Measurement of neutral strange particle production in the underlying event in proton-proton collisions at ffiffiffi s p ¼ 7 TeV S. Chatrchyan et al.* (CMS Collaboration) (Received 26 May 2013; published 3 September 2013) Measurements are presented of the production of primary K0 S and � particles in proton-proton collisions at ffiffiffi s p ¼ 7 TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of K0 S and � particles measured at pseudorapidities j�j< 2 rise with increasing charged-particle jet pT in the range 1–10 GeV=c and saturate in the region 10–50 GeV=c. The rise and saturation of the strange-particle yields and transverse momentum sums in the underlying event are similar to those observed for inclusive charged particles, which confirms the impact-parameter picture of multiple parton interactions. The results are compared to recent tunes of the PYTHIA Monte Carlo event generator. The PYTHIA simulations underestimate the data by 15%–30% for K0 S mesons and by about 50% for � baryons, a deficit similar to that observed for the inclusive strange-particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios with respect to the leading jet pT and similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage. DOI: 10.1103/PhysRevD.88.052001 PACS numbers: 12.38.Aw, 13.85.Ni I. INTRODUCTION This paper describes a measurement of the production of primary K0 S mesons, and � and �� baryons in the under- lying event in proton-proton (pp) collisions at a center-of- mass energy of 7 TeV with the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC). In the presence of a hard process, characterized by parti- cles or clusters of particles with large transverse momentum pT with respect to the beam direction, the final state of hadron-hadron interactions can be described as the super- position of several contributions: the partonic hard scatter- ing, initial- and final-state radiation, additional ‘‘multiple partonic interactions’’ (MPI), and ‘‘beam-beam remnants’’ (BBR) interactions. The products of initial- and final-state radiation,MPI andBBR, form the ‘‘underlying event’’ (UE). In this paper, the UE properties are analyzed with refer- ence to the direction of the highest-pT jet reconstructed from charged primary particles (leading charged-particle jet). This leading jet is expected to reflect the direction of the parton produced with the highest transverse momentum in the hard interaction. Three distinct topological regions in the hadronic final state are defined in terms of the azimuthal angle �� between the directions of the leading jet and that of any particle in the event. Particle production in the ‘‘toward’’ region, j��j< 60�, and in the ‘‘away’’ region, j��j>120�, is expected to be dominated by the hard parton-parton scattering. The UE structure can be best studied in the ‘‘transverse’’ region, 60� 1:4 to �d0 ¼ 10 �m and �dz ¼ 30 �m at pT ¼ 100 GeV=c and j�j< 0:9. A more detailed description of the CMS detector can be found in Ref. [18]. A. Event selection, data sets, and Monte Carlo simulation The event selection is identical to the one described in [1], unless explicitly stated otherwise. Minimum-bias events were triggered by requiring coincident signals in beam scintillator counters located on both sides of the experiment and covering the pseudorapidity range 3:23< j�j< 4:65, and in the beam pickup devices [18]. Events were then recorded with a prescaled trigger requiring the presence of at least one track segment in the pixel detector with pT > 200 MeV=c. The trigger conditions are applied to both data and simulated samples. The trigger efficiency for the events selected in the analysis is close to 100%, and no bias from the trigger selection is found. The data used in this analysis were collected in early 2010 when pileup (multiple pp collisions per proton bunch crossing) was very low. Selected events are required to contain a single reconstructed primary vertex, a condition that rejects about 1% of the events satisfying all the other selection criteria. The primary vertex is fit with an adaptive algorithm [19] and must have at least four tracks, a trans- verse distance to the beam line smaller than 2 cm, and a z coordinate within 10 cm of the nominal interaction point. Events are required to contain a track jet with recon- structed pT > 1 GeV=c and j�j< 2. Track jets are recon- structed from the tracks of charged particles, with the anti-kT algorithm [20,21] and a clustering radius �R ¼ 0:5, where �R¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffið��Þ2þð��Þ2p . The tracks are required to be well reconstructed, to have pT > 500 MeV=c, j�j< 2:5, and to be consistent with originating from the primary vertex. More details on the track selection can be found in [1]. The reconstructed track jet pT is the magnitude of the vector sum of the transverse momenta of the tracks in the jet. The leading track jet pT is corrected for detector response (track finding efficiency and pT measurement) with detailed simulations based on GEANT4 [22], which have been extensively validated with data [23–25]. This correction is approximately independent of the track jet pT and �, and its average value is 1.01. The leading corrected track jet is referred to as the leading charged-particle jet. The PYTHIA versions we consider all include MPI. The tunes used are the PYTHIA 6 D6T tune [2,14] and the PYTHIA 8 tune 1 [13], which have not been tuned to the LHC data, and the PYTHIA 6 Z1 [26] and Z2� tunes. The two latter S. CHATRCHYAN et al. PHYSICAL REVIEW D 88, 052001 (2013) 052001-2 PYTHIA 6 tunes, as well as PYTHIA 8, include pT ordering of the parton showers, and a new model [27] where MPI are interleaved with parton showering. PYTHIA 8 includes hard diffraction in addition to the new MPI model. The parton distribution functions used for PYTHIA 6 D6Tand PYTHIA 8 tune 1 are the CTEQ6L1 and CTEQ5L sets, respectively. The Z1 tune uses the CTEQ5L parton distribution set, whereas Z2� is updated to CTEQ6L1 [28] and retuned to the underlying event activity at 7 TeV fromRef. [1] with the PROFESSOR tool [15]. The simulated data are generated with PYTHIA 6 version 6.422 for tunes D6Tand Z1, version 6.424 for tune Z2�, and version 8.135 for PYTHIA 8 tune 1. Simulated primary stable charged particles with a proper lifetime c� > 1 cm are clustered into jets with the anti-kT algorithm (�R ¼ 0:5). The average rates and scalar pT sums of simulated primary K0 S and � particles are com- puted within the transverse region of the leading simulated charged-particle jet. A data sample of 11� 106 