Search for neutral resonances decaying into a Z boson and a pair of b jets or τ leptons

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

neutral

resonances

decaying

into

a

Z

boson

and

a

pair

of

b

jets

or

τ

leptons

.

The

CMS

Collaboration



CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory: Received9March2016

Receivedinrevisedform15May2016 Accepted27May2016

Availableonline31May2016 Editor: M.Doser Keywords: CMS Physics Higgs 2HDM BSM b-Tagging Tau Lepton

AsearchisperformedforanewresonancedecayingintoalighterresonanceandaZboson.Twochannels arestudied,targetingthedecayofthelighterresonanceintoeitherapairofoppositelycharged

τ

leptons orabb pair. TheZbosonis identifiedviaitsdecays toelectrons ormuons. The searchexploitsdata collectedbytheCMSexperiment atacentre-of-massenergyof8TeV,correspondingtoan integrated luminosityof19.8fb−1_{.Nosignificantdeviationsareobservedfromthestandardmodelexpectationand} limitsaresetonproductioncrosssectionsandparametersoftwo-Higgs-doubletmodels.

©2016TheAuthor.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Theobservationofanewparticlewithamassofapproximately 125GeV was reportedby theATLASandCMSexperiments atthe CERNLHC inthe WW,ZZand

γ γ

final states [1–3].Evidence of the decay of the particle to pairs of fermions (

τ τ

and bb) has also been reported in Refs. [4–6]. The measurements of branch-ing fractions, production rates,spin andparity are all consistent with the predictions for the standard model (SM) Higgs boson

[7,8],whereinasingledoubletofHiggsfieldsispresent.However, additionalHiggsbosons are expectedinsimpleextensions ofthe SM scalarsector, such asmodels withtwo Higgs-bosondoublets (2HDMs) [9]. These models predict five physical Higgs particles thatariseasaconsequenceoftheelectroweaksymmetry-breaking mechanism:twoneutralCP-evenscalars(h,H),oneneutralCP-odd pseudoscalar(A),andtwochargedscalars(H±).

Animportant motivationfor 2HDMsis that such models pro-vide away toaccommodate the asymmetry betweenmatterand antimatterobservedintheuniverse[9,10].AnextensionoftheSM scalarsectorwithtwo Higgsbosondoublets wouldalsonaturally arisein supersymmetry[11,12],which requiresa scalarstructure morecomplexthanasingle doublet.Axionmodels[13]providea

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

stronginteractionthatdoesnotviolateCPsymmetryandgiverise toaneffectivelow-energytheorywithtwoHiggsdoublets.Finally, ithasrecentlybeennoted[14] thatcertainrealisationsof2HDMs can accommodate the muon g-2 anomaly [15] without violating presenttheoreticalandexperimentalconstraints.

In the most general case, 14 parameters describe the scalar sector of a 2HDM[9].Only sixfree parameters remain once the experimental observationsareincludedby imposingtheso-called

Z

2 symmetry to suppressflavour changing neutralcurrents, and

by fixing both thevalues of themass of the recentlydiscovered SM-like Higgsboson(125GeV)[16] andtheelectroweakvacuum expectationvalue (246GeV).The compatibilityofaSM-likeHiggs boson with 2HDMs is possible in the so-called alignment limit. Thealignmentlimitisreachedwhencos

(β

−

α

)

→

0,wheretan

β

is the ratioof thevacuum expectationvaluesand

α

is the mix-ingangleofthetwoHiggsdoublets. Insucharegime,one ofthe CP-evenscalars, h or H,is identified withthe SM-like Higgs bo-son. Arecenttheoreticalstudy[10] hasshownthat,in thislimit, a large mass splitting (

>

100 GeV) betweenthe A andH bosons would favour the electroweak phase transition that wouldbe at theoriginofbaryogenesisintheearlyuniverse,satisfyingthereby thecurrentlyobservedmatter–antimatterasymmetry.Inthis con-text, themost frequentdecaymode ofthe pseudoscalarA boson would be A

→

ZH. Since the analysis strategy presented in this paperisindependentoftheassumedmodelandparityofthe

res-http://dx.doi.org/10.1016/j.physletb.2016.05.087

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

onance,theresultscanalsobeinterpretedinthereversedtopology H

→

ZA,wheretheexpected2HDMmasshierarchyisinvertedand themassofAisexpectedtobelight[17].Forbothtopologies,the lighterscalarresonance(AorH)isnotidentifiedwiththeSM-like Higgsboson.

Thispaperdescribesthefirst CMSsearch foranewresonance decayingintoalighterresonanceandaZboson.Twosearchesare performed,targetingthedecayofthelighterresonanceintoeither apairofoppositely charged

τ

leptonsorabb pair.Inbothcases, the Z boson is identified via its decay into a pair of oppositely chargedelectrons ormuons(lightleptons),labelledinthetextby thesymbol



.Thechoiceofbb and

τ τ

finalstatesismotivatedby thelargebranchingfractionspredictedinmostofthe2HDMphase space[18].Forthe



τ τ

channel,thefollowing

τ τ

finalstatesare considered:e

μ

,e

τ

h,

μτ

h,and

τ

h

τ

h,where

τ

hindicatesthedecays

τ

→

hadrons

+

ν

τ . Given its sensitivity to the 2HDMparameter spaceregion where cos

(β

−

α

)

≈

0,the search presented in this paperiscomplementarytootherrelatedsearchesperformedinthe samefinalstatebytheATLASandCMScollaborations[19,20].

