• Aucun résultat trouvé

Search for Gluinos in Events with Two Same-Sign Leptons, Jets, and Missing Transverse Momentum with the ATLAS Detector in <em>pp</em> Collisions at √s=7  TeV

N/A
N/A
Protected

Academic year: 2022

Partager "Search for Gluinos in Events with Two Same-Sign Leptons, Jets, and Missing Transverse Momentum with the ATLAS Detector in <em>pp</em> Collisions at √s=7  TeV"

Copied!
20
0
0

Texte intégral

(1)

Article

Reference

Search for Gluinos in Events with Two Same-Sign Leptons, Jets, and Missing Transverse Momentum with the ATLAS Detector in pp

Collisions at √s=7  TeV

ATLAS Collaboration

ABDELALIM ALY, Ahmed Aly (Collab.), et al .

Abstract

A search is presented for gluinos decaying via the supersymmetric partner of the top quark using events with two same-sign leptons, jets, and missing transverse momentum. The analysis is performed with 2.05  fb−1 of integrated luminosity from pp collisions at s√=7  TeV collected by the ATLAS detector at the LHC. No excess beyond the standard model expectation is observed, and exclusion limits are derived for simplified models where the gluino decays via the supersymmetric partner of the top quark and in the minimal supergravity and constrained minimal supersymmetric standard model framework. In those scenarios, gluino masses below 550 GeV are excluded at 95% C.L. within the parameter space considered, significantly extending the coverage with respect to existing limits. Depending on the model parameters, gluino masses up to 750 GeV can also be excluded at 95% C.L.

ATLAS Collaboration, ABDELALIM ALY, Ahmed Aly (Collab.), et al . Search for Gluinos in Events with Two Same-Sign Leptons, Jets, and Missing Transverse Momentum with the ATLAS Detector in pp Collisions at √s=7  TeV. Physical Review Letters , 2012, vol. 108, no. 04, p.

041802

DOI : 10.1103/PhysRevLett.108.241802

Available at:

http://archive-ouverte.unige.ch/unige:39781

Disclaimer: layout of this document may differ from the published version.

(2)

Search for Gluinos in Events with Two Same-Sign Leptons, Jets, and Missing Transverse Momentum with the ATLAS Detector in pp Collisions at ffiffiffi

p s

¼ 7 TeV

G. Aadet al.* (ATLAS Collaboration)

(Received 26 March 2012; published 15 June 2012)

A search is presented for gluinos decaying via the supersymmetric partner of the top quark using events with two same-sign leptons, jets, and missing transverse momentum. The analysis is performed with 2:05 fb1of integrated luminosity fromppcollisions atpffiffiffis

¼7 TeVcollected by the ATLAS detector at the LHC. No excess beyond the standard model expectation is observed, and exclusion limits are derived for simplified models where the gluino decays via the supersymmetric partner of the top quark and in the minimal supergravity and constrained minimal supersymmetric standard model framework. In those scenarios, gluino masses below 550 GeV are excluded at 95% C.L. within the parameter space considered, significantly extending the coverage with respect to existing limits. Depending on the model parameters, gluino masses up to 750 GeV can also be excluded at 95% C.L.

DOI:10.1103/PhysRevLett.108.241802 PACS numbers: 12.60.Jv, 13.85.Rm, 14.80.Ly

Supersymmetry (SUSY) [1–7] is a theory beyond the standard model (SM) which predicts new bosonic partners for the existing fermions and fermionic partners for the known bosons. In the framework of a generic R-parity conserving minimal supersymmetric extension of the SM, SUSY particles are produced in pairs [8,9] and the lightest supersymmetric particle is stable, providing a pos- sible candidate for dark matter.

In SUSY models, the gluino is a strongly interacting Majorana fermion. Pair-produced gluinos therefore have an equal probability to produce a pair of leptons that have the same charge [same-sign (SS)] and the opposite charge from their decays. The supersymmetric partner of the top quark (top squark) has two mass eigenstates with~t1 being the lightest. Top quarks and~t1squarks can be produced in the decay of the gluino viag~g~!tt~t1~t1; tt~t1~t1;tt~t1~t1 [10–

14]. The~t1squark can further decay to the lightest chargino (~1) or lightest neutralino (~01) via~t1!b~1 or~t1 !t~01 producing isolated leptons in the semileptonic top-quark decay or in the leptonic~1 decay and enriching the signal events with two or more leptons, jets, and missing trans- verse momentum (EmissT ) from the undetected neutralinos.

This analysis considers events with a pair of isolated SS leptons, multiple high-pTjets, and largeEmissT . The require- ment of SS leptons in the event suppresses the contribution from SM processes and thus enhances the potential signal significance even for final state topologies with relatively soft jet kinematics. This Letter presents the first search for gluino-mediated top squark production using the SS

signature, although other searches with SS leptons have been performed [15–18]. The analysis presented here com- plements the results of the ATLAS search based on a single lepton plus b jets [19], enhancing the sensitivity in the experimentally difficult region near the kinematic limit for the production of two top quarks and a neutralino and for the region with low top squark masses.

ATLAS is a general-purpose detector [20] at the LHC.

This search usesppcollision data recorded from March to August 2011 at a center-of-mass energy of 7 TeV. The data set corresponds to a total integrated luminosity of2:05 0:08 fb1 [21,22] after the application of data quality requirements. Events are selected by using single lepton and dilepton triggers that have constant efficiency as a function of lepton pT above the offline pT cuts used in the analysis.

Jets are reconstructed from three-dimensional calorime- ter energy clusters by using the anti-ktjet algorithm [23,24]

with a radius parameter of 0.4. The measured jet energy is corrected for inhomogeneities in, and for the noncompen- sating nature of, the calorimeter by using pT- and -dependent correction factors [25]. Only jet candidates with pT>20 GeV within jj<2:8 are retained. Events with any jet that fails the jet quality criteria designed to remove noise and noncollision backgrounds [25] are rejected.