events with at least one charged-particle jet with pT > 1 GeV=c and j�j< 2 is analyzed. The corresponding numbers of simulated events are 22� 106 for PYTHIA 6 D6T and 5� 106 for PYTHIA 6 Z1, Z2� and PYTHIA 8 tune 1. Corrections for detector effects and background are estimated with the PYTHIA 6 D6T sample, while the modeling of the underlying event is studied with all the tunes mentioned. The reconstruction of the leading charged-particle jet results in a bias in the measured average rates and pT sums in the transverse region. The value of this bias ranges from þ5% to þ10% for charged-particle jet pT below 10 GeV=c, and is consistent with zero for larger pT values. It is caused by events in which the leading jet formed by primary charged particles is not reconstructed as the lead- ing charged-particle jet because of tracking inefficiencies, and a subleading jet is thus reconstructed as the leading jet. This results in a reconstructed transverse region shifted in �. The correction for this bias is obtained from the detailed Monte Carlo simulations of the detector response de- scribed above. The primary vertex selection causes a small overesti- mate of the UE strangeness activity at low charged-particle jet pT, at most 5% for charged-particle jet pT ¼ 1 GeV=c. This is because the requirement that at least four tracks be associated to the primary vertex enriches the sample in events with higher UE activity when the charged-particle jets have very low multiplicity. This bias is corrected by means of detailed simulations as described in Sec. III. B. Selection of primary V0 candidates and analysis strategy The neutral strange particles K0 S, �, and ��, hereafter generically called V0s, are identified by means of their characteristic decay topology: a flight distance of several centimeters before decay, two tracks of opposite charge emerging from a secondary vertex, and an invariant mass consistent with that of a K0 S meson or a � baryon. The V0 momentum vector is further required to be collinear with the vector joining the primary and secondary vertices, in order to select primary particles. The V0 candidates are reconstructed by the standard CMS offline event reconstruction program [25]. Pairs of oppositely charged tracks with at least 3 hits in the CMS tracker and with a nonzero transverse impact parameter with respect to the beam line are selected (the transverse impact parameter divided by its uncertainty is required to be larger than 1.5). Pairs of tracks with a distance of closest approach to each other smaller than 1 cm are fit to a common secondary vertex, and those with a vertex fit �2 smaller than 7 and a significant distance between the beam line and the secondary vertex (transverse flight distance divided by its uncertainty larger than 8) are retained. Well-reconstructed V0 candidates are selected by apply- ing cuts on the pseudorapidity and transverse momentum of the decay tracks (j�j< 2:5, pT > 300 MeV=c), of the V0 candidate (j�j< 2; pT > 600 MeV=c for K0 S mesons, pT > 1:5 GeV=c for � baryons), and on the V0 transverse flight distance (>1 cm from the beam line). A kinematic fit is then performed on the candidates to further purify the sample of primary strange particles. The fit includes a secondary vertex constraint, a mass constraint, as well as the constraint that the V0 momentum points away from the primary vertex. All three hypotheses (K0 S ! �þ��, � ! p��, and �� ! �p�þ) are tested for each candidate and the most probable hypothesis is considered. Candidates with a kinematic-fit probability larger than 5% are retained. Since simulations enter in the determination of the V0 selection efficiency and purity, a good description of the distributions of the kinematic-fit input variables is impor- tant. The distributions of the invariant mass of the V0 candidates for the most probable particle-type hypothesis are shown in Fig. 1, together with the distributions of the invariant-mass pull. The invariant-mass pull is the differ- ence between the reconstructed mass and the accepted V0 mass value [29], divided by the uncertainty on the recon- structed mass calculated from the decay track parameter uncertainties. The signal and background fractions are shown as predicted by PYTHIA 6 D6T. The backgrounds in the K0 S sample are mostly misidentified � baryons. Backgrounds in the � sample are mostly nonprimary � baryons from cascade decays of � and � baryons, plus contributions from misidentified K0 S mesons and converted photons. In general, the simulation agrees with the data. As an example, the average mass values for K0 S mesons (� baryons) are 0:4981 GeV=c2 (1:116 GeV=c2) in the simu- lation and 0:4977 GeV=c2 (1:116 GeV=c2) in the data; the corresponding rms values for the mass pull distributions are 1.17 (0.512) in the simulation and 1.23 (0.531) in the data. For K0 S candidates, the data show larger tails than the simu- lation at mass pull values below (�2). The presence of a MEASUREMENT OF NEUTRAL STRANGE PARTICLE . . . PHYSICAL REVIEW D 88, 052001 (2013) 052001-3 similar tail in the component shown as the hatched histogram of the simulated distribution indicates that this excess is due to a larger contribution from misidentified baryons in the data compared to the simulation. This is accounted for in the background estimation as described below. The pointing requirement constrains the signed impact parameter dip of the V 0 with respect to the primary vertex. This variable is defined as the distance of closest approach of the V0 trajectory to the primary vertex, and its sign is that of the scalar product of the V0 momentum and the vector pointing from the primary vertex to the point of closest approach. The distributions of the signed impact parameter are shown in Fig. 2 together with the distribu- tions of the corresponding pull, defined as dip divided by its uncertainty �dip calculated from the decay track parameter uncertainties. The quality of the description of the data by the simulation is good, including the tails at positive impact-parameter values. The large pulls for secondary � baryons from cascade decays allow the suppression of this background by means of the kinematic fit. The uncorrected average rates of reconstructed V0 can- didates passing the selection cuts per unit pseudorapidity are shown in Fig. 3 as a function of the difference in azimuthal angle j��j between the V0 candidate and the leading charged-particle jet. Uncorrected data are com- pared to PYTHIA events passed through the detailed detec- tor simulation. The dependence of the