Search for pair production of first or second generation leptoquarks in proton-proton
collisions at
p
ffiffiffi
s
¼ 7 TeV using the ATLAS detector at the LHC
G. Aad et al.* (ATLAS Collaboration)
(Received 25 April 2011; published 15 June 2011)
This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35 pb1 of proton-proton collision data recorded by the ATLAS detector at pffiffiffis¼ 7 TeV. Leptoquarks are searched in events with two oppositely-charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses MLQ< 376 (319) GeV and MLQ< 422 (362) GeV for first and
second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).
DOI:10.1103/PhysRevD.83.112006 PACS numbers: 14.80.Sv, 13.85.t
I. INTRODUCTION
The standard model is extremely successful at describ-ing the elementary particles and their interactions, yet it gives no explanation for the striking symmetry between quarks (q) and leptons (‘). This has, in part, been the motivation for many beyond-the-standard-model theories that posit the existence of leptoquarks (LQ), particles that carry both lepton and baryon quantum numbers, which couple to both quarks and leptons, and carry the triplet charge of quantum chromodynamics (QCD), color. Theories that predict leptoquarks include models that con-tain quark and lepton substructure [1], theories that seek grand unification [2], and models of extended technicolor [3]. Experimental bounds from searches for flavor-chang-ing-neutral currents and lepton-family-number violation place restrictive limits on leptoquark decays to different generations of quarks and leptons [4,5]. Direct leptoquark searches at electron–proton colliders have sensitivity to first generation leptoquarks, but have a non-negligible dependence on the value of the LQ ‘ q coupling [6], whereas second and third generation leptoquarks are pro-duced via lepton-flavor-violation mechanisms [7]. The relatively large cross sections [8] for scalar leptoquark production from proton-proton collisions lead to the ex-pectation that early LHC data offer sensitivity to a mass range beyond that probed by other accelerators. Currently, the most stringent limits come from the Tevatron [9,10] and from the CMS experiment at the LHC [11,12].
Scalar leptoquarks can be produced in proton–proton collisions either in leptoquark–antileptoquark pairs
(LQLQ) or singly. Single LQ production involves an un-known LQ ‘ q coupling, whereas the pair-production reaction occurs mostly via QCD processes which involve only the strong coupling constant. Therefore, results from LQLQ searches have negligible model dependence, and the only relevant parameter for scalar LQ production is the leptoquark mass MLQ[13]. Final states from LQ pair pro-duction have either two same-flavor oppositely-charged leptons and two jets (lljj); a lepton, a neutrino, and two jets (ljj); or two neutrinos and two jets. The leptons l here and throughout the paper are either electrons for first gen-eration LQ or muons for the second gengen-eration [14]. The cross sections for the leptoquark-mediated processes pp ! lljj and ljj can be written as LQ 2and LQ 2ð1 Þ, respectively, where is the branching fraction for a single leptoquark to decay into a charged lepton and a quark.
II. ANALYSIS STRATEGY
This paper reports a search for scalar leptoquark pair production carried out using 35 pb1of data recorded by the ATLAS detector during the 2010 LHC proton-proton running period. The analysis is performed separately in the lljj final state and in the ljj final state. These searches are combined, leading to final results presented as a function of and MLQfor the first and second generations.
Analyses for both final states begin by selecting event samples that have high acceptance for signal production. At this initial stage, these samples are dominated by the major backgrounds, Z þ jets and tt for the lljj case, and W þ jets and tt for the ljj case. The samples are then subdivided into orthogonal control and signal regions.
The control regions are used to validate the background modeling by the Monte Carlo (MC) simulation, and the signal region is used to search for evidence of LQ produc-tion. The signal region is defined using an a priori opti-mization procedure based on simulated background and signal events.
*Full author list given at the end of the article.
Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distri-bution of this work must maintain attridistri-bution to the author(s) and the published article’s title, journal citation, and DOI.
A major difference between LQ events and back-grounds is the presence of jet-lepton (also jet-neutrino in the case of ljj) pairs coming from the decay of the parent LQ, giving a peak in the reconstructed jet-lepton mass spectrum for the signal. The approximate recon-struction of these masses provides the most important variables used to distinguish signal and background events. In addition, large LQ masses give rise to larger total measured transverse energy in LQ pair events than is seen for background events, giving another means to distinguish signal from background. Finally, reconstructed boson masses can be used to reject the dominant back-grounds from VðV ¼ W; ZÞ þ jets production where the boson decays into leptons.
In the lljj channel, an average reconstructed leptoquark mass MLQ is defined for each event by computing the average of the masses from the two lepton-jet combina-tions in the event. Both possible assignments of the two leptons and the two leading jets to LQ parents are consid-ered. The chosen assignment is that which gives the small-est absolute difference between the two reconstructed masses. The probability to get the correct pairing with this method is of the order of 90%. The transverse energy in an event S‘
Tis defined as the scalar sum of the transverse energy (momentum) of the two electrons (muons) and of the two leading jets, S‘T¼ p‘T1þ p‘T2þ þ, where the trans-verse plane is defined as relative to the beam axis [15]. The invariant mass of the dilepton pair Mllprovides rejection of the Z þ jets background.
In the ljj channel, LQ mass equivalents are also de-fined. The neutrino transverse momentum p
T is inferred from the missing transverse momentum in the event EmissT as described in Sec. V. As in the lljj final state, two pairings of lepton and jet and EmissT and jet are possible. However, because the component of the neutrino momen-tum along the beamline is undetermined, only one mass MLQ from the charged lepton and a jet can be reconstructed. The EmissT and the remaining jet are used to compute a transverse mass, MTLQ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2pj
TEmissT ð1 cosjÞ q
in which pjTis the transverse momentum of a jet, and jis the angle between the pjT and the EmissT vectors in the transverse plane. In analogy with the lljj final state, the chosen pairing is that which gives the smallest absolute difference between MLQ and MTLQ, also resulting in the correct assignment more than 90% of the time. The mea-sured transverse energy is defined as the scalar sum of the lepton transverse momentum, the missing transverse mo-mentum, and the momentum of the two leading jets in the event, ST¼ p‘T1þ EmissT þ þ. An additional transverse mass variable MT¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2p‘1 TEmissT ð1 cos‘Þ q provides re-jection against the dominant W þ jets background. Here, p‘
Tis the measured lepton transverse momentum, and ‘is the angle between the p‘Tand EmissT vectors.
III. ATLAS DETECTOR
ATLAS [16,17] is a multipurpose detector with a forward-backward symmetric cylindrical geometry and nearly 4 coverage in solid angle. The three major sub-components of ATLAS are the tracking detector, the calo-rimeter, and the muon spectrometer. Charged-particle tracks and vertices are reconstructed in silicon based track-ing detectors that cover jj < 2:5 and transition radiation detectors extending to jj < 2:0. The inner tracking sys-tem is immersed in a homogeneous 2 T magnetic field provided by a solenoid. Electron, photon, and jet transverse energies are measured in the calorimeter. The ATLAS calorimeter system is segmented into a central barrel and endcaps collectively covering the pseudorapidity range jj < 4:9, and is equipped with both electromagnetic and hadronic calorimeters. Surrounding the calorimeter, a muon spectrometer with air core toroids, a system of precision tracking chambers, and detectors with triggering capabilities provides precise muon identification and mea-surements. A three-level event-triggering system allows for the selection of inclusive muon events with muon transverse momentum (pT) greater than 13 GeV and in-clusive electron events with electron transverse energy (ET) greater than 15 GeV.
