Search for new resonances decaying via WZ to leptons in proton-proton collisions at √s=8TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

new

resonances

decaying

via

WZ

to

leptons

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 r a c t

Articlehistory: Received13July2014

Receivedinrevisedform27October2014 Accepted14November2014

Availableonline18November2014 Editor: M.Doser

Keywords: CMS Physics Technicolor

Asearchisperformedinproton–protoncollisionsat√s=8 TeV forexoticparticlesdecayingviaWZto fullyleptonicfinalstateswithelectrons,muons,andneutrinos.Thedatasetcorrespondstoanintegrated luminosityof19.5 fb−1_{.Nosignificantexcessisobservedabovetheexpectedstandardmodelbackground.}

Upperboundsat95%confidencelevelaresetontheproductioncrosssectionofaW′ _{bosonaspredicted}

byanextended gaugemodel,andontheW′_{WZ coupling.Theexpectedand observedmasslimits for}

a W′ _{boson,aspredictedbythismodel,are1.55and1.47 TeV,respectively.Stringentlimitsarealsoset}

inthecontextoflow-scaletechnicolormodelsunderarangeofassumptionsforthemodelparameters.

©2014TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense

(http://creativecommons.org/licenses/by/3.0/).FundedbySCOAP3_.

1. Introduction

Many extensions of the standard model (SM) predict heavy charged gauge bosons, generically called W′_{, that decay into a}

WZ bosonpair [1–6]. These extensions includemodels with ex-tended gauge sectors, designed to achieve gauge coupling unifi-cation,andtheories withextra spatial dimensions.There arealso modelsinwhichtheW′_{couplingstoSMfermionsaresuppressed,}

giving rise to a fermiophobic W′ _{with an enhanced coupling to}

W and Z bosons [7,8]. Further, searches for W′ _{bosons that}

de-cayinto WZ pairsare complementary to searchesinother decay channels [9–19], many of which assume that the W′_→WZ

de-cay mode is suppressed. New WZ resonances are also predicted intechnicolormodels ofdynamicalelectroweaksymmetry break-ing[20–22].

ThisLetterpresentsa search forexoticparticlesdecaying toa WZ pair with W→ ℓν and Z→ ℓℓ, where ℓ is either an

elec-tron (e) ora muon (µ), ν denotes a neutrino, andthe W andZ bosons are allowed to decay to differently flavored leptons. The data were collected with the CMS experiment in proton–proton collisionsatacenter-of-massenergy√s=8 TeV attheCERNLHC andcorrespondtoanintegratedluminosityof19.5 fb−1_.Previous searchesinthischannelhavebeenperformedattheTevatron[23] andattheLHC[24–26].Theresultshavetypicallybeeninterpreted within the context of benchmark models such as an extended gauge model (EGM) [2] and low-scale technicolor (LSTC)

mod-⋆ _{E-mailaddress:[email protected].}

els [21,22].Thesearch conductedbyCMSat√s₌7 TeV[25] ex-cludedEGMW′_{bosonswithmassesbelow1143 GeVandset}

strin-gent LSTC limits under a range of assumptions regarding model parameters. Complementary searches have also been conducted usingthehadronicdecaysoftheW andZ bosons[27–32].

The search at√s₌8 TeV presented in thispaper focuses on the fully leptonic channel, which is characterized by a pair of same-flavor,opposite-charge,isolatedleptonswithhightransverse momentum(pT)andaninvariantmassconsistentwiththatofthe Z boson.Athird,high-pT,isolated,chargedlepton isalsopresent, along with missing transverse momentum associated with the neutrino. Background arisesfrom other sources of three charged leptons, bothgenuine andmisidentified.The primary background is the irreducible SM WZ production. Non-resonant events with nogenuine Z bosoninthefinalstate, suchastopquark pair(t¯t), multijet,W+jet,Wγ+jet,andWW+jet production,arealso con-sidered. Only the firstof theseis expected tomake a significant contribution.AlsoincludedareeventswithagenuineZ boson de-cayingleptonicallyandathirdmisidentifiedornonisolatedlepton, suchasZ+jets (includingZ+heavy quarks)andZγ processes.The finalbackgroundcategoryincludeseventswithagenuineZ boson decaying leptonically and a third genuine isolated lepton, dom-inated by ZZ→4ℓ decays in which one of the four leptons is undetected.Althoughirreducible,thiscontributionisnotexpected tobe significantbecauseofthesmallZZ productioncrosssection anddileptondecaybranchingfraction.

The search presented here followsthe method applied in the previous analysis [25], whereby a counting experiment is used to compare the number of observed events to the number of

http://dx.doi.org/10.1016/j.physletb.2014.11.026

0370-2693/©2014TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/3.0/).Fundedby SCOAP3_.

expected signal and background events. However, the new anal-ysisbenefitsfromtheincrease incenter-of-massenergyto8 TeV andalso from improvementsin lepton identification, particularly at high pT. An increase in sensitivity is achieved at high W′

massesby usingoptimizedisolation criteriathatsuccessfullytake into account collimated leptons from highly boosted Z bosons. The larger center-of-mass energy alone increases the signal pro-duction crosssection by roughly 45–70% forW′ _{massesbetween}

1000–1500 GeV,whiletheimprovedleptonisolationcriteria con-tribute a 50% increase in signal efficiency over the same range. Additional improvements relatedto the optimizationof selection criteria are also incorporated. Finally, as in the previous anal-ysis [25], the results are interpreted within the context of W′

bosons in extended gauge models and vector particles in LSTC models.

2. TheCMSdetector

The central feature of the CMS apparatus is a superconduct-ing solenoidof6 m internaldiameter, providinga magneticfield of 3.8 T. Withinthe superconducting solenoid volume are a sili-conpixelandstriptracker,aleadtungstatecrystalelectromagnetic calorimeter(ECAL), and a brass andscintillator hadron calorime-ter(HCAL), each composed of a barreland two endcap sections. Muons are measured in gas-ionization detectors embedded in thesteelflux-returnyokeoutsidethesolenoid. Extensive forward calorimetrycomplementsthecoverageprovidedbythebarreland endcapdetectors.

TheECALenergyresolutionforelectronswithtransverseenergy ET≈45 GeV from Z→ee decaysis betterthan2% inthecentral region ofthe ECALbarrel (_|η| <0.8), andisbetween 2% and5% elsewhere.Forlow-bremsstrahlung electrons,where 94%or more oftheir energy iscontained within a 3×3 array ofcrystals,the energyresolutionimprovesto1.5%for|η|<0.8[33].

Muons are measured in the pseudorapidity range |η| <2.4,

withdetectionplanesmadeusingthree technologies:drifttubes, cathode strip chambers, and resistive-plate chambers. Matching muons to tracks measured in the silicon tracker results in a pT resolutionbetween1and5%,forpTvaluesupto1 TeV[34].

Theparticle-flowmethod[35,36]consistsinreconstructingand identifyingeach singleparticlewithan optimizedcombinationof allsubdetector information.The energyofphotonsis directly ob-tainedfromtheECALmeasurement,correctedforzero-suppression effects. The energy of electrons is determined from a combi-nation of the track momentum at the main interaction vertex, the corresponding ECAL cluster energy, and the energy sum of all bremsstrahlung photons attached to the track. The energy of muonsisobtainedfromthecorrespondingtrackmomentum.

