Search for R-parity violating decays of a top squark in proton-proton collisions at root s=8TeV

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Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

R-parity

violating

decays

of

a

top

squark

in

proton–proton

collisions

at

√

s

=

8 TeV

.CMSCollaboration CERN,Switzerland a r t i c l e i n f o a b s t ra c t Articlehistory: Received13February2016 Receivedinrevisedform7June2016 Accepted17June2016

Availableonline21June2016 Editor:M.Doser Keywords: CMS Physics Supersymmetry Leptons

Lowmissingtransverseenergy

The results ofasearchforasupersymmetric partnerofthe top quark(top squark),pair-produced in proton–proton collisionsat√s=8 TeV,arepresented.Thesearch,whichfocusesonR-parityviolating, chargino-mediateddecays ofthe topsquark, isperformedinfinal stateswithlow missing transverse momentum,twooppositelychargedelectronsormuons,and atleastfivejets.Theanalysisusesadata samplecorrespondingtoanintegratedluminosity of19.7 fb−1 _{collectedwiththeCMSdetectoratthe}

LHCin2012. Thedataare foundtobeinagreementwiththe standardmodelexpectation,andupper limits are placedon the top squark pairproduction crosssection at95% confidence level.Assuming a100% branchingfractionfor thetop squarkdecaychain,t→tχ₁±,χ₁±→ ±_{+jj,top squarkmasses}

less than890 (1000) GeVfor the electron(muon)channel are excluded for the firsttime inmodels withasinglenonzeroR-parityviolatingcouplingλ_{i jk}(i,j,k≤2),wherei,j,k correspondtothethree generations.

©2016TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.

1. Introduction

Supersymmetry (SUSY) [1,2] is an extension of the standard model (SM) that may provide a solution to the hierarchy prob-lem[3,4].IntheSUSYframework,quadraticallydivergentradiative correctionstotheHiggsbosonmass,dominatedbyloopsinvolving thetopquark,arecanceledbyloopswithasupersymmetric part-ner ofthe topquark (top squark).The massof thetop squarkis expectedtobewithin afewhundredGeVofthetopquark mass, andthesupersymmetricHiggsbosonpartnersarealsoexpectedto havemasseslessthan1 TeV[5,6].

SearchesforSUSY areperformedin manydecaychannelsand areclassifiedintoR-parityconserving(RPC)andR-parityviolating (RPV)scenarios.Thequantumnumber,R-parity, PR= (−1)3B+L+2s hasavalue +1 forSMparticlesand−1 forsuperpartners, where

B,L, ands are baryon number,leptonnumber, andspin, respec-tively[7].InRPC modelsthetopsquarkisexpectedtodecayinto thelightestSUSYparticle,whichescapesdetection.Thisresultsin aneventsignaturewithsubstantialmissingtransversemomentum. RecentsearchesperformedattheLHCatCERNineventswithhigh missingtransversemomentumhavereducedtheparameter space

 _{E-mailaddress:cms-publication-committee-chair@cern.ch.}

availableforalowmasstopsquark[8–13].However,R-paritymay notbe conserved,inwhichcasesearchesforSUSYparticle decay-ingtoSMparticleswithoutsubstantialmissingtransverse momen-tumareimportant.

The superpotential terms that result in R-parity violation are givenby: WRPV= 1 2λi jkLiLjEk+ λ  i jkLiQjDk +1 2λ  i jkUiDjDk+μiLiHu; (1) where λi jk, λ_{i jk}, and λ_{i jk} are three trilinear Yukawa couplings;

i,j,k=1,2,3 are generation indices; L and Q are the SU(2)L doubletsuperfieldsoftheleptonandquark; Hu istheHiggsfield that givesmass to theup-typequarks; μi are thebilinear terms that mix lepton and Higgssuperfields, and E , D, and U are the

SU(2)L singletsuperfieldsofthechargedlepton,down-typequark, and up-type quark. The third term violates the conservation of baryon number, while the first two violate the conservation of lepton number. If baryon number and lepton numberwere both violated, proton decay would proceed at a rate excluded by ex-perimentalobservations[14,15].Toavoidtheseexperimental con-straintsandtosimplifytheinterpretationofresults,itiscommonly

http://dx.doi.org/10.1016/j.physletb.2016.06.039

0370-2693/©2016TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

Fig. 1. DiagramfortheR-parityviolating,chargino-mediateddecayofatopsquark. Thecharginodecaystoaleptonandtwojetsviaanoff-shellsneutrinowithnonzero

λ_{i jk}coupling.

assumedthat onlyoneoftheλi jk,λ_{i jk},orλ_{i jk} couplingsis differ-entfromzero.Inthisanalysisonlyλ_{i jk}couplingswith(i,j,k)≤2 areconsidered.

InRPVSUSYmodelswiththecharginoχ₁±lighterthanthetop squarkandnonzeroλ_{i jk},thetopsquarkt candecayviat→bχ₁±, withsubsequentdecayofthecharginotoaleptonandtwojetsvia an off-shellsneutrino (χ₁±→ ±+jj)[16],as depictedin Fig. 1. Thebranchingfractionofdecayχ₁±→ν+jj viaanoff-shell slep-ton will be negligible unless the slepton and sneutrino masses are comparable. The decayχ₁±→W±χ₁0 is suppressed for mod-elswithχ₁± andχ0

1 almostdegenerateinmass.

We perform a search for top squark decays, as depicted in Fig. 1, using proton–proton (pp) collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb−1,collectedwiththeCMSdetectorattheLHCin2012.As top squarks are expected to be dominantlypair-produced at the LHC[17],the search is performedusingevents withexactly two oppositely charged electrons (e±e∓) or muons (μ±μ∓), at least fivejetsofwhich oneor morejetsare identified asarisingfrom hadronizationofabottomquark(b-taggedjet),andhighST,where

ST isdefinedasthescalarsumofthetransversemomentaof lep-tonsandjets. Asa consequenceofthe assumptionthat only one oftheλ_{i jk} couplingsisnonzero,thetwoleptonsmusthave oppo-sitecharge andthesameflavor. Detailsoftheeventselection are describedinSection3.

The sensitivity of the e±e∓ (μ±μ∓) search doesnot depend on which of the four RPV couplings associated with the second operator LQD (LiQjDk) in Eq. (1) are nonzero: λ111, λ112, λ121, andλ₁₂₂(λ₂₁₁,λ₂₁₂,λ₂₂₁,andλ₂₂₂), becausethefinal statesand kinematicdistributionsarethesameineach case.Weexpectthat thesearcheshavesomesensitivitytomodelswiththird-generation couplingsλ₃₁₁, λ₃₁₂, λ₃₂₁ , andλ₃₂₂, vialeptonic τ decays; how-ever, we do not include this possible extra contribution in this paper.The difference M_t,χ±

1 betweentop squark mass Mt, and

charginomass M_χ±

1,ischosen to be 100 GeV,sincethisvalue is

representativeofthebulkoftheM_t−M_χ±

1 parameterspacewhere

thesignal reconstructionefficiencyisslowlyvarying.Thisanalysis doesnotattempttoquantifythedecreaseinefficiency(andsignal sensitivity)intheregionsofparameterspacewhereeitherM_t,χ± 1

orM_χ±

1 isverysmall(<100 GeV).

Several searches for R-parity violating top squark decays via LQD couplings have been performed by the CMS [18–20] and ATLAS [21] Collaborations. These searches have focused on top squark pairs decaying via λ_i32 couplings into final states of two leptons(e±or μ±)andtwojetsortwoleptons(e±or μ±)andsix jets,fourofwhichareb-taggedjets[20,21];viaλ_{3 jk}couplingsinto afinal stateincludingtwotauleptonsandtwob-taggedjets[19]; andviatheλ₂₃₃ couplingintoafinalstateincludingthreeleptons andadditionaljets[18].Theanalysisdescribedinthispaperisthe firstsearchforR-parityviolatingtopsquarkdecaysviapurely first-orsecond-generation LQD couplings;in thiscase, thefinal states

aretwoleptons(e±or μ±)andsixjets,twoofwhichareb-tagged jets.