IV. SIMULATED SAMPLES
Event samples processed through a detailed detector simulation [18] based on GEANT4 [19] are used to deter-mine most background and all signal yields. As the re-corded data contain a non-negligible fraction of events with more than one interaction per beam crossing, simu-lated events passing the initial lepton selection criteria are reweighted in order to bring the vertex multiplicity distri-butions in data and simulation into agreement. All back-ground samples use ATLAS tune MC09 [20]. The vector-boson processes, W þ jets and Z þ jets, are generated usingALPGEN V2.13[21] withCTEQ6L1[22] for the parton distribution functions (PDFs), interfaced toHERWIG V6.510 [23] andJIMMY V4.31[24]. Exclusive samples with zero to four additional partons (np with n ¼ 0, 1, 2, 3, 4) and an inclusive sample with five or more additional partons (np with n ¼ 5) are used. The cross sections are computed using theALPGENcross sections scaled so that the sum of the np sample cross sections are equal to the next-to-next-to-leading-order inclusive cross sections times branching fraction to a single lepton species: ðW ! ‘Þ ¼ 10:46 0:42 nb and ðZ= ! ‘‘Þ ¼ 1:070 0:054 nb for Mll> 40 GeV [25,26]. Additional samples for cross checks are generated using SHERPA 1.1.3 [27] with PDF set CTEQ6L1, and PYTHIA 6.421 [28] with PDF MRST 2007 LO*[29]. Samples of tt events are produced usingMC@NLO V3.41 [30] and POWHEG 1.01 patch 4 [31] with PDF CTEQ6.6M[32] interfaced toHERWIGfor parton showering. Cross sections are scaled to the next-to-next-to-leading-log
prediction of 165þ1116 pb [33,34]. Single top events are generated using MC@NLOwith cross sections of 3.94 pb, 58.7 pb, and 13.1 pb for the s-, t- and tW-channels, re-spectively. Their uncertainties are10% [35,36]. Diboson events are generated usingHERWIG. Next-to-leading order (NLO) cross sections are calculated with MCFM [37]: 44:9 2:2 pb, 18:0 1:3 pb, and 5:96 0:30 pb for WW, WZ (M‘‘> 40 GeV) and ZZ (M‘‘> 60 GeV), re-spectively. Cross section uncertainties take into account scale and PDF uncertainties, as well as differences with other generators.
Signal events for LQ masses of 250 to 400 GeV with a 50 GeV binning are generated with PYTHIAand tune D6 [38] with cross sections and uncertainties determined from Ref. [8] using the CTEQ6.6 [39] PDF set. The unknown LQ ‘ q coupling value is set to 0:01 pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi4 EM. This corresponds to an LQ full width of less than 1 MeV, and a negligible decay length [40,41].
V. OBJECT IDENTIFICATION
Electron candidates are reconstructed from energy clus-ters in the electromagnetic calorimeter. Electron identifi-cation [42] is performed using the transverse shower shape, the longitudinal leakage into the hadronic calorimeter, and the requirement that a good-quality track points to the cluster. The electron transverse energy is measured in the calorimeter, while its direction is obtained from the track. Further rejection against hadrons is achieved by using the energy deposit patterns in the first layer of the electromag-netic calorimeter. In order to suppress the background from photon conversions, a hit in the first layer of the pixel detector is required. Electrons used in this analysis are required to have ET > 20 GeV and jj < 2:47, with the exclusion of the poorly instrumented region between the barrel and the end-cap calorimeters at 1:35 < jj < 1:52. A small fraction of events with electrons near problematic regions of the electromagnetic calorimeter readout is removed.
Muons selected for this analysis are required to have pT> 20 GeV and jj < 2:4. Muon tracks are recon-structed independently in the inner detector and in the muon spectrometer, with a minimum number of hits re-quired in each. A good match is rere-quired between the tracks found in the inner tracker and the muon spectrome-ter. In order to reject the cosmic ray background, tracks from muon candidates must extrapolate back to the recon-structed event vertex, satisfyingjd0j < 0:1 mm and jz0j < 1 cm, where d0is the minimum distance between the muon trajectory and the event primary vertex in the plane per-pendicular to the beam direction, and z0is the correspond-ing distance parallel to the beam direction.
Finally, both electrons and muons are required to be isolated from other energy in the calorimeters by imposing EconeT =ET< 0:2 and EconeT =pT < 0:25, for electrons and muons, respectively. Here EconeT is the transverse energy
in the calorimeter in a cone of size R ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ðÞ2þ ðÞ2 p
¼ 0:2 centered on the lepton direction, excluding the lepton contribution.
The presence of neutrinos is inferred from the missing transverse momentum EmissT . The EmissT is defined from the vector sum of the transverse energy in calorimeter cells included in topological clusters [16] and the transverse momentum of the muon, EmissT ¼ ð ~ETcellsþ ~pTÞ. The clusters are corrected to take into account the different response to hadrons compared to electrons or photons, as well as dead material and out-of-cluster energy losses [43]. Jets are reconstructed from calorimeter energy clusters using the anti-kt [44] algorithm with a radius parameter R ¼ 0:4. After applying quality requirements based on shower shape and signal timing with respect to the beam crossing [45], jets selected for this analysis must satisfy pT> 20 GeV and jj < 2:8 and must be separated from leptons by R > 0:5. Calibrations of lepton and jet trans-verse momenta, which are mostly derived from control samples in data, are applied prior to making the kinematic selections.
VI. PRESELECTION
Initial selection criteria define event samples with high signal acceptance and yields which are dominated by the major backgrounds V þ jets and tt. Events in both electron and muon analyses are required to have at least one re-constructed proton-proton interaction vertex with at least three charged-particle tracks associated to it. The dilepton channels additionally require exactly two electrons (muons) with ETðpTÞ > 20 GeV. The single lepton chan-nels require exactly one electron (muon) with ETðpTÞ > 20 GeV, Emiss
T > 25 GeV, and MT> 40 GeV. For the ejj channel only, a triangle cut ðjet; EmissT Þ > 1:5 ð1 EmissT =45Þ, where is in radians and EmissT in GeV is applied, in order to reduce the multijet background con-tamination. All analyses require at least two jets satisfying pT> 20 GeV. The two highest pT jets are used to calcu-late LQ masses.
The acceptance for both signal and background is esti-mated by applying all selection criteria to simulated events. Expected yields are obtained by scaling the acceptance by the predicted cross section and integrated luminosity.
After preselection, good agreement is observed between simulation and data in both the number of events and the shape of distributions of kinematic variables. The determi-nation of the expected backgrounds is discussed in Secs.VIIandVIII. The expected and observed yields for the four different channels are summarized in TableI.
VII. BACKGROUND DETERMINATION Small differences between data and simulation for res-olutions and trigger and reconstruction efficiencies are determined in control data samples and applied to the
simulated events. These corrections influence the obtained yields by less than 2%. The background arising from lepton misidentification is determined using data-driven methods in the four channels, as is the contribution from the Z þ jets background to lljj final states. All other backgrounds are modeled with Monte Carlo simulations and tested with data in control regions defined to enhance their contribu-tions, as described in Sec.VIII.
Because the Z þ jets yield in the signal region for the lljj final state arises in the tails of distributions, it is determined using a data-assisted method. The yield in the signal region NDsigis calculated as
NDsig¼ NZ D NZ MCN sig MC; (1) where NZ
Dand NZMCare the observed numbers of events in data and MC, respectively, in a 20 GeV wide dilepton mass window around the nominal Z boson mass, and NMCsig is the expected Z þ jets contribution to the signal region (defined in Table IV). To estimate a systematic uncertainty, the prediction of NsigD was derived with and without require-ments on the number of jets in the event, as well as with the different Monte Carlo generators described in Sec.IV. The 3% background in the 20 GeV mass window from tt and diboson events, estimated with Monte Carlo, is subtracted from the data, as is the <1% contamination from fake leptons. The data-assisted methods (with and without a cut on the number of jets and with various mass window definitions) and the purely Monte Carlo-based estimates agree within 10%. The largest difference is observed be-tween results obtained with ALPGEN and SHERPA, and is used as a systematic uncertainty. The final estimate is obtained usingALPGENfor NMCZ and NMCsig.
Jets misidentified as leptons and leptons from semi-leptonic decays of hadrons are referred to as fake leptons. In this paper, events with fake leptons are referred to as QCD background [46]. The QCD background in the lljj channel is estimated using a fitting method. Templates for both real and fake electrons (muons) are made for the EconeT =ET (EconeT =pT) variable, before applying the isola-tion cut. Simulaisola-tion is used to determine templates for real leptons. Templates for fake leptons are derived from the data by selecting events with exactly one lepton. Events containing W candidates are rejected by requiring
EmissT < 10 GeV. The small residual real lepton contami-nation is estimated from simulated events and is sub-tracted from the data. In the eejj channel, additional templates are made for the fraction of hits associated with transition radiation from electrons. For both chan-nels, fits with these templates are performed on dilepton events with two or more jets giving the probability that an event contains at least one fake lepton. Fits are made inside the Z mass window, as well as in the signal region. Both fits indicate a small expected contribution from fake leptons. In the signal region, an independent upper limit on the number of fakes is set by extrapolating from the number of fakes determined in lower jet multiplicity bins and with lower dilepton mass. The QCD background contribution to the jj analysis is determined using a scaled control sample method. In this method, a pair of variables that cleanly separate real muons from vector boson or leptoquark decay from fake muons is chosen to divide the full sample into four statistically independent regions. One of the four regions corresponds to the signal region, which also contains muons from vector-boson decays. The background in the signal region is then found by scaling the yield in one of the nonsignal regions by the ratio of yields in the remaining two regions. This analysis uses EmissT and muon impact parameter jd0j to define the different regions. The three background regions are de-fined as jd0j < 0:1 mm and EmissT < 25 GeV (A), jd0j > 0:1 mm and Emiss
T < 25 GeV (B) and jd0j > 0:1 mm and EmissT > 25 GeV (C). The signal region (D) is the region withjd0j < 0:1 mm and EmissT > 25 GeV. The correlation between these two variables is less than 10% in simulated samples, giving stability to the method. The yield ND in the signal region is given by ND¼NCNNBA, where N refer to the observed numbers of events in the four statistically independent regions after subtraction of the small, resid-ual contributions from events with real muons in the background regions, which are estimated using simulated events.