rates on j��j is qualitatively described by the PYTHIA tunes considered. The simulation underestimates significantly the V0 rates in the transverse region. The peak at j��j � 0� is more pronounced for baryons than for K0 S mesons. The simula- tion indicates that the harder pT cut applied to the baryon candidates is responsible for this feature; the distributions are similar when the same pT cut is applied to both V0 types. The backgrounds to the K0 S and � samples are estimated with two methods. The first is based on simulation. Candidates not matched to a generated primary V0 of the corresponding type are counted as background. The PYTHIA 6 D6T sample is used. To account for the known deficit of strange particles in the simulation (see Sec. I), the contribution from K0 S mesons misidentified as� baryons is weighted by the ratio of K0 S rates measured in nonsingle diffractive events to those in PYTHIA 6 D6T, 1.39 [11]. Similarly, the contribution from misidentified � baryons ]2mass [GeV/c 0.4 0.45 0.5 0.55 2 C an d id at es / 3 M eV /c 1 10 210 310 410 510 0 SK = 7 TeVsCMS, pp, Data 0 S Primary K 0Misidentified V Other sources ]2mass [GeV/c 1.08 1.1 1.12 1.14 2 C an d id at es / 1 M eV /c 1 10 210 310 410 Λ = 7 TeVsCMS, pp, Data ΛPrimary Cascade decays 0Misidentified V Other sources massσ)/ PDG (mass - mass -5 0 5 C an d id at es 1 10 210 310 410 0 SK = 7 TeVsCMS, pp, massσ)/ PDG (mass - mass -4 -2 0 2 4 C an d id at es 1 10 210 310 410 Λ = 7 TeVsCMS, pp, FIG. 1 (color online). Distributions of invariant mass and invariant-mass pull for the most probable particle-type hypothesis determined by the kinematic fit. The accepted K0 S and � mass values from Ref. [29] are denoted as massPDG. The black points indicate the data. The histograms show the backgrounds (hatched: misidentified V0; green: nonprimary � from � and � cascade decays; grey: other sources) and the signal (yellow) as predicted by PYTHIA 6 D6T. The PYTHIA prediction is normalized to the data. S. CHATRCHYAN et al. PHYSICAL REVIEW D 88, 052001 (2013) 052001-4 is weighted by a factor of 1.85, and the contribution arising from nonprimary baryons from � and � decays is weighted by the ratio of the measured and simulated � production rates, 2.67 [11]. The second method is based on data. The signal and background contributions are extracted from a fit to the distribution of the kinematic-fit �2 probability, with signal and background shapes obtained from simulation. Apart from the background normalization, the measured and simulated pull distributions of the constrained variables (Figs. 1 and 2), as well as the measured and simulated �2-probability distributions (not shown), are in good agreement. These facts, as well as goodness-of-fit tests, validate the approach. In both methods, the background is estimated as a function of the charged-particle jet pT for the rate mea- surements, and as a function of the V0 pT for the V0 pT spectra and the pT sum measurements. The background estimations from the two methods are in reasonable agree- ment, and they exhibit the same dependence on the charged-particle jet and V0 pT. The final background esti- mates are computed as the average of the results of the two methods, and the corresponding systematic uncertainties are taken as half the difference of the two results. The background fraction for K0 S increases from ð1:5� 1:1Þ% at charged-particle jet pT ¼ 1 GeV=c to ð3:3� 1:7Þ% at charged-particle jet pT ¼ 10 GeV=c and remains constant at higher charged-particle jet pT. The background is ð8� 2Þ% for baryons, independent of the charged-particle jet pT. The K0 S and � raw yields are corrected for purity (defined as 1—background fraction) as well as for accep- tance and reconstruction efficiency. Each V0 candidate is weighted by the product of the purity times 1 A� , where A denotes the acceptance of the cuts on the V0 transverse flight distance and on the pT, � of the decay particles, and denotes the reconstruction and selection efficiency for accepted V0 candidates. The product of acceptance times efficiency is computed in V0 ðpT; �Þ bins from a sample of 50� 106 PYTHIA 6 D6T minimum-bias events passed through the detailed detector simulation. The average val- ues of the product of acceptance and efficiency in this sample for K0 S mesons, and � and �� baryons within the kinematic cuts (j�j< 2; pT > 600 MeV=c for K0 S, pT > 1:5 GeV=c for � and ��) are 11.3%, 8.4%, and 6.6%, respectively, including the branching fractions BðK0 S ! �þ��Þ ¼ 69:2% and Bð� ! p��Þ ¼ Bð �� ! �p�þÞ ¼ 63:9% [29]. The acceptance depends strongly on the V0 [cm]ipd -5 0 5 C an d id at es / 0. 2 cm 1 10 210 310 410 510 = 7 TeVsCMS, pp, 0 SK Data 0 S Primary K 0Misidentified V Other sources [cm]ipd -2 -1 0 1 2 C an d id at es / 0. 05 c m 1 10 210 310 410 Data ΛPrimary Cascade decays 0Misidentified V Other sources Λ = 7 TeVsCMS, pp, ipdσ/ipd -40 -20 0 20 40 C an d id at es 1 10 210 310 410 510 0 SK = 7 TeVsCMS, pp, ipdσ/ipd -40 -20 0 20 40 C an d id at es 1 10 210 310 410 Λ = 7 TeVsCMS, pp, FIG. 2 (color online). Distributions of the signed impact parameter dip with respect to the primary vertex, and the corresponding pull distributions, for the most probable particle-type hypothesis determined by the kinematic fit. The black points indicate the data. The histograms show the backgrounds (hatched: misidentified V0; green: nonprimary� from� and� cascade decays; grey: other sources) and the signal (yellow) as predicted by PYTHIA 6 D6T. The PYTHIA prediction is normalized to the data. MEASUREMENT OF NEUTRAL STRANGE PARTICLE . . . PHYSICAL REVIEW D 88, 052001 (2013) 052001-5 pT, while the efficiency varies by a factor of about 2 in the V0 pT and � ranges selected. The smaller efficiency for �� baryons than for � baryons reflects the higher interaction cross section of antiprotons with the detector material compared to that of protons. The corrected � and �� yields are found to be compatible when accounting for the systematic uncertainty due to the modeling of the antiproton cross section in the GEANT4 version used [30] (see Sec. III). The consistency of the correction method was checked by applying it to all other Monte Carlo samples and com- paring the results to the known generated values. Further support to the correction procedure is provided by the fact that the simulation reproduces well several key aspects of the data, most notably the reconstruction efficiency [23,24] and the angular distributions of the V0 decay tracks as a function of the V0 pT. The reliability of the simulation for K0 S and � reconstruction