Search for
Z
0resonances decaying to
tt in dilepton þ jets final states
in
pp collisions at
p
ffiffiffi
s
¼ 7 TeV
S. Chatrchyan et al.* (CMS Collaboration)
(Received 14 November 2012; published 3 April 2013)
A search for resonances decaying to top quark-antiquark pairs is performed using a dileptonþ jets data sample recorded by the CMS experiment at the LHC inpp collisions atpffiffiffis¼ 7 TeV corresponding to an integrated luminosity of 5:0 fb1. No significant deviations from the standard model background are observed. Upper limits are presented for the production cross section times branching fraction of top quark-antiquark resonances for masses from 750 to 3000 GeV. In particular, the existence of a leptophobic topcolor particleZ0 is excluded at the 95% confidence level for resonance massesMZ0< 1:3 TeV for Z0¼ 0:012MZ0, andM < 1:9 TeV for Z0¼ 0:10MZ0.
DOI:10.1103/PhysRevD.87.072002 PACS numbers: 13.85.Rm, 12.60.Cn, 14.65.Ha
I. INTRODUCTION
Electroweak symmetry breaking is a cornerstone for the understanding of particle physics. However, despite the spectacular phenomenological success of the standard model (SM), and the recent observation of a new boson at the Large Hadron Collider (LHC) [1,2], the precise mechanism of electroweak symmetry breaking remains unknown. Various new models have been proposed to ex-plain this mechanism. One such class of models, topcolor-assisted technicolor (TC2) [3–5], provides a dynamical explanation for electroweak symmetry breaking and flavor symmetry breaking, giving masses to the weak gauge bo-sons and fermions. Under one of the scenarios of TC2, a heavy bosonZ0is predicted with preferential couplings to the third quark generation and with no significant cou-plings to the leptons (‘‘leptophobic’’).
Direct searches for massive resonances that decay pref-erentially to top quark-antiquark (tt) pairs are currently feasible only at hadron colliders. Experiments seek to observe an excess beyond that predicted by the SM, typi-cally in the distribution of the invariant mass of thettdecay products. Searches inp p collisions at the Tevatron and the early searches inpp collisions at the LHC by the ATLAS experiment have excluded a narrow-width, leptophobicZ0 with a mass lower than 900 GeV [6–8]. The searches by the Compact Muon Solenoid (CMS) experiment at the LHC have excluded a narrow-width, leptophobicZ0in the mass range 1.3–1.5 TeV and in a narrow window around 1 TeV [9,10]. This paper describes a search for a Z0! tt reso-nance in pp collisions in the 2‘ þ 2 þ jets final state, where‘ is an electron (e) or a muon (). This is the first
search for topcolor leptophobicZ0 in final states involving two leptons. The data sample corresponds to a total inte-grated luminosity of 5:0 fb1 [11] at pffiffiffis¼ 7 TeV col-lected by the CMS detector in 2011.
II. THE CMS DETECTOR
The central feature of the CMS apparatus is a super-conducting solenoid, 13 m in length and 6 m in diameter, which provides an axial magnetic field of 3.8 T. The bore of the solenoid is surrounded by various particle detection systems. Charged particle trajectories are measured by a silicon pixel and strip tracker, covering 0 < 2 in azimuth and jj < 2:5, where the pseudorapidity is defined as ¼ ln ½tan ð=2Þ, and is the polar angle of the trajectory of the particle with respect to the counterclockwise-beam direction. A crystal electromag-netic calorimeter and a brass/scintillator hadronic calo-rimeter surround the tracking volume. The calocalo-rimeter provides high-resolution energy measurement of electrons. Muons are measured in gas-ionization detectors embedded in the steel flux return yoke outside the solenoid. The detector is nearly hermetic, which facilitates the measure-ment of energy balance in the plane transverse to the beam direction. A two-tier trigger system selects the most interestingpp collision events for use in physics analysis. A more detailed description of the CMS detector can be found in Ref. [12].
III. EVENT RECONSTRUCTION
In theZ0 ! tt search, a tt decay topology is used where each top quark decays to a W boson and a b quark, and subsequently each W boson decays into a lepton and a neutrino. The signature for such an event is two oppositely charged, isolated leptons with high transverse momenta (pT), large momentum imbalance due to two undetected neutrinos, and at least two jets. Events are required to pass a trigger requiring at least two high-pTisolated leptons and
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are separated into three channels based on lepton flavor: ee, , and e. The principal sources of background are SMtt, Z= ! ‘ ‘ [Drell-Yan (DY)], single-top quark, and diboson (WW, WZ, and ZZ) production. Other minor contributions are from W ! ‘ and multijet production. Electrons, muons, jets, and the momentum imbalance are reconstructed using a particle-flow algorithm [13]. The negative of the vector sum of the momenta of all recon-structed particles in the plane transverse to the beams is the missing transverse momentum [14], whose magnitude is called missing transverse energy (6ET). The identification criteria of each object and additional selections are chosen to reduce all backgrounds other than SMtt production.
Electron candidates are reconstructed from clusters of energy deposits in the electromagnetic calorimeter, which are then matched to hits in the silicon tracker. Electron identification is based on shower-shape and track-cluster matching variables [15]. Electrons are required to have pT> 20 GeV and jj < 2:5 and are excluded if they are in the transition region between the barrel and endcap calorimeters, 1:4442 < jj < 1:5560, because their recon-struction in this region is degraded due to additional ma-terial there. The electron track must pass within 0.04 cm of the primary vertex in the plane transverse to the beam. Additionally, electrons coming from photon conversions in the detector material are rejected if there are missing hits in the inner tracker layers or if there is another close track with opposite charge and with a similar polar angle.
Muons are reconstructed using the information from the muon detectors and the silicon tracker [16]. The recon-structed muon track must be within 0.02 cm of the primary vertex in the plane transverse to the beam. Muons are required to havepT> 20 GeV and jj < 2:4.
To remove leptons arising from decays of hadrons immersed in jets, the electrons and muons are required to be isolated. The isolation requirement is based on the ratio of the total transverse energy observed from all particles in a cone of sizeR ¼pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðÞ2þ ðÞ2< 0:3 centered on the direction of the lepton to the transverse momentum of the lepton. This quantity must be less than 0.17 for electrons and less than 0.20 for muons.
In order to reduce the background from low-mass dilep-ton resonances, events are rejected if the dilepdilep-ton invariant mass M‘‘< 12 GeV. To suppress the contribution from Z-boson production, a veto on events with 76 < M‘‘< 106 GeV is applied in the ee and channels.
Events are required to contain at least two jets, reconstructed using an anti-kT clustering algorithm with a distance parameter of 0.5 [17]. Corrections are applied to account for the dependence of the detector response to jets as a function of and pTand the effect of pileup (multiple pp collisions) [18]. The corrections are based on in-situ calibration using dijet and =Z þ jet samples. In the pT region above1 TeV, where the statistics of the calibra-tion samples become insufficient, the jet energy scale is
constrained using the single particle response from test beam data [18]. All corrections are propagated to recalcu-late the missing transverse energy. The jets are required to have pT> 30 GeV and jj < 2:5. Additionally, at least one of the jets is required to be tagged as ab jet based on the identification of a secondary vertex [19].
Finally, in order to further reduce the DY and multijet backgrounds in theee channel, and the DY contribution in the channel, a requirement of 6ET> 30 GeV is applied in these channels. The DY and multijet backgrounds are negligible in thee channel.
IV. SIGNAL AND BACKGROUND MODELING The signal efficiency and background rejection of the selection outlined above are determined from simulation studies augmented where necessary by corrections based on control samples in data. The resonance signal Z0 ! tt is modeled using the MADGRAPH 5.1.1 [20] Monte Carlo (MC) event generator, with the top quark mass (Mt) set to 172.5 GeV and CTEQ6L [21] parton distribution functions. Samples are generated with resonance masses between 750 and 3000 GeV, and for two resonance-width scenarios: narrow (Z0 ¼ 0:012MZ0) and wide (Z0 ¼ 0:10MZ0). To calculate the expected number of signal events, we use cross sections for a leptophobic topcolorZ0 [22]. A scale factor of 1.3 is used to account for next-to-leading-order (NLO) corrections [23].