AmoredetaileddescriptionoftheCMSdetector,togetherwith adefinitionofthecoordinatesystemused andthe relevant kine-maticvariables,canbefoundelsewhere[37].

3. Eventsimulation

The pythia 6.426 eventgenerator [38] and the CTEQ6L1 [39] partondistribution functions(PDFs)were used forproducingthe EGM W′ _{and LSTC signal samples. For the detailed simulation}

of the W′ _{samples, pythia was used for parton showering and}

hadronization with the Z2* tune [40] for the underlying event simulation.Crosssectionsarescaledtonext-to-next-to-leading or-der(NNLO) valuescalculatedwith fewz 2.0[41],andrangefrom 27.96 fb to 0.33 fb for W′ _{massesbetween1000 and1500 GeV.}

Characteristicsignalwidthsarebetween100and168 GeVforthe same mass range and are dominated by the detector resolution, sincethenaturalwidthsvaryfrom33to54 GeV.

For the LSTC study we assume that the technihadrons ρTC and aTC decay to WZ. Since thesetwo statesare expected to be nearly mass-degenerate [22], they wouldappear as a single fea-ture in the WZ invariant mass spectrum,and we hereafter refer to them collectively as ρTC. Since we do not expect a difference in the kinematics between the W′ _{andLSTC signals, we use the}

W′_{samplesasthedefaultfortheanalysis,withthecrosssections}

for LSTC asgiven by pythia. We consider the same relationship between the masses of the ρTC and πTC technihadrons as used in Refs. [25] and[42], MπTC= 34MρTC−25 GeV, andalso

investi-gate the dependenceof the results on the relative values of the

ρTC and πTC masses. Therelationship betweenthemasses signif-icantly affects the ρTC branching fractions [42].If MρTC<2MπTC,

the decay ρTC→WπTC dominates,such that the branching frac-tion _B(ρTC→WZ) <10%. However, if the ρTC→WπTC decay is kinematicallyinaccessible,B(ρTC→WZ)approaches100%.

Follow-ingRef.[42]wealsoassumethattheLSTCparametersinχisequal to 1/3.Changesinthisparameteraffectthebranchingfractionsfor

decayintoWZ andWπTC.

The MadGraph 5.1[43]and powheg 1.1[44–47]generatorsare interfacedto pythia forpartonshowering,hadronization,and sim-ulationoftheunderlyingevent. TheSMWZ process,whichisthe dominantirreduciblebackground,was generatedwithMadGraph. The ZZ process, which contributes when one of the leptons is either outside the detector acceptance or misreconstructed, was generatedusing powheg.Theinstrumentalbackgroundswere pro-ducedusing MadGraph andincludeZ+jets,t¯t,Zγ,WW+jets,and W+jets.The backgroundcontribution fromQCD multijetevents andfromWγ eventswasalsostudiedinthesimulationandfound to be negligible. Next-to-leading order (NLO) cross sections are usedwiththeexceptionoftheW+jets process,wheretheNNLO cross section is used. The W′ _{signal and SM processes used to}

estimate backgroundweremodeledusingafull Geant4[48] sim-ulationoftheCMSdetector.

Forallthesimulatedsamples,theadditionalproton–proton in-teractionsineachbeamcrossing(pileup)weremodeledby super-imposing minimumbias interactions(obtained using pythia with the Z2*tune)onto simulatedevents,withthe multiplicity distri-butionmatchingtheoneobservedindata.

4. Objectreconstructionandeventselection

The WZ→3ℓν decay is characterized by a pair of same-flavor, opposite-charge,high-pT isolated leptonswithaninvariant mass consistent with a Z boson, a third, high-pT isolated lep-ton, and a significant amount of missing transverse momentum associatedwiththeescapingneutrino. The analysis,therefore, re-lies on the reconstruction of three types of objects: electrons, muons, and Emiss_T . The magnitude ofthe negative vector sum of transversemomentaofallreconstructedcandidatesisusedto cal-culate Emiss

T . The events are reconstructed using a particle-flow approach[35,36]andthedetailsoftheselectionare provided be-low.

Candidate events are required to have at least three recon-structed leptons (e, µ) within the chosen detectoracceptance of |η| <2.5 (2.4)forelectrons(muons). Theeventsare selected

on-lineusingadouble-electronordouble-muontriggerforfinalstates withtheZ bosondecayingintoelectronsormuons,respectively.

The double-electrontrigger requires two clustersin the ECAL with ET>33 GeV. The lateral spread in η of the energy de-posits comprising the cluster is required to be compatible with that of an electron. The trigger also requires that the sum of the energydetected in theHCAL in acone of )R <0.14,where

)R=!()φ)2+ ()η)2_{,centeredon thecluster,be nomorethan} 15%(10%)oftheclusterenergyinthebarrel(endcap)regionofthe

ECAL.Finally,theclustersarematchedin ηand φ toatrackthat includeshitsinthepixeldetector.

The double-muon trigger requires a global muon with pT>

22 GeV and a tracker muon with pT>8 GeV. The global muon

isreconstructedusinganoutside-inapproachwherebyeachmuon candidateinthemuonsystemismatchedtoatrackreconstructed inthetrackerandaglobalfitcombiningtrackerandmuonhitsis performed[34].Thetrackermuonisreconstructedusingan inside-outapproach in which all tracks that are considered aspossible muon candidates are extrapolatedout tothe muon system. Ifat leastone muonsegment matchestheextrapolatedtrack, it quali-fiesasa trackermuon.The trigger requirementsdescribed above have been changed from those in Ref. [25] wherein two global muons were required to pass the online selection. The new re-quirementsimprovesensitivityforcollimated muonsfrom highly boostedZ bosons.

Simulatedeventsareweighted accordingtotriggerefficiencies measured, in both observed and simulated data, using the “tag-and-probe” technique [49] with a large Z→ ℓℓ sample. In the electronchannel,weapplyaparametrizationbasedontheturn-on curvemeasured withobserved electronsandfindtrigger efficien-ciestobeabove 99%.Muontriggerefficiencies abovetheturn-on aretypicallymeasured tobe above90% inobservedevents.Scale factors are also applied to the simulated samples to account for differencesbetween the observed and simulated trigger efficien-cies.Theseareapproximatelyunityforboththeelectronandmuon channels.