2. TheCMSdetector

AdetaileddescriptionoftheCMSdetector,togetherwitha defi-nitionofthecoordinatesystemused,canbefoundelsewhere[22]. A notablefeature ofthe CMSdetectoris its6 m internal diame-tersuperconductingsolenoidmagnetthatprovidesafieldof3.8 T. Withinthefieldvolumeareasiliconpixelandstriptracker,alead tungstatecrystalelectromagneticcalorimeter,andabrassand scin-tillatorhadroncalorimeter.Muondetectorsbasedongasionization chambersareembeddedinasteelflux-returnyokelocatedoutside the solenoid. Events are collected by a two-layer trigger system basedonahardware level-1trigger,followedbyasoftware-based high-leveltrigger.

The pseudorapidity range covered by the tracking system is |η|<2.5, the muon detector extends up to |η|<2.4, and the calorimeters cover a region with |η|<3.0. The region of 3<|η|<5 is instrumented with steel and quartz fiber forward calorimeters. The hermeticity of the detector up to large values of |η| permits accurate measurement of the momentum balance transversetothebeamdirection.

3. Triggerandeventselection

Events are selected using a trigger that requires at least one electron (muon) with a transverse momentum (pT) threshold of 27 (24) GeV,and|η|<2.5 (2.1).Allobjectsarereconstructedusing aparticle-flow(PF)algorithm[23,24],whichusesinformationfrom all subsystems to reconstruct photons, electrons, muons, charged hadrons,andneutralhadrons.

Toreducethebackgroundfromjetscontainingleptons,we im-pose isolation constraints on the transverse energy ET,cone from charged-particle tracks or deposits in the calorimeter within a cone R=(η)2_{+ (φ)}2_{=0.3 (0.4)around the trajectory of} theelectron (muon),whereφ isthe azimuthalangle.The energy fromthe reconstructed lepton andtheaverage transverse energy density frompileup are subtracted from ET,cone, where pileup is definedasadditionalinelasticppcollisionswithinthesameorthe adjacent LHC bunch crossing.Tracking information together with calorimeterinformationis usedto identifyandsubtract hadronic energydepositionsfromchargedparticlesoriginatingfrompileup. The contributionsto theneutralhadronandphoton energy com-ponents dueto pileup are also computed andsubtracted. In the electronchannel,thecontributionstotheneutralhadronand pho-ton energycomponents dueto pileupinteractions are subtracted from ET,cone using the jet area technique [25], which computes the transverse energy density of neutral particles from the me-dian of the neutral energy distribution in jets with pT>3 GeV onan event-by-eventbasis.Inthemuonchannel,themethod as-sumesthepileup energydensityfromneutralparticlestobe half ofthatfromchargedhadrons, basedonmeasurementsperformed injets[24].

Electrons are reconstructed by matching an energy cluster in the ECAL with a track reconstructed using a Gaussian sum fil-ter[26].ElectronsarerequiredtohavepT>50 GeV and|η|<2.5. The transitionregionbetween theECALbarrelandendcap is ex-cluded (1.444<|η|<1.566) because the calorimeteris not well modeled inthisregion.Electronsare identifiedusinga multivari-ateidentificationalgorithm [26],whoseinput variablesare sensi-tivetobremsstrahlungalongtheelectronpath,matchingbetween tracksandECALenergydeposits,andshower-shapevariables.The algorithm is trained with a sample of simulated Drell–Yan (DY) eventsthatcontainstrueelectrons andadatasampleenriched in

misidentifiedelectrons. Inaddition,thetransverse impact param-eter of the electron track is required to be lessthan 2 mm. To reducebackgroundsthat arisefromphoton conversionsinthe in-ner pixel detector, at least one pixel hit in the innermost pixel layer isrequired andthe electron must be inconsistent withthe hypothesis that it resultedfromphoton pair creation.We ensure thattheelectronisisolatedfromotheractivityintheeventby re-quiringthat ET,conebelessthan10%oftheelectronpT.

Muontracks arereconstructedusingthe informationfromthe muonchambersandthesilicontrackerandarerequiredtobe con-sistent withthe reconstructed primary vertex. The tracksare re-quiredtohaveatleastonehitinboththepixeltrackerandmuon detector,andatleasttenhitsinthesiliconstriptrackertoensure a precise momentum measurement. Muonsare requiredto have

pT>50 GeV and |η|<2.1. Mostcosmic ray muons are rejected by requiring that the transverse (longitudinal) impact parameter be lessthan 2 (5) mmrelative to the primary vertex, definedas thevertexwiththelargestsumofthe pT2 fromalltracks associ-atedwithit.Isolationisimposed bytherequirementthat ET,cone belessthan12%ofthemuonpT[27].

Thedifferencesinleptonreconstructionandtriggerefficiencies betweendataandsimulationarecorrectedinsimulationinbinsof

pTand η,usingatag-and-probemethod[28].

Jets are reconstructed from PF objects [29] using the anti-kT clustering algorithm [30] with a distance parameter of 0.5. The tracker and ECAL granularity are exploited to precisely measure thechargedparticles,andhencetodeterminejetdirectionsatthe production vertex. To remove jetsarising frominstrumental and non-collisionbackgrounds,additionalcriteriaonchargedand neu-tralhadronenergyareapplied.

Theenergyandmomentumofeachjetarecorrectedasa func-tion of the jet pT and η to account for the combined response function of the calorimeters. The average energy from pileup is subtracted from the jet [31]. Only jets within |η|<2.4 are con-sidered. The corrected jet pT must be at least 100 GeV for the leadingjet,50 GeV forthesecond-leadingjet,and30 GeV forthe remainingjets.Atleastfivejetsarerequiredintheevent.

Events with at least one b-tagged jet are selected. The com-bined secondary-vertexalgorithm[32] uses informationfromthe trackimpactparameterandvertexinformationtodiscriminate be-tweenjetsthat originatefrombquarks andjetsfromlight-flavor quarksandgluons.Thealgorithmcorrectlyidentifiesjetsproduced bythehadronizationofabquark(bjets)withanefficiencyof ap-proximately70% andmisidentifies jetsfromlight-flavorquarksor gluons(charm quarks) at a rate of approximately1% (20%) [32]. The b-taggingefficiencyin thesimulation is scaledto matchthe measuredefficiencyindataasafunction of pT, η,andtheflavor ofthejet.

The missing transverse momentum pmiss_T in the event is de-finedastheprojectionofthenegativevectorsumofthemomenta of all reconstructed PF candidates on the plane perpendicular to thebeams.The magnitudeof pmiss_T in theeventis referredto as

Emiss_T . To suppress leptonic tt decays that often have significant

Emiss_T becauseofthepresenceofneutrinosinthefinalstate, Emiss_T

isrequiredtobelessthan100 GeV.Thedileptonmass M, com-putedfromthetwoleptonfour-momenta,isrequiredtobegreater than130 GeV,basedonanoptimizationtoreducethecontribution fromlow-massresonancesandZbosondecays.

Toenhancethestatisticalsignificance,foreachleptonflavorthe sampleisdividedintothreeexclusivecategoriesofjetmultiplicity:

Njets=5,6,or≥7.Toimprovethesensitivitytosignaldecays,we computeanSTthresholdSminT optimizedforeachtopsquarkmass hypothesisandforeachNjetsbin.The SminT isdeterminedby

max-imizingthevalue ofS/√S+B,whereS andB arethenumberof expectedsignalandbackgroundeventsabove Smin_T ,respectively.

4. Simulationofbackgroundandsignalevents

MonteCarlo(MC)simulationsofbackgroundandsignalevents are used to optimize the selection criteria for maximum signal sensitivity and to estimate backgrounds. The simulation of the hard-scattering event is performed using the leading-order (LO) matrix element event generator MadGraph 5 [33], unless noted otherwise. The CTEQ6L1 [34] set of partondistribution functions (PDF) is used to describe the proton structure. The simulation of the hard-scattering eventis then passed to pythia 6.426 [35] with the Z2* tune [36] to model the parton shower, hadroniza-tion,andtheunderlyingevent.A fullsimulationoftheresponseof theCMSdetectorisperformedusing Geant4[37].Additional sim-ulatedminimumbiaseventsare overlaidtoreproduce theeffects ofpileup.