Electron candidates are required to havepT>20 GeV, jj<2:47and satisfy the ‘‘tight’’ selection criteria defined in Ref. [26]. They are also required to be isolated: The scalar sum ofpTof tracks within a cone in theplane of radiusR¼0:2around the candidate excluding its own track,pT, must be less than 10% of the electronpT. Muon candidates are required to have pT>20 GeV, jj<2:4 and are identified by matching an extrapolated inner de- tector track and one or more track segments in the muon spectrometer [27]. They must have longitudinal and

*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 attribution to the author(s) and the published article’s title, journal citation, and DOI.

(3)

transverse impact parameters within 1 and 0.2 mm of the primary vertex [28], respectively, andpT<1:8 GeV.

The calculation of EmissT [29] is based on the vectorial sum of thepTof the reconstructed jets (withpT>20 GeV andjj<4:5), leptons, and the calorimeter energy clusters not belonging to reconstructed objects.

During part of the data-taking period, a localized elec- tronics failure in the electromagnetic calorimeter created a dead region (’1:40:2). For jets in this re- gion, a correction to their energy is made by using the energy depositions in the neighboring cells and is propa- gated toEmissT . If this correction projected onto the direc- tion of theEmissT is larger than 10 GeV or 10% of theEmissT , the event is discarded [30]. Events with reconstructed electrons in the calorimeter dead region are also rejected.

Events in which the two highest-pT leptons (‘¼e; ) have the same charge and with at least four jets withpT>

50 GeV are selected. In addition, two signal regions are considered: SR1, which requires EmissT >150 GeV, and SR2, which in addition requires mT>100 GeV, where mT is the transverse mass of theEmissT and the highest-pT lepton defined asm2T¼2pTEmissT f1cos½ð‘; EmissT Þg.

This final mT cut helps reduce the tt background. The signal regions are optimized based on several models where SS dileptons are produced in gluino decays. In signals such as the MSUGRA-CMSSM (minimal super- gravity or constrained minimal supersymmetric standard model) [31,32], the directions of the lepton and ~01 are strongly correlated, as they originate from the decay of a common parent particle (usually~1 or the next-to-lightest neutralino~02). This leads to a softermTspectrum than that found in gluino-mediated top squark signal models, where the lepton and the~01 originate from different parent par- ticles and are thus uncorrelated.

Simulated Monte Carlo (MC) event samples are used to aid in the description of the background and to model the SUSY signal. Top-quark pair and single-top production are simulated withMC@NLO[33], fixing the top-quark mass at 172.5 GeV and using the next-to-leading-order (NLO) parton density function (PDF) set CTEQ6.6 [34]. Samples ofWþjets andZþjets with both light- and heavy-flavor jets are generated withALPGEN[35] and PDF setCTEQ6L1

[36]. The fragmentation and hadronization for theALPGEN

and MC@NLO samples are performed with HERWIG [37], usingJIMMY[38] for the underlying event. Samples ofttZ, ttW, and ttWW(referred to asttþX) are generated with

MADGRAPH [39] interfaced toPYTHIA [40]. The total LO cross section for these samples is 0.39 pb and is normalized to NLO by using aK factor of 1.3 [41]. Diboson samples are generated with HERWIG for WW, WZ, and ZZ processes and with MADGRAPH for WWqq processes.

The total NLO cross section for the diboson background is 71 pb [42,43]. SUSY signal processes are simulated for various models by usingHERWIG++[37] v2.4.2. The SUSY sample yields are normalized to the results of NLO

calculations, as obtained by using PROSPINO [44] v2.1.

The CTEQ6.6M[45] parameterization of the PDFs is used.

The tunings of the MC parameters of Ref. [46] are used in the production of the MC samples, which are processed through a detector simulation [47] based onGEANT4[48].

Effects of multiple proton-proton interactions per bunch crossing are included in the simulation.

The SM backgrounds are evaluated by using a combina- tion of MC simulation and data-driven techniques. SM processes that generate events containing jets which are misidentified as leptons or where a lepton from a b- or c-hadron decay is selected are collectively referred to as

‘‘fake-lepton’’ background. It generally consists of semi- leptonic tt, single-top, Wþjets, and strong light- and heavy-flavor jet production. The contribution from the fake-lepton background is estimated from data with a method similar to that described in Refs. [49,50] by loosen- ing the lepton identification and isolation criteria. For elec- trons the ‘‘medium’’ criteria are used instead of the ‘‘tight’’

criteria [26], and for both electrons and muons the isolation criterion is relaxed. The method counts the number of observed events containing loose-loose, loose-tight, tight- loose, and tight-tight lepton pairs. The probability of loose real leptons passing the tight selection criteria is obtained by using a Z!‘þ sample. The probability of loose fake leptons to pass the tight selection criteria is determined as a function of the leptonpTby using multijet control samples obtained by requiring two SS leptons and low EmissT . By using these probabilities, relations are obtained for the observed event counts in the signal regions as functions of the numbers of events containing fake-fake, fake-real, real- fake, and real-real lepton pairs. These can be solved simul- taneously to estimate the number of background events [49,50]. The results of the estimations have been validated with data in control regions obtained by reversing theEmissT or jet multiplicity cuts used in the signal regions.

Background events from charge misidentification (dominated by electrons which have undergone hard bremsstrahlung with subsequent photon conversion) are estimated by using a partially data-driven technique [16].