In the ejj channel, the normalization of the QCD background is determined from a fit to data of the sum of the MT distributions for QCD events and all other back-grounds, primarily W þ jets and tt. This sum is constrained to equal the total data yield, with the QCD fraction being the fit parameter. The template for the QCD background shape is determined using a QCD enriched sample con-structed by taking the difference in shapes between two samples, a loose sample selected using only the electrons passing the trigger requirements, and the nominal sample, selected using the full electron identification requirements. Residual contamination from real electrons in the QCD enriched sample is estimated to be 7%. The latter is esti-mated with a loose-tight matrix method [33], and used to perform a shape-dependent subtraction. For both muon channels, the background from events containing cosmic ray muons is negligible.
TABLE I. The predicted and observed yields for the prese-lected sample for all channels. Both statistical and systematic uncertainties are included.
Channel Predicted Yield Observed Yield
eejj 610 240 626
ejj 6100 þ 1000 1100 6088
jj 830 þ 200 150 853
VIII. CONTROL REGIONS
Control samples are used to validate the background determination based on MC. The two most important control samples for the lljj analyses are (1) Z þ jet: events for which the dilepton invariant mass lies within the Z mass window 81 Mll 101 GeV and (2) tt: events that con-tain at least two jets and both an electron and a muon selected, as defined in Sec.V. By definition, the tt control region is common for both the eejj and jj channels. The most important control samples for the ljj analyses are (1) W þ 2 jets: events with exactly two jets, a charged lepton, and EmissT such that MT is in the region of the W Jacobian peak (40 GeV MT 150 GeV), (2) W þ 3 jets: as in (1) but with at least 3 jets, and (3) a tt enriched sample which requires at least four jets with >50 GeV, >40 GeV, and >30 GeV. The expected signal contamination in the control regions is at most 1%. The predicted and observed yields in these control samples are shown in TablesIIandIII. Distributions of S‘
Tare shown in Fig. 1 for the lljj samples in the Z þ jet and tt control regions, and distributions for the reconstructed MLQ are shown in Fig.2for the ljj samples in the W þ 2 jets and the tt control regions.
IX. SELECTION OPTIMIZATION
The signal regions in the four final states are defined using a random grid search optimization method [47]. The optimization is performed using simulated signal and background samples (determined as described in Sec. VII and VIII) after preselection, with the final cuts determined by minimizing the Poisson probability that the predicted background fluctuates to at least the predicted signal plus background. A 10% overall scale uncertainty on the yields, roughly matching the uncer-tainty on the luminosity, is included in the optimization as a systematic uncertainty. Optimization for the single lepton (dilepton) channels nominally is done using sig-nal samples with LQ masses of 300 (400) GeV. Cuts derived using different LQ masses typically differ from the nominal values within statistical uncertainties. A variety of input variables are considered. The require-ments that give the best separation between signal and background are shown in Table IV. The yields obtained after final selection for the various channels are shown in Table V, along with the predicted background and signal.
TABLE III. The predicted and observed yields in the control samples for the muon final states. Top refers to both single top and tt events. Both statistical and systematic uncertainties are included.
jj jj
Event Control Region Control Region
Source Zþ 2 jets tt W þ 2 jets Wþ 3 jet tt
V þ jets 190 24 0:3 0:1 3300 1100 900 300 250 80 Top 2:7 0:5 24 4 14 3 53 1 260 50 Diboson 0:2 0:1 0:8 0:1 28 6 14 3 3:0 0:7 QCD 6:0þ11:06:0 0:0þ0:10:0 300 100 130 50 54 32 Total Bkg 200 25 25 4 3600 1100 1100 330 570 120 Data 216 22 3588 1120 547
TABLE II. The predicted and observed yields in the control samples for the electron final states. Top refers to both single top and tt events. Both statistical and systematic uncertainties are included.
eejj ejj
Event Control Region Control Region
Source Zþ 2 jets tt W þ 2 jets Wþ 3 jet tt
V þ jets 150 23 0:3 0:1 2100 700 580 190 180 60 Top 2:0 0:3 24 4 21 4 44 9 210 40 Diboson 2:0 0:3 0:8 0:1 17 4 8:3 1:9 2:1 0:5 QCD 4:0þ14:04:0 0:0þ0:10:0 64 14 68 15 29 7 Total Bkg 158 25 25 4 2200 700 700 200 420 80 Data 140 22 2344 722 425
X. SYSTEMATIC UNCERTAINTIES
Systematic uncertainties are derived for a variety of sources, including data-simulation differences in trigger and reconstruction efficiencies and in the energy and mo-mentum resolutions for leptons, jets, and EmissT , instanta-neous and integrated luminosity, modeling of the underlying event, variations in the method used to deter-mine the QCD background, and uncertainty on the LQ pair-production cross section. A summary of the system-atic uncertainties for the four final states is shown in TableVI.
The lepton trigger and reconstruction efficiency system-atic uncertainties are derived by varying the selection of the Z event sample used to measure in situ efficiencies, and by varying the treatment of the (small) background in this sample. In addition, a 1% uncertainty is included on the muon isolation requirement that accounts for the difference of the efficiency of the isolation requirement in data and tt and LQ simulated samples. Finally, a 3% uncertainty is added to account for differences in the muonjd0j distribu-tions between data and simulation. Lepton momentum scale and resolution uncertainties are obtained by compar-ing the peak and width of Z ! ‘‘ events in data and Monte Carlo.
The jet energy scale and resolution are varied by their uncertainties [48,49] for all simulated events, and their impact estimated independently. In addition, a 5% uncer-tainty is added in quadrature to the jet energy scale un-certainties to account for differences in response for quark and gluon jets. These variations in scale and resolution are also propagated to the EmissT . The systematic uncertainty from instantaneous luminosity effects is evaluated by com-paring the results from simulated samples with and without additional minimum bias events (pileup) added. This is an overestimate of the systematic, but is still small (2%–6%, depending on the sample) compared to other sources.
Systematic uncertainties on the QCD background are determined by comparing results from alternate normal-izations to those described in Sec.VII. The uncertainty on the lljj final states is determined by varying the estimate between the nominal prediction and the upper level from the extrapolation method described in Sec. VII. The un-certainty in the ejj final state is determined by comparing the default method, based on fits to the MTdistribution, to alternate fits using the EmissT or the electron ET distribu-tions. The largest fractional difference (22%) between the nominal fit and fits using the alternate variables is taken as the systematic uncertainty. The uncertainty in the back-ground to the jj final state is determined by comparing the default method to one that uses the muon isolation instead of the d0variable The difference in yield between the two estimates is used to determine the systematic uncertainty, giving 27%.
The systematic uncertainties for the production models of W þ jets and Z þ jets events in the single lepton
[GeV] µ T S 200 300 400 500 600 700 800 Events / 20 GeV -1 10 1 10 2 10 3 10 [GeV] µ T S 200 300 400 500 600 700 800 Events / 20 GeV -1 10 1 10 2 10 3 10 ATLAS -1 L dt = 35 pb
∫
=7 TeV) s Data 2010 ( V+jets Top QCD Diboson MC Uncertainty [GeV] e T S 200 300 400 500 600 700 800 Events / 20 GeV -2 10 -1 10 1 10 2 10 3 10 4 10 5 10 [GeV] e T S 200 300 400 500 600 700 800 Events / 20 GeV -2 10 -1 10 1 10 2 10 3 10 4 10 5 10 Data 2010 (s = 7 TeV) V+jets Top QCD Diboson MC Uncertainty ATLAS -1 L dt = 35 pb∫
[GeV] l T S 200 300 400 500 600 700 800 Events / 20 GeV -1 10 1 10 2 10 [GeV] l T S 200 300 400 500 600 700 800 Events / 20 GeV -1 10 1 10 2 10 ATLAS -1 L dt = 35 pb∫
=7 TeV) s Data 2010 ( V+jets Top QCD Diboson MC UncertaintyFIG. 1 (color online). S‘
T distributions for the eejj (top) and
the jj final states (middle) in the Z control region. The bottom figure shows the S‘Tdistribution for the dilepton tt control
region. The data are indicated by the points and the standard model backgrounds are shown with cumulative distributions. The QCD background is estimated from data, while the other background contributions are obtained from simulated samples. The top background includes both tt and single top events. The expected contribution from a potential LQ signal is negligible and is not included in the figure. The MC uncertainty band shows the combined statistical and systematic uncertainties on the prediction in each bin.
analysis are determined by varying parameters at the gen-erator, level as described in [26], including variations of the renormalization and factorization scales and minimum parton pT. The largest absolute deviation (40%) is used as a systematic uncertainty. In the dilepton analysis, the systematic uncertainty is determined by varying the dilep-ton mass window and replacing theALPGENevent genera-tor with SHERPA. The difference between ALPGEN and SHERPA dominates, giving an uncertainty in the
eejjðjjÞ channel of 34 (45)% on the Z þ jets predic-tion in the signal region.