was checked by comparing the lifetimes obtained from fits to the corrected proper time distributions with the world averages [11]. The stability of the results when varying the V0 selection cuts was also checked. The resulting overall contribution of the V0 reconstruction to the systematic uncertainty is given in Sec. III. III. SYSTEMATIC UNCERTAINTIES The main sources of systematic uncertainties are described below, with numerical values summarized in Table I. Leading charged-particle jet selection: The bias in rates and pT sums due to mismatches between the reconstructed and the simulated leading charged-particle jets is corrected by means of detailed simulations. The systematic uncer- tainty is estimated from the residual difference in rates and pT sums when the reconstructed and the simulated leading charged-particle jets are matched within �R ¼ 0:3. Primary vertex selection: The bias caused by the require- ment of a minimum track multiplicity at the primary vertex is corrected by means of detailed simulations of minimum- bias events with the PYTHIA 6 Z1 tune. The primary charged-particle multiplicity in 7 TeV pp collisions is well described by this tune [1]. The corresponding uncer- tainty is estimated from the spread of the corrections com- puted with PYTHIA 6 tunes D6T, Z1 and PYTHIA 8 tune 1. Modeling of V0 reconstruction efficiency: The systematic uncertainty on the V0 reconstruction efficiency is estimated from closure tests and from the stability of the results with respect to the V0 selection cuts, as described in Sec. II B. 0.05 0.1 0.15 0.2 0.25 0.3 Data PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 = 7 TeVsCMS, pp, 0 sK | [deg]φ∆| 0 20 40 60 80 100 120 140 160 180 0.02 0.04 0.06 0.08 0.1 Λ ] -1 |) [ d eg φ∆ /d (| 〉 0 s K N 〈 d× η∆/3 10 ] -1 |) [ d eg φ∆ /d (| 〉 Λ N〈 d × η∆/3 10 FIG. 3 (color online). Uncorrected average rate of selected V0 candidates per event, per degree, and per unit pseudora- pidity within j�j< 2, as a function of the difference in azimuthal angle j��j between the V0 candidate and the leading charged- particle jet. Data and detailed simulation of minimum-bias events with different PYTHIA tunes are shown for recon- structed charged-particle jet pT > 1 GeV=c. Top: K0 S candidates with pT > 600 MeV=c; bottom: � candidates with pT > 1:5 GeV=c. TABLE I. Systematic uncertainties on the measured average V0 rates and pT sums. Average rates Source K0 S (%) � (%) Leading charged-particle jet selection 3 7 Primary vertex selection 1 1 Modeling of V0 efficiency Charged-particle jet pT � 2:5 GeV=c 3 10 Charged-particle jet pT > 2:5 GeV=c 3 3 Detector material 3 3 GEANT4 cross sections � � � 5 Statistical uncertainty on V0 weights 600 MeV=c < pV0 T < 700 MeV=c 0.1 � � � 1:5 GeV=c < pV0 T < 1:6 GeV=c 0.03 0.33 6 GeV=c < pV0 T < 8 GeV=c 1.4 8.3 Background estimation Charged-particle jet pT ¼ 1 GeV=c 1.1 2 Charged-particle jet pT ¼ 10 GeV=c 1.7 2 Total Charged-particle jet pT ¼ 1 GeV=c 6 14 Charged-particle jet pT ¼ 10 GeV=c 6 10 Average pT sums Source K0 S (%) � (%) Background estimation pV0 T ¼ 600 MeV=c 0.1 � � � pV0 T ¼ 1:5 GeV=c 0.8 0.3 pV0 T ¼ 8 GeV=c 3.6 4.0 Other sources as rates as rates S. CHATRCHYAN et al. PHYSICAL REVIEW D 88, 052001 (2013) 052001-6 Detector material: The overall mass of the tracker and the relative fractions of the different tracker materials are varied in the simulations, with the requirement that the resulting predicted tracker weight be consistent with the measured weight [31]. The difference between the results thus obtained and the nominal results is taken as a contri- bution to the systematic uncertainty. GEANT4 cross sections: A 5% systematic uncertainty is assigned to the baryon yields, as a result of the known imperfect modeling of the low-energy antiproton interac- tion cross section in the GEANT4 version used [30]. Statistical uncertainty on the V0 yield correction: A small contribution to the total uncertainty stems from the finite size of the sample of minimum-bias events passed through the full detector simulation (50� 106 events), from which the correction is computed. Estimation of V0 background: The uncertainty on the background remaining after V0 identification by means of the kinematic fit is taken as half the difference between the results of the two background estimation methods used. The uncertainty on the beam spot position and size gives a negligible contribution to the total uncertainty. IV. RESULTS The V0 production rates in the transverse region are shown in Fig. 4 as a function of the leading charged- particle jet pT, and the V 0 scalar pT sums in the transverse region are shown in Fig. 5. The rates and pT sums exhibit a rise with increasing hard scale, followed by a plateau. The turn-on of the plateau is located at charged-particle jet pT ’ 10 GeV=c for both primary mesons and baryons. Above the turn-on, the rates and pT sums are essentially constant, implying also a constant strange-particle average pT above the turn-on. A comparison can be made with the trends observed for charged primary particles [1] in spite of the different jet reconstruction algorithm used in Ref. [1] (SISCone). The dependence of the UE activity on the charged-particle jet pT is very similar to that observed for charged primary particles [1,3,4]. The most striking feature is that the pT scale at which the plateau starts, around 10 GeV=c in pp collisions at ffiffiffi s p ¼ 7 TeV, is independent of the type of primary particle used to probe the UE activity. These observations are consistent with the impact-parameter pic- ture of particle production in hadron collisions [6,7], in which the MPI contribution saturates at scales typical of central collisions. The PYTHIA 6 Z1 and Z2� tunes qualitatively reproduce the dependence of the K0 S rate and pT sum on the charged- particle jet pT, but exhibit a 10%–15% deficit in the yield, independent of the charged-particle jet pT. PYTHIA 8 tune 1 underestimates the activity by about 30%. For the � bary- ons, PYTHIA 6 tunes Z1, Z2� and PYTHIA 8 tune 1 under- estimate the rates by about 50%. After being tuned to the charged-particle data, PYTHIA 6 Z2� models strangeness 0 10 20 30 40 50 |φ ∆ | ∆ η ∆/〉 0 s K N〈 20 40 60 80 100 120 140 -310× Data PYTHIA 6 Z2* PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 = 7 TeVsCMS, pp, 0 S Primary K > 0.6 GeV/c T , po| < 120φ∆ < |o60 [GeV/c] T leading charged-particle jet p 0 10 20 30 40 50 〉 D at a 0 s K N〈/〉 M C 0 s K N〈 0.6 0.8 1 1.2 1.4 Syst. uncertainty Total uncertainty |φ∆ |∆ η∆/〉 Λ N〈 5 10 15 20 25 30 35 40 45 -310× Data