The probability of charge misidentification is calculated from MC simulations and corrected by consideration of the number of events in the data with SS electron pairs and invariant mass within 15 GeV of the Z-boson mass. This probability is applied to tt MC events producing e pairs to evaluate the number of SS events from incorrect charge assignment in each signal region. The probability of misidentifying the charge of a muon and the contributions in the signal regions from charge misidentification of Z=þjets and other SM backgrounds are negligible.

Contributions from other SM background sources (di- boson andttþX) are evaluated by using the MC samples described above. In these processes, real SS lepton pairs are produced, and their contribution to the signal regions can be described with MC simulations. In particular, the PRL108,241802 (2012) P H Y S I C A L R E V I E W L E T T E R S 15 JUNE 2012

(4)

contribution from the experimentally unmeasured ttþX processes has been studied by using several MC genera- tors. The background from cosmic rays is evaluated with data by using the method in Ref. [16], and its contribution is negligible in the signal regions.

Systematic uncertainties are estimated in the signal re- gions for the background and the SUSY signal processes.

The primary sources of systematic uncertainties in the background are the jet energy scale calibration (35%), the jet energy resolution (10%), uncertainties on lepton and jet reconstruction and identification (5%), and MC modeling and theoretical cross section uncertainties (40%–70%). In particular, the theoretical uncertainties on the cross section of the ttþX processes are found to be between 35% and 55% by varying factorization and renor- malization scales and 25% due to PDF uncertainties. In addition, a 50% uncertainty is assigned on the K factor used to obtain the NLO cross section [41]. In the fake- lepton background estimation, systematic uncertainties are assigned to the probabilities for loose fake leptons to pass the tight selection. This accounts for potentially different compositions of the signal and control regions. These uncertainties vary in the 10%–80% range depending on the leptonpTand are evaluated by using data samples with jets of different energies. The absolute uncertainty for each background source is given in TableI. Systematic uncer- tainties on the signal expectations are evaluated through variations of the factorization and renormalization scales between half and twice their default values and by includ- ing the uncertainty on s and on the PDF provided by

CTEQ6. Uncertainties are calculated for individual SUSY processes. The total uncertainty varies in the 20%–40%

range for the considered MC signals. Any correlations of the systematic uncertainties in signals and background are taken into account.

Figure 1 shows the distribution of the number of jets with pT>50 GeV for events with 2 SS leptons and the

EmissT distribution for events with 2 SS leptons and at least four jets withpT>50 GeV. The contributions from all the SM backgrounds are shown together with their total sta- tistical and systematic uncertainties. For illustration, the distribution for a signal obtained with the decayg~!tt~01 in g~g~ pair-produced events with mg~¼650 GeV and m~0

1¼150 GeVis also shown. The data are in agreement with the SM background expectation, and once four jets of pT>50 GeV are required no event is observed with EmissT >150 GeV.

Table I shows the number of expected events in the signal regions for each background source together with the observed number of events. The expectation from the SM is estimated to be less than one event for each signal region with no events observed in the data. Limits at 95%

confidence level (C.L.) are derived on the visible cross sectionvis¼A, whereis the total production cross section for any new signal producing SS dileptons,A is the acceptance defined by the fraction of events passing

TABLE I. Number of expected SM background events to- gether with the number of observed events in the data. The errors are a combination of the uncertainties due to MC statistics, statistical uncertainties in control regions, and systematic un- certainties. Observed and expected upper limits at 95% confi- dence level onvis¼A, together with the1errors on the expected limits, are also shown.

SR1 SR2

ttþX 0:370:26 0:210:16

Diboson 0:050:02 0:020:01

Fake-lepton 0:340:20 <0:17 Charge mis-ID 0:080:01 0:0390:007

Total SM 0:840:33 0:270:24

Observed 0 0

obsvis [fb] <1:6 <1:5 expvis [fb] <1:7þ00::51 <1:6þ00::21

>50 GeV) (pT

Njet

0 1 2 3 4 5 6

Events

10-1

1 10 102

103

104

ATLAS Data 2011 SM Background

*+jets γ Z/

Diboson Signal

t X+ t Fake-lepton = 7 TeV

s

-1, L dt = 2.05 fb

>5

[GeV]

miss

ET

0 50 100 150 200 250

Events / 50 GeV

10-1

1 10 ATLAS

Data 2011 SM Background

*+jets γ Z/

Diboson Signal

t X+ t Fake-lepton = 7 TeV

s

-1, L dt = 2.05 fb

>250

FIG. 1 (color online). Number of jets with pT>50 GeV for events with 2 SS leptons (top) and the EmissT distribution for events with 2 SS leptons and at least 4 jets with pT>50 GeV (bottom). Errors on data points are statistical, while the error band on the SM background represents the total uncertainty. The component labeled ‘‘Fake-lepton’’ is evaluated by using data as described in the text. The component labeled ‘‘Z=þjets’’ is estimated from MC simulations. No estimation of the charge mis-ID is included in the distribution. The component labeled

‘‘Signal’’ corresponds to a signal obtained with the decay g~! tt~01 via off mass-shell~t(m~t¼1:2 TeV) in g~g~pair-produced events withm~g¼650 GeVandm~0

1¼150 GeV.

(5)

geometric and kinematic cuts at particle level, andis the detector reconstruction, identification, and trigger effi- ciency. For the signal shown in Fig. 1, the acceptance and efficiency are 1.5% and 55%, respectively. Limits are set by using theCLsprescription, as described in Ref. [51].

The results are given in TableI.