2. TheCMSdetector

Thecentralfeature oftheCMSapparatusisasuperconducting solenoid of6 m internal diameter, providing a magnetic field of 3.8 T.Locatedinconcentriclayers withinthesolenoidvolumeare a silicon pixel andstrip tracker, a lead tungstate crystal electro-magnetic calorimeter(ECAL), anda brass and scintillator hadron calorimeter (HCAL), each composed of one barrel and two end-capsections.Theselayersprovidecoverageuptoapseudorapidity

|

η

|

=

2

.

5.Extensiveforwardcalorimetrycomplementsareprovided bytheendcapdetectorsfor

|

η

|

<

5

.

2.Combiningtheenergy mea-surementin the ECAL with the measurement in the tracker,the momentumresolutionforelectronswithpT

≈

45GeV fromZ

→

ee

decaysrangesfrom1.7% fornonshowering electronsinthe barrel regionto4.5%forshoweringelectronsintheendcaps[21].Muons are measured in gas-ionisation detectors embedded in the steel flux-return yoke outside the solenoid. They cover the pseudora-pidity range

|

η

|

<

2

.

4, with detection planes made using three technologies: drift tubes, cathode strip chambers, and resistive platechambers.Matchingmuonstotracksmeasuredinthesilicon tracker results in a relative transverse momentum resolution for muonswith20

<

pT

<

100GeV of1.3–2.0%inthebarreland

bet-terthan6% intheendcaps[22].The firstleveloftheCMStrigger systemusesinformationfromthecalorimetersandmuondetectors toselectthe mostinteresting events.Ahigh-level trigger proces-sorfarmdecreasestheeventratefromapproximately100 kHzto 600 Hzbeforedatastorage.AmoredetaileddescriptionoftheCMS detector,together witha definitionof thecoordinate systemand kinematicvariables,canbefoundinRef.[23].

3. Dataandsimulatedsamples

ThedatausedforthissearchwerecollectedbytheCMS exper-imentat

√

s

=

8TeV, andcorrespond to a total integrated lumi-nosityof19.8fb−1_{.Theaveragenumberofinteractionsperbunch}

crossing(pileup)inthedatawas21[24].Eventswereselected us-ingdielectronanddimuontriggers[21,22].ThesetriggershavepT

thresholdsof17and8GeV for theleadingandsubleadinglepton respectively,andrequirerelativelyloosereconstructionand identi-ficationcriteria.

Themain SMbackgroundprocesses givingrise toprompt lep-tonsareW/Z

+

jets, tt

+

jets,tW, anddibosonproduction(WW, ZZ, and WZ). The SM background contribution from ZZ is gen-erated at next-to-leading order (NLO) with powheg 1.0 [25] for the



τ τ

channelandusingtheleading-order(LO) MadGraph 5.1

Monte Carlo(MC) program [26],matched to pythia 6.4 [27] for the parton showering and hadronization, for the



bb channel. Single top quark events are generatedat NLO using powheg 1.0. Simulated eventsfor other samplesare obtainedusing the Mad-Graph 5.1 MC matched to pythia 6.4. The pythia parameters affecting thedescription oftheunderlying eventare setto those of the Z2*tune [28]. All generators used forprocesses including

τ

leptons in the final state are interfaced with tauola 2.4 [29]

forthe simulationofthe

τ

decays.Thedetectorresponse is sim-ulated usinga detaileddescriptionof CMS, basedon the Geant4 toolkit[30].Thesimulatedsamplesaccountforcontributionsfrom pileupcollisionsthatreflectthedistributionsobservedindata.The trigger andreconstruction efficiencyinthe simulationis rescaled byasmuchas2%inordertomatchthatmeasuredinthedata[24]. Twobenchmark2HDMprocessesareconsideredassignal:H

→

ZA and A

→

ZH,wherethelightestboson(pseudoscalarorscalar, according to the process) can decayto

τ τ

or bb,and the Z de-cays to



. The MadGraph 5.1program,interfacedto pythia 6.4 and tauola 2.4,wasusedtogeneratesignalsamplescorresponding to differentvaluesofAandH masses(mA andmH,respectively).

The same propertiesof the SM Higgs boson are assigned to the lightest scalarboson,h, andits massmhisfixed at125GeV. The

identification of the observed Higgs boson, together with all its measuredproperties,withthescalarh constrainsthe phenomeno-logically reliable parameterspace regions to not depart fromthe SM-likeconditioncos

(β

−

α

)

≈

0.Thiscorrespondstotheso-called alignmentlimit[31].Consideringtheparameterspacestillallowed bydirectsearches[12],thechosenvaluesforcos

(β

−

α

)

andtan

β

are0.01and1.5,respectively,andtype-IIYukawacouplingsare as-sumedforthebenchmarkprocesses.

The massesofthe chargedHiggsbosons (mH±) are keptequal

to the highest mass involved in the signal process (mH or mA)

topreserve thedegeneracym2_H±

≈

mH2/A [17],denotingwithmH/A

the massofthe scalarH or the massofthe pseudoscalarA. The value ofthem12 parameter,thesoft

Z

2 symmetrybreakingmass,

was set to m2

12

=

m2H±tan

β/(

1

+

tan

2

_β)

_{, accordingto the}

mini-malsupersymmetricstandardmodel(MSSM)parametrisation[11]. The value ofthecomplex couplings

λ

6 and

λ

7 in this

parametri-sation are set to zero, in order to avoid tree-level CP violation. The productioncross sections, used for the normalisation of the signal samples, are computed using the SusHi 1.4 program [32], which provides next-to-next-to-leading-order (NNLO) predictions. The branching fractionfor the heavy andlight Higgs bosons are obtainedusing the 2hdmc 1.6program [33], followingthe guide-linesinRefs.[34,35].