The background events from SMtt, DY, and W ! ‘ are generated usingMADGRAPH5.1.1. Diboson events are gen-erated usingPYTHIA6.424 [24], and single-top quark events are generated usingPOWHEG1.0 r1380 [25–27]. The same set of parton distribution functions are used for each process as for the resonance signalZ0. TheMADGRAPHandPOWHEG
events are processed through PYTHIA in order to add the initial- and final-state radiation and showering, together with the production of the underlying event [28]. To esti-mate the expected number of background events, the back-ground samples are normalized to the theoretical cross sections shown in Table I. All MC events are processed through a simulation of the CMS detector based onGEANT4
[34] and are overlaid with events from minimum-bias in-teraction to account for pileup effects at high instantaneous TABLE I. Theoretical cross sections, including higher-order corrections, for the SM backgrounds [29–33].
Background Cross section [pb]
tt 160 DY (M‘‘> 10 GeV) 15000 WW ! 2‘2 4.5 WZ ! 3‘ 0.61 ZZ (inclusive) 7.4 W ! ‘ 31000 Single top 85
luminosity. An additional set of corrections is applied to account for data-MC differences. These include reweight-ing MC events to match the overlaid pileup distribution to that inferred from the data and applying a scale factor of 0.95 per tagged b jet [19] to account for the observed difference in b-tagging efficiency between data and MC. Theb-tagging efficiency is measured using tt and muon þ jets events [19], with the uncertainty on the data/MC scale factor amounting to 10%–20%.
The simulation of the DY background does not ade-quately reproduce the production rate, especially in the presence of missing transverse energy. The overall normal-ization for the DY process is therefore obtained using data in the DY-enriched region of 76 < M‘‘< 106 GeV in the ee and channels. This region is excluded from the data set used for the main analysis and thus provides an inde-pendent DY control sample. In thee channel, the DY-enriched region is between 40 < M‘‘< 70 GeV since the main contribution to DY in this channel is fromZ= ! events. These events have a peak at lower dilepton masses on account of the invisible decay products of the lepton. As theZ-mass veto is not applied in the e channel, the requirement of at least two jets is modified to exactly one jet in order to ensure the exclusion of this calibration sample from the main signal sample. The normalization factors obtained are 1:34 0:03, 1:24 0:02, and 1:20 0:05 in the ee, , and e channels, respectively.
The multijet background is estimated directly from data. This background is from misidentified leptons or genuine leptons from semileptonic decays of b= b or c=c quarks, which pass the isolation requirement. It is determined from data by inverting the isolation criteria for both leptons, and then extrapolating that yield to the signal region. The extrapolation is performed by multiplying the yield by a normalization factor that accounts for the isolation effi-ciency obtained from like-sign lepton events, defined as
fQCD¼ N;isolated data NMC;isolated N;non-isolated data ; (1)
where N represents the number of like-sign lepton events with the isolation criteria on both leptons either applied or inverted, and MC represents background pre-dictions fortt, DY, diboson, W ! ‘, and single-top quark events. The multijet estimate was cross-checked with an alternate method in a similar analysis with the same final state, and good agreement was observed [35].
In order to check the background modeling, a control sample is created by requiring zero b-tagged jets. This sample is dominated by non-tt backgrounds. Figure 1 shows representative distributions from this sample in the ee, , and e channels. The shape of the multijet background distribution is derived directly from the data using a control sample of nonisolated leptons, in contrast to the other background shapes, which are taken from simu-lation. Good agreement is observed between data and background prediction in all three channels.
V. EVENT YIELDS
The number of events for the expected SM backgrounds and the observed data after all selections and corrections to account for data-MC differences are listed in TableII. The uncertainties shown for the backgrounds are from the systematic effects discussed in Sec. VII. There is good agreement between data and SM backgrounds in all three (leading lepton) [GeV]
T p 0 50 100 150 200 250 Entries 0 100 200 300 400 500 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb = 0 (ee) b-tag N / dof = 0.72 2 χ (leading jet) η -3 -2 -1 0 1 2 3 Entries 0 50 100 150 200 250 300 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb ) µ µ = 0 ( b-tag N / dof = 0.55 2 χ [GeV] T E 0 50 100 150 200 250 Entries 0 100 200 300 400 500 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb ) µ = 0 (e b-tag N / dof = 1.93 2 χ
FIG. 1 (color online). Distributions of the transverse momentum of the highest-pTelectron in theee channel, the pseudorapidity of the highest-pTjet in the channel, and the missing transverse energy in the e channel in the control sample (zero b-tagged jets).
The hatched region indicates systematic uncertainties on the sum of SM backgrounds discussed in Sec.VII.
TABLE II. Event yields for SM backgrounds and data in the
ee, , and e channels.
Sample ee e tt 2210 460 2550 550 7300 1500 DY 410 130 420130 179 57 Diboson 11:5 1:5 15:4 2:0 32:3 4:2 W ! ‘ 17þ2417 0þ3:40 26þ3726 Single top 106 15 121 18 34350 Multijets 41:8 6:9 50 10 103 14 Total background 2790 510 3150 600 8000 1500 Data 2690 3098 7704 Z RESONANCES DECAYING TO . . .
channels. For comparison, the numbers of expected Z0 signal events for MZ0 ¼ 750–3000 GeV are listed in TableIII.
Distributions of the transverse momentum of the highest-pT electron in theee channel, the pseudorapidity of the highest-pTjet in the channel, and between the missing transverse momentum and highest-pTlepton in the e channel are shown in Fig. 2. Also shown are the distributions of the missing transverse energy in the three
channels. There is good agreement between data and the sum of all SM backgrounds. Similarly, a good agreement is seen in all four-vector distributions (pT,, and ) of all final-state objects in the three channels.
The tt invariant mass is constructed using the four-vectors of the two leading leptons, the two leading jets, and the missing transverse energy. The longitudinal momentapzof the two neutrinos in the final state cannot be measured experimentally and are set to zero. The tt invariant mass distributions for the data, the sum of all backgrounds, and theZ0signals for the narrow-width sce-nario (Z0 ¼ 0:012MZ0) are shown in Fig.3for theee, , ande channels. The data are described well by the SM backgrounds, and there is no statistically significant evi-dence for the presence of aZ0signal.
VI. BAYESIAN NEURAL NETWORK ANALYSIS A multivariate analysis, based on Bayesian neural net-works (BNN) [36], has been carried out to provide a more powerful discriminant between backgrounds and the Z0 signal than that based on invariant mass alone. The dis-criminant lies in the interval [0, 1]. It is constructed such that the signal events tend to have a value closer to 1 than the background events that peak instead closer to 0. To build this discriminant the background is defined as the TABLE III. Event yields for a leptophobicZ0inee, , and
e channels. Sample ee e Z0=MZ0¼ 0:012 Z0(750 GeV) 67 79 200 Z0(1000 GeV) 26 28 68 Z0(1250 GeV) 8.2 9.8 22 Z0(1500 GeV) 2.9 3.1 7.0 Z0(2000 GeV) 0.3 0.4 0.8 Z0=MZ0 ¼ 0:10 Z0(1000 GeV) 180 200 480 Z0(1500 GeV) 23 26 57 Z0(2000 GeV) 2.9 2.9 7.0 Z0(3000 GeV) 0.1 0.1 0.2
(leading lepton) [GeV]
T p 0 50 100 150 200 250 Entries 0 200 400 600 800 1000 1200 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb (ee) χ2 / dof = 0.56 (leading jet) η -3 -2 -1 0 1 2 3 Entries 0 200 400 600 800 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb ) µ µ ( χ2 / dof = 0.19 ) [rad] T E (leading lepton, φ ∆ 0 1 2 3 4 Entries 0 500 1000 1500 2000 2500 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb ) µ (e χ2 / dof = 0.08 [GeV] T E 0 50 100 150 200 250 Entries 0 200 400 600 800 1000 1200 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb (ee) χ2 / dof = 0.93 [GeV] T E 0 50 100 150 200 250 Entries 0 200 400 600 800 1000 1200 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb ) µ µ ( / dof = 0.48 2 χ [GeV] T E 0 50 100 150 200 250 Entries 0 500 1000 1500 2000 2500 3000 Data t t DY Other SM Bkg. CMS = 7 TeV s at -1 5.0 fb ) µ (e χ2 / dof = 0.33
FIG. 2 (color online). Distributions of the transverse momentum of the highest-pTelectron in theee channel, the pseudorapidity of the highest-pTjet in the channel, and between the missing transverse momentum and highest-pTlepton in thee channel
(top row), and the missing transverse energy in the three channels (bottom row). The hatched region indicates systematic uncertainties on the sum of SM backgrounds.