Candidates for leptons from the W and Z boson decays are alsorequiredtopassa seriesofidentificationandisolation crite-riadesignedtoreducebackgroundfromjetsthataremisidentified as leptons. Electron candidates are reconstructed from a collec-tionofelectromagneticclusterswithmatchedtracks.Theelectron momentum is obtained from a fit to the electron track using a Gaussian-sumfilteralgorithm[50] alongits trajectorytakinginto account the possible emission of bremsstrahlung photons in the silicontracker.WerequirepT>35 (20)GeV fortheelectronsfrom

the Z (W) boson decay. We also require |η| <2.5 and exclude

the barreland endcap transition region (1.444 <|η| <1.566) as electronreconstruction in thisregion isnot optimal. In compari-sonwiththerequirementsimposed onelectrons fromthe W bo-son decays, a looser set of identification requirements, primarily basedon thespatial matchingbetweenthetrackandthe electro-magnetic cluster, is imposed forthe electrons from the Z boson decays.Electron candidates are alsorequired to be isolated with particle-flow-basedrelativeisolation,Irel,lessthan0.15,whereIrel is defined as the sum of the transverse momenta of all neutral andchargedreconstructed particle-flow candidates inside a cone of)R <0.3 aroundtheelectron in η–φ spacedividedby the pT ofthe electron. The Irel computation includes an event-by-event correctionappliedtoaccount fortheeffectofpileup[51].Finally, ifanelectromagneticclusterassociatedwithaphotonfrom inter-nalbremsstrahlunginW andZ bosondecayshappenstobeclosely alignedwithamuontrack,itmaybemisreconstructedasan elec-tron.Inordertoremovesuchinstancesofmisreconstruction, elec-tronsare rejectedifthey are withina coneof )R <0.01 around

a muon. Observed-to-simulated scale factors for these identifi-cationandisolation requirements,measured using tag-and-probe andparametrizedasafunctionofelectron pT and|η|,areapplied ascorrectionstothesimulatedsamples.

Global muon candidates are reconstructed using information fromboththesilicontrackerandthemuonsystem.Candidatesare requiredtohaveatleastonemuonchamberhitthatisincludedin theglobalmuontrackfitandatleasttwomatchedsegmentsinthe muonsystem.Werequiremuonswith|η| <2.4 andleading

(sub-leading)muon pT>25 (10)GeV forthemuonsfromthe Z decay

andpT>20 GeV forthemuonsfromtheW decay.Wealsorequire δpT/pT<0.3 forthetrackusedforthemomentumdetermination, where δpTistheuncertaintyonthemeasuredtransverse momen-tum, andwe eliminate cosmic ray background by requiring that thetransverseimpactparameter ofthemuon withrespectto the primary vertex position be less than 2 mm. Particle-flow-based relative isolation, withpileup correctionsapplied [52],is defined using a cone ofsize )R <0.4 around the primary muon and is requiredtobe lessthan0.12. Theabove identificationcriteriaare modified for muonscoming fromthe Z boson decay:one of the muonsisallowed tobeatrackermuononlyandtherequirement on the number of muon chamber hits is removed. Additionally, the isolation variable for each muon is modified to remove the contributionof theother muon.These modificationsimprove the signal efficiency and hence the overall sensitivity for high-mass W′ _{bosons. Simulated samples are corrected using}

observed-to-simulated scale factors that are parametrized as a function of muon|η|.

Opposite-sign,same-flavorleptonpairswithinvariantmass be-tween71and111 GeV,consistentwiththeZ bosonmass,areused to reconstruct Z bosoncandidates. Inthe caseof morethan one Z boson candidate,wherethe two candidatessharea lepton,the candidatewiththemassclosest tothenominalZ bosonmass[7] isselected.EventswithtwodistinctZ bosoncandidates,wherethe candidatesdonotsharealepton,arerejectedinordertosuppress the ZZ background.The charge misidentificationrateforthe lep-tonsconsideredintheanalysisisverysmallandthusneglected.

AcandidateforthechargedleptonfromthedecayofaW bo-son,inthefollowingreferredtoasaW lepton,isthenselectedout oftheremaining leptons.When severalcandidatesarefound, the one withthe highest pT isselected. Neutrinos fromthe leptonic W boson decays escape from the detector without registering a signal andresultinsignificant Emiss

T inthe event. Inorderto in-creasethepurityoftheselectionofW bosondecays,the Emiss

T in the eventis requiredto belarger than30 GeV. Thisrequirement discriminates against both high-pT jets misidentified as leptons andphoton conversions,wherethesourceofthemisidentifiedjet orphotoncancomefromZ+jets orZγ events,respectively.

Inordertosuppresseventswherefinal-stateradiationproduces additional leptons (via photon conversion) that are identified as theW lepton,weapplytwoadditionalrequirementsontheevent aftertheW leptonselection.First,eventswiththetrilepton invari-antmassm3ℓ<120 GeV arerejectedtoremoveeventswherem3ℓ

is close to the Z bosonmass. Second, events where the )R be-tween eitherleptonfromtheZ bosondecayandtheW lepton is lessthan0.3arerejected.ThisremovescaseswheretheW lepton candidatecomesfromaconvertedphotonandisunlikelytooccur intheboostedtopologyofamassiveW′_bosondecay.

After the W and Z candidate selection, the two bosons are combined into a WZ candidate. The invariant mass of this can-didatecannot bedetermined uniquelysince thelongitudinal mo-mentum of the neutrino is unknown. We follow the procedure used in the previous CMS analysis [25] and assume the W bo-son to have its nominal mass, thereby constraining the value of theneutrinolongitudinalmomentum tooneofthe twosolutions ofaquadraticequation.Detectorresolutioneffectscanresultina reconstructed transversemass larger than theinvariant W boson mass, MW,leading tocomplexsolutions fortheneutrino longitu-dinal momentum. In thesecases, a real solution is recovered by settingMW equaltothemeasuredtransversemass.Thisresultsin two identical solutions forthe neutrino longitudinal momentum. Insimulatedeventswithtwo distinct,realsolutions,the smaller-magnitudesolutionwas foundtobe correctinapproximately70% of the cases,and thissolution was therefore chosen for all such events. Fig. 1 (top) shows the WZ invariant mass distributions,

Fig. 1. TheWZ invariantmass(top)and LT (bottom) distributionsforthe

back-ground,signal,andobservedeventsaftertheWZ candidateselection.Thelastbin includesoverflowevents.The(obs−bkg)/σ inthelowerpanelisdefinedasthe differencebetweenthenumberofobservedeventsandthe numberofexpected backgroundeventsdividedbythetotalstatisticaluncertainty.

afterthe WZ-candidate selection,for signal,background, and ob-servedevents.Atthispoint,theirreducibleWZ processdominates thebackgroundcontribution,makingup∼85%ofthetotalnumber ofexpectedbackgroundevents.

Inorder to further suppressSM background events,we apply two additional selection requirements. The first is a requirement onLT,thescalarsumofthechargedleptons’transversemomenta, shown in Fig. 1 (bottom). The second is a requirement on the massof the WZ system. The thresholdsforthese selection crite-riaarevariedsimultaneouslyat100 GeVmassspacingfortheWZ invariant mass andoptimized forthe best expectedlimit onthe W′ _{production.These optimalvalues are then plotted asa}

func-tionofthe WZ massandan analyticfunction isfitto the result-ing distribution. Forthe mass-window requirement, two regimes of linearbehavior are observed: for massesless than 1200 GeV, a narrow mass window is optimal in order to reject as much background aspossible. Above 1200 GeV, the backgroundceases to contribute significantly and it is better to have a large mass window.The LT requirementexhibitsalinearrelationship: asthe

mass increases, it is optimalto require a larger LT, until around 1000 GeV, atwhichpointhaving LT greater than500 GeVis suf-ficient.ThesemasswindowsandLTrequirementsaresummarized inTable 1.