The main SM backgrounds for this search are DY and tt pair production. Additional SM backgrounds, which include diboson (WW, WZ, and ZZ) and single top quark production, are small. The tt sample is generated with up to three additional partons, the DY events are produced with up to four additional partons, andthedibosonsamplesaregeneratedwithup totwoadditional partons. Single top quark production (t-, s-, and tW-channels)is simulatedwith powheg v1.0[38–42].Simulatedsamplesoftt and DY arenormalizedusingcrosssectionscomputedat next-to-next-to-leading-order(NNLO)[43,44].Crosssectionscomputedat next-to-leading-order(NLO)[45,46]areusedtonormalizethesingletop quarkanddibosonsamples.

The signal samples are generated using MadGraph 5, pythia_{6.426, andtheCTEQ6L1PDF set.Thetop squarkpair} pro-duction cross section is computed at NLO as a function of M_t, including soft gluon resummation at next-to-leading logarithm (NLL) [47–50]. The uncertainty in the cross section includes un-certainties associated with the renormalization and factorization scale,andthePDFset[51].

5. Backgroundestimation

Corrections to the normalizationoftt and DY simulations are estimated by examining background enriched samples in data. A summary of the selection criteria forthe signal search region andthecontrolregions,includingselectionsonthedileptonmass, is presented in Table 1. Diboson and single top quark produc-tionyieldsmallcontributionstothebackgroundandareestimated fromsimulation.Insimulatedtt sample,eventsarereweightedso thatthe pT ofthetopquark matchesthedatainadedicated con-trolsample[52].

The leptonic tt decays contribute to 89% of the total back-ground. Since the signal produces only same-flavor leptons, we estimatethett backgroundfromacontrolsampleofe±μ∓events after correctingitforthe smallcontributionsof DY,diboson,and single top events using simulations. We use this control sample tocomputecorrectionfactorsforthett simulationfordifferentjet multiplicitiesinthesignalregion.Thee±μ∓controlsampleiswell modeledbythesimulation,thuscorrectionfactorsarestatistically consistentwithunity.

The Drell–Yan productionconstitutes approximately8% of the SM background in the signal region, and is reduced by requir-ing atleastoneb-taggedjet.The contributionfromthissourceis estimatedusingacontrolsampleoftwooppositelycharged same-flavor leptons, which have an invariant mass M in the range 50–130 GeV. We perform a fit to the M distribution to esti-mate the number of DY events. The DY shape is obtained from

Table 1

Summaryoftheselectioncriteriaforthesignalregionandthecontrolregions.Datainthecontrolregionsdescribedastt, DYnormalization,andDYshapeareusedtoestimateSMbackgroundsinthesignalregion.

Lepton selection Njets Nb-tags

Signal region e±e∓(μ±μ∓), M>130 GeV ≥5 ≥1 Control regions

tt shape e±μ∓ ≥5 ≥1

DY normalization e±e∓(μ±μ∓), 50<M<130 GeV ≥5 ≥1 DY shape e±e∓(μ±μ∓), 50<M<130 GeV ≥5 0

background-subtracted datausing a DY-enriched sample withno b-taggedjets. Thebackgroundfromdibosondecaysincluding lep-tonic Z boson decays is estimated from simulation and is con-strainedinthefit.The M shapefortheremaining backgrounds doesnot exhibit aZboson masspeak, andisdescribed bya lin-ear function. The fit determines the number NDY of DY events and the number of all other background events. To check that the procedure is insensitive to a potential signal contamination, weperformedafitwithsignaleventsincluded,andobservedthat theobtainedNDY is independentofthepresenceofthe potential signalinthe controlsample. Theratio ofNDY fromthe fittothe simulatednumberofDYeventsiscalculatedforeachvalueofNjets andisusedtocorrectthesimulation.Thiscorrectionfactorranges from1.2±0.1 to2.1±0.6 andincreaseswithjetmultiplicity.

We checkedthat the corrections to the DY normalization are validinthe signalregionwith M>130 GeV.Wecomparedthe numbers ofevents in different mass ranges using a DY-enriched samplewithatleastfivejetsandnob-taggedjets.Theratioofthe numberofevents withM inthe Z-peak(normalization region) to the number with M inthe high-mass tail (signal region)is predicted from simulation to be 11.8±0.4 and observed to be 14.0±3.5 indata,inreasonableagreement.

6. Systematicuncertainties

We evaluate systematic uncertainties related to each back-groundandtothesignalreconstructionefficiency;theseare sum-marizedinTable 2.

Since the tt correction factorfor the simulated sample is es-timated froma control sample of e±μ∓ eventsin data,the sys-tematicuncertainty inthis backgroundis givenby thestatistical uncertaintyinthecontrolsample.Thisuncertaintyrangesfrom10 to50%, dependingon thevalues of Njets andof SminT .The uncer-tainties related to lepton trigger, identification, and isolation are negligible. For the small DY background, we take 50 (100)% of correction factor asthe systematic uncertainty on the correction in5 (≥6) jet bin(s).We assign a 30% uncertaintyto thediboson andsingle topquark backgroundcontributions toaccountforthe difference between the NLO theoretical calculation and the CMS measurementsoftheWWandZZcrosssections[53]andthe sin-gle top crosssections [54]. The statisticaluncertainty dueto the finite size of the simulated background samples is 10–30%, de-pendingontheNjetsbinandSminT value.

The following systematicuncertainties in the signal efficiency are included:jet energy scale(5%) [31],jet b-tagging efficiencies (3%), integrated luminosity (2.6%) [55], lepton identification and reconstruction efficiency (3%), electron energy scale (2%), muon momentumscale(0.9%),andtriggerefficiency(1%). Notethat the effectoftheb-tagginguncertaintyonthesignalpredictionis eval-uatedbyvaryingtheefficiencyandmisidentificationratesbytheir uncertainties [32,56] andthe effecton thesignal prediction.The uncertaintyrelatedto the lepton isolation requirementfor signal eventswithmanyjetsis estimatedusinga tt control sample se-lectedasshowninTable 1,butwith≥7 jets,andisdeterminedto be5%.Theuncertaintyduetothelimitedsizeofthesimulated sig-nalsamplevariesfrom2to7%.Theimpactofuncertaintiesrelated

Table 2

Systematicuncertaintiesforbackgroundandexpectedsignalyields.

Source Uncertainty (%)

Background estimates

tt+jets 10–50 Drell–Yan 50–100

Diboson 30

Single top quark 30 MC statistics 10–30

Expected signal yield

Jet energy scale 5 b tagging scale factor 1–3 Integrated luminosity 2.6 Lepton identification 3 Electron energy scale 2 Muon momentum scale 0.9 Trigger efficiency 1 Lepton isolation 5 MC statistics 2–7

tothePDFsetchoice,modelingofthetopquark pT spectrum,and pileupmodelingisdeterminedtobenegligible.

7. Results

Fig. 2 showsthe observeddistributions ofjet multiplicity,the estimatedbackgrounddistributions,andtheexpecteddistributions forsignalswithamass M_t ofeither300 GeV or900 GeV. In Ta-bles 3 and 4 we presentthe numbers of expectedandobserved eventsfor eachvalue of Njets,for each Mt hypothesis and corre-sponding Smin_T value. The signal expectations are based on NLO crosssections[51].ThedataareinagreementwiththeSM expec-tation ineach bin.The corresponding distributions are displayed graphicallyinFig. 1ofthesupplementarymaterial.

We use these results to determine 95% confidence level (CL) limits,asafunctionofM_t,ontheproductofthetop-squark pair-production cross section and the square of the branching frac-tionB forthedecayt→b±qq.Weusethemodifiedfrequentist CLs method [57] with profilingof nuisance parameters. Foreach

M_t hypothesis,the Poissonlikelihoods ofthethree Njets binsare combined.Systematicuncertainties are incorporatedinto thetest statistic as nuisance parameters. The nuisance parameter proba-bility densityfunction (pdf) forthe tt backgroundnormalization, which is estimated from background control regions containing limited numbers of events in high Njets bins, is described by a gamma function. All other uncertainties are treated with log-normal pdfs. With the exception of uncertainties related to the finite size ofa control sample, we assume the systematic uncer-taintiesarefullycorrelatedacrossdifferentNjets bins.

