.G. Acosta, X.T. Huang, A. Lopez, H. Mendez, S. Oliveros, J.E. Ramirez Vargas,
A. Zatserklyaniy

Purdue University, West Lafayette, USA

E. Alagoz, V.E. Barnes, G. Bolla, L. Borrello, D. Bortoletto, A. Everett, A.F. Garfinkel,
L. Gutay, Z. Hu, M. Jones, O. Koybasi, M. Kress, A.T. Laasanen, N. Leonardo, C. Liu,
V. Maroussov, P. Merkel, D.H. Miller, N. Neumeister, I. Shipsey, D. Silvers, A. Svy-
atkovskiy, H.D. Yoo, J. Zablocki, Y. Zheng

Purdue University Calumet, Hammond, USA

P. Jindal, N. Parashar

Rice University, Houston, USA

C. Boulahouache, V. Cuplov, K.M. Ecklund, F.J.M. Geurts, 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,
H. Flacher, A. Garcia-Bellido, P. Goldenzweig, Y. Gotra, J. Han, A. Harel, D.C. Miner,
D. Orbaker, G. Petrillo, D. Vishnevskiy, M. Zielinski

The Rockefeller University, New York, USA

A. Bhatti, R. Ciesielski, L. Demortier, K. Goulianos, G. Lungu, S. Malik, C. Mesropian,
M. Yan

Rutgers, the State University of New Jersey, Piscataway, USA

O. Atramentov, A. Barker, D. Duggan, Y. Gershtein, R. Gray, E. Halkiadakis, D. Hidas,
D. Hits, A. Lath, S. Panwalkar, R. Patel, A. Richards, K. Rose, S. Schnetzer, S. Somalwar,
R. Stone, S. Thomas

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, A. Gurrola, T. Kamon, V. Khotilovich, R. Montalvo,
I. Osipenkov, Y. Pakhotin, J. Pivarski, A. Safonov, S. Sengupta, A. Tatarinov, D. Toback,
M. Weinberger

Texas Tech University, Lubbock, USA

N. Akchurin, C. Bardak, J. Damgov, C. Jeong, K. Kovitanggoon, S.W. Lee, P. Mane,
Y. Roh, A. Sill, I. Volobouev, R. Wigmans, E. Yazgan

Vanderbilt University, Nashville, USA

E. Appelt, E. Brownson, D. Engh, C. Florez, W. Gabella, M. Issah, W. Johns, P. Kurt,
C. Maguire, A. Melo, P. Sheldon, B. Snook, S. Tuo, J. Velkovska

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University of Virginia, Charlottesville, USA
M.W. Arenton, M. Balazs, S. Boutle, B. Cox, B. Francis, R. Hirosky, A. Ledovskoy, C. Lin,
C. Neu, R. Yohay

Wayne State University, Detroit, USA
S. Gollapinni, R. Harr, P.E. Karchin, P. Lamichhane, M. Mattson, C. Milstène, A. Sakharov

University of Wisconsin, Madison, USA
M. Anderson, M. Bachtis, J.N. Bellinger, D. Carlsmith, S. Dasu, J. Efron, K. Flood,
L. Gray, K.S. Grogg, M. Grothe, R. Hall-Wilton, M. Herndon, A. Hervé, P. Klabbers,
J. Klukas, A. Lanaro, C. Lazaridis, J. Leonard, R. Loveless, A. Mohapatra, F. Palmonari,
D. Reeder, I. Ross, A. Savin, W.H. Smith, J. Swanson, M. Weinberg

†: Deceased
1: Also at CERN, European Organization for Nuclear Research, Geneva, Switzerland
2: Also at Universidade Federal do ABC, Santo Andre, Brazil
3: Also at Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
4: Also at Suez Canal University, Suez, Egypt
5: Also at British University, Cairo, Egypt
6: Also at Fayoum University, El-Fayoum, Egypt
7: Also at Soltan Institute for Nuclear Studies, Warsaw, Poland
8: Also at Massachusetts Institute of Technology, Cambridge, USA
9: Also at Université de Haute-Alsace, Mulhouse, France

10: Also at Brandenburg University of Technology, Cottbus, Germany
11: Also at Moscow State University, Moscow, Russia
12: Also at Institute of Nuclear Research ATOMKI, Debrecen, Hungary
13: Also at Eötvös Loránd University, Budapest, Hungary
14: Also at Tata Institute of Fundamental Research - HECR, Mumbai, India
15: Also at University of Visva-Bharati, Santiniketan, India
16: Also at Sharif University of Technology, Tehran, Iran
17: Also at Shiraz University, Shiraz, Iran
18: Also at Isfahan University of Technology, Isfahan, Iran
19: Also at Facoltà Ingegneria Università di Roma, Roma, Italy
20: Also at Università della Basilicata, Potenza, Italy
21: Also at Laboratori Nazionali di Legnaro dell’ INFN, Legnaro, Italy
22: Also at Università degli studi di Siena, Siena, Italy
23: Also at California Institute of Technology, Pasadena, USA
24: Also at Faculty of Physics of University of Belgrade, Belgrade, Serbia
25: Also at University of California, Los Angeles, Los Angeles, USA
26: Also at University of Florida, Gainesville, USA
27: Also at Université de Genève, Geneva, Switzerland
28: Also at Scuola Normale e Sezione dell’ INFN, Pisa, Italy
29: Also at University of Athens, Athens, Greece
30: Also at The University of Kansas, Lawrence, USA
31: Also at Institute for Theoretical and Experimental Physics, Moscow, Russia
32: Also at Paul Scherrer Institut, Villigen, Switzerland
33: Also at University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences,

Belgrade, Serbia

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34: Also at Gaziosmanpasa University, Tokat, Turkey
35: Also at Adiyaman University, Adiyaman, Turkey
36: Also at The University of Iowa, Iowa City, USA
37: Also at Mersin University, Mersin, Turkey
38: Also at Izmir Institute of Technology, Izmir, Turkey
39: Also at Kafkas University, Kars, Turkey
40: Also at Suleyman Demirel University, Isparta, Turkey
41: Also at Ege University, Izmir, Turkey
42: Also at Rutherford Appleton Laboratory, Didcot, United Kingdom
43: Also at School of Physics and Astronomy, University of Southampton, Southampton, United

Kingdom
44: Also at INFN Sezione di Perugia; Università di Perugia, Perugia, Italy
45: Also at Utah Valley University, Orem, USA
46: Also at Institute for Nuclear Research, Moscow, Russia
47: Also at Los Alamos National Laboratory, Los Alamos, USA
48: Also at Erzincan University, Erzincan, Turkey

– 30 –


	Introduction
	Experimental details
	Underlying event in the transverse region
	Hard-scale dependence
	Multiplicity and transverse momentum distributions
	Centre-of-mass energy dependence

	Summary and conclusions
	The CMS collaboration