5. Systematicuncertainties

Systematicuncertainties affecting theanalysiscan be grouped intofourcategories.Inthefirstgroupweincludeuncertaintiesthat aredeterminedfromsimulation.Theseincludeuncertaintiesinthe leptonandEmiss_T energy scalesandresolution,aswellas uncertain-tiesinthe PDFs.Following therecommendationsofthePDF4LHC group [53,54], PDF and αs variations of the MSTW2008 [55], CT10[56],andNNPDF2.0[57]PDFsetsaretakenintoaccountand their impact on the WZ cross section estimated. Signal PDF un-certaintiesaretakenintoaccountonlytoderiveuncertaintybands around thesignal cross sections,asshown in Fig. 2,and do not impactthecentrallimit.Anuncertaintyassociatedwiththe simu-lationofpileupisalsotakenintoaccount.

The second groupincludesthe systematicuncertainties affect-ing the observed-to-simulatedscale factors forthe efficiencies of the trigger, reconstruction,andidentification requirements.These efficiencies are derived from tag-and-probe studies, and the un-certainty in the ratioof the efficiencies is typically takenas the systematicuncertainty.FortheZ→ee channel,weassigna2% un-certaintyrelatedtothetriggerscalefactors,another2%toaccount forthedifferencebetweentheobservedandsimulated reconstruc-tion efficiencies, andan additional 1% uncertainty related to the electronidentificationandisolation scalefactors.FortheZ→µµ

channel,weassigna5%uncertaintyrelatedtothetriggerand an-other 2% uncertainty dueto the differences inthe observed and simulated efficiencies of muon reconstruction. An additional 3% uncertainty is assigned to the muon identification and isolation scale factors tocover potential differencesrelatedto theboosted topologyofthesignal.

The third category comprises uncertainties in the background yield.Thesearedominatedbythetheoreticaluncertainties associ-ated withthe WZ background.Weconsider contributionscoming fromuncertaintiesrelatedtothechoiceofPDF(describedabove), renormalizationandfactorizationscales, andtheSM WZ produc-tionmodeling in MadGraph.Scaleuncertaintieswere determined by studying thevariation of thecross section inthe same phase space of the analysis by varying the renormalization and factor-ization scales by a factor of two upwards and downwards with respect to their nominalvalues.The largestobserved variation is takenasasystematicuncertainty.Thisprocedureresultsin uncer-tainties of5%forWZ masses upto500 GeVandup to15%from 600 GeV to2 TeV. As the MadGraph sampleusedforsimulating theWZ background containsexplicitproductionofadditionaljets atmatrix-elementlevel,itprovidesareasonabledescriptionofthe process. The predictionis thusonly rescaled witha globalfactor to the total NLO cross section computed with mcfm 6.6[58].To estimate uncertainties related to remaining modeling differences betweenthespectrapredictedby MadGraph andtrueNLO predic-tions, we studied the ratioof the WZ crosssection in the phase space defined by the analysis selection criteria (for each mass point) tothe inclusiveWZ cross section.We compared thisratio between MadGraph and mcfm andfounddifferencesoftheorder of5%forWZ massesupto1 TeV,andoftheorderof30%between 1 and2 TeV. Thesedifferencesaretakenasadditionalsystematic uncertaintiesintheSMWZ background.Forotherbackground pro-cesses,thecrosssectionsarevariedbyamountsestimatedforthe phase spacerelevant forthisanalysisas follows:ZZ and Z+jets by30%,t¯t by15%,andZγ by50%.

Table 1

MinimumLTrequirementsandsearchwindowsforeachEGMW′masspointalongwiththenumberofexpectedbackgroundevents(Nbkg),observedevents(Nobs),expected

W′_{signalevents(Nsig),andtheproductofthesignalefficiencyandacceptance(εsig×Acc.).Theindicateduncertaintiesarestatisticalonly.}

W′_{mass (GeV) LT(GeV) MWZwindow (GeV) Nbkg Nobs Nsig εsig×Acc.(%)}

170 110 163–177 9.0±0.3 8 18±1 1.33±0.09 180 115 172–188 38±2 49 140±7 1.97±0.09 190 120 181–199 62±1 76 371±14 2.6±0.1 200 125 190–210 81±4 86 610±20 3.2±0.1 210 130 199–221 86±3 101 786±23 3.9±0.1 220 135 208–232 91±3 84 896±24 4.5±0.1 230 140 217–243 92±4 80 977±25 5.2±0.1 240 145 226–254 91±4 84 1011±24 5.8±0.1 250 150 235–265 82±1 85 1021±23 6.4±0.1 275 162 258–292 73±3 85 970±20 8.0±0.2 300 175 280–320 60±1 74 858±16 9.6±0.2 325 188 302–348 56±3 53 792±13 11.8±0.2 350 200 325–375 48±3 37 699±10 13.9±0.2 400 225 370–430 32±1 40 542±7 18.1±0.2 450 250 415–485 23.1±0.8 26 399±5 21.5±0.2 500 275 460–540 16.6±0.5 13 297±3 24.8±0.3 550 300 505–595 13.2±0.6 14 220±2 27.6±0.3 600 325 550–650 10.0±0.5 10 167±2 30.4±0.3 700 375 640–760 4.7±0.2 4 96.9±0.8 34.3±0.3 800 425 730–870 2.8±0.2 5 56.5±0.5 36.5±0.3 900 475 820–980 2.1±0.2 4 35.0±0.3 38.6±0.3 1000 500 910–1090 1.4±0.1 0 23.7±0.2 43.3±0.3 1100 500 1000–1200 0.8±0.1 0 15.9±0.1 46.8±0.3 1200 500 1080–1320 0.58±0.08 1 10.77±0.07 49.1±0.3 1300 500 1108–1492 0.56±0.08 1 8.20±0.04 56.1±0.3 1400 500 1135–1665 0.60±0.08 1 5.64±0.03 57.3±0.3 1500 500 1162–1838 0.57±0.08 1 3.76±0.02 57.5±0.3 1600 500 1190–2010 0.56±0.08 1 2.56±0.01 57.7±0.3 1700 500 1218–2182 0.50±0.08 1 1.782±0.009 57.6±0.3 1800 500 1245–2355 0.44±0.07 1 1.255±0.007 58.0±0.3 1900 500 1272–2528 0.39±0.07 0 0.844±0.005 55.0±0.3 2000 500 1300–2700 0.36±0.07 0 0.595±0.003 54.7±0.3

Fig. 2. Limitsat 95%CLonσ_{× B(}W′_{→3ℓν)asafunctionofthemassofthe} EGM W′ _{(blue) and ρTC (red), along with the 1σ and 2σ combined} statisti-calandsystematicuncertaintiesindicatedbythe green(dark)andyellow(light) bands,respectively.Thetheoreticalcrosssectionsincludeamass-dependentNNLO K-factor.ThethicknessofthetheorylinesrepresentsthePDFuncertainty associ-atedwiththesignalcrosssections.Thepredictedcross sectionsfor ρTC assume

thatMπTC=34MρTC−25 GeV and thattheLSTCparametersinχ=1/3.(For inter-pretationofthereferencestocolorinthisfigurelegend,thereaderisreferredto thewebversionofthisarticle.)