The observedandexpectedlimitson theproduct ofthe cross sectionandthebranchingfractionsquaredareshowninFig. 3.The green(yellow)band correspondstoavariationofone(two) stan-dard deviation(s) on the expected limit. The dotted curve shows the signal cross section, with the width of the associated band showing the sensitivity to uncertainties in the renormalization

Fig. 2. Jetmultiplicitydistributionsfore±e∓(left)andμ±μ∓(right)forselectionsoptimizedforMthypothesesof300 GeV (top)and900 GeV (bottom).Theexpectedsignal

isshownbyanopenhistogramsuperimposedontheexpectedSMbackground.TheasymmetricerrorbarsindicatethecentralconfidenceintervalsforPoisson-distributed data.ThesystematicuncertaintiesfortheSMcontributionsareindicatedbyhatchedbands.Undereachhistogramisshownaplotingrayastheratioofdifferenceofdata frombackgroundexpectationtothesumoftheiruncertainties,includingthesystematicuncertaintiesinbackgroundexpectation.

Fig. 3. Observedandexpected95%CLupperlimitsontheproductofthecrosssectionandthebranchingfraction(B)squared,fore±e∓(left)andμ±μ∓(right).Thegreen (inner)andyellow(outer)bandsshowthe1s.d.and2s.d.uncertaintyrangesintheexpectedlimits,respectively.Thedottedcurveshowstheexpectedtopsquarkcross sectioncomputedatNLO+NLL.ThedifferenceMt−Mχ1± isassumedtobe100 GeV forthesignalmodel.(Forinterpretationofthereferencestocolorinthisfigurelegend, thereaderisreferredtothewebversionofthisarticle.)

andfactorization scales andthe PDF uncertainties [51]. Compar-ing the observed cross section limitsto the signal cross section, we exclude top squarks with masses less than 890 (1000) GeV forthe electron (muon) channel. The expectedmass exclusionis 950 (970) GeV fortheelectron(muon)channel.

These cross section limits strictly apply to models withmass differenceM_t,χ±

1 =100 GeV;however,thesensitivitiesfor

mod-elswithM_t,χ±

1 >50 GeV aresimilar.Themassexclusionsassume

B =100%. As described earlier, the limitsfor the electron chan-nelapplyequallytomodelswithnonzeroλ₁₁₁,λ₁₁₂,λ₁₂₁,orλ₁₂₂

andthelimitsforthemuonchannelapplyequallytomodelswith nonzero λ₂₁₁, λ₂₁₂, λ₂₂₁ , or λ₂₂₂. Because the coupling strength does not affect the production cross section and the branching fraction is assumed to be 100%, the value of λ_{i jk} is not impor-tant aslongasitissufficientlylargetoensurethat thesneutrino decays promptly. For couplingvalues smaller than 10−5_{, the} de-caylengthsareoforder1 mmorgreater,resultinginadecreased signal reconstruction efficiencyandsensitivity.Theseare thefirst limits on chargino-mediated top squark decays via a single LQD couplingλ_{i jk} with(i,j,k≤2).

Table 3

Observedevents,estimatedbackground,andexpectedsignalyields,forNjets=5,6,and≥7,alongwiththeoptimizedvalueofSminT ,fordifferentMtintheelectronchannel.

Thesignalandbackgrounduncertaintiesincludebothstatisticalandsystematiccontributions.

Mt(GeV) Njets SminT (GeV) Data Estimated

background Expected signal Signal efficiency(%) 300 5 325 39 38.1±5.9 622±49 2.4±0.2 300 6 325 13 9.0±3.3 442±41 1.8±0.1 300 ≥7 325 4 2.9±1.7 266±33 0.9±0.1 400 5 525 27 28.7±5.6 256±14 5.6±0.2 400 6 325 13 9.0±3.3 245±13 5.3±0.2 400 ≥7 325 4 2.9±1.7 180±11 3.8±0.2 500 5 725 12 14.1±3.3 69.2±3.3 6.0±0.2 500 6 675 9 5.3±2.5 88.1±3.7 7.9±0.3 500 ≥7 675 4 2.2±1.4 89.7±3.8 8.1±0.3 600 5 925 1 3.4±1.1 19.0±0.9 5.8±0.2 600 6 875 3 2.7±1.0 28.8±1.1 8.9±0.3 600 ≥7 825 4 1.8±0.9 38.7±1.3 11.6±0.3 700 5 1025 1 1.6±0.5 7.1±0.3 6.6±0.2 700 6 975 2 1.3±0.5 10.5±0.4 9.6±0.3 700 ≥7 975 2 1.1±0.6 14.8±0.5 13.6±0.3 800 5 1225 1 0.4±0.2 2.7±0.1 7.0±0.2 800 6 1175 0 0.4±0.2 3.6±0.2 9.5±0.3 800 ≥7 1075 2 0.7±0.4 5.7±0.2 15.1±0.4 900 5 1325 1 0.2±0.1 1.0±0.1 6.7±0.3 900 6 1375 0 0.2±0.1 1.5±0.1 10.1±0.3 900 ≥7 1375 1 0.2±0.1 2.4±0.1 16.4±0.4 1000 5 1475 0 0.06±0.07 0.34±0.10 5.7±0.2 1000 6 1425 0 0.18±0.10 0.61±0.09 10.6±0.3 1000 ≥7 1525 0 0.05±0.06 0.98±0.09 16.6±0.4 1100 5 1475 0 0.06±0.07 0.12±0.04 5.3±0.2 1100 6 1425 0 0.18±0.10 0.26±0.04 11.2±0.3 1100 ≥7 1525 0 0.05±0.06 0.42±0.04 17.6±0.4 Table 4

Observedevents,estimatedbackground,andexpectedsignalyields,forNjets=5,6,and≥7,alongwiththeoptimizedvalueofSminT ,fordifferentMtinthemuonchannel.

Thesignalandbackgrounduncertaintiesincludebothstatisticalandsystematiccontributions.

Mt(GeV) Njets SminT (GeV) Data Estimated

background Expected signal Signal efficiency(%) 300 5 475 43 46.4±7.2 696±52 2.5±0.2 300 6 475 10 11.3±3.8 450±43 1.7±0.1 300 ≥7 325 4 4.1±1.9 261±33 0.9±0.1 400 5 525 39 36.8±7.2 266±13 5.4±0.2 400 6 525 10 10.8±3.9 281±14 5.3±0.2 400 ≥7 325 4 4.1±1.9 223±12 4.3±0.2 500 5 725 16 16.0±3.8 81.1±4.0 6.3±0.3 500 6 675 9 7.3±3.2 114.4±4.8 8.8±0.3 500 ≥7 675 3 3.1±1.6 101.8±4.5 8.3±0.3 600 5 875 5 5.2±1.5 23.7±1.1 6.6±0.3 600 6 825 5 4.6±1.6 36.0±1.3 10.0±0.3 600 ≥7 825 2 2.4±1.0 44.2±1.5 12.3±0.3 700 5 1075 2 1.3±0.4 7.7±0.4 6.3±0.2 700 6 975 4 2.4±0.8 13.2±0.5 11.2±0.3 700 ≥7 975 2 1.0±0.5 17.8±0.5 14.9±0.4 800 5 1175 0 0.9±0.3 2.9±0.2 6.8±0.3 800 6 1175 2 0.8±0.3 4.5±0.2 10.6±0.3 800 ≥7 1125 1 0.4±0.3 7.3±0.2 17.6±0.4 900 5 1475 0 0.1±0.1 0.9±0.1 5.6±0.2 900 6 1325 0 0.4±0.2 1.8±0.1 11.0±0.3 900 ≥7 1175 1 0.4±0.3 2.9±0.1 18.1±0.4 1000 5 1575 0 0.07±0.06 0.4±0.1 5.9±0.2 1000 6 1525 0 0.01±0.04 0.6±0.1 10.0±0.3 1000 ≥7 1425 0 0.25±0.16 1.2±0.1 18.9±0.4 1100 5 1575 0 0.07±0.06 0.13±0.04 5.2±0.3 1100 6 1525 0 0.01±0.04 0.25±0.04 9.9±0.3 1100 ≥7 1425 0 0.25±0.16 0.50±0.04 19.7±0.4