The results obtained in SR2 are interpreted in a simpli- fied model where gluinos are produced only in pairs, the top squark (m~t¼1:2 TeV) is heavier than the gluino, and only the gluino three-body decayg~!tt~01via an off-shell top squark is allowed. Figure 2 shows the limit in the gluino-neutralino mass plane. For a gluino mass of 650 GeV, neutralino masses below 215 GeV are excluded at 95% C.L. For a neutralino mass of 100 GeV, gluino masses below 715 GeV are similarly excluded. The 1 uncertainty limit on the expected limit lies outside the range of the figure as a consequence of the low number of expected signal events and a total signal uncertainty that reaches close to 50%. The results can be generalized in terms of production cross section upper limits at 95% C.L.

forg~g~pair production processes with the produced parti- cles decaying intott~01final states, as also shown in Fig.2.

The results in SR2 are also interpreted by considering gluino pair production followed by theg~!~t1tdecay. Only top squark decays via ~t1 !b~1 are considered with m~

1 2m~0

1 andm~0

1 ¼60 GeV. Figure3shows the ex- clusion limit as a function of gluino and top squark masses, where gluino masses below 660 GeV are excluded at 95% C.L. for top squark masses below 460 GeV.

The results in SR1 are interpreted within the MSUGRA- CMSSM framework in terms of limits on the universal scalar and gaugino mass parametersm0andm1=2, as shown in Fig. 4. These are presented for fixed values of the universal trilinear coupling parameter A0 ¼0, ratio of

the vacuum expectation values of the two Higgs doublets tan ¼10, and Higgs mixing parameter >0. In this model, values of m1=2 below 300 GeV are excluded at 95% C.L. form0 values below 750 GeV, andm1=2 values below 180 GeV are excluded over the entire m0 region considered. These are equivalent to the exclusion of gluino masses below550 GeVindependent of the squark mass (and gluino masses below 750 GeV for squark masses below 1 TeV).

In summary, a search for SUSY with two SS leptons, jets, and missing transverse momentum has been per- formed by using2:05 fb1of ATLAS data. With no events observed in the signal regions, limits have been derived in the context of models where top quarks are produced in gluino decays and MSUGRA-CMSSM scenarios. In all these signal models, gluino masses below550 GeV are

0.74 0.39 0.32 0.31 0.12 0.17 0.10 0.13 0.53 0.30 0.26 0.18 0.14 0.14 0.11 0.58 0.28 0.16 0.22 0.13 0.10 0.40 0.20 0.23 0.17 0.12 0.36 0.32 0.22 0.17 0.40 0.21 0.17 0.44 0.30

[GeV]

~g

m

400 450 500 550 600 650 700 750 800 [GeV]0 1χ∼m

50 100 150 200 250 300 350

10-1

1

forbidden

0

χ1

tt g

~

0

χ∼1

t

t

~g production,

~g

~ L dt = 2.05 fb-1, s=7 TeV

95% C.L. limit Obs. CLs

95% C.L. limit Exp. CLs

σ

±1 Expected limit 1 lepton plus b jets 2.05 fb-1

2-lepton SS, 4 jets

g~

> m

~t

>> m

q1,2

m~

Maximum cross section [pb]

ATLAS

g-

FIG. 2 (color online). Expected and observed 95% C.L. exclu- sion limits in theg~!tt~01(via off mass-shell~t,m~t¼1:2 TeV) simplified model as a function of the gluino and neutralino masses, together with existing limits [19]. The 1limit lies outside the range of the figure. The production cross section upper limits at 95% C.L. are also shown.

[GeV]

~g

m

400 450 500 550 600 650 700 750 800 [GeV] 1t~m

200 250 300 350 400 450 500 550 600 650

95% C.L. limit Obs. CLs

95% C.L. limit Exp. CLs

σ

±1 Expected limit 1 lepton plus b jets 2.05 fb-1

t forbidden t1

~ g

~

±

χ∼1

b+

t1

+t,~ t1

~ g~ production, g~

~ L dt = 2.05 fb-1, s=7 TeV

2-lepton SS, 4 jets = 60 GeV

0 χ∼1

m

0 χ∼1

2 m

± χ∼1

m

~g

>> m

q1,2

m~

ATLAS

g-

FIG. 3 (color online). Expected and observed 95% C.L. exclu- sion limits in theg~!~t1twith~t1!b~1 model as a function of the gluino and top squark masses assuming that m~

1 2m~0 1. The1band lies outside the range of the figure.

(600) g~

(800) g~ (1000) g~ (1000)

q~ (200

0) q ~

(300 0) q ~

[GeV]

m0

500 1000 1500 2000 2500 3000 3500 [GeV]1/2m

150 200 250 300 350 400 450

500 Obs. CLs 95% C.L. limit

95% C.L. limit Exp. CLs

σ

±1 Expected limit

1.34 fb-1 miss Multijet plus ET 0 lepton 1.04 fb-1

1 χ∼± LEP2

<0, 2.1 fb-1 µ β=3, q,tan g ,~ D0~

<0, 2 fb-1 µ β=5, q,tan g ,~ CDF~

Theoretically excluded

>0 µ

= 0, = 10, A0

β

MSUGRA/CMSSM: tanL dt = 2.05 fb-1, s=7 TeV

ATLAS

FIG. 4 (color online). Expected and observed 95% C.L. exclu- sion limits in the MSUGRA-CMSSM (m0, m1=2) plane for tan ¼10, A0¼0, and >0, compared to existing limits [52–56].

PRL108,241802 (2012) P H Y S I C A L R E V I E W L E T T E R S 15 JUNE 2012

(6)

excluded at 95% C.L. within the parameter space consid- ered, and gluino masses up to750 GeVare excluded at 95% C.L., depending on the model parameters. The results of this analysis are complementary to and extend the current exclusion limits on the gluino mass beyond those from other ATLAS searches [19,52].

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 and ERC, European Union; IN2P3-CNRS and 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 America. The crucial computing support from all WLCG partners is acknowl- edged gratefully, in particular, from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, and Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (The Netherlands), PIC (Spain), ASGC (Taiwan), RAL (United Kingdom), and BNL (USA) and in the Tier-2 facilities worldwide.