Finally,an additionaluncertainty of2.6% duetothe measure-mentoftheintegratedluminosityisincluded[59].Table 2presents asummaryoftheabovesystematicuncertainties.

Table 2

Summaryofsystematicuncertainties.Valuesaregivenfortheimpactonsignaland backgroundeventyields.Whenthe valueoftheuncertaintydiffersbetweenthe differentdecaymodesoftheW andZ bosonsand/orbetweendifferentW′_masses considered,arangeisquotedinordertoprovideanideaofthemagnitudeofthe uncertainty,i.e.itsimpact.

Systematic uncertainty Signal impact Background impact Emiss

T resolution & scale 1–3% 1–23%

Muon pTresolution 1–3% 0.5–5%

Muon pTscale 1–2% 1–22%

Electron energy scale & resolution 0.5–2% 1.5–12%

Pileup 0.1–0.8% 0.5–5%

Electron trigger efficiency 2% 2% Electron reconstruction efficiency 2% 2% Electron ID & isolation efficiencies 1% 1%

Muon trigger efficiency 5% 5%

Muon reconstruction efficiency 2% 2% Muon ID & isolation efficiencies 3% 3%

Z+jets – 30% t¯t – 15% Zγ – 50% ZZ – 30% WZ PDF – 5–10% WZ scale – 5–15% WZ MadGraph modeling – 5–30% Luminosity 2.6% 2.6% 6. Results

As shown in Fig. 1, the data are compatible with the ex-pected SM backgroundandno significant excessis observed. Ex-clusion limitson theproductioncrosssection σ(pp →W′_/ρTC→

WZ) × B(WZ→3ℓν)aredeterminedusingacountingexperiment andcomparing thenumberof observedeventsto the numberof

Fig. 3. Two-dimensionalexclusionlimitat95%CLfortheLSTCmodelasafunction oftheρTCandπTCmasses.

expectedsignal and backgroundevents.The limitsare calculated at95% confidencelevel(CL)by employing the RooStats[60] im-plementation of Bayesian statistics [7]and assuming a flat prior for the signal production cross section. Systematic uncertainties, other than signal PDF uncertainties, are represented by nuisance parameters.Theresultsforthenumberofobservedandexpected backgroundandsignal events atdifferentW′ _{masses, along with}

theefficiencytimesacceptance,aregiveninTable 1.

The expected (observed) lower limit on the mass of the W′ boson is 1.55 (1.47) TeV in the EGM. For LSTC, with the chosen parameters MπTC = 34MρTC−25 GeV, the expected and observed

ρTC masslimitsare1.09and1.14 TeV,respectively.Foreachofthe above cases the lower bound on the exclusionlimit is 0.17 TeV. Fig. 2 showsthese limits asa function of the mass of the EGM W′ bosonandthe ρTC particlealongwiththecombinedstatistical andsystematicuncertainties. Fig. 3 showsthe LSTC crosssection limitsinatwo-dimensionalplaneasafunctionofthe ρTC and πTC masses.

The W′ production cross section and the branching fraction

B(W′_{→WZ)areaffectedbythestrengthofthecouplingbetween}

theW′_{bosonandWZ,whichwe refertoas gW′WZ.The EGM}

as-sumesthat gW′WZ=gWWZ×MWMZ/M2_W′ where gWWZ istheSM WWZ couplingandMW′,MZ,andMW arethemassesoftheW′,Z, andW particles,respectively.IfthecouplingbetweentheW′

bo-son and WZ happens to be stronger than that predicted by the EGM, the observed and expected limits will be more stringent. This is illustrated in Fig. 4, where an upper limit at 95% CL on theW′_{WZ couplingis givenasa functionof themass oftheW}′

resonance.

7. Summary

A search has been performed in proton–proton collisions at

√

s=8 TeV for new particles decaying via WZ to fully leptonic finalstateswithelectrons,muons,andneutrinos.Thedataset cor-responds toan integrated luminosity of19.5 fb−1_{. No significant} excess is found in the mass distribution of the WZ candidates compared to the background expectation from standard model processes. The results are interpreted in the context of different theoreticalmodelsandstringentlowerboundsaresetat95%

con-Fig. 4. The 95%CLupperlimitonthestrengthofW′_{WZ couplingnormalizedto} theEGMpredictionasafunctionoftheW′ _{mass.The1σ and2σ combined} sta-tisticalandsystematicuncertaintiesareindicatedbythegreen(dark)andyellow (light)bands,respectively.PDFuncertaintiesonthetheoreticalcrosssectionarenot included.

fidence levelonthemassesofhypotheticalparticlesdecayingvia WZ to thefullyleptonic final state. Assumingan extendedgauge model, an expected (observed) exclusion limit of 1.55(1.47) TeV on the mass of the W′ _{boson is set. Low-scale technicolor ρTC}

hadrons with masses below 1.14 TeV are also excluded assum-ing MπTC = 34MρTC−25 GeV. These exclusion limits represent a

large improvementover previously published results obtained in proton–protoncollisionswith√s₌7 TeV.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technical andadministrativestaffs atCERNand atother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcenters and personneloftheWorldwideLHCComputingGridfordeliveringso effectively thecomputinginfrastructure essentialto our analyses. Finally, we acknowledge the enduring support for the construc-tion andoperationofthe LHCandtheCMSdetectorprovided by 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); AcademyofFinland,MEC,andHIP (Finland); CEA andCNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Republic of Korea); LAS (Lithuania); MOE andUM (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);TUBITAK andTAEK (Turkey);NASU andSFFR (Ukraine);STFC(United Kingdom);DOE andNSF(USA).

Individuals have received support from the Marie-Curie programme and the European Research Council and EPLANET

(European Union); the Leventis Foundation; the Alfred P. Sloan Foundation; the Alexander von Humboldt-Stiftung; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherchedansl’Industrieetdansl’Agriculture(FRIA-Belgium);the AgentschapvoorInnovatiedoorWetenschapenTechnologie (IWT-Belgium);the Ministryof Education,Youth andSports(MEYS) of theCzechRepublic;theCouncilofScienceandIndustrialResearch, India; the HOMING PLUS programme of Foundation For Polish Science, cofinanced fromEuropean Union, Regional Development Fund;theCompagnia diSanPaolo (Torino); theConsorzioper la Fisica(Trieste); MIURproject 20108T4XTM(Italy); theThalisand Aristeia programmes cofinancedby EU-ESF and the Greek NSRF; andtheNationalPrioritiesResearchProgrambyQatarNational Re-searchFund.