8. Summary

A search for new phenomena using events with two oppo-sitely chargedelectrons ormuons, atleastfive jets,withatleast oneb-taggedjet,andlowmissingtransversemomentumhasbeen performed.No excessoverthe estimatedbackgroundisobserved. Theresultsareinterpretedintheframeworkofchargino-mediated, R-parityviolating top squarkdecays, assuming a 100% branching fractionforthetopsquarkdecaychain,t→bχ₁±,χ₁±→ ±+jj.In models witha single nonzero λ_{i jk} couplingwith (i,j,k≤2),the resultsexcludetopsquarkswithmasslessthan890 (1000) GeV for theelectron(muon)channelat95%confidencelevel.Theselimits arethefirstobtainedforthismodel.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrativestaffs atCERN andatother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythe computinginfrastructureessential to ouranalyses. Finally, we acknowledge the enduring support for the construc-tionandoperation oftheLHCandthe CMSdetectorprovidedby thefollowingfundingagencies:BMWFWandFWF(Austria);FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES(Bulgaria);CERN;CAS,MOST,andNSFC(China);COLCIENCIAS (Colombia);MSESandCSF(Croatia);RPF(Cyprus);MoER,ERCIUT andERDF(Estonia);Academy ofFinland,MEC,andHIP(Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM(Malaysia); CINVESTAV, CONACYT,SEP,andUASLP-FAI(Mexico);MBIE(NewZealand);PAEC (Pakistan);MSHEandNSC(Poland);FCT(Portugal);JINR(Dubna); MON,RosAtom,RASandRFBR(Russia);MESTD(Serbia);SEIDIand CPAN(Spain);SwissFundingAgencies(Switzerland);MST(Taipei); ThEPCenter,IPST,STARandNSTDA(Thailand);TUBITAKandTAEK (Turkey);NASUandSFFR(Ukraine); STFC(United Kingdom);DOE andNSF(USA).

Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandEPLANET(European Union); the Leventis Foundation; the A.P. Sloan Foundation; the Alexandervon HumboldtFoundation;the BelgianFederal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); theMinistry ofEducation,Youth andSports (MEYS)of theCzech Republic;theCouncilofScienceandIndustrialResearch,India;the HOMING PLUSprogram ofthe Foundation for PolishScience, co-financed from European Union, Regional Development Fund; the OPUSprogram oftheNationalScience Center(Poland);the Com-pagnia di San Paolo (Torino); MIUR project 20108T4XTM (Italy); the Thalis and Aristeia programs cofinanced by EU-ESF and the Greek NSRF; the National Priorities Research Program by Qatar NationalResearchFund;theRachadapisek SompotFund for Post-doctoralFellowship,ChulalongkornUniversity(Thailand);the Chu-lalongkorn Academic into Its 2nd Century Project Advancement Project(Thailand);andtheWelchFoundation,contractC-1845.

Appendix A. Supplementarymaterial

Supplementarymaterialrelatedtothisarticlecanbefound on-lineathttp://dx.doi.org/10.1016/j.physletb.2016.06.039.

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CMSCollaboration

V. Khachatryan,A.M. Sirunyan, A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam, E. Asilar,T. Bergauer, J. Brandstetter, E. Brondolin, M. Dragicevic, J. Erö,M. Flechl, M. Friedl,

R. Frühwirth1, V.M. Ghete, C. Hartl, N. Hörmann, J. Hrubec,M. Jeitler1,V. Knünz, A. König,

M. Krammer1, I. Krätschmer,D. Liko, T. Matsushita,I. Mikulec, D. Rabady2,B. Rahbaran, H. Rohringer,

J. Schieck1, R. Schöfbeck, J. Strauss, W. Treberer-Treberspurg,W. Waltenberger, C.-E. Wulz1

InstitutfürHochenergiephysikderOeAW,Wien,Austria

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

S. Alderweireldt, T. Cornelis,E.A. De Wolf, X. Janssen,A. Knutsson, J. Lauwers,

S. Luyckx, M. Van De Klundert,H. Van Haevermaet, P. Van Mechelen,N. Van Remortel,

A. Van Spilbeeck

UniversiteitAntwerpen,Antwerpen,Belgium

S. Abu Zeid,F. Blekman, J. D’Hondt, N. Daci, I. De Bruyn, K. Deroover, N. Heracleous,J. Keaveney,

S. Lowette,L. Moreels, A. Olbrechts,Q. Python, D. Strom, S. Tavernier, W. Van Doninck,

P. Van Mulders, G.P. Van Onsem,I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

P. Barria, H. Brun, C. Caillol, B. Clerbaux, G. De Lentdecker, G. Fasanella, L. Favart, A. Grebenyuk,

G. Karapostoli,T. Lenzi, A. Léonard,T. Maerschalk, A. Marinov, L. Perniè, A. Randle-conde,T. Seva,

C. Vander Velde, P. Vanlaer, R. Yonamine,F. Zenoni, F. Zhang3

UniversitéLibredeBruxelles,Bruxelles,Belgium

K. Beernaert,L. Benucci, A. Cimmino, S. Crucy, D. Dobur, A. Fagot,G. Garcia,M. Gul, J. Mccartin,

A.A. Ocampo Rios, D. Poyraz,D. Ryckbosch, S. Salva, M. Sigamani, M. Tytgat,W. Van Driessche,

E. Yazgan, N. Zaganidis

GhentUniversity,Ghent,Belgium

S. Basegmez, C. Beluffi4,O. Bondu,S. Brochet, G. Bruno, A. Caudron, L. Ceard, G.G. Da Silveira,

C. Delaere, D. Favart,L. Forthomme, A. Giammanco5,J. Hollar, A. Jafari,P. Jez, M. Komm, V. Lemaitre,

A. Mertens, M. Musich, C. Nuttens, L. Perrini, A. Pin, K. Piotrzkowski,A. Popov6,L. Quertenmont,

M. Selvaggi,M. Vidal Marono

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

N. Beliy, G.H. Hammad

UniversitédeMons,Mons,Belgium

W.L. Aldá Júnior, F.L. Alves,G.A. Alves, L. Brito,M. Correa Martins Junior,M. Hamer, C. Hensel,

A. Moraes,M.E. Pol, P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas, W. Carvalho,J. Chinellato7,A. Custódio, E.M. Da Costa,

D. De Jesus Damiao,C. De Oliveira Martins, S. Fonseca De Souza, L.M. Huertas Guativa, H. Malbouisson,

D. Matos Figueiredo, C. Mora Herrera,L. Mundim, H. Nogima,W.L. Prado Da Silva, A. Santoro,

A. Sznajder,E.J. Tonelli Manganote7, A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahujaa, C.A. Bernardesb, A. De Souza Santosb,S. Dograa, T.R. Fernandez Perez Tomeia,

E.M. Gregoresb, P.G. Mercadanteb,C.S. Moona,8,S.F. Novaesa,Sandra S. Padulaa,D. Romero Abad,

J.C. Ruiz Vargas

a_{UniversidadeEstadualPaulista,SãoPaulo,Brazil} b_{UniversidadeFederaldoABC,SãoPaulo,Brazil}

A. Aleksandrov, R. Hadjiiska, P. Iaydjiev,M. Rodozov, S. Stoykova, G. Sultanov, M. Vutova

InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria

A. Dimitrov, I. Glushkov,L. Litov, B. Pavlov,P. Petkov

M. Ahmad, J.G. Bian, G.M. Chen,H.S. Chen, M. Chen, T. Cheng,R. Du, C.H. Jiang, R. Plestina9, F. Romeo,

S.M. Shaheen,A. Spiezia, J. Tao, C. Wang,Z. Wang, H. Zhang

InstituteofHighEnergyPhysics,Beijing,China

C. Asawatangtrakuldee, Y. Ban,Q. Li, S. Liu, Y. Mao,S.J. Qian, D. Wang, Z. Xu

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

C. Avila,A. Cabrera, L.F. Chaparro Sierra, C. Florez,J.P. Gomez, B. Gomez Moreno,

J.C. Sanabria

UniversidaddeLosAndes,Bogota,Colombia

N. Godinovic, D. Lelas,I. Puljak, P.M. Ribeiro Cipriano

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,K. Kadija, J. Luetic,S. Micanovic, L. Sudic