sum of all SM processes, and the signal is set to MZ0 ¼ 750 GeV for narrow width, and MZ0 ¼ 1000 GeV for wide width. The separation power increases with hypotheticalZ0 mass. Thus, using theZ0simulated sample with the lowest Z0mass for the signal when training the BNN ensures good
discrimination between signal and background even for the higherZ0masses. A separate discriminant is constructed in each of the three channels. As inputs to the training, the following 17 variables are used in each of the twoZ0-width scenarios, and in each channel:
) [GeV] t M(t 500 1000 1500 Entries 0 500 1000 1500 Data t t DY Other SM Bkg. Z' 750 GeV (x10) Z' 1250 GeV (x100) Z' 1500 GeV (x200) CMS = 7 TeV s at -1 5.0 fb (ee) ) [GeV] t M(t 500 1000 1500 Entries 0 500 1000 1500 Data t t DY Other SM Bkg. Z' 750 GeV (x10) Z' 1250 GeV (x100) Z' 1500 GeV (x200) CMS = 7 TeV s at -1 5.0 fb ) µ µ ( ) [GeV] t M(t 500 1000 1500 Entries 0 1000 2000 3000 4000 5000 Data t t DY Other SM Bkg. Z' 750 GeV (x10) Z' 1250 GeV (x100) Z' 1500 GeV (x200) CMS = 7 TeV s at -1 5.0 fb ) µ (e
FIG. 3 (color online). Distributions of thett invariant mass for the ee, , and e channels. The pzvalues for both neutrinos are set to zero. The hatched region indicates systematic uncertainties on the sum of SM backgrounds. TheZ0signal corresponds to a resonance width of Z0 ¼ 0:012MZ0 and has been scaled up so as to be visible.
BNN output 0 0.2 0.4 0.6 0.8 1 Entries 0 200 400 600 800 1000 Data t t DY Other SM Bkg. Z' 750 GeV (x10) Z' 1250 GeV (x100) Z' 1500 GeV (x200) CMS = 7 TeV s at -1 5.0 fb (ee) BNN output 0 0.2 0.4 0.6 0.8 1 Entries 0 200 400 600 800 1000 Data t t DY Other SM Bkg. Z' 750 GeV (x10) Z' 1250 GeV (x100) Z' 1500 GeV (x200) CMS = 7 TeV s at -1 5.0 fb ) µ µ ( BNN output 0 0.2 0.4 0.6 0.8 1 Entries 0 500 1000 1500 2000 2500 Data t t DY Other SM Bkg. Z' 750 GeV (x10) Z' 1250 GeV (x100) Z' 1500 GeV (x200) CMS = 7 TeV s at -1 5.0 fb ) µ (e
FIG. 4 (color online). Distributions of the BNN output discriminant for theee, , and e channels. The hatched region indicates systematic uncertainties on the sum of SM backgrounds. TheZ0signal corresponds to a resonance width of Z0¼ 0:012MZ0and has been scaled up so as to be visible.
BNN output 0 0.2 0.4 0.6 0.8 1 Entries 0 200 400 600 800 1000 Data t t DY Other SM Bkg. Z' 1000 GeV (x5) Z' 1500 GeV (x20) Z' 2000 GeV (x100) CMS = 7 TeV s at -1 5.0 fb (ee) BNN output 0 0.2 0.4 0.6 0.8 1 Entries 0 200 400 600 800 1000 Data t t DY Other SM Bkg. Z' 1000 GeV (x5) Z' 1500 GeV (x20) Z' 2000 GeV (x100) CMS = 7 TeV s at -1 5.0 fb ) µ µ ( BNN output 0 0.2 0.4 0.6 0.8 1 Entries 0 500 1000 1500 2000 2500 Data t t DY Other SM Bkg. Z' 1000 GeV (x5) Z' 1500 GeV (x20) Z' 2000 GeV (x100) CMS = 7 TeV s at -1 5.0 fb ) µ (e
FIG. 5 (color online). Distributions of the BNN output discriminant for theee, , and e channels. The hatched region indicates systematic uncertainties on the sum of SM backgrounds. TheZ0signal corresponds to a resonance width of Z0 ¼ 0:10MZ0 and has been scaled up so as to be visible.
(i) pTand of the highest-pTlepton,
(ii) pT,, and of the second highest-pTlepton, (iii) pT,, and of the highest-pT jet,
(iv) pT,, and of the second highest-pTjet, (v) 6ET, and of the missing transverse momentum, (vi) pT,, and of the highest-pTb-tagged jet, and
numbernb ofb-tagged jets,
where is the difference in azimuth between the object and the highest-pTlepton. All input variables are internally transformed by the BNN to have a range of½1; 1. This set of input variables constitutes the full array of four-vectors of final-state objects that are measured in the analysis, along with additional information about the b-tagged jets. Using additional derived quantities such as the reconstructedtt invariant mass as an input to the BNN does not improve the performance of the BNN.
The resulting BNN outputs for the observed data, the SM background, and theZ0signals for Z0 ¼ 0:012MZ0and Z0 ¼ 0:10MZ0are shown in Figs.4and5, respectively, for the ee, , and e channels. There is good agreement between data and the SM background in all three channels with no evidence of a resonance signal. Upper limits are set on the production cross section of Z0 times its branching fraction to top quark-antiquark pairs [ Z0BðZ0! ttÞ].
VII. SYSTEMATIC UNCERTAINTIES
The signal and background models are affected by a number of systematic uncertainties, which are propagated into the limit calculation. The uncertainties are divided into two categories: those that affect only the overall normal-ization of a process (‘‘rate’’) and those that affect also the distribution of the BNN discriminant (‘‘shape’’). The rate effects include the uncertainty on predicted cross section and normalization for each SM background based on data, as discussed in Sec. IV, and the uncertainties from integrated luminosity, lepton identification and isolation, b-tagging scale factor, jet energy scale, and pileup reweighting for both SM background andZ0signals. Rate uncertainties are also included for the SMtt and W ! ‘ events from variations in the renormalization and factori-zation scales () and the matching scale for jet production threshold between jets from matrix-element generation in MADGRAPH and parton showering in PYTHIA [37]. The nominal value of is set to a dynamical mass scale of ð2MtÞ2þ ðPpTjetÞ2 for SM tt events, and ðMWÞ2þ ðPpjet
TÞ2 withMW ¼ 80:4 GeV for W ! ‘ events. The nominal value of matching scale is set to 20 GeV. The and matching scales are each varied up and down by a factor of 2 with respect to their nominal values in order to estimate the uncertainty. The shape effects include the change in shape of the BNN distributions from the uncer-tainties from jet energy scale, pileup reweighting, and and matching scales. The uncertainty due to parton distri-bution functions is negligible and therefore not included. The uncertainty on the multijet background is dominated
by the statistical uncertainty of the same-sign samples in Eq. (1). All uncertainties are summarized in Table IV, where each row represents an independent entity. The dominant source of systematic uncertainty in the back-ground estimate is due to the tt cross section uncertainty of 15% which is fully correlated between the channels. The total uncertainty on the sum of all SM backgrounds is 18%.