Systematic uncertainties are evaluated for the tt produc-tion model by comparing the predicproduc-tions obtained with MC@NLO and POWHEG. The result is a 35% uncertainty for both lljj and ljj channels.
An integrated luminosity uncertainty of 11% [50] is applied to all backgrounds determined from simulated events and to the signal. Additional signal uncertainties are obtained from varying the renormalization scale pa-rameter to 0:5MLQ and to 2MLQ (15%), from different PDF choices (13%-17%) for LQ masses in the range 300– 400 GeV, and from initial- and final-state-radiation effects (2%). The systematic uncertainties on the theory cross sections used to normalize backgrounds are given in Sec.IV.
XI. RESULTS
The expected and observed numbers of events are shown in Table V. Data and standard model expectations are in good agreement. 95% CL upper limits on LQ pair-production cross sections are determined using a modified LQ M(e,jet) [GeV] 0 50 100 150 200 250 300 350 400 Events / 20 GeV -1 10 1 10 2 10 3 10 4 10 =7 TeV) s Data 2010 ( QCD V+jets Top Diboson MC Uncertainty ATLAS -1 L dt = 35 pb
∫
0 50 100 150 200 250 300 350 400 -1 10 1 10 2 10 3 10 4 10 0 50 100 150 200 250 300 350 400 -1 10 1 10 2 10 3 10 4 10 0 50 100 150 200 250 300 350 400 -1 10 1 10 2 10 3 10 4 10 LQ M(e,jet) [GeV] 100 200 300 400 500 600 Events / 20 GeV -1 10 1 10 2 10 3 10 4 10 =7 TeV) s Data 2010 ( QCD V+jets Top Diboson MC Uncertainty ATLAS -1 L dt = 35 pb∫
100 200 300 400 500 600 -1 10 1 10 2 10 3 10 4 10 100 200 300 400 500 600 -1 10 1 10 2 10 3 10 4 10 100 200 300 400 500 600 -1 10 1 10 2 10 3 10 4 10 , jet) [GeV] µ LQ M( 0 50 100 150 200 250 300 350 400 Events / 20 GeV -1 10 1 10 2 10 3 10 4 10 5 10 , jet) [GeV] µ LQ M( 0 50 100 150 200 250 300 350 400 Events / 20 GeV -1 10 1 10 2 10 3 10 4 10 5 10 , jet) [GeV] µ LQ M( 0 50 100 150 200 250 300 350 400 Events / 20 GeV -1 10 1 10 2 10 3 10 4 10 5 10 Data 2010 (s=7 TeV) QCD V+jets Top Diboson MC Uncertainty ATLAS -1 L dt = 35 pb∫
, jet) [GeV] µ LQ M( 100 200 300 400 500 600 Events / 20 GeV -1 10 1 10 2 10 3 10 , jet) [GeV] µ LQ M( 100 200 300 400 500 600 Events / 20 GeV -1 10 1 10 2 10 3 10 , jet) [GeV] µ LQ M( 100 200 300 400 500 600 Events / 20 GeV -1 10 1 10 2 10 3 10 =7 TeV) s Data 2010 ( QCD V+jets Top Diboson MC Uncertainty ATLAS -1 L dt = 35 pb∫
FIG. 2 (color online). Reconstructed MLQdistributions for the ejj (top) and the jj (bottom) final states in the W þ 2 jets (left)
and tt (right) control regions. The data are indicated by the points and the standard model backgrounds are shown with cumulative distributions. The QCD background is estimated from data, while the other background contributions are obtained from simulated samples. The top background includes both tt and single top events. The expected contribution from a potential LQ signal is negligible and is not included in the figure. The MC uncertainty band indicates the combined statistical and systematic uncertainties on the prediction in each bin.
TABLE IV. The selection requirements used to define the signal region, as obtained from the optimization procedure. pallT > 30 GeV implies that the pT of both the two leading
leptons and the two leading jets in the dilepton samples should exceed 30 GeV.
eejj and jj ejj jj
Mll> 120 GeV MT> 200 GeV MT> 160 GeV
MLQ> 150 GeV MLQ> 180 GeV MLQ> 150 GeV
pallT > 30 GeV MTLQ> 180 GeV MTLQ> 150 GeV
S‘
TABLE V. The predicted and observed yields in the signal region for all channels. The lljj (ljj) channel signal yields are computed assuming ¼ 1:0ð0:5Þ. Both statistical and system-atic uncertainties are included. Top refers to both single top and tt events.
Source eejj ejj jj jj
V þ jets 0:50 0:28 0:65 0:38 0:28 0:22 2:6 1:4 Top 0:51 0:23 0:67 0:39 0:52 0:23 1:6 0:9 Diboson 0:03 0:01 0:10 0:03 0:04 0:01 0:10 0:03 QCD 0:02þ0:030:02 0:06 0:01 0:00þ0:010:00 0:0 0:0 Total Bkg 1:1 0:4 1:4 0:5 0:8 0:3 4:4 1:9 Data 2 2 0 4 LQ(250 GeV) 38 8 9:6 2:1 45 10 13 3 LQ(300 GeV) 17 4 5:1 1:1 21 5 6:4 1:4 LQ(350 GeV) 7:7 1:7 2:6 0:6 9:4 2:1 3:0 0:7 LQ(400 GeV) 3:5 0:8 4:4 1:0 [GeV] e T S 600 800 1000 1200 1400 1600 Events / 120 GeV 0 1 2 3 4 5 6 [GeV] e T S 600 800 1000 1200 1400 1600 Events / 120 GeV 0 1 2 3 4 5 6 =7 TeV) s Data 2010 ( V+jets Top Diboson LQ (m=300 GeV) LQ (m=350 GeV) LQ (m=400 GeV) -1 L dt = 35 pb
∫
ATLAS [GeV] µ T S 600 800 1000 1200 1400 1600 Events / 120 GeV 0 1 2 3 4 5 6 7 [GeV] µ T S 600 800 1000 1200 1400 1600 Events / 120 GeV 0 1 2 3 4 5 6 7 =7 TeV) s Data 2010 ( V+jets Top Diboson LQ (m=300 GeV) LQ (m=350 GeV) LQ (m=400 GeV) -1 L dt = 35 pb∫
ATLASFIG. 3 (color online). S‘
Tdistribution for the eejj (left) and the jj final states (right) after all selections. The data are indicated by
the points and the standard model backgrounds are shown with cumulative distributions. The expected LQ signals for various masses are also shown.
TABLE VI. Systematic uncertainties for the lljj and the ljj final states. The lepton trigger, identification, and momentum (energy) scale and resolution uncertainties are small and grouped together. Single top and tt events are also grouped together. Uncertainties marked with * (**) are only for the electron (muon) channels. QCD modeling systematics are not shown. All numbers are in percentages.
V þ jets Top Diboson LQ (300 GeV)
Channel lljj ljj lljj ljj lljj ljj lljj ljj
Production Cross Section 4 13 13 5 5 18 18
Modeling 34*, 45** 40 35 35
Electron Energy Scale & Resolution* þ13, 0:2 5 10 2 7 1 8 1
Muon Momentum Scale & Resolution** 20 5 7 2 8 1 6.7 1
Jet Energy Scale 6 þ22, 13 þ9, 18 32 þ16, 6 þ17, 24 2 3
Jet Energy Resolution 16 10 0.3 26 4 14 0.3 3
Luminosity 0.3 11 11 11 11 11 11 11
Pile up <0:1 5 <0:1 4 <0:1 6 <0:1 2
Total Systematics 39* þ49, 45 47* 57 (þ 22, 16) þ26, 31 22 22
frequentist approach [51,52]. Systematic uncertainties are incorporated in the limit calculation as nuisance parame-ters and are integrated out. The limits are translated into bounds in the versus LQ mass plane.