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CMSCollaboration

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W. Adam, T. Bergauer, M. Dragicevic,J. Erö, C. Fabjan1,M. Friedl, R. Frühwirth1,V.M. Ghete, C. Hartl, N. Hörmann, J. Hrubec, M. Jeitler1, W. Kiesenhofer,V. Knünz, M. Krammer1, I. Krätschmer,D. Liko, I. Mikulec,D. Rabady2_{, B. Rahbaran, H. Rohringer,R. Schöfbeck, J. Strauss,A. Taurok,}

W. Treberer-Treberspurg,W. Waltenberger, C.-E. Wulz1 InstitutfürHochenergiephysikderOeAW,Wien,Austria

V. Mossolov,N. Shumeiko, J. Suarez Gonzalez NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus

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UniversiteitAntwerpen,Antwerpen,Belgium

F. Blekman, S. Blyweert,J. D’Hondt, N. Daci,N. Heracleous, J. Keaveney, T.J. Kim, S. Lowette,M. Maes, A. Olbrechts,Q. Python, D. Strom, S. Tavernier, W. Van Doninck, P. Van Mulders, G.P. Van Onsem, I. Villella

VrijeUniversiteitBrussel,Brussel,Belgium

C. Caillol, B. Clerbaux, G. De Lentdecker, D. Dobur, L. Favart, A.P.R. Gay, A. Grebenyuk,A. Léonard, A. Mohammadi, L. Perniè2, T. Reis,T. Seva, L. Thomas, C. Vander Velde, P. Vanlaer, J. Wang UniversitéLibredeBruxelles,Bruxelles,Belgium

V. Adler,K. Beernaert, L. Benucci, A. Cimmino,S. Costantini, S. Crucy, S. Dildick,A. Fagot, G. Garcia, J. Mccartin, A.A. Ocampo Rios,D. Ryckbosch, S. Salva Diblen, M. Sigamani,N. Strobbe, F. Thyssen, M. Tytgat, E. Yazgan, N. Zaganidis

S. Basegmez, C. Beluffi3, G. Bruno,R. Castello, A. Caudron, L. Ceard, G.G. Da Silveira,C. Delaere, T. du Pree,D. Favart,L. Forthomme, A. Giammanco4_{,J. Hollar, P. Jez, M. Komm,V. Lemaitre, J. Liao,} C. Nuttens, D. Pagano,L. Perrini, A. Pin, K. Piotrzkowski,A. Popov5,L. Quertenmont, M. Selvaggi, M. Vidal Marono, J.M. Vizan Garcia

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

N. Beliy,T. Caebergs, E. Daubie, G.H. Hammad UniversitédeMons,Mons,Belgium

W.L. Aldá Júnior, G.A. Alves,M. Correa Martins Junior,T. Dos Reis Martins, M.E. Pol CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

W. Carvalho,J. Chinellato6_{, A. Custódio, E.M. Da Costa, D. De Jesus Damiao,C. De Oliveira Martins,} S. Fonseca De Souza, H. Malbouisson,D. Matos Figueiredo, L. Mundim, H. Nogima,W.L. Prado Da Silva, J. Santaolalla,A. Santoro, A. Sznajder,E.J. Tonelli Manganote6_{, A. Vilela Pereira}

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

C.A. Bernardesb, F.A. Diasa,7_{, T.R. Fernandez Perez Tomei}a_{,E.M. Gregores}b_{,P.G. Mercadante}b_, S.F. Novaesa, Sandra S. Padulaa

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

A. Aleksandrov, V. Genchev2_{, P. Iaydjiev, A. Marinov,S. Piperov, M. Rodozov,G. Sultanov, M. Vutova}

InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria

A. Dimitrov,I. Glushkov, R. Hadjiiska, V. Kozhuharov,L. Litov, B. Pavlov,P. Petkov UniversityofSofia,Sofia,Bulgaria

J.G. Bian,G.M. Chen, H.S. Chen, M. Chen, R. Du,C.H. Jiang, D. Liang,S. Liang,R. Plestina8_{, J. Tao,} X. Wang,Z. Wang

InstituteofHighEnergyPhysics,Beijing,China

C. Asawatangtrakuldee, Y. Ban,Y. Guo, Q. Li, W. Li, S. Liu,Y. Mao, S.J. Qian, D. Wang,L. Zhang, W. Zou StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

C. Avila,L.F. Chaparro Sierra, C. Florez, J.P. Gomez, B. Gomez Moreno,J.C. Sanabria UniversidaddeLosAndes,Bogota,Colombia

N. Godinovic, D. Lelas,D. Polic, I. Puljak TechnicalUniversityofSplit,Split,Croatia

Z. Antunovic,M. Kovac UniversityofSplit,Split,Croatia

V. Brigljevic,K. Kadija, J. Luetic,D. Mekterovic, L. Sudic InstituteRudjerBoskovic,Zagreb,Croatia

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

M. Bodlak,M. Finger,M. Finger Jr.9

Y. Assran10, S. Elgammal11,M.A. Mahmoud12,A. Radi11,13

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt M. Kadastik, M. Murumaa, M. Raidal, A. Tiko

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia P. Eerola, G. Fedi,M. Voutilainen DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Härkönen,V. Karimäki, R. Kinnunen, M.J. Kortelainen, T. Lampén, K. Lassila-Perini,S. Lehti, T. Lindén, P. Luukka, T. Mäenpää,T. Peltola, E. Tuominen, J. Tuominiemi,E. Tuovinen, L. Wendland

HelsinkiInstituteofPhysics,Helsinki,Finland 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, J. Malcles,J. Rander, A. Rosowsky, M. Titov

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

S. Baffioni,F. Beaudette, P. Busson, C. Charlot, T. Dahms, M. Dalchenko,L. Dobrzynski, N. Filipovic, A. Florent,R. Granier de Cassagnac, L. Mastrolorenzo, P. Miné, C. Mironov, I.N. Naranjo, M. Nguyen, C. Ochando, P. Paganini, R. Salerno,J.B. Sauvan, Y. Sirois, C. Veelken, Y. Yilmaz,A. Zabi

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

J.-L. Agram14_{, J. Andrea, A. Aubin, D. Bloch,J.-M. Brom, E.C. Chabert,C. Collard, E. Conte}14_, J.-C. Fontaine14,D. Gelé, U. Goerlach, C. Goetzmann,A.-C. Le Bihan, P. Van Hove

InstitutPluridisciplinaireHubertCurien,UniversitédeStrasbourg,UniversitédeHauteAlsaceMulhouse,CNRS/IN2P3,Strasbourg,France S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,N. Beaupere, G. Boudoul2,S. Brochet, C.A. Carrillo Montoya, J. Chasserat, R. Chierici, D. Contardo2_{, P. Depasse,H. El Mamouni, J. Fan, J. Fay, S. Gascon, M. Gouzevitch, B. Ille, T. Kurca,} M. Lethuillier, L. Mirabito,S. Perries, J.D. Ruiz Alvarez,D. Sabes,L. Sgandurra, V. Sordini,

M. Vander Donckt, P. Verdier, S. Viret,H. Xiao

UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS–IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France Z. Tsamalaidze9

InstituteofHighEnergyPhysicsandInformatization,TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann, S. Beranek,M. Bontenackels, M. Edelhoff,L. Feld, O. Hindrichs, K. Klein, A. Ostapchuk, A. Perieanu, F. Raupach, J. Sammet, S. Schael, H. Weber, B. Wittmer, V. Zhukov5