VIII. RESULTS
With no excess observed, upper limits on Z0BðZ0! ttÞ at the 95% confidence level (C.L.) for different values ofMZ0 are set using the CLscriteria [38,39]. All systematic effects are included with correlations across the different samples and channels. The sensitivity of the results is estimated using the invariant mass distributions shown in Fig.3and the BNN output distributions shown in Fig. 4 and comparing the expected limit on Z0BðZ0! ttÞ for the two methods at MZ0 ¼ 750 GeV and Z0 ¼ 0:012MZ0. An expected limit is obtained from an ensemble of simulated pseudodata sets, where each set is constructed from the background-only hypothesis. Using the BNN distribution improves the ex-pected limit by 29% compared to using invariant mass distribution. For this reason, the more sensitive BNN tech-nique is used for the subsequent measurements. The result-ing expected limits and the observed limits usresult-ing data are shown in Fig.6for both narrow and wide resonances.
The theoretical predictions for a leptophobicZ0[22,23] are used to exclude heavyZ0resonances of massesMZ0< 1:3 TeV for a width Z0 ¼ 0:012MZ0, and M < 1:9 TeV for a width Z0 ¼ 0:10MZ0. In the current analysis, the expected lower limits on MZ0 are 1.1 TeV and 1.7 TeV for Z0 ¼ 0:012MZ0 and Z0 ¼ 0:10MZ0, respectively. TABLE IV. Rate (top part) and shape (bottom part) uncertain-ties, from different components, affecting the total expected number of signal and background events. The uncertainties on the and matching scales in SM tt, the jet energy scale, and the pileup reweighting are indicated by their range across bins of the BNN distribution.
Component Uncertainty [%]
tt cross section 15
DY normalization 30
Diboson cross section 3.8
W ! ‘ cross section 5.0
Single top cross section 7.7
QCD normalization 13 (ee), 18.2 (), 9.7 (e)
Integrated luminosity 2.2
Lepton identification 2.0
b-tagging scale factor 10
scale (W ! ‘) 100
Matching scale (W ! ‘) 100
scale (tt) 1.9–2.9
Matching scale (tt) 3.4–5.5
Jet energy scale 0.3–4.7
IX. SUMMARY
A data sample, corresponding to an integrated luminos-ity of 5:0 fb1 collected inpp collisions atpffiffiffis¼ 7 TeV, has been analyzed in a search for heavy resonances decay-ing to top quark-antiquark pairs with subsequent leptonic decay of both top quark and antiquark. No excess beyond the standard model prediction is observed. Upper limits at the 95% C.L. are derived on the product of the production cross section and branching fraction for these decays, for various masses of narrow and wide resonances. The exis-tence of a leptophobicZ0topcolor particle is excluded for MZ0< 1:3 TeV with Z0 ¼ 0:012MZ0, and for MZ0 < 1:9 TeV with Z0 ¼ 0:10MZ0.
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 effectively the
computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMWF and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MEYS (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09 and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/ IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MON, RosAtom, RAS, and RFBR (Russia); MSTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); ThEP, IPST, and NECTEC (Thailand); TUBITAK and TAEK (Turkey); NASU (Ukraine); STFC (United Kingdom); DOE and NSF (USA).
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.ch/record/1299116. [TeV] Z' M 0.8 1 1.2 1.4 1.6 1.8 2 ) [pb]t t → B(Z'× Z' σ Upper limit on -1 10 1 10 2 10 Observed (95% CL) S CL Expected (95% CL) S CL Expected σ 1 ± Expected σ 2 ± = 0.012) Z' /M Z' Γ Z' ( = 7 TeV s at -1 5.0 fb CMS [TeV] Z' M 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 ) [pb]t t → B(Z'× Z' σ Upper limit on -1 10 1 10 2 10 Observed (95% CL) S CL Expected (95% CL) S CL Expected σ 1 ± Expected σ 2 ± = 0.10) Z' /M Z' Γ Z' ( = 7 TeV s at -1 5.0 fb CMS
FIG. 6 (color online). Upper limits on Z0BðZ0! ttÞ versus MZ0 for narrow and wide resonances. Also shown is the theoretical prediction for theZ0.
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N. Amapane,65a,65bR. Arcidiacono,65a,65cS. Argiro,65a,65bM. Arneodo,65a,65cC. Biino,65aN. Cartiglia,65a S. Casasso,65a,65bM. Costa,65a,65bN. Demaria,65aC. Mariotti,65a,cS. Maselli,65aE. Migliore,65a,65bV. Monaco,65a,65b
M. Musich,65a,cM. M. Obertino,65a,65cN. Pastrone,65aM. Pelliccioni,65aA. Potenza,65a,65bA. Romero,65a,65b M. Ruspa,65a,65cR. Sacchi,65a,65bA. Solano,65a,65bA. Staiano,65aS. Belforte,66aV. Candelise,66a,66bM. Casarsa,66a
F. Cossutti,66a,cG. Della Ricca,66a,66bB. Gobbo,66aM. Marone,66a,66b,cD. Montanino,66a,66bA. Penzo,66a A. Schizzi,66a,66bT. Y. Kim,67S. K. Nam,67S. Chang,68D. H. Kim,68G. N. Kim,68D. J. Kong,68H. Park,68 D. C. Son,68T. Son,68J. Y. Kim,69Zero J. Kim,69S. Song,69S. Choi,70D. Gyun,70B. Hong,70M. Jo,70H. Kim,70
T. J. Kim,70K. S. Lee,70D. H. Moon,70S. K. Park,70Y. Roh,70M. Choi,71J. H. Kim,71C. Park,71I. C. Park,71 S. Park,71G. Ryu,71Y. Choi,72Y. K. Choi,72J. Goh,72M. S. Kim,72E. Kwon,72B. Lee,72J. Lee,72S. Lee,72H. Seo,72
I. Yu,72M. J. Bilinskas,73I. Grigelionis,73M. Janulis,73A. Juodagalvis,73H. Castilla-Valdez,74 E. De La Cruz-Burelo,74I. Heredia-de La Cruz,74R. Lopez-Fernandez,74J. Martı´nez-Ortega,74 A. Sa´nchez Herna´ndez,74L. M. Villasenor-Cendejas,74S. Carrillo Moreno,75F. Vazquez Valencia,75 H. A. Salazar Ibarguen,76E. Casimiro Linares,77A. Morelos Pineda,77M. A. Reyes-Santos,77D. Krofcheck,78 A. J. Bell,79P. H. Butler,79R. Doesburg,79S. Reucroft,79H. Silverwood,79M. Ahmad,80M. I. Asghar,80J. Butt,80 H. R. Hoorani,80S. Khalid,80W. A. Khan,80T. Khurshid,80S. Qazi,80M. A. Shah,80M. Shoaib,80H. Bialkowska,81