The signal benchmark where the light boson decays into

τ τ

is simulated for values of mH/A andmA/H varying in the ranges

200–1000 and 15–900 GeV, respectively, with the constraint mH/A

>

mA/H

+

mZ.Forthe



bb analysisthelowerboundforthe

invariant massmA/H goesdownto10GeV. TheregionwheremH

issmallerthanmhisnotpertinentinthismodel. 4. Eventreconstructionandselection

Event reconstruction is based on the particle-flow algorithm

[36,37], which exploits information from all the CMS subdetec-tors to identify andreconstruct individual particles in theevent: muons,electrons,photons,chargedandneutralhadrons.Such par-ticles are algorithmically combined to form the jets, the

τ

h

can-didates, the missing transverse momentum p



miss_T , definedas the projectionontheplaneperpendiculartothebeamsofthenegative vector sumoftheparticles momentaandits magnitude, denoted as Emiss_T . To minimisethe contributions from pileup interactions, charged tracks are requiredto originate fromthe primary vertex (reconstructed using the deterministic annealing algorithm [38]),

whichistheonecharacterisedbythelargestp2

Tsumofits

associ-atedtracks.

Electronsare identified by combininginformation fromtracks and ECAL clusters, including energy depositions from final-state radiation[21].Muonsareidentifiedthroughacombinedfitto po-sition measurements from both the inner tracker and the muon detectors[22].The

τ

hobjectsareidentifiedandreconstructed

us-ing the “hadron-plus-strips” algorithm [39], which uses charged hadrons and photons to reconstruct the main hadronic decay modesofthe

τ

lepton: onechargedhadron, one chargedhadron and photons, and three charged hadrons. Electrons and muons can be misidentified as hadronic taus if produced in jets or if close-byactivityfrompile-uporbremsstrahlungispresent.These misidentifications are suppressed using dedicated criteria based ontheconsistencybetweenthe measurementsinthetracker,the calorimeters,andthemuondetector[39].Torejectnonpromptor misidentified leptons, requirements are imposed on the isolation criteria,basedonthesumofdepositedenergies.Theabsolute lep-ton isolation Iabs is definedby the scalar sum of the pT of the

charged particles from the primary vertex, neutral hadrons, and photonsinan isolationcone ofsize



R

=

√

(

η

)

2

+ (φ)

2

=

0

.

4 (



R

=

0

.

3 for electrons),centred around the leptondirection. To reduce theeffectfrompileup, theenergydepositreleased inthe isolation cone by charged particles not associated with the pri-mary vertex is subtracted from the neutral particles pT scalar

sum. For electrons and muons the relative isolation, defined as Irel

=

Iabs

/

pT,isused.

Jetsare clusteredusingtheanti-kT algorithm[40],witha

dis-tance parameter of 0.5, as implemented in the Fastjet software package [41]. Charged particles not associated with the primary vertexare excluded by means of the charged-hadronsubtraction technique [42]. Theremaining energy originatingfrompileup in-teractions, includingthe neutralcomponents,is subtracted based onthe medianenergydensityin the detectorcomputedthrough theeffectivejet areatechnique [43].The identificationofb quark initiated jetsisachieved throughthe combined secondaryvertex (CSV) algorithm [44], which exploits observables related to the longlifetimeofBhadrons.

4.1.SelectionforZ

→ 

Inselecting



bb and



τ τ

events, theleptons fromZ boson decayare requiredto be well within the CMStrigger and detec-tor acceptance of pT

>

20 GeV and

|

η

|

<

2

.

5 for electrons, and

pT

>

20 GeV,

|

η

|

<

2

.

4 for muons. Muon momentum-scale [22]

and electron energy corrections [21] are applied to recover the globalshiftofthescaleobservedbetweendataandsimulation.The requirementontherelativeisolationfortheleptonsissetto Irel

<

0.15forelectronsandIrel

<

0.2formuonsinselecting



bb events.

For the leptons from the Z boson, in the case of



τ τ

events, the required relative isolation is Irel

<

0.3. The presence of two

reconstructed same-flavour, oppositely charged lepton candidates forming a pair with invariant mass in the range of 76–106 GeV isrequired to suppress contamination of non-resonant Drell–Yan

+

jets and tt processes. In events where multiple Z candidates arepresent,theleptonpairwiththeinvariantmassclosesttothe nominalZbosonmass[45]ischosen.

4.2.Eventselectionfor



bb

For the



bb search, the jets are selected to be in the kine-maticregionpT

>

30GeV and

|

η

|

<

2

.

4.AtleasttwoCSVb-tagged

jetsare requiredto bepresentintheevent, toreduce the contri-bution of Z

+

light-parton jets(originating from gluons oru, d,

or s quarks) events. The threshold on the b tagging discrimina-torcorresponds toa btaggingefficiencygreater than65% andto amisidentificationprobabilityforlight-partonjetsof1%[44].The twob-taggedjetswithhighestvaluesoftheCSVdiscriminantare consideredascandidatedecayproductsofthenewlightresonance.