[1] P. Ramond,Phys. Rev. D3, 2415 (1971).

[2] Y. Golfand and E. Likhtman, JETP Lett.13, 323 (1971).

[3] A. Neveu and J. H. Schwarz,Nucl. Phys.B31, 86 (1971).

[4] A. Neveu and J. H. Schwarz,Phys. Rev. D4, 1109 (1971).

[5] D. Volkov and V. Akulov,Phys. Lett.46B, 109 (1973).

[6] J. Wess and B. Zumino,Phys. Lett.49B, 52 (1974).

[7] J. Wess and B. Zumino,Nucl. Phys.B70, 39 (1974).

[8] P. Fayet,Phys. Lett.69B, 489 (1977).

[9] G. R. Farrar and P. Fayet,Phys. Lett.76B, 575 (1978).

[10] W. Beenakker, R. Hopker, T. Plehn, and P. Zerwas, Z.

Phys. C75, 349 (1997).

[11] J. Hisano, K. Kawagoe, and M. M. Nojiri,Phys. Rev. D68, 035007 (2003).

[12] C. Bala´zs, M. Carena, and C. E. M. Wagner,Phys. Rev. D 70, 015007 (2004).

[13] M. Mu¨hlleitner, A. Djouadi, and Y. Mambrini, Comput.

Phys. Commun.168, 46 (2005).

[14] S. Kraml and A. R. Raklev, Phys. Rev. D 73, 075002 (2006).

[15] ATLAS Collaboration,Eur. Phys. J. C71, 1682 (2011).

[16] ATLAS Collaboration,Phys. Lett. B709, 137 (2012).

[17] ATLAS Collaboration, J. High Energy Phys. 04 (2012) 069.

[18] A. Abulenciaet al.(CDF Collaboration),Phys. Rev. Lett.

98, 221803 (2007).

[19] ATLAS Collaboration,arXiv:1203.6193.

[20] ATLAS Collaboration,JINST3, S08003 (2008).

[21] ATLAS Collaboration,Eur. Phys. J. C71, 1630 (2011).

[22] ATLAS Collaboration, Report No. ATLAS-CONF-2011- 116, 2011.

[23] M. Cacciari, G. P. Salam, and G. Soyez,J. High Energy Phys. 04 (2008) 063.

[24] M. Cacciari and G. Salam,Phys. Lett. B641, 57 (2006).

[25] ATLAS Collaboration,arXiv:1112.6426.

[26] ATLAS Collaboration,Eur. Phys. J. C72, 1909 (2012).

[27] ATLAS Collaboration, Report No. ATLAS-CONF-2011- 063, 2011.

[28] ATLAS Collaboration, Report No. ATLAS-CONF-2010- 069, 2010.

[29] ATLAS Collaboration,Eur. Phys. J. C72, 1844 (2012).

[30] ATLAS Collaboration,Phys. Rev. D85, 012006 (2012).

[31] A. H. Chamseddine, R. L. Arnowitt, and P. Nath, Phys.

Rev. Lett. 49, 970 (1982); R. Barbieri, S. Ferrara, and C. A. Savoy, Phys. Lett.119B, 343 (1982); L. E. Ibanez, Phys. Lett.118B, 73 (1982); L. J. Hall, J. D. Lykken, and S. Weinberg,Phys. Rev. D27, 2359 (1983); N. Ohta,Prog.

Theor. Phys.70, 542 (1983).

[32] G. Kane, C. Kolda, L. Roszkowski, and J. Wells, Phys.

Rev. D49, 6173 (1994).

[33] S. Frixione and B. Webber,arXiv:hep-ph/0601192.

[34] P. Nadolsky, H.-L. Lai, Q.-H. Cao, J. Huston, J. Pumplin, D. Stump, W.-K. Tung, and C.-P. Yuan,Phys. Rev. D78, 013004 (2008).

[35] M. Mangano, F. Piccinini, A. D. Polosa, M. Moretti, and R. Pittau,J. High Energy Phys. 07 (2003) 001.

[36] J. Pumplin, D. R. Stump, J. Huston, H.-L. Lai, P.

Nadolsky, and W.-K. Tung, J. High Energy Phys. 07 (2002) 012.

[37] G. Corcella, I. G. Knowles, G. Marchesini, S. Moretti, K.

Odagiri, P. Richardson, M. H. Seymour, and B. R. Webber, J. High Energy Phys. 01 (2001) 010.

[38] J. Butterworth, J. R. Forshaw, and M. Seymour,Z. Phys. C 72, 637 (1996).

[39] J. Alwall, M. Herquet, F. Maltoni, O. Mattelaer, and T.

Stelzer,J. High Energy Phys. 06 (2011) 128.

[40] T. Sjo¨strand, S. Mrenna, and P. Skands,J. High Energy Phys. 05 (2006) 026.

[41] A. Lazopoulos, T. McElmurry, K. Melnikov, and F.

Petriello,Phys. Lett. B666, 62 (2008); F. Petriello (private communication).

[42] J. M. Campbell and R. K. Ellis,Phys. Rev. D60, 113006 (1999).

[43] J. Campbell, R. Ellis, and C. Williams, J. High Energy Phys. 07 (2011) 018.

(7)

[44] W. Beenakker, M. Kramer, T. Plehn, M. Spira, and P.

Zerwas,Nucl. Phys.B515, 3 (1998).

[45] D. Stump, J. Huston, J. Pumplin, W.-K. Tung, H.-L. Lai, S.

Kuhlmann, and J. F. Owens, J. High Energy Phys. 10 (2003) 046.