M. Szleper,81G. Wrochna,81P. Zalewski,81G. Brona,82K. Bunkowski,82M. Cwiok,82W. Dominik,82K. Doroba,82 A. Kalinowski,82M. Konecki,82J. Krolikowski,82M. Misiura,82W. Wolszczak,82N. Almeida,83P. Bargassa,83
A. David,83P. Faccioli,83P. G. Ferreira Parracho,83M. Gallinaro,83J. Seixas,83J. Varela,83P. Vischia,83 I. Belotelov,84P. Bunin,84M. Gavrilenko,84I. Golutvin,84I. Gorbunov,84A. Kamenev,84V. Karjavin,84G. Kozlov,84 A. Lanev,84A. Malakhov,84P. Moisenz,84V. Palichik,84V. Perelygin,84S. Shmatov,84V. Smirnov,84A. Volodko,84 A. Zarubin,84S. Evstyukhin,85V. Golovtsov,85Y. Ivanov,85V. Kim,85P. Levchenko,85V. Murzin,85V. Oreshkin,85
I. Smirnov,85V. Sulimov,85L. Uvarov,85S. Vavilov,85A. Vorobyev,85An. Vorobyev,85Yu. Andreev,86 A. Dermenev,86S. Gninenko,86N. Golubev,86M. Kirsanov,86N. Krasnikov,86V. Matveev,86A. Pashenkov,86 D. Tlisov,86A. Toropin,86V. Epshteyn,87M. Erofeeva,87V. Gavrilov,87M. Kossov,87N. Lychkovskaya,87V. Popov,87
G. Safronov,87S. Semenov,87I. Shreyber,87V. Stolin,87E. Vlasov,87A. Zhokin,87A. Belyaev,88E. Boos,88 M. Dubinin,88,fL. Dudko,88A. Ershov,88A. Gribushin,88V. Klyukhin,88O. Kodolova,88I. Lokhtin,88A. Markina,88
S. Obraztsov,88M. Perfilov,88S. Petrushanko,88A. Popov,88L. Sarycheva,88,aV. Savrin,88A. Snigirev,88 V. Andreev,89M. Azarkin,89I. Dremin,89M. Kirakosyan,89A. Leonidov,89G. Mesyats,89S. V. Rusakov,89 A. Vinogradov,89I. Azhgirey,90I. Bayshev,90S. Bitioukov,90V. Grishin,90,cV. Kachanov,90D. Konstantinov,90 V. Krychkine,90V. Petrov,90R. Ryutin,90A. Sobol,90L. Tourtchanovitch,90S. Troshin,90N. Tyurin,90A. Uzunian,90
A. Volkov,90P. Adzic,91,hhM. Djordjevic,91M. Ekmedzic,91D. Krpic,91,hhJ. Milosevic,91M. Aguilar-Benitez,92 J. Alcaraz Maestre,92P. Arce,92C. Battilana,92E. Calvo,92M. Cerrada,92M. Chamizo Llatas,92N. Colino,92 B. De La Cruz,92A. Delgado Peris,92D. Domı´nguez Va´zquez,92C. Fernandez Bedoya,92J. P. Ferna´ndez Ramos,92 A. Ferrando,92J. Flix,92M. C. Fouz,92P. Garcia-Abia,92O. Gonzalez Lopez,92S. Goy Lopez,92J. M. Hernandez,92 M. I. Josa,92G. Merino,92J. Puerta Pelayo,92A. Quintario Olmeda,92I. Redondo,92L. Romero,92J. Santaolalla,92
M. S. Soares,92C. Willmott,92C. Albajar,93G. Codispoti,93J. F. de Troco´niz,93H. Brun,94J. Cuevas,94 J. Fernandez Menendez,94S. Folgueras,94I. Gonzalez Caballero,94L. Lloret Iglesias,94J. Piedra Gomez,94 J. A. Brochero Cifuentes,95I. J. Cabrillo,95A. Calderon,95S. H. Chuang,95J. Duarte Campderros,95M. Felcini,95,ii
M. Fernandez,95G. Gomez,95J. Gonzalez Sanchez,95A. Graziano,95C. Jorda,95A. Lopez Virto,95J. Marco,95 R. Marco,95C. Martinez Rivero,95F. Matorras,95F. J. Munoz Sanchez,95T. Rodrigo,95A. Y. Rodrı´guez-Marrero,95
A. Ruiz-Jimeno,95L. Scodellaro,95I. Vila,95R. Vilar Cortabitarte,95D. Abbaneo,96E. Auffray,96G. Auzinger,96 M. Bachtis,96P. Baillon,96A. H. Ball,96D. Barney,96J. F. Benitez,96C. Bernet,96,gG. Bianchi,96P. Bloch,96
A. Bocci,96A. Bonato,96C. Botta,96H. Breuker,96T. Camporesi,96G. Cerminara,96T. Christiansen,96 J. A. Coarasa Perez,96D. D’Enterria,96A. Dabrowski,96A. De Roeck,96S. Di Guida,96M. Dobson,96 N. Dupont-Sagorin,96A. Elliott-Peisert,96B. Frisch,96W. Funk,96G. Georgiou,96M. Giffels,96D. Gigi,96K. Gill,96
D. Giordano,96M. Girone,96M. Giunta,96F. Glege,96R. Gomez-Reino Garrido,96P. Govoni,96S. Gowdy,96 R. Guida,96J. Hammer,96M. Hansen,96P. Harris,96C. Hartl,96J. Harvey,96B. Hegner,96A. Hinzmann,96 V. Innocente,96P. Janot,96K. Kaadze,96E. Karavakis,96K. Kousouris,96P. Lecoq,96Y.-J. Lee,96P. Lenzi,96 C. Lourenc¸o,96N. Magini,96T. Ma¨ki,96M. Malberti,96L. Malgeri,96M. Mannelli,96L. Masetti,96F. Meijers,96 S. Mersi,96E. Meschi,96R. Moser,96M. Mulders,96P. Musella,96E. Nesvold,96L. Orsini,96E. Palencia Cortezon,96
E. Perez,96L. Perrozzi,96A. Petrilli,96A. Pfeiffer,96M. Pierini,96M. Pimia¨,96D. Piparo,96G. Polese,96 L. Quertenmont,96A. Racz,96W. Reece,96J. Rodrigues Antunes,96G. Rolandi,96,jjC. Rovelli,96,kkM. Rovere,96 H. Sakulin,96F. Santanastasio,96C. Scha¨fer,96C. Schwick,96I. Segoni,96S. Sekmen,96A. Sharma,96P. Siegrist,96
P. Silva,96M. Simon,96P. Sphicas,96,llD. Spiga,96A. Tsirou,96G. I. Veres,96,uJ. R. Vlimant,96H. K. Wo¨hri,96 S. D. Worm,96,mmW. D. Zeuner,96W. Bertl,97K. Deiters,97W. Erdmann,97K. Gabathuler,97R. Horisberger,97 Q. Ingram,97H. C. Kaestli,97S. Ko¨nig,97D. Kotlinski,97U. Langenegger,97F. Meier,97D. Renker,97T. Rohe,97 F. Bachmair,98L. Ba¨ni,98P. Bortignon,98M. A. Buchmann,98B. Casal,98N. Chanon,98A. Deisher,98G. Dissertori,98
M. Dittmar,98M. Donega`,98M. Du¨nser,98P. Eller,98J. Eugster,98K. Freudenreich,98C. Grab,98D. Hits,98 P. Lecomte,98W. Lustermann,98A. C. Marini,98P. Martinez Ruiz del Arbol,98N. Mohr,98F. Moortgat,98 C. Na¨geli,98,nnP. Nef,98F. Nessi-Tedaldi,98F. Pandolfi,98L. Pape,98F. Pauss,98M. Peruzzi,98F. J. Ronga,98 M. Rossini,98L. Sala,98A. K. Sanchez,98A. Starodumov,98,ooB. Stieger,98M. Takahashi,98L. Tauscher,98,a A. Thea,98K. Theofilatos,98D. Treille,98C. Urscheler,98R. Wallny,98H. A. Weber,98L. Wehrli,98C. Amsler,99,pp V. Chiochia,99S. De Visscher,99C. Favaro,99M. Ivova Rikova,99B. Kilminster,99B. Millan Mejias,99P. Otiougova,99 P. Robmann,99H. Snoek,99S. Tupputi,99M. Verzetti,99Y. H. Chang,100K. H. Chen,100C. Ferro,100C. M. Kuo,100
S. W. Li,100W. Lin,100Y. J. Lu,100A. P. Singh,100R. Volpe,100S. S. Yu,100P. Bartalini,101P. Chang,101 Y. H. Chang,101Y. W. Chang,101Y. Chao,101K. F. Chen,101C. Dietz,101U. Grundler,101W.-S. Hou,101Y. Hsiung,101
K. Y. Kao,101Y. J. Lei,101R.-S. Lu,101D. Majumder,101E. Petrakou,101X. Shi,101J. G. Shiu,101Y. M. Tzeng,101 X. Wan,101M. Wang,101B. Asavapibhop,102E. Simili,102N. Srimanobhas,102N. Suwonjandee,102A. Adiguzel,103