InstituteRudjerBoskovic,Zagreb,Croatia

A. Attikis, G. Mavromanolakis,J. Mousa, C. Nicolaou, F. Ptochos,P.A. Razis,

H. Rykaczewski

UniversityofCyprus,Nicosia,Cyprus

M. Bodlak,M. Finger10, M. Finger Jr.10

CharlesUniversity,Prague,CzechRepublic

Y. Assran11,12, S. Elgammal11,A. Ellithi Kamel13,M.A. Mahmoud14

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

B. Calpas,M. Kadastik, M. Murumaa, M. Raidal, A. Tiko,C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,J. Pekkanen, M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Härkönen,V. Karimäki, R. Kinnunen, T. Lampén, K. Lassila-Perini,S. Lehti, T. Lindén,P. Luukka,

T. Peltola,E. Tuominen, J. Tuominiemi,E. Tuovinen, L. Wendland

HelsinkiInstituteofPhysics,Helsinki,Finland

J. Talvitie,T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

M. Besancon,F. Couderc, M. Dejardin, D. Denegri,B. Fabbro, J.L. Faure, C. Favaro, F. Ferri, S. Ganjour,

A. Givernaud, P. Gras, G. Hamel de Monchenault,P. Jarry, E. Locci, M. Machet,J. Malcles, J. Rander,

A. Rosowsky,M. Titov, A. Zghiche

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

I. Antropov,S. Baffioni, F. Beaudette, P. Busson, L. Cadamuro, E. Chapon,C. Charlot,O. Davignon,

M. Nguyen, C. Ochando, G. Ortona,P. Paganini, P. Pigard,S. Regnard, R. Salerno,J.B. Sauvan, Y. Sirois,

T. Strebler, Y. Yilmaz, A. Zabi

LaboratoireLeprince-Ringuet,EcolePolytechnique,IN2P3–CNRS,Palaiseau,France

J.-L. Agram15, J. Andrea, A. Aubin, D. Bloch,J.-M. Brom, M. Buttignol,E.C. Chabert, N. Chanon, C. Collard,

E. Conte15, X. Coubez, J.-C. Fontaine15,D. Gelé, U. Goerlach,C. Goetzmann, A.-C. Le Bihan, J.A. Merlin2,

K. Skovpen, P. Van Hove

InstitutPluridisciplinaireHubertCurien,UniversitédeStrasbourg,UniversitédeHauteAlsaceMulhouse,CNRS/IN2P3,Strasbourg,France

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,C. Bernet, G. Boudoul, E. Bouvier, C.A. Carrillo Montoya, R. Chierici,D. Contardo,

B. Courbon, P. Depasse, H. El Mamouni, J. Fan, J. Fay, S. Gascon, M. Gouzevitch, B. Ille, F. Lagarde,

I.B. Laktineh,M. Lethuillier, L. Mirabito,A.L. Pequegnot, S. Perries, J.D. Ruiz Alvarez,D. Sabes,

L. Sgandurra,V. Sordini, M. Vander Donckt, P. Verdier, S. Viret

UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS–IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France

T. Toriashvili16

GeorgianTechnicalUniversity,Tbilisi,Georgia

L. Rurua

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann, S. Beranek,L. Feld, A. Heister, M.K. Kiesel, K. Klein, M. Lipinski, A. Ostapchuk, M. Preuten,

F. Raupach, S. Schael, J.F. Schulte,T. Verlage, H. Weber, V. Zhukov6

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Ata, M. Brodski,E. Dietz-Laursonn, D. Duchardt, M. Endres, M. Erdmann,S. Erdweg, T. Esch,

R. Fischer,A. Güth, T. Hebbeker, C. Heidemann, K. Hoepfner,S. Knutzen, P. Kreuzer,M. Merschmeyer,

A. Meyer, P. Millet,M. Olschewski, K. Padeken, P. Papacz,T. Pook, M. Radziej, H. Reithler,M. Rieger,

F. Scheuch,L. Sonnenschein, D. Teyssier, S. Thüer

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

V. Cherepanov, Y. Erdogan,G. Flügge, H. Geenen, M. Geisler, F. Hoehle, B. Kargoll, T. Kress, Y. Kuessel,

A. Künsken, J. Lingemann, A. Nehrkorn, A. Nowack,I.M. Nugent, C. Pistone,O. Pooth, A. Stahl

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,I. Asin, N. Bartosik, O. Behnke, U. Behrens,A.J. Bell, K. Borras17,A. Burgmeier,

A. Campbell,F. Costanza, C. Diez Pardos,G. Dolinska, S. Dooling,T. Dorland,G. Eckerlin, D. Eckstein,

T. Eichhorn, G. Flucke, E. Gallo18,J. Garay Garcia, A. Geiser, A. Gizhko, P. Gunnellini, J. Hauk,

M. Hempel19,H. Jung, A. Kalogeropoulos, O. Karacheban19, M. Kasemann,P. Katsas, J. Kieseler,

C. Kleinwort,I. Korol, W. Lange, J. Leonard,K. Lipka, A. Lobanov, W. Lohmann19,R. Mankel, I. Marfin19,

I.-A. Melzer-Pellmann,A.B. Meyer, G. Mittag, J. Mnich, A. Mussgiller, S. Naumann-Emme,A. Nayak,

E. Ntomari,H. Perrey, D. Pitzl,R. Placakyte, A. Raspereza, B. Roland,M.Ö. Sahin, P. Saxena,

T. Schoerner-Sadenius,M. Schröder, C. Seitz, S. Spannagel, K.D. Trippkewitz, R. Walsh, C. Wissing

DeutschesElektronen-Synchrotron,Hamburg,Germany

V. Blobel, M. Centis Vignali, A.R. Draeger,J. Erfle, E. Garutti, K. Goebel, D. Gonzalez, M. Görner, J. Haller,

M. Hoffmann,R.S. Höing, A. Junkes, R. Klanner, R. Kogler,N. Kovalchuk, T. Lapsien, T. Lenz,I. Marchesini,

D. Rathjens,C. Sander, C. Scharf, H. Schettler, P. Schleper, E. Schlieckau, A. Schmidt,J. Schwandt, V. Sola,

H. Stadie,G. Steinbrück, H. Tholen, D. Troendle,E. Usai, L. Vanelderen, A. Vanhoefer, B. Vormwald

UniversityofHamburg,Hamburg,Germany

C. Barth,C. Baus, J. Berger,C. Böser, E. Butz, T. Chwalek, F. Colombo, W. De Boer,A. Descroix,

A. Dierlamm,S. Fink, F. Frensch, R. Friese,M. Giffels, A. Gilbert,D. Haitz, F. Hartmann2,S.M. Heindl,

U. Husemann,I. Katkov6, A. Kornmayer2, P. Lobelle Pardo, B. Maier, H. Mildner, M.U. Mozer, T. Müller,

Th. Müller, M. Plagge, G. Quast, K. Rabbertz,S. Röcker, F. Roscher,G. Sieber, H.J. Simonis, F.M. Stober,

R. Ulrich, J. Wagner-Kuhr,S. Wayand, M. Weber, T. Weiler, S. Williamson,C. Wöhrmann, R. Wolf

InstitutfürExperimentelleKernphysik,Karlsruhe,Germany

G. Anagnostou,G. Daskalakis, T. Geralis,V.A. Giakoumopoulou, A. Kyriakis, D. Loukas,A. Psallidas,

I. Topsis-Giotis

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

A. Agapitos,S. Kesisoglou, A. Panagiotou,N. Saoulidou, E. Tziaferi

NationalandKapodistrianUniversityofAthens,Athens,Greece

I. Evangelou,G. Flouris, C. Foudas, P. Kokkas, N. Loukas, N. Manthos,I. Papadopoulos, E. Paradas,

J. Strologas

UniversityofIoánnina,Ioánnina,Greece

G. Bencze,C. Hajdu, A. Hazi,P. Hidas, D. Horvath20, F. Sikler,V. Veszpremi, G. Vesztergombi21,

A.J. Zsigmond

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,S. Czellar, J. Karancsi22,J. Molnar, Z. Szillasi2