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Ata, E. Dietz-Laursonn, D. Duchardt, M. Erdmann,R. Fischer,A. Güth, T. Hebbeker, C. Heidemann, K. Hoepfner,D. Klingebiel, S. Knutzen,P. Kreuzer, M. Merschmeyer,A. Meyer, M. Olschewski,

K. Padeken,P. Papacz, H. Reithler,S.A. Schmitz, L. Sonnenschein, D. Teyssier,S. Thüer, M. Weber RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

V. Cherepanov, Y. Erdogan,G. Flügge, H. Geenen, M. Geisler, W. Haj Ahmad, F. Hoehle,B. Kargoll, T. Kress,Y. Kuessel, J. Lingemann2_{,A. Nowack, I.M. Nugent,L. Perchalla, O. Pooth, A. Stahl}

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

I. Asin,N. Bartosik, J. Behr,W. Behrenhoff, U. Behrens,A.J. Bell, M. Bergholz15_{,A. Bethani, K. Borras,} A. Burgmeier,A. Cakir,L. Calligaris, A. Campbell, S. Choudhury, F. Costanza, C. Diez Pardos,S. Dooling, T. Dorland,G. Eckerlin, D. Eckstein, T. Eichhorn, G. Flucke, J. Garay Garcia, A. Geiser, P. Gunnellini, J. Hauk, G. Hellwig,M. Hempel, D. Horton, H. Jung, A. Kalogeropoulos,M. Kasemann, P. Katsas,

J. Kieseler, C. Kleinwort,D. Krücker, W. Lange, J. Leonard,K. Lipka, A. Lobanov,W. Lohmann15,B. Lutz, R. Mankel, I. Marfin,I.-A. Melzer-Pellmann, A.B. Meyer, J. Mnich, A. Mussgiller, S. Naumann-Emme, A. Nayak,O. Novgorodova, F. Nowak,E. Ntomari, H. Perrey,D. Pitzl, R. Placakyte, A. Raspereza, P.M. Ribeiro Cipriano,E. Ron, M.Ö. Sahin,J. Salfeld-Nebgen, P. Saxena, R. Schmidt15_,

T. Schoerner-Sadenius,M. Schröder, S. Spannagel, A.D.R. Vargas Trevino, R. Walsh, C. Wissing DeutschesElektronen-Synchrotron,Hamburg,Germany

M. Aldaya Martin,V. Blobel, M. Centis Vignali, J. Erfle,E. Garutti, K. Goebel, M. Görner, J. Haller, M. Hoffmann,R.S. Höing,H. Kirschenmann, R. Klanner, R. Kogler,J. Lange, T. Lapsien, T. Lenz,

I. Marchesini,J. Ott, T. Peiffer, N. Pietsch, D. Rathjens, C. Sander,H. Schettler, P. Schleper, E. Schlieckau, A. Schmidt,M. Seidel, J. Sibille16,V. Sola, H. Stadie,G. Steinbrück, D. Troendle, E. Usai, L. Vanelderen UniversityofHamburg,Hamburg,Germany

C. Barth,C. Baus, J. Berger,C. Böser, E. Butz, T. Chwalek, W. De Boer,A. Descroix, A. Dierlamm, M. Feindt,F. Frensch, M. Giffels, F. Hartmann2_{, T. Hauth}2_{,U. Husemann, I. Katkov}5_{,A. Kornmayer}2_, E. Kuznetsova, P. Lobelle Pardo, M.U. Mozer,Th. Müller, A. Nürnberg, G. Quast, K. Rabbertz, F. Ratnikov, S. Röcker,H.J. Simonis, F.M. Stober,R. Ulrich, J. Wagner-Kuhr, S. Wayand, T. Weiler, R. Wolf

InstitutfürExperimentelleKernphysik,Karlsruhe,Germany

G. Anagnostou,G. Daskalakis, T. Geralis,V.A. Giakoumopoulou, A. Kyriakis, D. Loukas,A. Markou, C. Markou, A. Psallidas,I. Topsis-Giotis

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece A. Panagiotou,N. Saoulidou, E. Stiliaris

UniversityofAthens,Athens,Greece

X. Aslanoglou,I. Evangelou, G. Flouris,C. Foudas, P. Kokkas, N. Manthos, I. Papadopoulos,E. Paradas UniversityofIoánnina,Ioánnina,Greece

G. Bencze,C. Hajdu, P. Hidas,D. Horvath17_{, F. Sikler,V. Veszpremi, G. Vesztergombi}18_{, A.J. Zsigmond}

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,S. Czellar, J. Karancsi19,J. Molnar, J. Palinkas, Z. Szillasi InstituteofNuclearResearchATOMKI,Debrecen,Hungary

P. Raics,Z.L. Trocsanyi, B. Ujvari UniversityofDebrecen,Debrecen,Hungary

S.K. Swain

NationalInstituteofScienceEducationandResearch,Bhubaneswar,India

S.B. Beri,V. Bhatnagar, N. Dhingra, R. Gupta, U. Bhawandeep, A.K. Kalsi,M. Kaur, M. Mittal, N. Nishu, J.B. Singh

Ashok Kumar, Arun Kumar,S. Ahuja, A. Bhardwaj, B.C. Choudhary,A. Kumar, S. Malhotra,M. Naimuddin, K. Ranjan,V. Sharma

UniversityofDelhi,Delhi,India

S. Banerjee, S. Bhattacharya, K. Chatterjee,S. Dutta, B. Gomber, Sa. Jain, Sh. Jain,R. Khurana, A. Modak, S. Mukherjee,D. Roy, S. Sarkar, M. Sharan

SahaInstituteofNuclearPhysics,Kolkata,India

A. Abdulsalam, D. Dutta, S. Kailas,V. Kumar, A.K. Mohanty2, L.M. Pant, P. Shukla,A. Topkar BhabhaAtomicResearchCentre,Mumbai,India

T. Aziz, S. Banerjee, S. Bhowmik20,R.M. Chatterjee, R.K. Dewanjee, S. Dugad, S. Ganguly,S. Ghosh, M. Guchait,A. Gurtu21,G. Kole, S. Kumar, M. Maity20, G. Majumder, K. Mazumdar,G.B. Mohanty, B. Parida,K. Sudhakar, N. Wickramage22

TataInstituteofFundamentalResearch,Mumbai,India

H. Bakhshiansohi,H. Behnamian, S.M. Etesami23_{, A. Fahim}24_{, R. Goldouzian, A. Jafari,M. Khakzad,} M. Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi, B. Safarzadeh25, M. Zeinali

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran M. Felcini,M. Grunewald

UniversityCollegeDublin,Dublin,Ireland

M. Abbresciaa,b_{, L. Barbone}a,b_{,C. Calabria}a,b_{,S.S. Chhibra}a,b_{,A. Colaleo}a_{,D. Creanza}a,c_,

N. De Filippisa,c_{, M. De Palma}a,b_{,L. Fiore}a_{,G. Iaselli}a,c_{,G. Maggi}a,c_{,M. Maggi}a_{, S. My}a,c_{, S. Nuzzo}a,b_, A. Pompilia,b_{,G. Pugliese}a,c_{,R. Radogna}a,b,2_{, G. Selvaggi}a,b_{, L. Silvestris}a,2_{,G. Singh}a,b_{, R. Venditti}a,b_, P. Verwilligena, G. Zitoa