M. N. Bakirci,103,qqS. Cerci,103,rrC. Dozen,103I. Dumanoglu,103E. Eskut,103S. Girgis,103G. Gokbulut,103 E. Gurpinar,103I. Hos,103E. E. Kangal,103T. Karaman,103G. Karapinar,103,ssA. Kayis Topaksu,103G. Onengut,103
K. Ozdemir,103S. Ozturk,103,ttA. Polatoz,103K. Sogut,103,uuD. Sunar Cerci,103,rrB. Tali,103,rrH. Topakli,103,qq L. N. Vergili,103M. Vergili,103I. V. Akin,104T. Aliev,104B. Bilin,104S. Bilmis,104M. Deniz,104H. Gamsizkan,104 A. M. Guler,104K. Ocalan,104A. Ozpineci,104M. Serin,104R. Sever,104U. E. Surat,104M. Yalvac,104E. Yildirim,104 M. Zeyrek,104E. Gu¨lmez,105B. Isildak,105,vvM. Kaya,105,wwO. Kaya,105,wwS. Ozkorucuklu,105,xxN. Sonmez,105,yy H. Bahtiyar,106,zzE. Barlas,106K. Cankocak,106Y. O. Gu¨naydin,106,aaaF. I. Vardarl,106M. Yu¨cel,106L. Levchuk,107
J. J. Brooke,108E. Clement,108D. Cussans,108H. Flacher,108R. Frazier,108J. Goldstein,108M. Grimes,108 G. P. Heath,108H. F. Heath,108L. Kreczko,108S. Metson,108D. M. Newbold,108,mmK. Nirunpong,108A. Poll,108
S. Senkin,108V. J. Smith,108T. Williams,108L. Basso,109,bbbK. W. Bell,109A. Belyaev,109,bbbC. Brew,109 R. M. Brown,109D. J. A. Cockerill,109J. A. Coughlan,109K. Harder,109S. Harper,109J. Jackson,109B. W. Kennedy,109
E. Olaiya,109D. Petyt,109B. C. Radburn-Smith,109C. H. Shepherd-Themistocleous,109I. R. Tomalin,109 W. J. Womersley,109R. Bainbridge,110G. Ball,110R. Beuselinck,110O. Buchmuller,110D. Colling,110N. Cripps,110
M. Cutajar,110P. Dauncey,110G. Davies,110M. Della Negra,110W. Ferguson,110J. Fulcher,110D. Futyan,110 A. Gilbert,110A. Guneratne Bryer,110G. Hall,110Z. Hatherell,110J. Hays,110G. Iles,110M. Jarvis,110 G. Karapostoli,110M. Kenzie,110L. Lyons,110A.-M. Magnan,110J. Marrouche,110B. Mathias,110R. Nandi,110
J. Nash,110A. Nikitenko,110,ooJ. Pela,110M. Pesaresi,110K. Petridis,110M. Pioppi,110,cccD. M. Raymond,110 S. Rogerson,110A. Rose,110C. Seez,110P. Sharp,110,aA. Sparrow,110M. Stoye,110A. Tapper,110
M. Vazquez Acosta,110T. Virdee,110S. Wakefield,110N. Wardle,110T. Whyntie,110M. Chadwick,111J. E. Cole,111 P. R. Hobson,111A. Khan,111P. Kyberd,111D. Leggat,111D. Leslie,111W. Martin,111I. D. Reid,111P. Symonds,111 L. Teodorescu,111M. Turner,111K. Hatakeyama,112H. Liu,112T. Scarborough,112O. Charaf,113S. I. Cooper,113
C. Henderson,113P. Rumerio,113A. Avetisyan,114T. Bose,114C. Fantasia,114A. Heister,114J. St. John,114 P. Lawson,114D. Lazic,114J. Rohlf,114D. Sperka,114L. Sulak,114J. Alimena,115S. Bhattacharya,115 G. Christopher,115D. Cutts,115Z. Demiragli,115A. Ferapontov,115A. Garabedian,115U. Heintz,115S. Jabeen,115
G. Kukartsev,115E. Laird,115G. Landsberg,115M. Luk,115M. Narain,115M. Segala,115T. Sinthuprasith,115 T. Speer,115R. Breedon,116G. Breto,116M. Calderon De La Barca Sanchez,116S. Chauhan,116M. Chertok,116
J. Conway,116R. Conway,116P. T. Cox,116J. Dolen,116R. Erbacher,116M. Gardner,116R. Houtz,116W. Ko,116 A. Kopecky,116R. Lander,116O. Mall,116T. Miceli,116R. Nelson,116D. Pellett,116F. Ricci-Tam,116B. Rutherford,116
M. Searle,116J. Smith,116M. Squires,116M. Tripathi,116R. Vasquez Sierra,116R. Yohay,116V. Andreev,117 D. Cline,117R. Cousins,117J. Duris,117S. Erhan,117P. Everaerts,117C. Farrell,117J. Hauser,117M. Ignatenko,117
C. Jarvis,117G. Rakness,117P. Schlein,117,aP. Traczyk,117V. Valuev,117M. Weber,117J. Babb,118R. Clare,118 M. E. Dinardo,118J. Ellison,118J. W. Gary,118F. Giordano,118G. Hanson,118H. Liu,118O. R. Long,118A. Luthra,118 H. Nguyen,118S. Paramesvaran,118J. Sturdy,118S. Sumowidagdo,118R. Wilken,118S. Wimpenny,118W. Andrews,119
J. G. Branson,119G. B. Cerati,119S. Cittolin,119D. Evans,119A. Holzner,119R. Kelley,119M. Lebourgeois,119 J. Letts,119I. Macneill,119B. Mangano,119S. Padhi,119C. Palmer,119G. Petrucciani,119M. Pieri,119M. Sani,119
V. Sharma,119S. Simon,119E. Sudano,119M. Tadel,119Y. Tu,119A. Vartak,119S. Wasserbaech,119,ddd F. Wu¨rthwein,119A. Yagil,119J. Yoo,119D. Barge,120R. Bellan,120C. Campagnari,120M. D’Alfonso,120 T. Danielson,120K. Flowers,120P. Geffert,120C. George,120F. Golf,120J. Incandela,120C. Justus,120P. Kalavase,120 D. Kovalskyi,120V. Krutelyov,120S. Lowette,120R. Magan˜a Villalba,120N. Mccoll,120V. Pavlunin,120J. Ribnik,120
J. Richman,120R. Rossin,120D. Stuart,120W. To,120C. West,120A. Apresyan,121A. Bornheim,121Y. Chen,121 E. Di Marco,121J. Duarte,121M. Gataullin,121Y. Ma,121A. Mott,121H. B. Newman,121C. Rogan,121M. Spiropulu,121
V. Timciuc,121J. Veverka,121R. Wilkinson,121S. Xie,121Y. Yang,121R. Y. Zhu,121V. Azzolini,122A. Calamba,122 R. Carroll,122T. Ferguson,122Y. Iiyama,122D. W. Jang,122Y. F. Liu,122M. Paulini,122H. Vogel,122I. Vorobiev,122
J. P. Cumalat,123B. R. Drell,123W. T. Ford,123A. Gaz,123E. Luiggi Lopez,123J. G. Smith,123K. Stenson,123 K. A. Ulmer,123S. R. Wagner,123J. Alexander,124A. Chatterjee,124N. Eggert,124L. K. Gibbons,124B. Heltsley,124
W. Hopkins,124A. Khukhunaishvili,124B. Kreis,124N. Mirman,124G. Nicolas Kaufman,124J. R. Patterson,124 A. Ryd,124E. Salvati,124W. Sun,124W. D. Teo,124J. Thom,124J. Thompson,124J. Tucker,124J. Vaughan,124
Y. Weng,124L. Winstrom,124P. Wittich,124D. Winn,125S. Abdullin,126M. Albrow,126J. Anderson,126 L. A. T. Bauerdick,126A. Beretvas,126J. Berryhill,126P. C. Bhat,126K. Burkett,126J. N. Butler,126V. Chetluru,126
H. W. K. Cheung,126F. Chlebana,126V. D. Elvira,126I. Fisk,126J. Freeman,126Y. Gao,126D. Green,126O. Gutsche,126 J. Hanlon,126R. M. Harris,126J. Hirschauer,126B. Hooberman,126S. Jindariani,126M. Johnson,126U. Joshi,126
B. Klima,126S. Kunori,126S. Kwan,126C. Leonidopoulos,126,eeeJ. Linacre,126D. Lincoln,126R. Lipton,126 J. Lykken,126K. Maeshima,126J. M. Marraffino,126V. I. Martinez Outschoorn,126S. Maruyama,126D. Mason,126