InstituteofNuclearResearchATOMKI,Debrecen,Hungary

M. Bartók23,A. Makovec,P. Raics, Z.L. Trocsanyi, B. Ujvari

UniversityofDebrecen,Debrecen,Hungary

S. Choudhury24,P. Mal, K. Mandal, D.K. Sahoo, N. Sahoo,S.K. Swain

NationalInstituteofScienceEducationandResearch,Bhubaneswar,India

S. Bansal,S.B. Beri, V. Bhatnagar, R. Chawla, R. Gupta,U. Bhawandeep, A.K. Kalsi, A. Kaur, M. Kaur,

R. Kumar,A. Mehta,M. Mittal, J.B. Singh, G. Walia

PanjabUniversity,Chandigarh,India

Ashok Kumar,A. Bhardwaj, B.C. Choudhary, R.B. Garg,A. Kumar, S. Malhotra,M. Naimuddin,

N. Nishu, K. Ranjan,R. Sharma, V. Sharma

UniversityofDelhi,Delhi,India

S. Bhattacharya, K. Chatterjee,S. Dey, S. Dutta, Sa. Jain, N. Majumdar, A. Modak, K. Mondal,

S. Mukherjee,S. Mukhopadhyay, A. Roy, D. Roy, S. Roy Chowdhury, S. Sarkar, M. Sharan

SahaInstituteofNuclearPhysics,Kolkata,India

A. Abdulsalam,R. Chudasama, D. Dutta, V. Jha, V. Kumar, A.K. Mohanty2,L.M. Pant,

P. Shukla,A. Topkar

T. Aziz, S. Banerjee, S. Bhowmik25,R.M. Chatterjee, R.K. Dewanjee, S. Dugad, S. Ganguly,

S. Ghosh, M. Guchait,A. Gurtu26, G. Kole, S. Kumar, B. Mahakud, M. Maity25, G. Majumder,

K. Mazumdar,S. Mitra, G.B. Mohanty, B. Parida,T. Sarkar25, N. Sur, B. Sutar,

N. Wickramage27

TataInstituteofFundamentalResearch,Mumbai,India

S. Chauhan,S. Dube, A. Kapoor, K. Kothekar, S. Sharma

IndianInstituteofScienceEducationandResearch(IISER),Pune,India

H. Bakhshiansohi,H. Behnamian, S.M. Etesami28, A. Fahim29, R. Goldouzian, M. Khakzad,

M. Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi, F. Rezaei Hosseinabadi,

B. Safarzadeh30, M. Zeinali

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran

M. Felcini,M. Grunewald

UniversityCollegeDublin,Dublin,Ireland

M. Abbresciaa,b, C. Calabriaa,b,C. Caputoa,b,A. Colaleoa,D. Creanzaa,c, L. Cristellaa,b,

N. De Filippisa,c, M. De Palmaa,b,L. Fiorea,G. Iasellia,c,G. Maggia,c,M. Maggia,

G. Minielloa,b,S. Mya,c, S. Nuzzoa,b,A. Pompilia,b,G. Pugliesea,c, R. Radognaa,b,

A. Ranieria, G. Selvaggia,b,L. Silvestrisa,2,R. Vendittia,b,P. Verwilligena

a_{INFNSezionediBari,Bari,Italy} b_{UniversitàdiBari,Bari,Italy} c_{PolitecnicodiBari,Bari,Italy}

G. Abbiendia,C. Battilana2, A.C. Benvenutia,D. Bonacorsia,b,S. Braibant-Giacomellia,b,

L. Brigliadoria,b, R. Campaninia,b, P. Capiluppia,b,A. Castroa,b,F.R. Cavalloa,

S.S. Chhibraa,b, G. Codispotia,b, M. Cuffiania,b,G.M. Dallavallea, F. Fabbria,

A. Fanfania,b, D. Fasanellaa,b,P. Giacomellia,C. Grandia,L. Guiduccia,b, S. Marcellinia,

G. Masettia, A. Montanaria, F.L. Navarriaa,b,A. Perrottaa, A.M. Rossia,b, T. Rovellia,b,

G.P. Sirolia,b,N. Tosia,b,2,R. Travaglinia,b

a_{INFNSezionediBologna,Bologna,Italy} b_{UniversitàdiBologna,Bologna,Italy}

G. Cappelloa,M. Chiorbolia,b,S. Costaa,b,A. Di Mattiaa, F. Giordanoa,b,R. Potenzaa,b, A. Tricomia,b,

C. Tuvea,b

a_{INFNSezionediCatania,Catania,Italy} b_{UniversitàdiCatania,Catania,Italy}

G. Barbaglia, V. Ciullia,b,C. Civininia, R. D’Alessandroa,b,E. Focardia,b,V. Goria,b, P. Lenzia,b,

M. Meschinia, S. Paolettia,G. Sguazzonia,L. Viliania,b,2

a_{INFNSezionediFirenze,Firenze,Italy} b_{UniversitàdiFirenze,Firenze,Italy}

L. Benussi, S. Bianco, F. Fabbri,D. Piccolo, F. Primavera2

INFNLaboratoriNazionalidiFrascati,Frascati,Italy

V. Calvellia,b, F. Ferroa, M. Lo Veterea,b, M.R. Mongea,b,E. Robuttia,S. Tosia,b

a_{INFNSezionediGenova,Genova,Italy} b_{UniversitàdiGenova,Genova,Italy}

L. Brianza,M.E. Dinardoa,b,S. Fiorendia,b,S. Gennaia, R. Gerosaa,b,A. Ghezzia,b, P. Govonia,b,

S. Malvezzia,R.A. Manzonia,b,2,B. Marzocchia,b,2, D. Menascea, L. Moronia, M. Paganonia,b,D. Pedrinia,

S. Ragazzia,b,N. Redaellia,T. Tabarelli de Fatisa,b

a_{INFNSezionediMilano-Bicocca,Milano,Italy} b_{UniversitàdiMilano-Bicocca,Milano,Italy}

S. Buontempoa, N. Cavalloa,c,S. Di Guidaa,d,2, M. Espositoa,b, F. Fabozzia,c,A.O.M. Iorioa,b, G. Lanzaa,

L. Listaa,S. Meolaa,d,2,M. Merolaa,P. Paoluccia,2,C. Sciaccaa,b,F. Thyssen

a_{INFNSezionediNapoli,Napoli,Italy} b_{UniversitàdiNapoli‘FedericoII’,Napoli,Italy} c_{UniversitàdellaBasilicata,Potenza,Italy} d_{UniversitàG.Marconi,Roma,Italy}

P. Azzia,2,N. Bacchettaa,L. Benatoa,b, D. Biselloa,b, A. Bolettia,b, R. Carlina,b, P. Checchiaa,

M. Dall’Ossoa,b,2,T. Dorigoa, U. Dossellia,F. Gasparinia,b,U. Gasparinia,b,F. Gonellaa, A. Gozzelinoa,

M. Gulminia,31, S. Lacapraraa,M. Margonia,b,A.T. Meneguzzoa,b,F. Montecassianoa, J. Pazzinia,b,2,

N. Pozzobona,b, P. Ronchesea,b,F. Simonettoa,b, E. Torassaa,M. Tosia,b, M. Zanetti,P. Zottoa,b,

A. Zucchettaa,b,2_{,G. Zumerle}a,b

a_{INFNSezionediPadova,Padova,Italy} b_{UniversitàdiPadova,Padova,Italy} c_{UniversitàdiTrento,Trento,Italy}