The Emiss

T significance[46,47],representinga

χ

2difference

be-tweenthe observedresultfor Emiss_T andthe Emiss_T

=

0 hypothesis, is used to suppress background events originating from tt pro-cesses.Thisvariableprovidesanevent-by-eventassessmentofthe likelihood that the observedmissing transverse energyis consis-tent with zero giventhe reconstructed content of the eventand known measurement resolutions. This variable is a stronger dis-criminantagainsttt backgroundthanEmiss_T aloneandalsoprovides smaller systematic uncertainties. The distribution of the tt com-ponentmotivatesthe requirementonthe Emiss_T significancetobe smallerthan 10.

4.3. Eventselectionfor



τ τ

To increase thesignal sensitivityin thehigh

τ τ

mass region, the



τ τ

event selection includes the requirement of a trans-versely boosted Z boson (pT

>

20 GeV), together with a large

(

>

1.5 rad) azimuthal anglebetween the Z boson flight direction and



pmiss_T ,particularlyeffectivein suppressingtheZ

+

jets back-ground.Inadditiontothetwolightleptonsrequiredtoreconstruct theZboson,twoadditionaloppositelychargedanddifferent-flavor leptons (e,

μ

, and

τ

h) are used to reconstructthe Aor H boson

candidate. The requirements on the pseudorapidity forlight lep-tonsarethesameasfortheZdecayleptons,withthe pT

thresh-old lowered to 10 GeV. The

τ

h candidates are required to have

pT

>

20GeV and

|

η

|

<

2

.

3.Therelativeisolationforelectronsand

muons, andtheabsoluteisolationfor

τ

leptons arerequiredtobe smallerthan0.3and2GeV,respectively.SincetheZ

+

jets back-groundis characterisedby a softer lepton transversemomentum spectrum than thesignal one, this backgroundis reducedby se-lecting events with high LT, where LT indicates the scalar sum

ofthe visible pT ofthe decayproducts froma

τ τ

pair. Both the

isolation requirements andthe value ofthe LT thresholdare

de-terminedasa resultofanoptimisationprocedurethatmaximises the expectedsignificance of thesearched signal. The optimal re-quirementonthe LT quantity isfound byscanning thethreshold

between20and200GeV,atintervalsof20GeV.

Jetsare requiredtohave pT

>

30GeV and

|

η

|

<

4

.

7.Toreduce

thelargett background,alleventswithatleastonejetwithpT

>

20GeV and

|

η

|

<

2

.

4,reconstructed asa jetoriginatingfroma b quark according to the output of the CSV discriminator used for tagging,arevetoed.

To calculate the

τ τ

invariant mass, the secondary-vertex fit algorithm(svfit)[48]isused,alikelihood-basedmethodthat com-binesthereconstructed



pmiss_T anditsresolutionwiththe momen-tumofthevisible

τ

decayproducts toobtainanestimatorofthe massoftheparentparticle.

5. Modellingofthebackground

5.1. The



bb channel

The relevant sources of background for the



bb final state originate fromZ

+

jetsprocesses,tt and tWproduction,diboson production,andvectorbosonproductioninassociationwithaSM Higgsboson.ThecontributionsofZ

+

jetsandtt backgroundsare measuredby meansofadata-basedmethod,thedibosonandtW backgroundsare normalisedto theCMSmeasurements.Forthese backgrounds, the shapes are taken from MC, while the normali-sations are extracted fromdata. The vector boson production in

associationwithaSMHiggsbosonisnormalisedtothetheoretical prediction.

The comparisonof data andpredictions after the selection of events for the



bb final state shows the importance of an ac-curate theoretical calculation of the Z

+

jetsproduction rate. In particular, in the 400–700 GeV range of the mbb distribution,

thedataisfound toexceedtheLOpredictionbyup totwo stan-darddeviations,depending ontheconsideredmass.Thisexcessis nolongersignificant whenNLO QCDcorrections, asimplemented in amc@nlo [49],are included in the modellingof the Z

+

jets process.For thisreason, theLOpredictions arecorrected usinga reweightingtechnique,inordertoaccountforNLOQCDeffects.To thisend,itbecomesnecessarytoapplythereweightingaccording totheparton(orhadron)flavourofthejetsinthegeneratedevent. The ratio NLO/LO of the light- and heavy-flavour components of themjj distributioniseach fittedwitha third-orderpolynomial

and a separate reweighting of the shape of the light and heavy flavour components ofmjj isapplied, resulting inbetter

agree-mentwiththedata.

Todetermine the Z

+

jetsandtt normalisation, a data-based methodisexploited.Data-derivedcorrectionfactorsforsimulation areobtainedafteranadditionalcategorisationoftheZ

+

jet back-groundevents,basedontheflavour(bjetornot)andmultiplicity (exactly twojetsor threeormore jets)ofthe reconstructedjets. Thesecategoriesare sensitive to NLO effectsrelatedto the mod-ellingofextra jets[50].Scale factors(SFs)are introducedforthe tt backgroundandthelightandheavyflavourcomponentsofZ

+

jetsbackground.Theseareleft free tofloatin atwo-dimensional fitofthedistributionspredictedbythesimulationtothedata.The distributions used as input are the product of the CSV discrimi-nantsofthetwoselectedjets,andtheinvariantmassofthelepton pair from the Z boson decay in the range 60

<

m

<

120 GeV.

The first observable is sensitive to the contribution from non-b jets,whereasthesecondoneissensitivetothecontributionofthe tt productionprocess.Thefitisperformedsimultaneouslyinfour differentcategories:electrons, muons, exactlytwo jets,andmore than two jets. The SF forthe tt is foundto be very close tothe unity,whilefortheZ

+

jetsprocesstheSFsdepartfromunityby asmuchas1.3forthelightflavourcomponent.