Monte Carlo studies show that a better sensitivity is achieved when using kinematic shapes rather than just the total number of events. For the eejj and jj final states, the observed and predicted STdistributions are used
[GeV] LQ M 250 300 350 400 450 )) [pb]β (1-β +2 2 β (× ) LQ LQ → (ppσ -2 10 -1 10 1 10 µ σ δ ⊕ pdf σ δ ⊕ ) LQ LQ → (pp σ Expected Limit σ 1 ± Expected σ 2 ± Expected Observed limit [GeV] LQ M 250 300 350 400 450 )) [pb]β (1-β +2 2 β (× ) LQ LQ → (ppσ -2 10 -1 10 1 10 = 7 TeV s
∫
Ldt = 35 pb-1 =1) β Generation LQ ( st 1 ATLAS [GeV] LQ M 200 250 300 350 400 450 )) [pb]β (1-β +2 2 β (× ) LQ LQ → (ppσ -2 10 -1 10 1 10 µ σ δ ⊕ pdf σ δ ⊕ ) LQ LQ → (pp σ Expected Limit σ 1 ± Expected σ 2 ± Expected Observed limit [GeV] LQ M 200 250 300 350 400 450 )) [pb]β (1-β +2 2 β (× ) LQ LQ → (ppσ -2 10 -1 10 1 10 = 7 TeV s∫
Ldt = 35 pb-1 =0.5) β Generation LQ ( st 1 ATLAS [GeV] LQ M 250 300 350 400 450 )) [pb]β (1-β +2 2β (× ) LQ LQ → (ppσ 10-2 -1 10 1 10 µ σ δ ⊕ pdf σ δ ⊕ ) LQ LQ → (pp σ Expected Limit σ 1 ± Expected σ 2 ± Expected Observed limit [GeV] LQ M 250 300 350 400 450 )) [pb]β (1-β +2 2β (× ) LQ LQ → (ppσ 10-2 -1 10 1 10 = 7 TeV s∫
Ldt = 35 pb-1 =1) β Generation LQ ( nd 2 ATLAS [GeV] LQ M 200 250 300 350 400 450 )) [pb]β (1-β +2 2β (× ) LQ LQ → (ppσ 10-2 -1 10 1 10 µ σ δ ⊕ pdf σ δ ⊕ ) LQ LQ → (pp σ Expected Limit σ 1 ± Expected σ 2 ± Expected Observed limit [GeV] LQ M 200 250 300 350 400 450 )) [pb]β (1-β +2 2β (× ) LQ LQ → (ppσ 10-2 -1 10 1 10 = 7 TeV s∫
Ldt = 35 pb-1 =0.5) β Generation LQ ( nd 2 ATLASFIG. 5 (color online). 95% CL upper bounds on the LQ pair production cross sections as a function of LQ mass for the combination of the eejj and the ejj channels (top), and for the jj and the jj channels (bottom). The figures on the left (right) show the limit for ¼ 1:0 (0.5). The expected limit is indicated by the dashed line. The light yellow (dark green) solid band contains 68% (95%) of possible outcomes from pseudoexperiments in which the yield is Poisson fluctuated around the background-only expectation. Systematic uncertainties are included. The observed limit is indicated by the solid line. The theory prediction is indicated by the dotted line, which includes systematic uncertainties due to the choice of the PDF and to the renormalization and factorization scales ().
LQ M(e,jet) [GeV] 150 200 250 300 350 400 450 500 550 600 Events / 50 GeV 0 1 2 3 4 5 6 7 8 Data 2010 (s=7 TeV) V+jets Top Diboson LQ(m=250GeV) LQ(m=300 GeV) LQ(m=350GeV) ATLAS -1 L dt = 35 pb
∫
150 200 250 300 350 400 450 500 550 600 0 1 2 3 4 5 6 7 8 150 200 250 300 350 400 450 500 550 600 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 , jet) [GeV] µ LQ M( 150 200 250 300 350 400 450 500 550 600 Events / 50 GeV 0 1 2 3 4 5 6 7 , jet) [GeV] µ LQ M( 0 1 2 3 4 5 6 7 Data 2010 (s=7 TeV) V+jets Top Diboson LQ (m=250 GeV) LQ (m=300 GeV) LQ (m=350 GeV) ATLAS -1 L dt = 35 pb∫
FIG. 4 (color online). MLQdistribution for the ejj (left) and the jj final state (right) after all selections. The data are indicated
by the points and the standard model backgrounds are shown with cumulative distributions. The expected LQ signals for various masses are also shown.
in the limit-setting procedure, and for the ejj and jj final states the observed and predicted MLQ distributions are used. The STdistributions are shown in Fig.3for the lljj channels. Figure4shows the MLQdistributions for the single lepton final states.
The 95% CL upper bounds on the cross section for first and second generation LQ pair production as a function of mass are shown in Fig. 5for ¼ 1:0 and ¼ 0:5. The combined limits are also shown in the vs MLQplane in Fig. 6 for both generations. The expected and observed combined limits including all systematic uncertainties are shown in TableVIIfor both ¼ 1:0 and 0.5. The system-atic uncertainties, of the order of 50%, only change the limits by 5 to 10 GeV, depending on the value of .
XII. CONCLUSIONS
This paper reports the results of searches for pair pro-duction of first or second generation scalar leptoquarks using a data sample corresponding to an integrated lumi-nosity of 35 pb1. The data in the high signal-to-background signal region are in good agreement with the
standard model expectations. 95% CL upper bounds on the production cross section are determined. These are trans-lated into lower bounds for first (second) generation lepto-quark masses of MLQ> 376 (422) GeV and MLQ> 319 (362) GeV for ¼ 1:0 and ¼ 0:5, respectively. These are the most stringent bounds to date from direct searches for leptoquarks in much of the phase space.
ACKNOWLEDGMENTS
We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC, and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST, and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR, and VSC CR, Czech Republic; DNRF, DNSRC, and Lundbeck Foundation, Denmark; ARTEMIS, European Union;
IN2P3-CNRS, CEA-DSM/IRFU, France; GNAS,
Georgia; BMBF, DFG, HGF, MPG, and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP, and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS and MVZT, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF, and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society, and Leverhulme Trust, United Kingdom; DOE and NSF, United States of [GeV] LQ M 200 250 300 350 400 450 500 550 eq) → B(LQ ≡ β 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 eejj jj νe jj (Exp.) ν eejj + e jj (Obs.) ν eejj + e ) -1 D0 (1 fb ) -1 CMS (33 pb [hep-ex/1012.4031] [GeV] LQ M 200 250 300 350 400 450 500 550 eq) → B(LQ ≡ β 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 = 7 TeV s -1 Ldt = 35 pb
∫
ATLAS [GeV] LQ M 200 250 300 350 400 450 500 550 q)µ → B(LQ ≡ β 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 jj µ µ jjν µ jj (Exp.) ν µ jj + µ µ jj (Obs.) ν µ jj + µ µ ) -1 D0 (1 fb ) -1 CMS (34 pb [hep-ex/1012.4033] [GeV] LQ M 200 250 300 350 400 450 500 550 q)µ → B(LQ ≡ β 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 = 7 TeV s -1 Ldt = 35 pb∫
ATLASFIG. 6 (color online). 95% CL exclusion region obtained from the combination of the two electron channels (left) and the muon channels (right) shown in the versus leptoquark mass plane. The gray area indicates the D0 exclusion limit [9,10], and the thick dotted line the CMS exclusion [11,12]. The dotted and dotted-dashed lines show the individual limits for the lljj and the ljj channels, respectively. The combined expected limit is indicated by the thick dashed line. The solid band contains 68% of possible outcomes from pseudoexperiments in which the yield is Poisson fluctuated around the background-only expectation. Systematic uncertainties are included. The combined observed limit is indicated by the solid line.
TABLE VII. 95% CL expected and observed limits on the first and second generation LQs under different assumptions on . The expected limits include systematic uncertainties.