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

G. Abbiendia,A.C. Benvenutia,D. Bonacorsia,b_{, S. Braibant-Giacomelli}a,b_{, L. Brigliadori}a,b_, R. Campaninia,b_{, P. Capiluppi}a,b_{,A. Castro}a,b_{,F.R. Cavallo}a_{, G. Codispoti}a,b_{, M. Cuffiani}a,b_,

G.M. Dallavallea_{,F. Fabbri}a_{, A. Fanfani}a,b_{, D. Fasanella}a,b_{,P. Giacomelli}a_{,C. Grandi}a_{,L. Guiducci}a,b_, S. Marcellinia, G. Masettia,2_{,A. Montanari}a_{,F.L. Navarria}a,b_{, A. Perrotta}a_{,F. Primavera}a,b_{,A.M. Rossi}a,b_, T. Rovellia,b_{,G.P. Siroli}a,b_{,N. Tosi}a,b_{,R. Travaglini}a,b

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

S. Albergoa,b_{,G. Cappello}a_{, M. Chiorboli}a,b_{, S. Costa}a,b_{, F. Giordano}a,c,2_{, R. Potenza}a,b_{, A. Tricomi}a,b_, C. Tuvea,b

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

G. Barbaglia, V. Ciullia,b_{,C. Civinini}a_{, R. D’Alessandro}a,b_{,E. Focardi}a,b_{,E. Gallo}a_{,S. Gonzi}a,b_, V. Goria,b,2_{,P. Lenzi}a,b_{, M. Meschini}a_{, S. Paoletti}a_{,G. Sguazzoni}a_{,A. Tropiano}a,b

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

L. Benussi, S. Bianco, F. Fabbri,D. Piccolo INFNLaboratoriNazionalidiFrascati,Frascati,Italy

F. Ferroa_{, M. Lo Vetere}a,b_{, E. Robutti}a_{,S. Tosi}a,b

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

M.E. Dinardoa,b_{, S. Fiorendi}a,b,2_{, S. Gennai}a,2_{,R. Gerosa}2_{, A. Ghezzi}a,b_{,P. Govoni}a,b_{,M.T. Lucchini}a,b,2_, S. Malvezzia, R.A. Manzonia,b_{, A. Martelli}a,b_{, B. Marzocchi,D. Menasce}a_{,L. Moroni}a_{,M. Paganoni}a,b_, D. Pedrinia_{,S. Ragazzi}a,b_{,N. Redaelli}a_{, T. Tabarelli de Fatis}a,b

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

S. Buontempoa, N. Cavalloa,c_{,S. Di Guida}a,d,2_{, F. Fabozzi}a,c_{,A.O.M. Iorio}a,b_{, L. Lista}a_{,S. Meola}a,d,2_, M. Merolaa_{, P. Paolucci}a,2

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

P. Azzia_{, M. Biasotto}a,26_{, D. Bisello}a,b_{, A. Branca}a,b_{,R. Carlin}a,b_{,P. Checchia}a_{, M. Dall’Osso}a,b_, T. Dorigoa,U. Dossellia, F. Fanzagoa,M. Galantia,b_{,F. Gasparini}a,b_{,U. Gasparini}a,b_{, A. Gozzelino}a_, K. Kanishcheva,c_{,S. Lacaprara}a_{, M. Margoni}a,b_{, A.T. Meneguzzo}a,b_{,J. Pazzini}a,b_{,N. Pozzobon}a,b_, P. Ronchesea,b_{,F. Simonetto}a,b_{, E. Torassa}a_{, M. Tosi}a,b_{, P. Zotto}a,b_{, A. Zucchetta}a,b_{, G. Zumerle}a,b

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

M. Gabusia,b_{,S.P. Ratti}a,b_{, C. Riccardi}a,b_{,P. Salvini}a_{,P. Vitulo}a,b

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

M. Biasinia,b_{,G.M. Bilei}a_{,D. Ciangottini}a,b_{, L. Fanò}a,b_{,P. Lariccia}a,b_{,G. Mantovani}a,b_{, M. Menichelli}a_, F. Romeoa,b_{,A. Saha}a_{,A. Santocchia}a,b_{, A. Spiezia}a,b,2

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

K. Androsova,27_{,P. Azzurri}a_{,G. Bagliesi}a_{,J. Bernardini}a_{,T. Boccali}a_{,G. Broccolo}a,c_{,R. Castaldi}a_,

M.A. Cioccia,27_{,R. Dell’Orso}a_{, S. Donato}a,c_{, F. Fiori}a,c_{, L. Foà}a,c_{,A. Giassi}a_{, M.T. Grippo}a,27_{, F. Ligabue}a,c_, T. Lomtadzea, L. Martinia,b_{,A. Messineo}a,b_{,C.S. Moon}a,28_{,F. Palla}a,2_{,A. Rizzi}a,b_{,A. Savoy-Navarro}a,29_, A.T. Serbana_{, P. Spagnolo}a_{,P. Squillacioti}a,27_{, R. Tenchini}a_{,G. Tonelli}a,b_{, A. Venturi}a_{, P.G. Verdini}a_, C. Vernieria,c,2

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

c_{ScuolaNormaleSuperiorediPisa,Pisa,Italy}

L. Baronea,b_{, F. Cavallari}a_{,D. Del Re}a,b_{, M. Diemoz}a_{, M. Grassi}a,b_{,C. Jorda}a_{,E. Longo}a,b_{,F. Margaroli}a,b_, P. Meridiania_{,F. Micheli}a,b,2_{,S. Nourbakhsh}a,b_{, G. Organtini}a,b_{,R. Paramatti}a_{, S. Rahatlou}a,b_,

C. Rovellia,F. Santanastasioa,b_{,L. Soffi}a,b,2_{, P. Traczyk}a,b

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

N. Amapanea,b_{,R. Arcidiacono}a,c_{, S. Argiro}a,b,2_{,M. Arneodo}a,c_{,R. Bellan}a,b_{, C. Biino}a_{, N. Cartiglia}a_, S. Casassoa,b,2_{, M. Costa}a,b_{,A. Degano}a,b_{,N. Demaria}a_{, L. Finco}a,b_{, C. Mariotti}a_{, S. Maselli}a_,

E. Migliorea,b_{,V. Monaco}a,b_{, M. Musich}a_{, M.M. Obertino}a,c,2_{,G. Ortona}a,b_{,L. Pacher}a,b_{,N. Pastrone}a_, M. Pelliccionia_{, G.L. Pinna Angioni}a,b_{,A. Potenza}a,b_{, A. Romero}a,b_{,M. Ruspa}a,c_{,R. Sacchi}a,b_,

A. Solanoa,b_{,A. Staiano}a_{, U. Tamponi}a

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