The overall yields from diboson and tW processes are nor-malisedtotheCMSmeasurements[51–54].Theassociated produc-tionofaZbosontogetherwiththeHiggs-likescalarboson(Zh)is alsoaccountedforasbackground,andnormalisedtotheexpected theoreticalcrosssection[55].

5.2. The



τ τ

channel

Methods basedon both data andsimulationare used to esti-matetheresidualbackgroundaftereventselection.Normalisations andmassdistributionsintheZZ,Zh,aswellasfortheminorfully leptonicWWZ,WZZ,ZZZandttZ backgroundsareestimatedfrom simulation. The Z

+

jets andWZ

+

jetscontributions are mea-suredbymeansofadata-basedmethod.

Production of Z

+

jets and WZ

+

jets constitutes the main source of background when at least one lepton is misidenti-fied. Misidentified light leptons arise from semileptonic decays of heavy-flavour quarks,decays in flight of hadrons, and photon conversions, while jetsoriginating fromquarks orgluons can be misidentified as

τ

h. Backgrounds with at leastone misidentified

lepton are estimated from control samples in data starting from the estimation of the lepton misidentification probabilities. The lepton misidentification probability is defined as the probability that a genuine jet, satisfying loose lepton identification criteria (whichrefertotheso-called“loose”lepton),alsopassesthe identi-ficationcriteriarequiredforaleptoncandidateinthesignalregion

(so-called“tight”lepton).Thisprobabilityismeasuredforeach lep-ton flavour using a datasample where a Zcandidateis selected, andanadditionalsinglelepton(electron, muon,or

τ

h)passesthe

loose identification requirements. Counting the fraction of such loose leptons that also pass the tight lepton identification crite-ria inthe pT bins ofthe reconstructedjet closest, in



R, to the

loose lepton,yields themisidentification probability f as a func-tionofpT.Thecontributionfromgenuineleptonsarisingfromthe

WZ andZZproduction aresubtracted. Once themisidentification probabilitiesarecomputed,threecontrolregions(C R)aredefined withaZcandidateandtwo opposite-signleptons,asfollows:the C R00 wherein both leptons pass loose identification criteria but

not the tightones; C R10 region,whereinone lepton passestight

identification requirements,the other onlyloose criteria, andthe looseleptonisthe

τ

hwithlower pT inthe

τ

h

τ

hchannel,thelight

lepton in the



τ

h channels, andthe electron in the e

μ

channel;

the C R01 region,whichis similartoC R10 butthelooseleptonis

the

τ

hwithhigherpTinthe

τ

h

τ

hchannel,the

τ

hinthe



τ

h

chan-nels,andthemuoninthee

μ

channel.TheestimatedNmisIDofthe

background withatleastone misidentified lepton froma pairof closest-jetpTbinsisgivenby:

NmisID

=

N10 f1 1

−

f1

+

N01 f2 1

−

f2

−

N00 f1f2

(

1

−

f1

)(

1

−

f2

)

,

(1)

where N00, N01, and N10 denotethe numberofevents fromthe

C R00, C R01, and C R10 control regions, respectively, with closest

jetsintheconsideredpTbins,and f1 and f2 indicatethe

misiden-tificationprobabilitiesassociatedwiththetwodifferentflavor (ex-cept for the

τ

h

τ

h final state) loose leptons in the pT bins. The

expressioninEq.(1)takesintoaccountboththebackgroundwith twomisidentifiedleptons(mostlyfromZ

+

jets)andthatfromonly onemisidentifiedlepton(primarilyfromWZ

+

jets).

Thecontaminationfromgenuineleptonsinthecontrolregions from the SM Zh, WWZ, WZZ,ZZZ, ttZ,and ZZprocesses is esti-mated fromsimulation, and subtracted from N00, N01, and N10.

Thetotalbackgroundinthesignalregionisobtainedbysumming thecontributionsfromallpairsofpT bins.

6. Systematicuncertainties

Thesystematicuncertaintiesarereportedinthefollowing para-graphsandsummarisedin

Table 1

.

TheuncertaintyontheintegratedluminosityrecordedbyCMS isestimatedtobe2.6%[56].

The systematic uncertainties associated with the lepton effi-ciencySFs,usedtocorrectthesimulationandderivedfromstudies atthe Zpeak usingthe tag-and-probe (T&P)method[22,21], are approximately1%formuonsand2%forelectrons, andaffectboth signalandbackgroundprocessesinthesameway.Also,the uncer-tainties onthedoublemuon anddoubleelectrontrigger efficien-ciesareevaluatedtobe1%fromsimilarstudiesattheZpeak[24]. The uncertainty on the jet energy scale is derived from the method of Ref. [57] and the parameters describing the shape of theenergydistributionarevariedbyone standarddeviation(SD). The effectis estimatedseparately on the backgroundandon the signal, resulting ina 3–5% variation,depending onthe pT and

η

of the jets. The uncertainty on signal and backgroundyields in-ducedby theimperfectknowledge ofthejet energyresolutionis estimatedtobe3%

[57]

.

Theuncertainties affectingbtaggingefficienciesare pT

-depen-dent,andvaryfrom3%to12%(forpT

>

30GeV)

[44]

.Theimpact

oftheseuncertaintiesonthenormalisationofsignalis5%for back-groundand4–6%forsignalinthe



bb analysis,andabout1%in the



τ τ

analysis.Theuncertaintyinthemistaggingrateisfound tohaveanegligibleimpact.

Table 1

Summaryofsystematicuncertaintiesforbothτ τ andbb finalstates.