Type (Þ Expected limit (GeV) Observed limit (GeV) 1st generation (1.0) 387 376 1st generation (0.5) 348 319 2nd generation (1.0) 393 422 2nd generation (0.5) 353 362
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J. Boyd,29I. R. Boyko,65N. I. Bozhko,128I. Bozovic-Jelisavcic,12bJ. Bracinik,17A. Braem,29P. Branchini,134a G. W. Brandenburg,57A. Brandt,7G. Brandt,15O. Brandt,54U. Bratzler,156B. Brau,84J. E. Brau,114H. M. Braun,174 B. Brelier,158J. Bremer,29R. Brenner,166S. Bressler,152D. Breton,115N. D. Brett,118D. Britton,53F. M. Brochu,27
I. Brock,20R. Brock,88T. J. Brodbeck,71E. Brodet,153F. Broggi,89aC. Bromberg,88G. Brooijmans,34 W. K. Brooks,31bG. Brown,82H. Brown,7E. Brubaker,30P. A. Bruckman de Renstrom,38D. Bruncko,144b R. Bruneliere,48S. Brunet,61A. Bruni,19aG. Bruni,19aM. Bruschi,19aT. Buanes,13F. Bucci,49J. Buchanan,118
N. J. Buchanan,2P. Buchholz,141R. M. Buckingham,118A. G. Buckley,45S. I. Buda,25aI. A. Budagov,65 B. Budick,108V. Bu¨scher,81L. Bugge,117D. Buira-Clark,118E. J. Buis,105O. Bulekov,96M. Bunse,42T. Buran,117
H. Burckhart,29S. Burdin,73T. Burgess,13S. Burke,129E. Busato,33P. Bussey,53C. P. Buszello,166F. Butin,29 B. Butler,143J. M. Butler,21C. M. Buttar,53J. M. Butterworth,77W. Buttinger,27T. Byatt,77S. Cabrera Urba´n,167
D. Caforio,19a,19bO. Cakir,3aP. Calafiura,14G. Calderini,78P. Calfayan,98R. Calkins,106L. P. Caloba,23a R. Caloi,132a,132bD. Calvet,33S. Calvet,33R. Camacho Toro,33A. Camard,78P. Camarri,133a,133b M. Cambiaghi,119a,119bD. Cameron,117J. Cammin,20S. Campana,29M. Campanelli,77V. Canale,102a,102b
F. Canelli,30A. Canepa,159aJ. Cantero,80L. Capasso,102a,102bM. D. M. Capeans Garrido,29I. Caprini,25a M. Caprini,25aD. Capriotti,99M. Capua,36a,36bR. Caputo,148C. Caramarcu,25aR. Cardarelli,133aT. Carli,29
G. Carlino,102aL. Carminati,89a,89bB. Caron,159aS. Caron,48C. Carpentieri,48G. D. Carrillo Montoya,172 A. A. Carter,75J. R. Carter,27J. Carvalho,124a,hD. Casadei,108M. P. Casado,11M. Cascella,122a,122bC. Caso,50a,50b,a
A. M. Castaneda Hernandez,172E. Castaneda-Miranda,172V. Castillo Gimenez,167N. F. Castro,124aG. Cataldi,72a F. Cataneo,29A. Catinaccio,29J. R. Catmore,71A. Cattai,29G. Cattani,133a,133bS. Caughron,88D. Cauz,164a,164c
A. Cavallari,132a,132bP. Cavalleri,78D. Cavalli,89aM. Cavalli-Sforza,11V. Cavasinni,122a,122bA. Cazzato,72a,72b F. Ceradini,134a,134bA. S. Cerqueira,23aA. Cerri,29L. Cerrito,75F. Cerutti,47S. A. Cetin,18bF. Cevenini,102a,102b A. Chafaq,135aD. Chakraborty,106K. Chan,2B. Chapleau,85J. D. Chapman,27J. W. Chapman,87E. Chareyre,78
D. G. Charlton,17V. Chavda,82S. Cheatham,71S. Chekanov,5S. V. Chekulaev,159aG. A. Chelkov,65 M. A. Chelstowska,104C. Chen,64H. Chen,24L. Chen,2S. Chen,32cT. Chen,32cX. Chen,172S. Cheng,32a A. Cheplakov,65V. F. Chepurnov,65R. Cherkaoui El Moursli,135eV. Chernyatin,24E. Cheu,6S. L. Cheung,158
L. Chevalier,136G. Chiefari,102a,102bL. Chikovani,51J. T. Childers,58aA. Chilingarov,71G. Chiodini,72a M. V. Chizhov,65G. Choudalakis,30S. Chouridou,137I. A. Christidi,77A. Christov,48D. Chromek-Burckhart,29 M. L. Chu,151J. Chudoba,125G. Ciapetti,132a,132bK. Ciba,37A. K. Ciftci,3aR. Ciftci,3aD. Cinca,33V. Cindro,74
M. D. Ciobotaru,163C. Ciocca,19a,19bA. Ciocio,14M. Cirilli,87M. Ciubancan,25aA. Clark,49P. J. Clark,45 W. Cleland,123J. C. Clemens,83B. Clement,55C. Clement,146a,146bR. W. Clifft,129Y. Coadou,83M. Cobal,164a,164c
A. Coccaro,50a,50bJ. Cochran,64P. Coe,118J. G. Cogan,143J. Coggeshall,165E. Cogneras,177C. D. Cojocaru,28 J. Colas,4A. P. Colijn,105C. Collard,115N. J. Collins,17C. Collins-Tooth,53J. Collot,55G. Colon,84G. Comune,88
P. Conde Muin˜o,124aE. Coniavitis,118M. C. Conidi,11M. Consonni,104S. Constantinescu,25aC. Conta,119a,119b F. Conventi,102a,iJ. Cook,29M. Cooke,14B. D. Cooper,77A. M. Cooper-Sarkar,118N. J. Cooper-Smith,76K. Copic,34
T. Cornelissen,50a,50bM. Corradi,19aF. Corriveau,85,jA. Cortes-Gonzalez,165G. Cortiana,99G. Costa,89a M. J. Costa,167D. Costanzo,139T. Costin,30D. Coˆte´,29R. Coura Torres,23aL. Courneyea,169G. Cowan,76 C. Cowden,27B. E. Cox,82K. Cranmer,108F. Crescioli,122a,122bM. Cristinziani,20G. Crosetti,36a,36bR. Crupi,72a,72b
S. Cre´pe´-Renaudin,55C.-M. Cuciuc,25aC. Cuenca Almenar,175T. Cuhadar Donszelmann,139S. Cuneo,50a,50b M. Curatolo,47C. J. Curtis,17P. Cwetanski,61H. Czirr,141Z. Czyczula,117S. D’Auria,53M. D’Onofrio,73 A. D’Orazio,132a,132bA. Da Rocha Gesualdi Mello,23aP. V. M. Da Silva,23aC. Da Via,82W. Dabrowski,37 A. Dahlhoff,48T. Dai,87C. Dallapiccola,84M. Dam,35M. Dameri,50a,50bD. S. Damiani,137H. O. Danielsson,29 R. Dankers,105D. Dannheim,99V. Dao,49G. Darbo,50aG. L. Darlea,25bC. Daum,105J. P. Dauvergne,29W. Davey,86
T. Davidek,126N. Davidson,86R. Davidson,71M. Davies,93A. R. Davison,77E. Dawe,142I. Dawson,139 J. W. Dawson,5,aR. K. Daya,39K. De,7R. de Asmundis,102aS. De Castro,19a,19bP. E. De Castro Faria Salgado,24 S. De Cecco,78J. de Graat,98N. De Groot,104P. de Jong,105C. De La Taille,115H. De la Torre,80B. De Lotto,164a,164c
L. De Mora,71L. De Nooij,105M. De Oliveira Branco,29D. De Pedis,132aP. de Saintignon,55A. De Salvo,132a U. De Sanctis,164a,164cA. De Santo,149J. B. De Vivie De Regie,115S. Dean,77D. V. Dedovich,65J. Degenhardt,120
M. Dehchar,118M. Deile,98C. Del Papa,164a,164cJ. Del Peso,80T. Del Prete,122a,122bA. Dell’Acqua,29 L. Dell’Asta,89a,89bM. Della Pietra,102a,iD. della Volpe,102a,102bM. Delmastro,29P. Delpierre,83N. Delruelle,29