PYTHIA 6 Z2* PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 = 7 TeVsCMS, pp, ΛPrimary > 1.5 GeV/c T , po| < 120φ∆ < |o60 T 0 10 20 30 40 50 〉 D at a Λ N 〈/〉 M C Λ N〈 0.5 1 1.5 Syst. uncertainty Total uncertainty [GeV/c]leading charged-particle jet p FIG. 4 (color online). Average multiplicity per unit of pseu- dorapidity and per radian in the transverse region (j�j< 2, 60� < j��j< 120�), as a function of the pT of the leading charged-particle jet: (top) K0 S with pT > 0:6 GeV=c; (bottom) � with pT > 1:5 GeV=c. Predictions of PYTHIA tunes are compared to the data, and the ratios of simulations to data are shown in the bottom panels. For the data, the statistical uncer- tainties (error bars) and the quadratic sum of statistical and systematic uncertainties (error band) are shown, while for simu- lations the uncertainty is only shown for PYTHIA 6 tune Z2�, for clarity. MEASUREMENT OF NEUTRAL STRANGE PARTICLE . . . PHYSICAL REVIEW D 88, 052001 (2013) 052001-7 production in the UE in a very similar way as Z1, in spite of the different parton distribution set used. PYTHIA 6 D6T shows a dependence of the activity on the charged-particle jet pT that differs from that of the data and of the other tunes. In addition, the V0 pT distributions predicted by PYTHIA 6 D6T in the transverse region are in strong disagreement with the data. As an illustration, the pT spectra are shown in Fig. 6 for events with a [GeV/c] T leading charged-particle jet p 0 10 20 30 40 50 | [ G eV /c ] φ∆ |∆ η∆/ 〉0 s K T pΣ〈 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Data PYTHIA 6 Z2* PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 = 7 TeVsCMS, pp, 0 S Primary K > 0.6 GeV/c T , po| < 120φ∆ < |o60 [GeV/c] T leading charged-particle jet p 0 10 20 30 40 50 〉 D at a 0 s T, K pΣ〈/〉 M C 0 s T, K pΣ〈 0.6 0.8 1 1.2 1.4 Syst. uncertainty Total uncertainty [GeV/c] T leading charged-particle jet p 0 10 20 30 40 50 | [ G eV /c ] φ∆ |∆ η∆/〉 Λ T pΣ〈 0.02 0.04 0.06 0.08 0.1 0.12 0.14 Data PYTHIA 6 Z2* PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 = 7 TeVsCMS, pp, ΛPrimary > 1.5 GeV/c T , po| < 120φ∆ < |o60 0 10 20 30 40 50 〉 D at a Λ T, p Σ〈/〉 M C Λ T, pΣ〈 0.5 1 1.5 Syst. uncertainty Total uncertainty [GeV/c] T leading charged-particle jet p FIG. 5 (color online). Average scalar pT sum per unit of pseudorapidity and per radian in the transverse region (j�j<2, 60� < j��j< 120�), as a function of the pT of the leading charged-particle jet: (top) K0 S with pT > 0:6 GeV=c; (bottom) � with pT > 1:5 GeV=c. Predictions of PYTHIA tunes are compared to the data, and the ratios of simulations to data are shown in the bottom panels. For the data, the statistical uncer- tainties (error bars) and the quadratic sum of statistical and systematic uncertainties (error band) are shown, while for simulations the uncertainty is only shown for PYTHIA 6 tune Z2�, for clarity. [GeV/c] T p0 sK 0 2 4 6 8 C an d id at es / G eV /c 310 410 510 610 Data PYTHIA 6 Z1 (x0.98) PYTHIA 6 D6T (x1.54) PYTHIA 8 Tune 1 (x1.33) = 7 TeVs s CMS, pp, 0 S Primary K > 3 GeV/cjet T p o| < 120φ∆ < |o60 [GeV/c] T pΛ 0 2 4 6 8 C an d id at es / G eV /c 310 410 510 610 = 7 TeVCMS, pp, Data PYTHIA 6 Z1 (x1.88) PYTHIA 6 D6T (x1.97) PYTHIA 8 Tune 1 (x2.32) ΛPrimary > 3 GeV/cjet T p o| < 120φ∆ < |o60 FIG. 6 (color online). V0 pT distributions corrected for selec- tion efficiency and background without a correction to the leading charged-particle jet, in the region transverse to a leading reconstructed charged-particle jet with pT > 3 GeV=c, com- pared to predictions from different PYTHIA tunes (top: K0 S; bottom: �). Error bars indicate the quadratic sum of the statis- tical and systematic uncertainties. Simulations are normalized to the first pT bin in the data, with normalization factors given in parentheses. S. CHATRCHYAN et al. PHYSICAL REVIEW D 88, 052001 (2013) 052001-8 reconstructed charged-particle jet pT > 3 GeV=c (without a correction to the leading charged hadron jet). For the K0 S case, in the pT range observed (pT > 600 MeV=c), PYTHIA 6 tune D6T shows a much harder spectrum than the data, while tune Z1 shows a softer spectrum and PYTHIA 8 tune 1 reproduces the shape well. For the � case, in the pT > 1:5 GeV=c range, PYTHIA 6 D6T shows a much harder spectrum than the data, while the other simulations describe the data reasonably well. The ratios of the rates and pT sums of primary V0 mesons to the rates and pT sums of primary charged particles from Ref. [1] are shown in Fig. 7. The data are integrated over the same pseudorapidity range for strange and charged particles, j�j< 2. The K0 S to charged-particle activity ratios are constant in the charged-particle jet pT range 3–50 GeV=c, i.e. almost throughout the whole range studied and, specifically, across the turn-on of the plateau around 10 GeV=c. An increase is seen below 3 GeV=c. This feature is also present in the simulations but is not as pronounced as in the data, and not in all tunes studied. The � to charged-particle activity ratios exhibit a rise for charged-particle jet pT < 10 GeV=c, followed by a plateau. A similar dependence is visible in PYTHIA. Simulations indicate that the rise is related to the observed hardening of the baryon pT spectrum as the charged- particle jet pT increases, combined with the 1:5 GeV=c pT cut applied to the baryon sample. When the baryon pT cut is decreased to 0:5 GeV=c as for charged particles, constant ratios are predicted. Constant strange- to charged-particle activity ratios have thus been measured for K0 S mesons for charged-particle jet pT > 3 GeV=c and for � baryons for charged-particle jet pT > 10 GeV=c. In addition, as just discussed, when accounting for the acceptance of the baryon pT cut, a [GeV/c] T leading charged-particle jet p 0 10 20 30 40 50 〉 ch ar g ed N〈 / 〉 0 s K N〈 0.02 0.04 0.06 0.08 0.1 0.12 0.14 = 7 TeVsCMS, pp, Data PYTHIA 6 Z2* PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 o| < 120φ∆ < |o60 > 0.5 GeV/c charged T > 0.6 GeV/c, p 0 SK T p [GeV/c] T leading charged-particle jet p 0 10 20 30 40 50 〉 ch ar g ed T pΣ 〈 / 〉0 s K T pΣ〈 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 = 7 TeVsCMS, pp, Data PYTHIA 6 Z2* PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 o| < 120φ∆ < |o60 > 0.5 GeV/c charged T > 0.6 GeV/c, p 0 SK T p [GeV/c] T leading charged-particle jet p 0 10 20 30 40 50 〉 ch ar g ed N〈 / 〉 Λ N〈 5 10 15 20 25 30 35 40 -310× = 7 TeVsCMS, pp, Data PYTHIA 6 Z2* PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 o| < 120φ∆ < |o60 > 0.5 GeV/c charged T > 1.5 GeV/c, pΛ T p [GeV/c] T