A. Braghieria, A. Magnania,b, P. Montagnaa,b,S.P. Rattia,b,V. Rea, C. Riccardia,b, P. Salvinia, I. Vaia,b,

P. Vituloa,b

a_{INFNSezionediPavia,Pavia,Italy} b_{UniversitàdiPavia,Pavia,Italy}

L. Alunni Solestizia,b, G.M. Bileia,D. Ciangottinia,b,2, L. Fanòa,b,P. Laricciaa,b,G. Mantovania,b,

M. Menichellia,A. Sahaa,A. Santocchiaa,b

a_{INFNSezionediPerugia,Perugia,Italy} b_{UniversitàdiPerugia,Perugia,Italy}

K. Androsova,32,P. Azzurria,2,G. Bagliesia, J. Bernardinia,T. Boccalia,R. Castaldia, M.A. Cioccia,32,

R. Dell’Orsoa,S. Donatoa,c,2, G. Fedi,L. Foàa,c,†,A. Giassia, M.T. Grippoa,32, F. Ligabuea,c,T. Lomtadzea,

L. Martinia,b,A. Messineoa,b,F. Pallaa, A. Rizzia,b, A. Savoy-Navarroa,33, A.T. Serbana,P. Spagnoloa,

R. Tenchinia,G. Tonellia,b, A. Venturia,P.G. Verdinia

a_{INFNSezionediPisa,Pisa,Italy} b_{UniversitàdiPisa,Pisa,Italy}

c_{ScuolaNormaleSuperiorediPisa,Pisa,Italy}

L. Baronea,b, F. Cavallaria,G. D’imperioa,b,2, D. Del Rea,b,2, M. Diemoza,S. Gellia,b, C. Jordaa,

E. Longoa,b, F. Margarolia,b, P. Meridiania,G. Organtinia,b, R. Paramattia,F. Preiatoa,b, S. Rahatloua,b,

C. Rovellia,F. Santanastasioa,b,P. Traczyka,b,2

a_{INFNSezionediRoma,Roma,Italy} b_{UniversitàdiRoma,Roma,Italy}

N. Amapanea,b,R. Arcidiaconoa,c,2,S. Argiroa,b,M. Arneodoa,c,R. Bellana,b, C. Biinoa, N. Cartigliaa,

M. Costaa,b_{,R. Covarelli}a,b_{, A. Degano}a,b_{, N. Demaria}a_{,L. Finco}a,b,2_{, B. Kiani}a,b_{, C. Mariotti}a_,

S. Masellia,E. Migliorea,b, V. Monacoa,b, E. Monteila,b, M.M. Obertinoa,b,L. Pachera,b,

N. Pastronea,M. Pelliccionia,G.L. Pinna Angionia,b, F. Raveraa,b,A. Romeroa,b, M. Ruspaa,c,

R. Sacchia,b, A. Solanoa,b,A. Staianoa

a_{INFNSezionediTorino,Torino,Italy} b_{UniversitàdiTorino,Torino,Italy}

S. Belfortea,V. Candelisea,b,M. Casarsaa, F. Cossuttia,G. Della Riccaa,b, B. Gobboa, C. La Licataa,b,

M. Maronea,b,A. Schizzia,b, A. Zanettia

a_{INFNSezionediTrieste,Trieste,Italy} b_{UniversitàdiTrieste,Trieste,Italy}

A. Kropivnitskaya,S.K. Nam

KangwonNationalUniversity,Chunchon,RepublicofKorea

D.H. Kim,G.N. Kim, M.S. Kim,D.J. Kong, S. Lee, Y.D. Oh,A. Sakharov, D.C. Son

KyungpookNationalUniversity,Daegu,RepublicofKorea

J.A. Brochero Cifuentes, H. Kim,T.J. Kim

ChonbukNationalUniversity,Jeonju,RepublicofKorea

S. Song

ChonnamNationalUniversity,InstituteforUniverseandElementaryParticles,Kwangju,RepublicofKorea

S. Choi, Y. Go, D. Gyun,B. Hong,H. Kim, Y. Kim,B. Lee, K. Lee, K.S. Lee, S. Lee, S.K. Park,Y. Roh

KoreaUniversity,Seoul,RepublicofKorea

H.D. Yoo

SeoulNationalUniversity,Seoul,RepublicofKorea

M. Choi,H. Kim, J.H. Kim, J.S.H. Lee, I.C. Park, G. Ryu, M.S. Ryu

UniversityofSeoul,Seoul,RepublicofKorea

Y. Choi,J. Goh, D. Kim, E. Kwon, J. Lee,I. Yu

SungkyunkwanUniversity,Suwon,RepublicofKorea

V. Dudenas, A. Juodagalvis,J. Vaitkus

VilniusUniversity,Vilnius,Lithuania

I. Ahmed,Z.A. Ibrahim, J.R. Komaragiri, M.A.B. Md Ali34,F. Mohamad Idris35,W.A.T. Wan Abdullah,

M.N. Yusli

NationalCentreforParticlePhysics,UniversitiMalaya,KualaLumpur,Malaysia

E. Casimiro Linares, H. Castilla-Valdez, E. De La Cruz-Burelo,I. Heredia-De La Cruz36,

A. Hernandez-Almada,R. Lopez-Fernandez, A. Sanchez-Hernandez

CentrodeInvestigacionydeEstudiosAvanzadosdelIPN,MexicoCity,Mexico

S. Carrillo Moreno, F. Vazquez Valencia

UniversidadIberoamericana,MexicoCity,Mexico

I. Pedraza, H.A. Salazar Ibarguen

BenemeritaUniversidadAutonomadePuebla,Puebla,Mexico

A. Morelos Pineda

UniversidadAutónomadeSanLuisPotosí,SanLuisPotosí,Mexico

D. Krofcheck

P.H. Butler

UniversityofCanterbury,Christchurch,NewZealand

A. Ahmad, M. Ahmad, Q. Hassan,H.R. Hoorani, W.A. Khan,T. Khurshid, M. Shoaib

NationalCentreforPhysics,Quaid-I-AzamUniversity,Islamabad,Pakistan

H. Bialkowska,M. Bluj, B. Boimska,T. Frueboes, M. Górski, M. Kazana, K. Nawrocki,

K. Romanowska-Rybinska,M. Szleper, P. Zalewski

NationalCentreforNuclearResearch,Swierk,Poland

G. Brona,K. Bunkowski, A. Byszuk37,K. Doroba, A. Kalinowski, M. Konecki, J. Krolikowski, M. Misiura,

M. Olszewski,M. Walczak

InstituteofExperimentalPhysics,FacultyofPhysics,UniversityofWarsaw,Warsaw,Poland

P. Bargassa,C. Beirão Da Cruz E Silva, A. Di Francesco, P. Faccioli,P.G. Ferreira Parracho, M. Gallinaro,

N. Leonardo,L. Lloret Iglesias, F. Nguyen, J. Rodrigues Antunes, J. Seixas,O. Toldaiev, D. Vadruccio,

J. Varela, P. Vischia

LaboratóriodeInstrumentaçãoeFísicaExperimentaldePartículas,Lisboa,Portugal

S. Afanasiev,P. Bunin, M. Gavrilenko,I. Golutvin, I. Gorbunov, A. Kamenev,V. Karjavin, A. Lanev,

A. Malakhov,V. Matveev38,39, P. Moisenz, V. Palichik,V. Perelygin, S. Shmatov, S. Shulha,N. Skatchkov,

V. Smirnov,A. Zarubin

JointInstituteforNuclearResearch,Dubna,Russia

V. Golovtsov,Y. Ivanov, V. Kim40,E. Kuznetsova, P. Levchenko, V. Murzin, V. Oreshkin, I. Smirnov,

V. Sulimov,L. Uvarov, S. Vavilov, A. Vorobyev

PetersburgNuclearPhysicsInstitute,Gatchina(St.Petersburg),Russia

Yu. Andreev,A. Dermenev,S. Gninenko, N. Golubev, A. Karneyeu, M. Kirsanov,N. Krasnikov,

A. Pashenkov,D. Tlisov, A. Toropin

InstituteforNuclearResearch,Moscow,Russia

V. Epshteyn,V. Gavrilov, N. Lychkovskaya,V. Popov, I. Pozdnyakov,G. Safronov, A. Spiridonov,

E. Vlasov,A. Zhokin

InstituteforTheoreticalandExperimentalPhysics,Moscow,Russia

A. Bylinkin

NationalResearchNuclearUniversity‘MoscowEngineeringPhysicsInstitute’(MEPhI),Moscow,Russia

V. Andreev,M. Azarkin39,I. Dremin39, M. Kirakosyan, A. Leonidov39,G. Mesyats, S.V. Rusakov

P.N.LebedevPhysicalInstitute,Moscow,Russia

A. Baskakov,A. Belyaev, E. Boos,M. Dubinin41,L. Dudko, A. Ershov, A. Gribushin, V. Klyukhin,

O. Kodolova,I. Lokhtin,I. Myagkov, S. Obraztsov,S. Petrushanko, V. Savrin, A. Snigirev

SkobeltsynInstituteofNuclearPhysics,LomonosovMoscowStateUniversity,Moscow,Russia

I. Azhgirey,I. Bayshev,S. Bitioukov, V. Kachanov, A. Kalinin, D. Konstantinov,V. Krychkine,

V. Petrov, R. Ryutin,A. Sobol, L. Tourtchanovitch, S. Troshin, N. Tyurin,A. Uzunian,

A. Volkov