P. McBride,126K. Mishra,126S. Mrenna,126Y. Musienko,126,fffC. Newman-Holmes,126V. O’Dell,126 O. Prokofyev,126E. Sexton-Kennedy,126S. Sharma,126W. J. Spalding,126L. Spiegel,126L. Taylor,126S. Tkaczyk,126 N. V. Tran,126L. Uplegger,126E. W. Vaandering,126R. Vidal,126J. Whitmore,126W. Wu,126F. Yang,126J. C. Yun,126
D. Acosta,127P. Avery,127D. Bourilkov,127M. Chen,127T. Cheng,127S. Das,127M. De Gruttola,127 G. P. Di Giovanni,127D. Dobur,127A. Drozdetskiy,127R. D. Field,127M. Fisher,127Y. Fu,127I. K. Furic,127 J. Gartner,127J. Hugon,127B. Kim,127J. Konigsberg,127A. Korytov,127A. Kropivnitskaya,127T. Kypreos,127 J. F. Low,127K. Matchev,127P. Milenovic,127,gggG. Mitselmakher,127L. Muniz,127M. Park,127R. Remington,127
A. Rinkevicius,127P. Sellers,127N. Skhirtladze,127M. Snowball,127J. Yelton,127M. Zakaria,127V. Gaultney,128 S. Hewamanage,128L. M. Lebolo,128S. Linn,128P. Markowitz,128G. Martinez,128J. L. Rodriguez,128T. Adams,129
A. Askew,129J. Bochenek,129J. Chen,129B. Diamond,129S. V. Gleyzer,129J. Haas,129S. Hagopian,129 V. Hagopian,129M. Jenkins,129K. F. Johnson,129H. Prosper,129V. Veeraraghavan,129M. Weinberg,129 M. M. Baarmand,130B. Dorney,130M. Hohlmann,130H. Kalakhety,130I. Vodopiyanov,130F. Yumiceva,130 M. R. Adams,131L. Apanasevich,131Y. Bai,131V. E. Bazterra,131R. R. Betts,131I. Bucinskaite,131J. Callner,131 R. Cavanaugh,131O. Evdokimov,131L. Gauthier,131C. E. Gerber,131D. J. Hofman,131S. Khalatyan,131F. Lacroix,131
C. O’Brien,131C. Silkworth,131D. Strom,131P. Turner,131N. Varelas,131U. Akgun,132E. A. Albayrak,132 B. Bilki,132,hhhW. Clarida,132F. Duru,132S. Griffiths,132J.-P. Merlo,132H. Mermerkaya,132,iiiA. Mestvirishvili,132
A. Moeller,132J. Nachtman,132C. R. Newsom,132E. Norbeck,132Y. Onel,132F. Ozok,132,zzS. Sen,132P. Tan,132 E. Tiras,132J. Wetzel,132T. Yetkin,132K. Yi,132B. A. Barnett,133B. Blumenfeld,133S. Bolognesi,133D. Fehling,133
G. Giurgiu,133A. V. Gritsan,133Z. J. Guo,133G. Hu,133P. Maksimovic,133M. Swartz,133A. Whitbeck,133 P. Baringer,134A. Bean,134G. Benelli,134R. P. Kenny Iii,134M. Murray,134D. Noonan,134S. Sanders,134 R. Stringer,134G. Tinti,134J. S. Wood,134A. F. Barfuss,135T. Bolton,135I. Chakaberia,135A. Ivanov,135S. Khalil,135
M. Makouski,135Y. Maravin,135S. Shrestha,135I. Svintradze,135J. Gronberg,136D. Lange,136F. Rebassoo,136 D. Wright,136A. Baden,137B. Calvert,137S. C. Eno,137J. A. Gomez,137N. J. Hadley,137R. G. Kellogg,137M. Kirn,137
T. Kolberg,137Y. Lu,137M. Marionneau,137A. C. Mignerey,137K. Pedro,137A. Peterman,137A. Skuja,137 J. Temple,137M. B. Tonjes,137S. C. Tonwar,137A. Apyan,138G. Bauer,138J. Bendavid,138W. Busza,138E. Butz,138
I. A. Cali,138M. Chan,138V. Dutta,138G. Gomez Ceballos,138M. Goncharov,138Y. Kim,138M. Klute,138 K. Krajczar,138,jjjA. Levin,138P. D. Luckey,138T. Ma,138S. Nahn,138C. Paus,138D. Ralph,138C. Roland,138 G. Roland,138M. Rudolph,138G. S. F. Stephans,138F. Sto¨ckli,138K. Sumorok,138K. Sung,138D. Velicanu,138 E. A. Wenger,138R. Wolf,138B. Wyslouch,138M. Yang,138Y. Yilmaz,138A. S. Yoon,138M. Zanetti,138V. Zhukova,138
B. Dahmes,139A. De Benedetti,139G. Franzoni,139A. Gude,139S. C. Kao,139K. Klapoetke,139Y. Kubota,139 J. Mans,139N. Pastika,139R. Rusack,139M. Sasseville,139A. Singovsky,139N. Tambe,139J. Turkewitz,139 L. M. Cremaldi,140R. Kroeger,140L. Perera,140R. Rahmat,140D. A. Sanders,140E. Avdeeva,141K. Bloom,141
S. Bose,141D. R. Claes,141A. Dominguez,141M. Eads,141J. Keller,141I. Kravchenko,141J. Lazo-Flores,141 S. Malik,141G. R. Snow,141A. Godshalk,142I. Iashvili,142S. Jain,142A. Kharchilava,142A. Kumar,142 S. Rappoccio,142Z. Wan,142G. Alverson,143E. Barberis,143D. Baumgartel,143M. Chasco,143J. Haley,143D. Nash,143 T. Orimoto,143D. Trocino,143D. Wood,143J. Zhang,143A. Anastassov,144K. A. Hahn,144A. Kubik,144L. Lusito,144 N. Mucia,144N. Odell,144R. A. Ofierzynski,144B. Pollack,144A. Pozdnyakov,144M. Schmitt,144S. Stoynev,144
M. Velasco,144S. Won,144D. Berry,145A. Brinkerhoff,145K. M. Chan,145M. Hildreth,145C. Jessop,145 D. J. Karmgard,145J. Kolb,145K. Lannon,145W. Luo,145S. Lynch,145N. Marinelli,145D. M. Morse,145T. Pearson,145 M. Planer,145R. Ruchti,145J. Slaunwhite,145N. Valls,145M. Wayne,145M. Wolf,145L. Antonelli,146B. Bylsma,146 L. S. Durkin,146C. Hill,146R. Hughes,146K. Kotov,146T. Y. Ling,146D. Puigh,146M. Rodenburg,146C. Vuosalo,146
G. Williams,146B. L. Winer,146E. Berry,147P. Elmer,147V. Halyo,147P. Hebda,147J. Hegeman,147A. Hunt,147 P. Jindal,147S. A. Koay,147D. Lopes Pegna,147P. Lujan,147D. Marlow,147T. Medvedeva,147M. Mooney,147
J. Olsen,147P. Piroue´,147X. Quan,147A. Raval,147H. Saka,147D. Stickland,147C. Tully,147J. S. Werner,147 S. C. Zenz,147A. Zuranski,147E. Brownson,148A. Lopez,148H. Mendez,148J. E. Ramirez Vargas,148E. Alagoz,149 V. E. Barnes,149D. Benedetti,149G. Bolla,149D. Bortoletto,149M. De Mattia,149A. Everett,149Z. Hu,149M. Jones,149 O. Koybasi,149M. Kress,149A. T. Laasanen,149N. Leonardo,149V. Maroussov,149P. Merkel,149D. H. Miller,149
N. Neumeister,149I. Shipsey,149D. Silvers,149A. Svyatkovskiy,149M. Vidal Marono,149H. D. Yoo,149J. Zablocki,149 Y. Zheng,149S. Guragain,150N. Parashar,150A. Adair,151B. Akgun,151C. Boulahouache,151K. M. Ecklund,151 F. J. M. Geurts,151W. Li,151B. P. Padley,151R. Redjimi,151J. Roberts,151J. Zabel,151B. Betchart,152A. Bodek,152
Y. S. Chung,152R. Covarelli,152P. de Barbaro,152R. Demina,152Y. Eshaq,152T. Ferbel,152A. Garcia-Bellido,152 P. Goldenzweig,152J. Han,152A. Harel,152D. C. Miner,152D. Vishnevskiy,152M. Zielinski,152A. Bhatti,153 R. Ciesielski,153L. Demortier,153K. Goulianos,153G. Lungu,153S. Malik,153C. Mesropian,153S. Arora,154 A. Barker,154J. P. Chou,154C. Contreras-Campana,154E. Contreras-Campana,154D. Duggan,154D. Ferencek,154 Y. Gershtein,154R. Gray,154E. Halkiadakis,154D. Hidas,154A. Lath,154S. Panwalkar,154M. Park,154R. Patel,154 V. Rekovic,154J. Robles,154K. Rose,154S. Salur,154S. Schnetzer,154C. Seitz,154S. Somalwar,154R. Stone,154