leading charged-particle jet p 0 10 20 30 40 50 〉 ch ar g ed T pΣ〈 / 〉 Λ T p Σ〈 0.02 0.04 0.06 0.08 0.1 = 7 TeVsCMS, pp, Data PYTHIA 6 Z2* PYTHIA 6 Z1 PYTHIA 6 D6T PYTHIA 8 Tune 1 o| < 120φ∆ < |o60 > 0.5 GeV/c charged T > 1.5 GeV/c, pΛ T p FIG. 7 (color online). Ratios of the average multiplicities and scalar pT sums for primary V0 in the transverse region to the same quantities for primary charged particles [1] as a function of charged-particle jet pT. The error bars indicate the quadratic sum of the statistical and systematic uncertainties. MEASUREMENT OF NEUTRAL STRANGE PARTICLE . . . PHYSICAL REVIEW D 88, 052001 (2013) 052001-9 constant ratio is also predicted for � baryons at charged- particle jet pT < 10 GeV=c. Since the trends observed are very similar for charged and strange particles, as well as for mesons and baryons, the present measurements suggest that hadronization and MPI are decoupled. V. CONCLUSIONS This paper describes measurements of the underlying event activity in pp collisions at ffiffiffi s p ¼ 7 TeV, probed through the production of primary K0 S mesons and � baryons. The production of K0 S mesons and � baryons in the kinematic range p K0 S T > 0:6 GeV=c, p� T > 1:5 GeV=c and j�j< 2 is analyzed in the transverse region, defined as 60� < j��j< 120�, with �� the difference in azimu- thal angle between the leading charged-particle jet and the strange-particle directions. The average multiplicity and the average scalar pT sum of primary particles per event are studied as a function of the leading charged- particle jet pT. A steep rise of the underlying event activity is seen with increasing leading jet pT, followed by a ‘‘saturation’’ region for jet pT > 10 GeV=c. This trend and the pT scale above which saturation occurs are very similar to those observed with charged primary particles. The similarity of the behavior for strange and charged particles is consistent with the impact-parameter picture of multiple parton inter- actions in pp collisions, in which the centrality of the pp collision and the MPI activity are correlated. The results are compared to recent tunes of the PYTHIA Monte Carlo event generator. The PYTHIA simulations underestimate the data by 15%–30% for K0 S mesons and by about 50% for � baryons, a MC deficit similar to that observed for the inclusive strange-particle production in pp collisions. The constant strange- to charged-particle activity ratios and the similar trends for mesons and baryons indicate that the MPI dynamics is decoupled from parton hadronization, with the latter occurring at a later stage. ACKNOWLEDGMENTS 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 centers and personnel of the Worldwide LHC Computing Grid for delivering so effec- tively the computing infrastructure essential to our analy- ses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: the Austrian Federal Ministry of Science and Research and the Austrian Science Fund; the Belgian Fonds de la Recherche Scientifique, and Fonds voor Wetenschappelijk Onderzoek; the Brazilian Funding Agencies (CNPq, CAPES, FAPERJ, and FAPESP); the Bulgarian Ministry of Education, Youth and Science; CERN; the Chinese Academy of Sciences, Ministry of Science and Technology, and National Natural Science Foundation of China; the Colombian Funding Agency (COLCIENCIAS); the Croatian Ministry of Science, Education and Sport; the Research Promotion Foundation, Cyprus; the Ministry of Education and Research, Recurrent financing Contract No. SF0690030s09 and European Regional Development Fund, Estonia; theAcademy of Finland, FinnishMinistry of Education and Culture, and Helsinki Institute of Physics; the Institut National de Physique Nucléaire et de Physique des Particules/CNRS, and Commissariat à l’Énergie Atomique et aux Énergies Alternatives/CEA, France; the Bundesministerium für Bildung und Forschung, Deutsche Forschungsgemeinschaft, and Helmholtz-Gemeinschaft Deutscher Forschungszentren, Germany; the General Secretariat for Research and Technology, Greece; the National Scientific Research Foundation, and National Office for Research and Technology, Hungary; the Department of Atomic Energy and the Department of Science and Technology, India; the Institute for Studies in Theoretical Physics and Mathematics, Iran; the Science Foundation, Ireland; the Istituto Nazionale di Fisica Nucleare, Italy; the Korean Ministry of Education, Science and Technology and the World Class University program of NRF, Republic of Korea; the Lithuanian Academy of Sciences; the Mexican Funding Agencies (CINVESTAV, CONACYT, SEP, and UASLP-FAI); the Ministry of Science and Innovation, New Zealand; the Pakistan Atomic Energy Commission; the Ministry of Science and Higher Education and the National Science Centre, Poland; the Fundação para a Ciência e a Tecnologia, Portugal; JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); the Ministry of Education and Science of the Russian Federation, the Federal Agency of Atomic Energy of the Russian Federation, Russian Academy of Sciences, and theRussianFoundation forBasicResearch; theMinistry of Science and Technological Development of Serbia; the Secretarı́a de Estado de Investigación, Desarrollo e Innovación and Programa Consolider-Ingenio 2010, Spain; the Swiss Funding Agencies (ETHBoard, ETHZurich, PSI, SNF, UniZH, Canton Zurich, and SER); the National Science Council, Taipei; the Thailand Center of Excellence in Physics, the Institute for the Promotion of Teaching Science and Technology of Thailand and the National Science and Technology Development Agency of Thailand; the Scientific and Technical Research Council of Turkey, and Turkish Atomic Energy Authority; the Science and Technology Facilities Council, UK; and the US Department of Energy and National Science Foundation. 