Source Uncertainty [%]

H→ZA→ bb H→ZA→ τ τ

Luminosity 2.6 2.6

Lepton identification/isolation/scale 1–2 1–2

Lepton trigger efficiency 1 1

Jet energy scale 3–5 3–5

Jet energy resolution 3 3

b-tagging and mistag efficiency 4–6 1

Signal modelling (PDF, scale) 5–6 5–6

Background norm. (Z Z ) 11 11

Background norm. (Z+jets and tt) <8 – Background norm. (tW, WW, WZ and Zh) 8–23 –

Z+jet background modelling 5–30 –

Signal efficiency extrapolation 3–50 –

Tau identification/isolation – 6

Tau energy scale – 3

Reducible background estimate – 40

Thesystematicuncertaintyonthesignal isevaluated by vary-ing the set of parton distribution functions (PDFs) according to thePDF4LHCprescriptions[58–60]andthefactorisationand renor-malisationscalesby varyingtheir valuesby afactoronehalf and two.Aneffectof5–6% isestimatedfortheentiremassrangefor both



τ τ

and



bb finalstates.This uncertaintyisestimatedby propagatingthesevariationsthroughthesignalsimulationand re-constructionsequenceandthusaccountsforuncertaintiesrelated tobothsignalcrosssectionandacceptance.

Finally,an 11%uncertaintyisassignedtotheZZnormalisation fromthecrosssectionmeasuredbyCMS[51].

Forthe



bb final state, the uncertainty on the SFs used for normalisationofZ

+

jetsandtt backgrounds isderivedfromthe statisticaluncertainty resulting fromthe fit used to derive these SFsanditisestimatedtobe

<

8%.Anadditionalsystematic uncer-taintyassociatedwiththembbspectrumcorrection,describedin

Sec.5,rangesfrom5%formbbbelow700GeV to30%formasses

attheTeVscale.An uncertaintyof8% isassignedtothe normal-isationof theWWprocess, corresponding to theuncertainties in thecrosssection measured by CMS[52].Asimilar uncertaintyis assignedalso tothe WZ process, whichshares the same sources ofuncertainties inthecross section measurement.Forthe minor tWbackground,theuncertaintyisestimatedas23%,alsobasedon themeasured cross section [54].A 7% uncertainty is assignedto theZhprocess,reflecting theuncertaintyon thetheoreticalcross section [55]. Given the small cross section for this SM process compared to other background processes,its contribution to the background normalisation uncertainty has been calculated to be lessthan 1% andis thus considered negligible.In order to inter-polate smoothly thesignal efficiencyacross the parameter space, additionalmasspointsforthe



bb finalstateareprocessedusing a parametric simulation [61], tuned for delivering a realistic ap-proximationofthe CMSresponse inthe reconstructionofphysics objects usedin this search. Forthis reason, an additional source ofuncertaintyisintroducedfortheSFappliedtothesesamplesto reproducetheefficiencymeasuredwiththefullsimulation.Thisis measuredforthedifferentsignal pointsinthemH–mA plane and

itiscloseto3%inmostofthephasespace,butrisesto50%atthe boundariesofthesensitivityregion.

In the



τ τ

final state, the uncertainty of 6% [39] in the

τ

h

identificationefficiency, whichhas been determined usinga T&P method,hasbeentakenintoaccount.The

τ

h energyscale

uncer-taintyiswithin3%[39]andonlyaffectstheshapesofthe

τ τ

mass distributions. The systematicuncertainties estimated fore,

μ

,

τ

h

andjetenergyscalesarepropagatedto



pmiss

T andtothemass

dis-tributions.Thepropagationto



pmiss

T involvesasumoftheenergies

of each objectfirst and a consequent subtractionof such contri-butionsoncethenominalenergyscales(orresolutions)arevaried up anddown byone SD(fore,

μ

,

τ

h,andjets).Oneofthe main

systematic uncertainties is related to the nonprompt background estimation. Thisuncertainty hasbeen evaluated using simulation bycomparingthedirectestimateofthebackgroundswiththat ob-tained using the procedure adopted in the analysis, but applied to simulated events.The discrepancybetween the two estimates neverexceeds40%.Thisvalueisthusconsideredastheuncertainty ontheestimatesofthereduciblebackgroundyieldforallchannels andall LTthresholds.

7. Results

The analysissearchesfornewresonancedecays bycomparing data to simulation in the two-dimensional plane defined by the four-body (mbb ormτ τ )andtwo-body(mbb ormττ )invariant

masses. The numerical valuesforthe upper limitsorthe signifi-canceofalocalexcessareobtainedusingtheasymptoticmethod describedinRef.[62].TheCLSmethod[63,64]isusedtodetermine

the95% confidencelevel(CL)upperlimitsonthe excludedsignal crosssection.Forbothfinalstates,thelimitsinthelower-right tri-angleofthemassplane,whichcorrespondstotheprocessA

→

ZH, are obtainedby mirroring the results obtained in the upper-left triangle,sincethe signal efficienciesforH

→

ZA andA

→

ZH are equalforthesamemassesoftheheavyandlightHiggsbosonsin thetwoprocesses.