S. Thomas,154M. Walker,154G. Cerizza,155M. Hollingsworth,155S. Spanier,155Z. C. Yang,155A. York,155 R. Eusebi,156W. Flanagan,156J. Gilmore,156T. Kamon,156,kkkV. Khotilovich,156R. Montalvo,156I. Osipenkov,156 Y. Pakhotin,156A. Perloff,156J. Roe,156A. Safonov,156T. Sakuma,156S. Sengupta,156I. Suarez,156A. Tatarinov,156 D. Toback,156N. Akchurin,157J. Damgov,157C. Dragoiu,157P. R. Dudero,157C. Jeong,157K. Kovitanggoon,157
S. W. Lee,157T. Libeiro,157I. Volobouev,157E. Appelt,158A. G. Delannoy,158C. Florez,158S. Greene,158 A. Gurrola,158W. Johns,158P. Kurt,158C. Maguire,158A. Melo,158M. Sharma,158P. Sheldon,158B. Snook,158 S. Tuo,158J. Velkovska,158M. W. Arenton,159M. Balazs,159S. Boutle,159B. Cox,159B. Francis,159J. Goodell,159
R. Hirosky,159A. Ledovskoy,159C. Lin,159C. Neu,159J. Wood,159S. Gollapinni,160R. Harr,160P. E. Karchin,160 C. Kottachchi Kankanamge Don,160P. Lamichhane,160A. Sakharov,160M. Anderson,161Donald A. Belknap,161 L. Borrello,161D. Carlsmith,161M. Cepeda,161S. Dasu,161E. Friis,161L. Gray,161K. S. Grogg,161M. Grothe,161
R. Hall-Wilton,161M. Herndon,161A. Herve´,161P. Klabbers,161J. Klukas,161A. Lanaro,161C. Lazaridis,161 R. Loveless,161A. Mohapatra,161M. U. Mozer,161I. Ojalvo,161F. Palmonari,161G. A. Pierro,161I. Ross,161
A. Savin,161W. H. Smith,161and J. Swanson161 (CMS Collaboration)
1
Yerevan Physics Institute, Yerevan, Armenia
2Institut fu¨r Hochenergiephysik der OeAW, Wien, Austria 3National Centre for Particle and High Energy Physics, Minsk, Belarus
4Universiteit Antwerpen, Antwerpen, Belgium 5Vrije Universiteit Brussel, Brussel, Belgium 6Universite´ Libre de Bruxelles, Bruxelles, Belgium
7Ghent University, Ghent, Belgium
8Universite´ Catholique de Louvain, Louvain-la-Neuve, Belgium 9Universite´ de Mons, Mons, Belgium
10Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil 11Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
12aInstituto de Fisica Teorica, Sao Paulo, Brazil 12bUniversidade Estadual Paulista, Sao Paulo, Brazil 13Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
14University of Sofia, Sofia, Bulgaria 15Institute of High Energy Physics, Beijing, China 16
State Key Lab. of Nucl. Phys. and Tech., 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
30Institut Pluridisciplinaire Hubert Curien, Universite´ de Strasbourg,
Universite´ de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France
31Universite´ de Lyon, Universite´ Claude Bernard Lyon 1, CNRS-IN2P3, Institut de Physique Nucle´aire de Lyon, Villeurbanne, France 32Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi, Georgia
33RWTH Aachen University, I, Physikalisches Institut, Aachen, Germany 34RWTH Aachen University, III, Physikalisches Institut A, Aachen, Germany 35RWTH Aachen University, III, Physikalisches Institut B, Aachen, Germany
36Deutsches Elektronen-Synchrotron, Hamburg, Germany 37
University of Hamburg, Hamburg, Germany
38Institut fu¨r Experimentelle Kernphysik, Karlsruhe, Germany 39Institute of Nuclear Physics ‘‘Demokritos,’’ Aghia Paraskevi, Greece
40University of Athens, Athens, Greece 41University of Ioa´nnina, Ioa´nnina, Greece
42KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary 43Institute of Nuclear Research ATOMKI, Debrecen, Hungary
44University of Debrecen, Debrecen, Hungary 45Panjab University, Chandigarh, India
46University of Delhi, Delhi, India 47Saha Institute of Nuclear Physics, Kolkata, India
48Bhabha Atomic Research Centre, Mumbai, India 49Tata Institute of Fundamental Research-EHEP, Mumbai, India 50Tata Institute of Fundamental Research-HECR, Mumbai, India 51Institute for Research in Fundamental Sciences (IPM), Tehran, Iran
52aINFN Sezione di Bari, Bari, Italy 52b
Universita` di Bari, Bari, Italy
52cPolitecnico di Bari, Bari, Italy 53aINFN Sezione di Bologna, Bologna, Italy
53bUniversita` di Bologna, Bologna, Italy 54aINFN Sezione di Catania, Catania, Italy
54bUniversita` di Catania, Catania, Italy 55aINFN Sezione di Firenze, Firenze, Italy
55bUniversita` di Firenze, Firenze, Italy
56INFN Laboratori Nazionali di Frascati, Frascati, Italy 57aINFN Sezione di Genova, Genova, Italy
57bUniversita` di Genova, Genova, Italy 58aINFN Sezione di Milano-Bicocca, Milano, Italy
58bUniversita` di Milano-Bicocca, Milano, Italy 59aINFN Sezione di Napoli, Napoli, Italy 59bUniversita` di Napoli ‘‘Federico II’’, Napoli, Italy
60aINFN Sezione di Padova, Padova, Italy 60bUniversita` di Padova, Padova, Italy 60cUniversita` di Trento (Trento), Padova, Italy
61aINFN Sezione di Pavia, Pavia, Italy 61bUniversita` di Pavia, Pavia, Italy 62aINFN Sezione di Perugia, Perugia, Italy
62bUniversita` di Perugia, Perugia, Italy 63aINFN Sezione di Pisa, Pisa, Italy
63b
Universita` di Pisa, Pisa, Italy
63cScuola Normale Superiore di Pisa, Pisa, Italy 64aINFN Sezione di Roma, Roma, Italy
64bUniversita` di Roma, Roma, Italy 65aINFN Sezione di Torino, Torino, Italy
65bUniversita` di Torino, Torino, Italy
65cUniversita` del Piemonte Orientale (Novara), Torino, Italy 66aINFN Sezione di Trieste, Trieste, Italy
66bUniversita` di Trieste, Trieste, Italy 67
Kangwon National University, Chunchon, Korea
68Kyungpook National University, Daegu, Korea
69Chonnam National University, Institute for Universe and Elementary Particles, Kwangju, Korea 70Korea University, Seoul, Korea
71University of Seoul, Seoul, Korea