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Swanson163 (CMS Collaboration) 1Yerevan Physics Institute, Yerevan, Armenia 2Institut für Hochenergiephysik der OeAW, Wien, Austria 3National Centre for Particle and High Energy Physics, Minsk, Belarus 4Universiteit Antwerpen, Antwerpen, Belgium 5Vrije Universiteit Brussel, Brussel, Belgium 6Université Libre de Bruxelles, Bruxelles, Belgium 7Ghent University, Ghent, Belgium 8Université Catholique de Louvain, Louvain-la-Neuve, Belgium 9Université de Mons, Mons, Belgium 10Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil 11Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil 12aUniversidade Estadual Paulista, São Paulo, Brazil 12bUniversidade Federal do ABC, São Paulo, Brazil 13Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria 14University of Sofia, Sofia, Bulgaria 15Institute of High Energy Physics, Beijing, China MEASUREMENT OF NEUTRAL STRANGE PARTICLE . . . PHYSICAL REVIEW D 88, 052001 (2013) 052001-17 16State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China 17Universidad de Los Andes, Bogota, Colombia 18Technical University of Split, Split, Croatia 19University of Split, Split, Croatia 20Institute Rudjer Boskovic, Zagreb, Croatia 21University of Cyprus, Nicosia, Cyprus 22Charles University, Prague, Czech Republic 23Academy of Scientific Research and Technology of the Arab Republic of Egypt, Egyptian Network of High Energy Physics, Cairo, Egypt 24National Institute of Chemical Physics and Biophysics, Tallinn, Estonia 25Department of Physics, University of Helsinki, Helsinki, Finland 26Helsinki Institute of Physics, Helsinki, Finland 27Lappeenranta University of Technology, Lappeenranta, Finland 28DSM/IRFU, CEA/Saclay, Gif-sur-Yvette, France 29Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France 30Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Université de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France 31Centre de Calcul de l’Institut National de Physique Nucleaire et de Physique des Particules, CNRS/IN2P3, Villeurbanne, France 32Université de Lyon, Université Claude Bernard Lyon 1, CNRS-IN2P3, Institut de Physique Nucléaire de Lyon, Villeurbanne, France 33Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi, Georgia 34RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany 35RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany 36RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany 37Deutsches Elektronen-Synchrotron, Hamburg, Germany 38University of Hamburg, Hamburg, Germany 39Institut für Experimentelle Kernphysik, Karlsruhe, Germany 40Institute of Nuclear and Particle Physics (INPP), NCSR Demokritos, Aghia Paraskevi, Greece 41University of Athens, Athens, Greece 42University of Ioánnina, Ioánnina, Greece 43KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary 44Institute of Nuclear Research ATOMKI, Debrecen, Hungary 45University of Debrecen, Debrecen, Hungary 46Panjab University, Chandigarh, India 47University of Delhi, Delhi, India 48Saha Institute of Nuclear Physics, Kolkata, India 49Bhabha Atomic Research Centre, Mumbai, India 50Tata Institute of Fundamental Research-EHEP, Mumbai, India 51Tata Institute of Fundamental Research-HECR, Mumbai, India 52Institute for Research in Fundamental Sciences (IPM), Tehran, Iran 53University College Dublin, Dublin, Ireland 54aINFN Sezione di Bari, Bari, Italy 54bUniversità di Bari, Bari, Italy 54cPolitecnico di Bari, Bari, Italy 55aINFN Sezione di Bologna, Bologna, Italy 55bUniversità di Bologna, Bologna, Italy 56aINFN Sezione di Catania, Catania, Italy 56bUniversità di Catania, Catania, Italy 57aINFN Sezione di Firenze, Firenze, Italy 57bUniversità di Firenze, Firenze, Italy 58INFN Laboratori Nazionali di Frascati, Frascati, Italy 59aINFN Sezione di Genova, Genova, Italy 59bUniversità di Genova, Genova, Italy 60aINFN Sezione di Milano-Bicocca, Milano, Italy 60bUniversità di Milano-Bicocca, Milano, Italy 61aINFN Sezione di Napoli, Napoli, Italy 61bUniversità di Napoli ‘Federico II’, Napoli, Italy 61cUniversità della Basilicata (Potenza), Napoli, Italy 61dUniversità G. Marconi (Roma), Napoli, Italy 62aINFN Sezione di Padova, Padova, Italy 62bUniversità di Padova, Padova, Italy 62cUniversità di Trento (Trento), Padova, Italy S. CHATRCHYAN et al. PHYSICAL REVIEW D 88, 052001 (2013) 052001-18 63aINFN Sezione di Pavia, Pavia, Italy 63bUniversità di Pavia, Pavia, Italy 64aINFN Sezione di Perugia, Perugia, Italy 64bUniversità di Perugia, Perugia, Italy 65aINFN Sezione di Pisa, Pisa, Italy 65bUniversità di Pisa, Pisa, Italy 65cScuola Normale Superiore di Pisa, Pisa, Italy 66aINFN Sezione di Roma, Roma, Italy 66bUniversità di Roma, Roma, Italy 67aINFN Sezione di Torino, Torino, Italy 67bUniversità di Torino, Torino, Italy 67cUniversità del Piemonte Orientale (Novara), Torino, Italy 68aINFN Sezione di Trieste, Trieste, Italy 68bUniversità di Trieste, Trieste, Italy 69Kangwon National University, Chunchon, Korea 70Kyungpook National University, Daegu, Korea 71Chonnam National University, Institute for Universe and Elementary Particles, Kwangju, Korea 72Korea University, Seoul, Korea 73University of Seoul, Seoul, Korea 74Sungkyunkwan University, Suwon, Korea 75Vilnius University, Vilnius, Lithuania 76Centro de Investigacion y de Estudios Avanzados del IPN, Mexico City, Mexico 77Universidad Iberoamericana, Mexico City, Mexico 78Benemerita Universidad Autonoma de Puebla, Puebla, Mexico 79Universidad Autónoma de San Luis Potosı́, San Luis Potosı́, Mexico 80University of Auckland, Auckland, New Zealand 81University of Canterbury, Christchurch, New Zealand 82National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan 83National Centre for Nuclear Research, Swierk, Poland 84Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland 85Laboratório de Instrumentação e Fı́sica Experimental de Partı́culas, Lisboa, Portugal 86Joint Institute for Nuclear Research, Dubna, Russia 87Petersburg Nuclear Physics Institute, Gatchina (St. Petersburg), Russia 88Institute for Nuclear Research, Moscow, Russia 89Institute for Theoretical and Experimental Physics, Moscow, Russia 90P.N. Lebedev Physical Institute, Moscow, Russia 91Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia 92State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, Russia 93University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia 94Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain 95Universidad Autónoma de Madrid, Madrid, Spain 96Universidad de Oviedo, Oviedo, Spain 97Instituto de Fı́sica de Cantabria (IFCA), CSIC-Universidad de Cantabria, Santander, Spain 98CERN, European Organization for Nuclear Research, Geneva, Switzerland 99Paul Scherrer Institut, Villigen, Switzerland 100Institute for Particle Physics, ETH Zurich, Zurich, Switzerland 101Universität Zürich, Zurich, Switzerland 102National Central University, Chung-Li, Taiwan 103National Taiwan University (NTU), Taipei, Taiwan 104Chulalongkorn University, Bangkok, Thailand 105Cukurova University, Adana, Turkey 106Middle East Technical University, Physics Department, Ankara, Turkey 107Bogazici University, Istanbul, Turkey 108Istanbul Technical University, Istanbul, Turkey 109National Scientific Center, Kharkov Institute of Physics and Technology, Kharkov, Ukraine 110University of Bristol, Bristol, United Kingdom 111Rutherford Appleton Laboratory, Didcot, United