P. A. Delsart,55C. Deluca,148S. Demers,175M. Demichev,65B. Demirkoz,11,kJ. Deng,163S. P. Denisov,128 D. Derendarz,38J. E. Derkaoui,135dF. Derue,78P. Dervan,73K. Desch,20E. Devetak,148P. O. Deviveiros,158
A. Dewhurst,129B. DeWilde,148S. Dhaliwal,158R. Dhullipudi,24,lA. Di Ciaccio,133a,133bL. Di Ciaccio,4 A. Di Girolamo,29B. Di Girolamo,29S. Di Luise,134a,134bA. Di Mattia,88B. Di Micco,29R. Di Nardo,133a,133b
A. Di Simone,133a,133bR. Di Sipio,19a,19bM. A. Diaz,31aF. Diblen,18cE. B. Diehl,87H. Dietl,99J. Dietrich,48 T. A. Dietzsch,58aS. Diglio,115K. Dindar Yagci,39J. Dingfelder,20C. Dionisi,132a,132bP. Dita,25aS. Dita,25a F. Dittus,29F. Djama,83R. Djilkibaev,108T. Djobava,51M. A. B. do Vale,23aA. Do Valle Wemans,124aT. K. O. Doan,4 M. Dobbs,85R. Dobinson,29,aD. Dobos,42E. Dobson,29M. Dobson,163J. Dodd,34O. B. Dogan,18a,aC. Doglioni,118
T. Doherty,53Y. Doi,66,aJ. Dolejsi,126I. Dolenc,74Z. Dolezal,126B. A. Dolgoshein,96,aT. Dohmae,155 M. Donadelli,23bM. Donega,120J. Donini,55J. Dopke,29A. Doria,102aA. Dos Anjos,172M. Dosil,11A. Dotti,122a,122b
M. T. Dova,70J. D. Dowell,17A. D. Doxiadis,105A. T. Doyle,53Z. Drasal,126J. Drees,174N. Dressnandt,120 H. Drevermann,29C. Driouichi,35M. Dris,9J. G. Drohan,77J. Dubbert,99T. Dubbs,137S. Dube,14E. Duchovni,171
G. Duckeck,98A. Dudarev,29F. Dudziak,64M. Du¨hrssen,29I. P. Duerdoth,82L. Duflot,115M-A. Dufour,85 M. Dunford,29H. Duran Yildiz,3bR. Duxfield,139M. Dwuznik,37F. Dydak,29D. Dzahini,55M. Du¨ren,52 W. L. Ebenstein,44J. Ebke,98S. Eckert,48S. Eckweiler,81K. Edmonds,81C. A. Edwards,76W. Ehrenfeld,41 T. Ehrich,99T. Eifert,29G. Eigen,13K. Einsweiler,14E. Eisenhandler,75T. Ekelof,166M. El Kacimi,135cM. Ellert,166
S. Elles,4F. Ellinghaus,81K. Ellis,75N. Ellis,29J. Elmsheuser,98M. Elsing,29R. Ely,14D. Emeliyanov,129 R. Engelmann,148A. Engl,98B. Epp,62A. Eppig,87J. Erdmann,54A. Ereditato,16D. Eriksson,146aJ. Ernst,1 M. Ernst,24J. Ernwein,136D. Errede,165S. Errede,165E. Ertel,81M. Escalier,115C. Escobar,167X. Espinal Curull,11 B. Esposito,47F. Etienne,83A. I. Etienvre,136E. Etzion,153D. Evangelakou,54H. Evans,61L. Fabbri,19a,19bC. Fabre,29
R. M. Fakhrutdinov,128S. Falciano,132aA. C. Falou,115Y. Fang,172M. Fanti,89a,89bA. Farbin,7A. Farilla,134a J. Farley,148T. Farooque,158S. M. Farrington,118P. Farthouat,29D. Fasching,172P. Fassnacht,29D. Fassouliotis,8 B. Fatholahzadeh,158A. Favareto,89a,89bL. Fayard,115S. Fazio,36a,36bR. Febbraro,33P. Federic,144aO. L. Fedin,121
I. Fedorko,29W. Fedorko,88M. Fehling-Kaschek,48L. Feligioni,83D. Fellmann,5C. U. Felzmann,86C. Feng,32d E. J. Feng,30A. B. Fenyuk,128J. Ferencei,144bJ. Ferland,93W. Fernando,109S. Ferrag,53J. Ferrando,53V. Ferrara,41
A. Ferrari,166P. Ferrari,105R. Ferrari,119aA. Ferrer,167M. L. Ferrer,47D. Ferrere,49C. Ferretti,87
A. Ferretto Parodi,50a,50bM. Fiascaris,30F. Fiedler,81A. Filipcˇicˇ,74A. Filippas,9F. Filthaut,104M. Fincke-Keeler,169 M. C. N. Fiolhais,124a,hL. Fiorini,11A. Firan,39G. Fischer,41P. Fischer,20M. J. Fisher,109S. M. Fisher,129
J. Flammer,29M. Flechl,48I. Fleck,141J. Fleckner,81P. Fleischmann,173S. Fleischmann,174T. Flick,174 L. R. Flores Castillo,172M. J. Flowerdew,99F. Fo¨hlisch,58aM. Fokitis,9T. Fonseca Martin,16D. A. Forbush,138 A. Formica,136A. Forti,82D. Fortin,159aJ. M. Foster,82D. Fournier,115A. Foussat,29A. J. Fowler,44K. Fowler,137
H. Fox,71P. Francavilla,122a,122bS. Franchino,119a,119bD. Francis,29T. Frank,171M. Franklin,57S. Franz,29 M. Fraternali,119a,119bS. Fratina,120S. T. French,27R. Froeschl,29D. Froidevaux,29J. A. Frost,27C. Fukunaga,156 E. Fullana Torregrosa,29J. Fuster,167C. Gabaldon,29O. Gabizon,171T. Gadfort,24S. Gadomski,49G. Gagliardi,50a,50b
P. Gagnon,61C. Galea,98E. J. Gallas,118M. V. Gallas,29V. Gallo,16B. J. Gallop,129P. Gallus,125E. Galyaev,40 K. K. Gan,109Y. S. Gao,143,fV. A. Gapienko,128A. Gaponenko,14F. Garberson,175M. Garcia-Sciveres,14 C. Garcı´a,167J. E. Garcı´a Navarro,49R. W. Gardner,30N. Garelli,29H. Garitaonandia,105V. Garonne,29J. Garvey,17
C. Gatti,47G. Gaudio,119aO. Gaumer,49B. Gaur,141L. Gauthier,136I. L. Gavrilenko,94C. Gay,168G. Gaycken,20 J-C. Gayde,29E. N. Gazis,9P. Ge,32dC. N. P. Gee,129D. A. A. Geerts,105Ch. Geich-Gimbel,20K. Gellerstedt,146a,146b
C. Gemme,50aA. Gemmell,53M. H. Genest,98S. Gentile,132a,132bM. George,54S. George,76P. Gerlach,174 A. Gershon,153C. Geweniger,58aH. Ghazlane,135bP. Ghez,4N. Ghodbane,33B. Giacobbe,19aS. Giagu,132a,132b
V. Giakoumopoulou,8V. Giangiobbe,122a,122bF. Gianotti,29B. Gibbard,24A. Gibson,158S. M. Gibson,29 G. F. Gieraltowski,5L. M. Gilbert,118M. Gilchriese,14V. Gilewsky,91D. Gillberg,28A. R. Gillman,129 D. M. Gingrich,2,eJ. Ginzburg,153N. Giokaris,8R. Giordano,102a,102bF. M. Giorgi,15P. Giovannini,99P. F. Giraud,136
D. Giugni,89aM. Giunta,132a,132bP. Giusti,19aB. K. Gjelsten,117L. K. Gladilin,97C. Glasman,80J. Glatzer,48 A. Glazov,41K. W. Glitza,174G. L. Glonti,65J. Godfrey,142J. Godlewski,29M. Goebel,41T. Go¨pfert,43 C. Goeringer,81C. Go¨ssling,42T. Go¨ttfert,99S. Goldfarb,87D. Goldin,39T. Golling,175S. N. Golovnia,128 A. Gomes,124a,cL. S. Gomez Fajardo,41R. Gonc¸alo,76J. Goncalves Pinto Firmino Da Costa,41L. Gonella,20
A. Gonidec,29S. Gonzalez,172S. Gonza´lez de la Hoz,167M. L. Gonzalez Silva,26S. Gonzalez-Sevilla,49 J. J. Goodson,148L. Goossens,29P. A. Gorbounov,95H. A. Gordon,24I. Gorelov,103G. Gorfine,174B. Gorini,29 E. Gorini,72a,72bA. Gorisˇek,74E. Gornicki,38S. A. Gorokhov,128V. N. Goryachev,128B. Gosdzik,41M. Gosselink,105