[46] ATLAS Collaboration, Reports No. ATL-PHYS-PUB- 2010-014 and No. ATLAS-CONF-2010-031, 2010.

[47] ATLAS Collaboration,Eur. Phys. J. C70, 823 (2010).

[48] S. Agostinelli et al.,Nucl. Instrum. Methods Phys. Res., Sect. A506, 250 (2003).

[49] ATLAS Collaboration,Eur. Phys. J. C71, 1577 (2011).

[50] ATLAS Collaboration,Phys. Lett. B707, 459 (2012).

[51] A. L. Read,J. Phys. G28, 2693 (2002).

[52] ATLAS Collaboration,J. High Energy Phys. 11 (2011) 099.

[53] T. Aaltonenet al.(CDF Collaboration), Phys. Rev. Lett.

102, 121801 (2009).

[54] V. M. Abazovet al.(D0 Collaboration),Phys. Lett. B660, 449 (2008).

[55] V. M. Abazovet al.(D0 Collaboration),Phys. Lett. B693, 95 (2010).

[56] LEP SUSY Working Group (ALEPH, DELPHI, L3, and OPAL Collaborations), Notes No. LEPSUSYWG/01-03.1 and No. 04-02.1, http://lepsusy.web.cern.ch/lepsusy/

Welcome.html.

G. Aad,47B. Abbott,109J. Abdallah,11S. Abdel Khalek,113A. A. Abdelalim,48A. Abdesselam,116O. Abdinov,10 B. Abi,110M. Abolins,86O. S. AbouZeid,156H. Abramowicz,151H. Abreu,113E. Acerbi,87a,87bB. S. Acharya,162a,162b

L. Adamczyk,37D. L. Adams,24T. N. Addy,55J. Adelman,173M. Aderholz,97S. Adomeit,96P. Adragna,73 T. Adye,127S. Aefsky,22J. A. Aguilar-Saavedra,122b,bM. Aharrouche,79S. P. Ahlen,21F. Ahles,47A. Ahmad,146 M. Ahsan,40G. Aielli,131a,131bT. Akdogan,18aT. P. A. A˚ kesson,77G. Akimoto,153A. V. Akimov,92A. Akiyama,65

M. S. Alam,1M. A. Alam,74J. Albert,167S. Albrand,54M. Aleksa,29I. N. Aleksandrov,63F. Alessandria,87a C. Alexa,25aG. Alexander,151G. Alexandre,48T. Alexopoulos,9M. Alhroob,20M. Aliev,15G. Alimonti,87a

J. Alison,118M. Aliyev,10B. M. M. Allbrooke,17P. P. Allport,71S. E. Allwood-Spiers,52J. Almond,80 A. Aloisio,100a,100bR. Alon,169A. Alonso,77B. Alvarez Gonzalez,86M. G. Alviggi,100a,100bK. Amako,64 P. Amaral,29C. Amelung,22V. V. Ammosov,126A. Amorim,122a,cG. Amoro´s,165N. Amram,151C. Anastopoulos,29

L. S. Ancu,16N. Andari,113T. Andeen,34C. F. Anders,20G. Anders,57aK. J. Anderson,30A. Andreazza,87a,87b V. Andrei,57aM-L. Andrieux,54X. S. Anduaga,68A. Angerami,34F. Anghinolfi,29A. Anisenkov,105N. Anjos,122a A. Annovi,46A. Antonaki,8M. Antonelli,46A. Antonov,94J. Antos,142bF. Anulli,130aS. Aoun,81L. Aperio Bella,4

R. Apolle,116,dG. Arabidze,86I. Aracena,141Y. Arai,64A. T. H. Arce,44S. Arfaoui,146J-F. Arguin,14E. Arik,18a,a M. Arik,18aA. J. Armbruster,85O. Arnaez,79V. Arnal,78C. Arnault,113A. Artamonov,93G. Artoni,130a,130b

D. Arutinov,20S. Asai,153R. Asfandiyarov,170S. Ask,27B. A˚ sman,144a,144bL. Asquith,5K. Assamagan,24 A. Astbury,167A. Astvatsatourov,51B. Aubert,4E. Auge,113K. Augsten,125M. Aurousseau,143aG. Avolio,161

R. Avramidou,9D. Axen,166C. Ay,53G. Azuelos,91,eY. Azuma,153M. A. Baak,29G. Baccaglioni,87a C. Bacci,132a,132bA. M. Bach,14H. Bachacou,134K. Bachas,29M. Backes,48M. Backhaus,20E. Badescu,25a

P. Bagnaia,130a,130bS. Bahinipati,2Y. Bai,32aD. C. Bailey,156T. Bain,156J. T. Baines,127O. K. Baker,173 M. D. Baker,24S. Baker,75E. Banas,38P. Banerjee,91Sw. Banerjee,170D. Banfi,29A. Bangert,148V. Bansal,167 H. S. Bansil,17L. Barak,169S. P. Baranov,92A. Barashkou,63A. Barbaro Galtieri,14T. Barber,47E. L. Barberio,84

D. Barberis,49a,49bM. Barbero,20D. Y. Bardin,63T. Barillari,97M. Barisonzi,172T. Barklow,141N. Barlow,27 B. M. Barnett,127R. M. Barnett,14A. Baroncelli,132aG. Barone,48A. J. Barr,116F. Barreiro,78

J. Barreiro Guimara˜es da Costa,56P. Barrillon,113R. Bartoldus,141A. E. Barton,69V. Bartsch,147R. L. Bates,52 L. Batkova,142aJ. R. Batley,27A. Battaglia,16M. Battistin,29F. Bauer,134H. S. Bawa,141,fS. Beale,96T. Beau,76 P. H. Beauchemin,159R. Beccherle,49aP. Bechtle,20H. P. Beck,16S. Becker,96M. Beckingham,136K. H. Becks,172