7.1. The



bb channel

Forthe



bb final state, resultsare obtainedusinga counting approach,which canbe reinterpreted inother theoretical models withthesamefinal state.Resultsarereportedinbinsofmbband

mbbmasses,intherangefrom10GeV to1TeV formbb,andfrom

140GeV to1TeV formbb.Todefinethepropergranularityofthe

binning,a studyisperformedusingsignal benchmarkpoints and evaluatingthewidthofthembbandmbbpeaksintheconsidered

mass range.Theaverage reconstructed width, definedasone SD, formbbandmbbisfoundtobeapproximately15%ofthe

consid-eredmass.Thebinwidthshavebeenchosentobe

±

1.5 SDaround eachconsideredmasspoint.

Theefficiency,definedasthefractionofgeneratedsignalevents reconstructed after the final selection, is calculated withthe full CMS simulationand reconstruction softwareat 13representative signalpoints inthemH–mA massplane.Thesignalefficienciesfor

the rest ofthe plane are obtained by interpolating theratio be-tweenthefullsimulationandtheparametricsimulation(typically

Fig. 1. Observed95%CLupperlimitsonσH/A→ZA/H→bb asafunctionofmAand mH.

0.9),calculated ineach of the13 signal masspoints, andscaling theefficienciescalculatedusingtheparametricsimulationby this interpolatedratio.Theresultingsignalefficiencyrangesfrom8%at

(

mA

,

mH

)

= (

100

,

300

)

GeV to13%at

(

300

,

600

)

GeV.

Fig. 1 showsthe observedupper limitsonthe product ofthe crosssection(

σ

)andbranchingfraction(

B

)forthe



bb finalstate in themH–mA plane. The achieved sensitivityprovides an

exclu-sionlimitat95% CLofapproximately10 fbforalargefractionof thetwo-dimensionalmass plane.Inparticular,the observedlimit ranges fromjustabove 1 fbformH close to 1TeV to 100 fb for

mH

<

300GeV.Thevalidityoftheseresultsisapplicableto

mod-elsallowing theexistenceofboth AandHbosons witha natural widthsmallerthan15%oftheirmasses.

Two moderate excesses are observed for the



bb chan-nel in the regions around

(

mbb

,

mbb

)

= (

95

,

285

)

GeV and

(

575

,

660

)

GeV.Accordingtotheproceduredescribed atRef.[65], theyhavelocalsignificancesof2.6and2.85 SDrespectively,which become globally 1.6 and 1.9 SD, once accounting for the look-elsewhere effect [66]. The low-mass excess is more compatible with the signal hypothesis, both in terms of yield and width. The reconstructed invariant mass distributions for the bb and



bb systems, in the regions around this excess,are reported in

Fig. 2andcomparedwiththeexpectationsfrombackground pro-cesses. A 2HDM type-IIbenchmark signal at mH

=

270 GeV and

mA

=

104GeV,normalised to theNNLO SusHi prediction, is also

superimposed. 7.2. The



τ τ

channel

Inthecontextofthe



τ τ

analysis,asearchbasedonthemττ distribution is performed. For every considered pair of H and A mass values, the search is performed in eight

τ τ

svfit binned mass distributions, each corresponding to one of the eight con-sidered final states. Variable bin widths are adopted in order to account for themass resolution. A simultaneous likelihoodfit to the observed distributions is performed with the expected dis-tributions from the background-only and signal plus background hypotheses.The normalisation of thesignal distributionis a free parameterinthefit.Nosignificantdeviationsareobservedindata fromthe SM expectation. The svfit massdistributions ofthe

τ τ

pairintheeightdifferentfinalstatesareshownin

Fig. 3

.The cho-sensignalcorresponds tomH

=

350GeV andmA

=

90GeV,which

is the one closest to the centreof the bin in which the highest

Fig. 2. (Top)Thembbspectrumforeventsselectedinthe222<mbb<350GeV re-gionfordataandsimulationandtherelativeratio.(Bottom)Thembbspectrumfor eventsselectedinsidethe72<mbb<114GeV regionfordataandsimulationand therelativeratio.ThesignalcorrespondingtomH=270GeV andmA=104GeV, normalisedtotheNNLO SusHi crosssection,issuperimposedfortanβ=1.5 and cos(β−α)=0.01 inthe2HDMtype-IIscenario.Theoverallsystematicuncertainties inthesimulationarereportedasahatchedband.

excess isobservedinthe



bb channel.The shownshapes corre-spondto LT

>

40GeV fore

μ

,LT

>

60GeV for e

τ

hand

μτ

h,and

LT

>

80GeV for

τ

h

τ

h.

Fig. 4 showsthe limit on

σ

B

for the



τ τ

final state in the mH–mA plane.Signalcrosssectionsofabout5–10 fbareexcluded

in mostofthe mH–mA plane (500

<

mH/A

<

1000 GeV and90

<

Fig. 3. svfit massdistributionsfordifferentfinalstatesoftheH→ZA→ τ τprocess,wheretheZ bosondecaystoee (rightcolumn)andμμ(leftcolumn).Theexpected signalcorrespondingtomH=350GeV andmA=90GeV,whosecrosssectiontimesbranchingfractionisnormalisedtotheNNLO SusHi prediction,issuperimposedfor tanβ=1.5 andcos(β−α)=0.01 inthe2HDMtype-IIscenario.Onlystatisticaluncertaintiesarereportedasahatchedband.

Fig. 4. Observed95%CLupperlimitsonσH/A→ZA/H→τ τ asafunctionofmAand mH.