Kingdom 112Imperial College, London, United Kingdom 113Brunel University, Uxbridge, United Kingdom 114Baylor University, Waco, Texas, USA 115The University of Alabama, Tuscaloosa, Alabama, USA MEASUREMENT OF NEUTRAL STRANGE PARTICLE . . . PHYSICAL REVIEW D 88, 052001 (2013) 052001-19 116Boston University, Boston, Massachusetts, USA 117Brown University, Providence, Rhode Island, USA 118University of California, Davis, Davis, California, USA 119University of California, Los Angeles, California, USA 120University of California, Riverside, Riverside, California, USA 121University of California, San Diego, La Jolla, California, USA 122University of California, Santa Barbara, Santa Barbara, California, USA 123California Institute of Technology, Pasadena, California, USA 124Carnegie Mellon University, Pittsburgh, Pennsylvania, USA 125University of Colorado at Boulder, Boulder, Colorado, USA 126Cornell University, Ithaca, New York, USA 127Fairfield University, Fairfield, Connecticut, USA 128Fermi National Accelerator Laboratory, Batavia, Illinois, USA 129University of Florida, Gainesville, Florida, USA 130Florida International University, Miami, Florida, USA 131Florida State University, Tallahassee, Florida, USA 132Florida Institute of Technology, Melbourne, Florida, USA 133University of Illinois at Chicago (UIC), Chicago, Illinois, USA 134The University of Iowa, Iowa City, Iowa, USA 135Johns Hopkins University, Baltimore, Maryland, USA 136The University of Kansas, Lawrence, Kansas, USA 137Kansas State University, Manhattan, Kansas, USA 138Lawrence Livermore National Laboratory, Livermore, California, USA 139University of Maryland, College Park, Maryland, USA 140Massachusetts Institute of Technology, Cambridge, Massachusetts, USA 141University of Minnesota, Minneapolis, Minnesota, USA 142University of Mississippi, Oxford, Mississippi, USA 143University of Nebraska-Lincoln, Lincoln, Nebraska, USA 144State University of New York at Buffalo, Buffalo, New York, USA 145Northeastern University, Boston, Massachusetts, USA 146Northwestern University, Evanston, Illinois, USA 147University of Notre Dame, Notre Dame, Indiana, USA 148The Ohio State University, Columbus, Ohio, USA 149Princeton University, Princeton, New Jersey, USA 150University of Puerto Rico, Mayaguez, Puerto Rico, USA 151Purdue University, West Lafayette, Indiana, USA 152Purdue University Calumet, Hammond, Indiana, USA 153Rice University, Houston, Texas, USA 154University of Rochester, Rochester, New York, USA 155The Rockefeller University, New York, New York, USA 156Rutgers, The State University of New Jersey, Piscataway, New Jersey, USA 157University of Tennessee, Knoxville, Tennessee, USA 158Texas A&M University, College Station, Texas, USA 159Texas Tech University, Lubbock, Texas, USA 160Vanderbilt University, Nashville, Tennessee, USA 161University of Virginia, Charlottesville, Virginia, USA 162Wayne State University, Detroit, Michigan, USA 163University of Wisconsin, Madison, Wisconsin, USA aDeceased. bAlso at Vienna University of Technology, Vienna, Austria. cAlso at CERN, European Organization for Nuclear Research, Geneva, Switzerland. dAlso at Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Université de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France. eAlso at National Institute of Chemical Physics and Biophysics, Tallinn, Estonia. fAlso at Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia. gAlso at Universidade Estadual de Campinas, Campinas, Brazil. hAlso at California Institute of Technology, Pasadena, CA, USA. iAlso at Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France. jAlso at Suez Canal University, Suez, Egypt. S. CHATRCHYAN et al. PHYSICAL REVIEW D 88, 052001 (2013) 052001-20 kAlso at Cairo University, Cairo, Egypt. lAlso at Fayoum University, El-Fayoum, Egypt. mAlso at Helwan University, Cairo, Egypt. nAlso at British University in Egypt, Cairo, Egypt. oNow at Ain Shams University, Cairo, Egypt. pAlso at National Centre for Nuclear Research, Swierk, Poland. qAlso at Université de Haute Alsace, Mulhouse, France. rAlso at Joint Institute for Nuclear Research, Dubna, Russia. sAlso at Brandenburg University of Technology, Cottbus, Germany. tAlso at The University of Kansas, Lawrence, KS, USA. uAlso at Institute of Nuclear Research ATOMKI, Debrecen, Hungary. vAlso at Eötvös Loránd University, Budapest, Hungary. wAlso at Tata Institute of Fundamental Research-HECR, Mumbai, India. xNow at King Abdulaziz University, Jeddah, Saudi Arabia. yAlso at University of Visva-Bharati, Santiniketan, India. zAlso at University of Ruhuna, Matara, Sri Lanka. aaAlso at Sharif University of Technology, Tehran, Iran. bbAlso at Isfahan University of Technology, Isfahan, Iran. ccAlso at Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran. ddAlso at Università degli Studi di Siena, Siena, Italy. eeAlso at Universidad Michoacana de San Nicolas de Hidalgo, Morelia, Mexico. ffAlso at Faculty of Physics, University of Belgrade, Belgrade, Serbia. ggAlso at Facoltà Ingegneria, Università di Roma, Roma, Italy. hhAlso at Scuola Normale e Sezione dell’INFN, Pisa, Italy. iiAlso at INFN Sezione di Roma, Roma, Italy. jjAlso at University of Athens, Athens, Greece. kkAlso at Rutherford Appleton Laboratory, Didcot, United Kingdom. llAlso at Paul Scherrer Institut, Villigen, Switzerland. mmAlso at Institute for Theoretical and Experimental Physics, Moscow, Russia. nnAlso at Albert Einstein Center for Fundamental Physics, Bern, Switzerland. ooAlso at Gaziosmanpasa University, Tokat, Turkey. ppAlso at Adiyaman University, Adiyaman, Turkey. qqAlso at Cag University, Mersin, Turkey. rrAlso at Mersin University, Mersin, Turkey. ssAlso at Izmir Institute of Technology, Izmir, Turkey. ttAlso at Ozyegin University, Istanbul, Turkey. uuAlso at Kafkas University, Kars, Turkey. vvAlso at Suleyman Demirel University, Isparta, Turkey. wwAlso at Ege University, Izmir, Turkey. xxAlso at Mimar Sinan University, Istanbul, Istanbul, Turkey. yyAlso at Kahramanmaras Sütcü Imam University, Kahramanmaras, Turkey. zzAlso at School of Physics and Astronomy, University of Southampton, Southampton, United Kingdom. aaaAlso at INFN Sezione di Perugia, Università di Perugia, Perugia, Italy. bbbAlso at Utah Valley University, Orem, UT, USA. cccAlso at University of Edinburgh, Scotland, Edinburgh, United Kingdom. dddAlso at Institute for Nuclear Research, Moscow, Russia. eeeAlso at University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia. fffAlso at Argonne National Laboratory, Argonne, IL, USA. gggAlso at Erzincan Universi