A. J. Beddall,18cA. Beddall,18cS. Bedikian,173V. A. Bednyakov,63C. P. Bee,81M. Begel,24S. Behar Harpaz,150 P. K. Behera,61M. Beimforde,97C. Belanger-Champagne,83P. J. Bell,48W. H. Bell,48G. Bella,151L. Bellagamba,19a

F. Bellina,29M. Bellomo,29A. Belloni,56O. Beloborodova,105,gK. Belotskiy,94O. Beltramello,29O. Benary,151 D. Benchekroun,133aM. Bendel,79N. Benekos,163Y. Benhammou,151E. Benhar Noccioli,48J. A. Benitez Garcia,157b

D. P. Benjamin,44M. Benoit,113J. R. Bensinger,22K. Benslama,128S. Bentvelsen,103D. Berge,29 E. Bergeaas Kuutmann,41N. Berger,4F. Berghaus,167E. Berglund,103J. Beringer,14P. Bernat,75R. Bernhard,47 C. Bernius,24T. Berry,74C. Bertella,81A. Bertin,19a,19bF. Bertinelli,29F. Bertolucci,120a,120bM. I. Besana,87a,87b

N. Besson,134S. Bethke,97W. Bhimji,45R. M. Bianchi,29M. Bianco,70a,70bO. Biebel,96S. P. Bieniek,75 K. Bierwagen,53J. Biesiada,14M. Biglietti,132aH. Bilokon,46M. Bindi,19a,19bS. Binet,113A. Bingul,18c C. Bini,130a,130bC. Biscarat,175U. Bitenc,47K. M. Black,21R. E. Blair,5J.-B. Blanchard,134G. Blanchot,29

T. Blazek,142aC. Blocker,22J. Blocki,38A. Blondel,48W. Blum,79U. Blumenschein,53G. J. Bobbink,103 V. B. Bobrovnikov,105S. S. Bocchetta,77A. Bocci,44C. R. Boddy,116M. Boehler,41J. Boek,172N. Boelaert,35 PRL108,241802 (2012) P H Y S I C A L R E V I E W L E T T E R S 15 JUNE 2012

(8)

J. A. Bogaerts,29A. Bogdanchikov,105A. Bogouch,88,aC. Bohm,144aJ. Bohm,123V. Boisvert,74T. Bold,37 V. Boldea,25aN. M. Bolnet,134M. Bomben,76M. Bona,73V. G. Bondarenko,94M. Bondioli,161M. Boonekamp,134

C. N. Booth,137S. Bordoni,76C. Borer,16A. Borisov,126G. Borissov,69I. Borjanovic,12aM. Borri,80S. Borroni,85 V. Bortolotto,132a,132bK. Bos,103D. Boscherini,19aM. Bosman,11H. Boterenbrood,103D. Botterill,127J. Bouchami,91 J. Boudreau,121E. V. Bouhova-Thacker,69D. Boumediene,33C. Bourdarios,113N. Bousson,81A. Boveia,30J. Boyd,29

I. R. Boyko,63N. I. Bozhko,126I. Bozovic-Jelisavcic,12bJ. Bracinik,17A. Braem,29P. Branchini,132a G. W. Brandenburg,56A. Brandt,7G. Brandt,116O. Brandt,53U. Bratzler,154B. Brau,82J. E. Brau,112H. M. Braun,172 B. Brelier,156J. Bremer,29K. Brendlinger,118R. Brenner,164S. Bressler,169D. Britton,52F. M. Brochu,27I. Brock,20

R. Brock,86T. J. Brodbeck,69E. Brodet,151F. Broggi,87aC. Bromberg,86J. Bronner,97G. Brooijmans,34 W. K. Brooks,31bG. Brown,80H. Brown,7P. A. Bruckman de Renstrom,38D. Bruncko,142bR. Bruneliere,47

S. Brunet,59A. Bruni,19aG. Bruni,19aM. Bruschi,19aT. Buanes,13Q. Buat,54F. Bucci,48J. Buchanan,116 N. J. Buchanan,2P. Buchholz,139R. M. Buckingham,116A. G. Buckley,45S. I. Buda,25aI. A. Budagov,63 B. Budick,106V. Bu¨scher,79L. Bugge,115O. Bulekov,94M. Bunse,42T. Buran,115H. Burckhart,29S. Burdin,71

T. Burgess,13S. Burke,127E. Busato,33P. Bussey,52C. P. Buszello,164F. Butin,29B. Butler,141J. M. Butler,21 C. M. Buttar,52J. M. Butterworth,75W. Buttinger,27S. Cabrera Urba´n,165D. Caforio,19a,19bO. Cakir,3aP. Calafiura,14

G. Calderini,76P. Calfayan,96R. Calkins,104L. P. Caloba,23aR. Caloi,130a,130bD. Calvet,33S. Calvet,33 R. Camacho Toro,33P. Camarri,131a,131bM. Cambiaghi,117a,117bD. Cameron,115L. M. Caminada,14S. Campana,29

M. Campanelli,75V. Canale,100a,100bF. Canelli,30,hA. Canepa,157aJ. Cantero,78L. Capasso,100a,100b M. D. M. Capeans Garrido,29I. Caprini,25aM. Caprini,25aD. Capriotti,97M. Capua,36a,36bR. Caputo,79 R. Cardarelli,131aT. Carli,29G. Carlino,100aL. Carminati,87a,87bB. Caron,83S. Caron,102E. Carquin,31b G. D. Carrillo Montoya,170A. A. Carter,73J. R. Carter,27J. Carvalho,122a,iD. Casadei,106M. P. Casado,11