M. I. Gostkin,65M. Gouane`re,4I. Gough Eschrich,163M. Gouighri,135aD. Goujdami,135cM. P. Goulette,49 A. G. Goussiou,138C. Goy,4I. Grabowska-Bold,163,gV. Grabski,176P. Grafstro¨m,29C. Grah,174K-J. Grahn,41
F. Grancagnolo,72aS. Grancagnolo,15V. Grassi,148V. Gratchev,121N. Grau,34H. M. Gray,29J. A. Gray,148 E. Graziani,134aO. G. Grebenyuk,121D. Greenfield,129T. Greenshaw,73Z. D. Greenwood,24,lI. M. Gregor,41
P. Grenier,143E. Griesmayer,46J. Griffiths,138N. Grigalashvili,65A. A. Grillo,137S. Grinstein,11Ph. Gris,33 Y. V. Grishkevich,97J.-F. Grivaz,115J. Grognuz,29M. Groh,99E. Gross,171J. Grosse-Knetter,54J. Groth-Jensen,79 M. Gruwe,29K. Grybel,141V. J. Guarino,5D. Guest,175C. Guicheney,33A. Guida,72a,72bT. Guillemin,4S. Guindon,54
H. Guler,85,mJ. Gunther,125B. Guo,158J. Guo,34A. Gupta,30Y. Gusakov,65V. N. Gushchin,128A. Gutierrez,93 P. Gutierrez,111N. Guttman,153O. Gutzwiller,172C. Guyot,136C. Gwenlan,118C. B. Gwilliam,73A. Haas,143 S. Haas,29C. Haber,14R. Hackenburg,24H. K. Hadavand,39D. R. Hadley,17P. Haefner,99F. Hahn,29S. Haider,29 Z. Hajduk,38H. Hakobyan,176J. Haller,54K. Hamacher,174P. Hamal,113A. Hamilton,49S. Hamilton,161H. Han,32a L. Han,32bK. Hanagaki,116M. Hance,120C. Handel,81P. Hanke,58aC. J. Hansen,166J. R. Hansen,35J. B. Hansen,35
J. D. Hansen,35P. H. Hansen,35P. Hansson,143K. Hara,160G. A. Hare,137T. Harenberg,174S. Harkusha,90 D. Harper,87R. D. Harrington,21O. M. Harris,138K. Harrison,17J. Hartert,48F. Hartjes,105T. Haruyama,66 A. Harvey,56S. Hasegawa,101Y. Hasegawa,140S. Hassani,136M. Hatch,29D. Hauff,99S. Haug,16M. Hauschild,29 R. Hauser,88M. Havranek,20B. M. Hawes,118C. M. Hawkes,17R. J. Hawkings,29D. Hawkins,163T. Hayakawa,67 D Hayden,76H. S. Hayward,73S. J. Haywood,129E. Hazen,21M. He,32dS. J. Head,17V. Hedberg,79L. Heelan,7
S. Heim,88B. Heinemann,14S. Heisterkamp,35L. Helary,4M. Heldmann,48M. Heller,115S. Hellman,146a,146b C. Helsens,11R. C. W. Henderson,71M. Henke,58aA. Henrichs,54A. M. Henriques Correia,29S. Henrot-Versille,115
F. Henry-Couannier,83C. Hensel,54T. Henß,174C. M. Hernandez,7Y. Herna´ndez Jime´nez,167R. Herrberg,15 A. D. Hershenhorn,152G. Herten,48R. Hertenberger,98L. Hervas,29N. P. Hessey,105A. Hidvegi,146a E. Higo´n-Rodriguez,167D. Hill,5,aJ. C. Hill,27N. Hill,5K. H. Hiller,41S. Hillert,20S. J. Hillier,17I. Hinchliffe,14
E. Hines,120M. Hirose,116F. Hirsch,42D. Hirschbuehl,174J. Hobbs,148N. Hod,153M. C. Hodgkinson,139 P. Hodgson,139A. Hoecker,29M. R. Hoeferkamp,103J. Hoffman,39D. Hoffmann,83M. Hohlfeld,81M. Holder,141
A. Holmes,118S. O. Holmgren,146aT. Holy,127J. L. Holzbauer,88Y. Homma,67T. M. Hong,120
L. Hooft van Huysduynen,108T. Horazdovsky,127C. Horn,143S. Horner,48K. Horton,118J-Y. Hostachy,55S. Hou,151 M. A. Houlden,73A. Hoummada,135aJ. Howarth,82D. F. Howell,118I. Hristova,41J. Hrivnac,115I. Hruska,125 T. Hryn’ova,4P. J. Hsu,175S.-C. Hsu,14G. S. Huang,111Z. Hubacek,127F. Hubaut,83F. Huegging,20T. B. Huffman,118
E. W. Hughes,34G. Hughes,71R. E. Hughes-Jones,82M. Huhtinen,29P. Hurst,57M. Hurwitz,14U. Husemann,41 N. Huseynov,65,nJ. Huston,88J. Huth,57G. Iacobucci,102aG. Iakovidis,9M. Ibbotson,82I. Ibragimov,141 R. Ichimiya,67L. Iconomidou-Fayard,115J. Idarraga,115M. Idzik,37P. Iengo,102a,102bO. Igonkina,105Y. Ikegami,66
M. Ikeno,66Y. Ilchenko,39D. Iliadis,154D. Imbault,78M. Imhaeuser,174M. Imori,155T. Ince,20J. Inigo-Golfin,29 P. Ioannou,8M. Iodice,134aG. Ionescu,4A. Irles Quiles,167K. Ishii,66A. Ishikawa,67M. Ishino,66
R. Ishmukhametov,39C. Issever,118S. Istin,18aY. Itoh,101A. V. Ivashin,128W. Iwanski,38H. Iwasaki,66J. M. Izen,40 V. Izzo,102aB. Jackson,120J. N. Jackson,73P. Jackson,143M. R. Jaekel,29V. Jain,61K. Jakobs,48S. Jakobsen,35 J. Jakubek,127D. K. Jana,111E. Jankowski,158E. Jansen,77A. Jantsch,99M. Janus,20G. Jarlskog,79L. Jeanty,57 K. Jelen,37I. Jen-La Plante,30P. Jenni,29A. Jeremie,4P. Jezˇ,35S. Je´ze´quel,4M. K. Jha,19aH. Ji,172W. Ji,81J. Jia,148
Y. Jiang,32bM. Jimenez Belenguer,41G. Jin,32bS. Jin,32aO. Jinnouchi,157M. D. Joergensen,35D. Joffe,39 L. G. Johansen,13M. Johansen,146a,146bK. E. Johansson,146aP. Johansson,139S. Johnert,41K. A. Johns,6 K. Jon-And,146a,146bG. Jones,82R. W. L. Jones,71T. W. Jones,77T. J. Jones,73O. Jonsson,29C. Joram,29 P. M. Jorge,124a,cJ. Joseph,14X. Ju,130V. Juranek,125P. Jussel,62V. V. Kabachenko,128S. Kabana,16M. Kaci,167 A. Kaczmarska,38P. Kadlecik,35M. Kado,115H. Kagan,109M. Kagan,57S. Kaiser,99E. Kajomovitz,152S. Kalinin,174
L. V. Kalinovskaya,65S. Kama,39N. Kanaya,155M. Kaneda,155T. Kanno,157V. A. Kantserov,96J. Kanzaki,66 B. Kaplan,175A. Kapliy,30J. Kaplon,29D. Kar,43M. Karagoz,118M. Karnevskiy,41K. Karr,5V. Kartvelishvili,71
A. N. Karyukhin,128L. Kashif,172A. Kasmi,39R. D. Kass,109A. Kastanas,13M. Kataoka,4Y. Kataoka,155 E. Katsoufis,9J. Katzy,41V. Kaushik,6K. Kawagoe,67T. Kawamoto,155G. Kawamura,81M. S. Kayl,105
V. A. Kazanin,107M. Y. Kazarinov,65S. I. Kazi,86J. R. Keates,82R. Keeler,169R. Kehoe,39M. Keil,54 G. D. Kekelidze,65M. Kelly,82J. Kennedy,98C. J. Kenney,143M. Kenyon,53O. Kepka,125N. Kerschen,29 B. P. Kersˇevan,74S. Kersten,174K. Kessoku,155C. Ketterer,48M. Khakzad,28F. Khalil-zada,10H. Khandanyan,165
A. Khanov,112D. Kharchenko,65A. G. Kholodenko,128A. Khomich,58aT. J. Khoo,27G. Khoriauli,20 A. Khoroshilov,174N. Khovanskiy,65V. Khovanskiy,95E. Khramov,65J. Khubua,51G. Kilvington,76H. Kim,7
M. S. Kim,2P. C. Kim,143S. H. Kim,160N. Kimura,170O. Kind,15B. T. King,73M. King,67R. S. B. King,118 J. Kirk,129G. P. Kirsch,118L. E. Kirsch,22A. E. Kiryunin,99D. Kisielewska,37T. Kittelmann,123A. M. Kiver,128