M. Cascella,120a,120bC. Caso,49a,49b,aA. M. Castaneda Hernandez,170E. Castaneda-Miranda,170 V. Castillo Gimenez,165N. F. Castro,122aG. Cataldi,70aA. Catinaccio,29J. R. Catmore,29A. Cattai,29 G. Cattani,131a,131bS. Caughron,86D. Cauz,162a,162cP. Cavalleri,76D. Cavalli,87aM. Cavalli-Sforza,11 V. Cavasinni,120a,120bF. Ceradini,132a,132bA. S. Cerqueira,23bA. Cerri,29L. Cerrito,73F. Cerutti,46S. A. Cetin,18b F. Cevenini,100a,100bA. Chafaq,133aD. Chakraborty,104K. Chan,2B. Chapleau,83J. D. Chapman,27J. W. Chapman,85

E. Chareyre,76D. G. Charlton,17V. Chavda,80C. A. Chavez Barajas,29S. Cheatham,83S. Chekanov,5 S. V. Chekulaev,157aG. A. Chelkov,63M. A. Chelstowska,102C. Chen,62H. Chen,24S. Chen,32cT. Chen,32c X. Chen,170S. Cheng,32aA. Cheplakov,63V. F. Chepurnov,63R. Cherkaoui El Moursli,133eV. Chernyatin,24E. Cheu,6

S. L. Cheung,156L. Chevalier,134G. Chiefari,100a,100bL. Chikovani,50aJ. T. Childers,29A. Chilingarov,69 G. Chiodini,70aA. S. Chisholm,17R. T. Chislett,75M. V. Chizhov,63G. Choudalakis,30S. Chouridou,135 I. A. Christidi,75A. Christov,47D. Chromek-Burckhart,29M. L. Chu,149J. Chudoba,123G. Ciapetti,130a,130b A. K. Ciftci,3aR. Ciftci,3aD. Cinca,33V. Cindro,72M. D. Ciobotaru,161C. Ciocca,19aA. Ciocio,14M. Cirilli,85

M. Citterio,87aM. Ciubancan,25aA. Clark,48P. J. Clark,45W. Cleland,121J. C. Clemens,81B. Clement,54 C. Clement,144a,144bR. W. Clifft,127Y. Coadou,81M. Cobal,162a,162cA. Coccaro,170J. Cochran,62P. Coe,116 J. G. Cogan,141J. Coggeshall,163E. Cogneras,175J. Colas,4A. P. Colijn,103N. J. Collins,17C. Collins-Tooth,52 J. Collot,54G. Colon,82P. Conde Muin˜o,122aE. Coniavitis,116M. C. Conidi,11M. Consonni,102S. M. Consonni,87a,87b

V. Consorti,47S. Constantinescu,25aC. Conta,117a,117bG. Conti,56F. Conventi,100a,jJ. Cook,29M. Cooke,14 B. D. Cooper,75A. M. Cooper-Sarkar,116K. Copic,14T. Cornelissen,172M. Corradi,19aF. Corriveau,83,k A. Cortes-Gonzalez,163G. Cortiana,97G. Costa,87aM. J. Costa,165D. Costanzo,137T. Costin,30D. Coˆte´,29 R. Coura Torres,23aL. Courneyea,167G. Cowan,74C. Cowden,27B. E. Cox,80K. Cranmer,106F. Crescioli,120a,120b M. Cristinziani,20G. Crosetti,36a,36bR. Crupi,70a,70bS. Cre´pe´-Renaudin,54C.-M. Cuciuc,25aC. Cuenca Almenar,173

T. Cuhadar Donszelmann,137M. Curatolo,46C. J. Curtis,17C. Cuthbert,148P. Cwetanski,59H. Czirr,139 P. Czodrowski,43Z. Czyczula,173S. D’Auria,52M. D’Onofrio,71A. D’Orazio,130a,130bP. V. M. Da Silva,23a

C. Da Via,80W. Dabrowski,37A. Dafinca,116T. Dai,85C. Dallapiccola,82M. Dam,35M. Dameri,49a,49b D. S. Damiani,135H. O. Danielsson,29D. Dannheim,97V. Dao,48G. Darbo,49aG. L. Darlea,25bW. Davey,20 T. Davidek,124N. Davidson,84R. Davidson,69E. Davies,116,dM. Davies,91A. R. Davison,75Y. Davygora,57a

E. Dawe,140I. Dawson,137J. W. Dawson,5,aR. K. Daya-Ishmukhametova,22K. De,7R. de Asmundis,100a S. De Castro,19a,19bP. E. De Castro Faria Salgado,24S. De Cecco,76J. de Graat,96N. De Groot,102P. de Jong,103

C. De La Taille,113H. De la Torre,78B. De Lotto,162a,162cL. de Mora,69L. De Nooij,103D. De Pedis,130a A. De Salvo,130aU. De Sanctis,162a,162cA. De Santo,147J. B. De Vivie De Regie,113G. De Zorzi,130a,130bS. Dean,75

Références

Documents relatifs

51b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia. 52 II Physikalisches Institut, Justus-Liebig-Universita¨t Giessen,

51b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia. 52 II Physikalisches Institut, Justus-Liebig-Universita¨t Giessen,

50b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia. 51 II Physikalisches Institut, Justus-Liebig-Universita¨t Giessen,

51b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia. 52 II Physikalisches Institut, Justus-Liebig-Universita¨t Giessen,

51b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia. 52 II Physikalisches Institut, Justus-Liebig-Universita¨t Giessen,

50b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia. 51 II Physikalisches Institut, Justus-Liebig-Universit¨at Giessen,

50b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia. 51 II Physikalisches Institut, Justus-Liebig-Universita¨t Giessen,

51b High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia. 52 II Physikalisches Institut, Justus-Liebig-Universita¨t Giessen,