7.3. Combinationinthecontextof2HDM

Observed and expected upper limits on the signal cross sec-tionmodifier

μ

=

σ

95%

/

σ

tharealsoderivedandreportedin

Fig. 5

,

where

σ

th isthe theorycrosssection ofthe2HDMsignal

bench-markusedinthisanalysis.Theresultsareobtainedfromthe com-binationofthe



bb and



τ τ

finalstates.Thissearchisnotable toexcludethehigh-massregionswheremA

>

300GeV andmH

>

300GeV, dueto the drop in thesignal cross section, wherethe A

/

H

→

tt channelopensup formA/H

>

2mt, wheremt isthetop

quarkmass[18].Furthermore,intheregionwherehighly-boosted topologiesstartcontributing(mH

≈

10mA),thesensitivityislower

relative to the rest of the plane, primarily caused by the ineffi-ciency in reconstructing signal decay products insuch a regime. Still,asignificantportionofthebenchmarkmassesisexcludedfor a2HDMtype-IIscenario withtan

β

=

1

.

5 and cos

(β

−

α

)

=

0

.

01, delimitedbythesolid contourin

Fig. 5

.Theobserved95% CL ex-clusion region is localised in the range mH

=

200–700 GeV and

mA

=

20–270 GeV forthedecayH

→

ZA,andsimilarlyintherange

mA

=

200–700 GeV andmH

=

120–270 GeV fortheA

→

ZH decay.

Thefeature observedintheexclusionlimit forthe regionaround

(

mA

,

mH

)

= (

75–100

,

200–300

)

GeV is the result of an interplay

between the larger Z

+

jets background yields expected in this regionandthe quicklyevolving signal crosssection.The effectis visibleintheexpectedlimitsandbecomesslightlybroaderinthe observed onesgiventhe concurrent presence inthe sameregion of a moderatedata excess. The region where

|

mH

−

mA

|

<

mZ is

kinematicallyinaccessible.

The limits on

μ

can be also visualised as a function of the 2HDMparameterstan

β

andcos

(β

−

α

)

foragivenpairofmAand

mH,fromthe combinationof



bb and



τ τ

final states.Results

are given in Fig. 6, where the exclusion limits on the parame-tersareshownformH

=

378GeV andmA

=

188GeV,amasspair

chosen tobe within theexclusionregion ofFig. 5.The area con-tainedwithin the solid lineshowsthe parameter spaceexcluded for the chosen mass pair, where tan

β

lies between 0.5 and 2.3 andcos

(β

−

α

)

between

−

0

.

7 and0.3.

8. Summary

Thepaperdescribesthe firstCMSsearch foranewresonance decaying into a lighter resonance and a Z boson. Two searches havebeenperformed,targetingthedecayofthelighterresonance

Fig. 5. Observedlimitsonthesignalstrengthμ=σ95%/σthforthe2HDM bench-mark,aftercombiningresultsfrombb andτ τ finalstates.Thecrosssections arenormalisedtothe NNLO SusHi prediction,for a2HDM type-IIscenariowith tanβ=1.5 andcos(β−α)=0.01.Thedashedcontourshowstheregionexpected tobeexcluded.Thesolidcontourshowstheregionexcludedbythedata.

Fig. 6. Observedlimitsonthesignalstrengthμ=σ95%/σthforthe2HDM bench-markaftercombiningresultsfrombb andτ τ finalstates.Thecrosssectionsare normalisedtotheNNLO SusHi prediction.Limitsareshowninthe2HDM parame-terscos(β−α)andtanβforthesignalmassesofmH=378GeV andmA=188GeV. Thedashedcontourshowstheregionexpectedtobeexcluded.Thesolidcontour showstheregionexcludedbythedata.

into either a pair of oppositely charged

τ

leptons or a bb pair. TheZbosonisidentifiedviaitsdecaystoelectronsormuons.The searchisbasedondatacorrespondingtoanintegratedluminosity of19.8 fb−1inproton–protoncollisions at

√

s

=

8TeV.Deviations fromtheSM expectationsare observedwithaglobalsignificance oflessthan2SDandupperlimitsontheproductofcrosssection andbranchingfractionareset.The searchexcludes

σ

B

aslowas 5 fband1 fbforthe



bb and



τ τ

final states,respectively, de-pendingonthelightandheavyresonancemassvalues.

Limitsarealsosetonthemassparametersofthetype-II2HDM modelthat predicts theprocessesH

→

ZA andA

→

ZH,whereH andAareCP-evenandCP-oddscalarbosons,respectively. Combin-ingthe



bb and



τ τ

finalstates,thespecificmodel correspond-ing tothe parameterchoice cos

(β

−

α

)

=

0

.

01 andtan

β

=

1

.

5 is excluded formH inthe range200–700 GeV andmA in therange

20–270 GeV with mH

>

mA, oralternatively for mA in therange

200–700GeV andmHintherange120–270GeV withmA

>

mH.

Limitsonthe signalcross sectionmodifier are alsoderived as a function of tan

β

and cos

(β

−

α

)

parameters. As a result, for specific mH–mA mass values, a fairly large region in the

param-eterspace tan

β

vs. cos

(β

−

α

)

is excluded. This covers a region unexplored so far, that cannot be probed by studying produc-tion anddecay modes of the SM-like Higgs boson. In particular, formH

=

378 GeV and mA

=

188 GeV, a range where tan

β

lies

between0.5and2.3andcos

(β

−

α

)

between

−

0

.

7 and0.3is ex-cluded,afterthecombinationofthe



bb and



τ τ

finalstates.

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,wegratefullyacknowledgethecomputingcentresand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythecomputinginfrastructure essential toour analyses. Finally, we acknowledge the enduring support for the construc-tionandoperationofthe 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); Academy of Finland,MEC, and HIP(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 ofKorea); LAS (Lithuania);MOE andUM (Malaysia); CINVESTAV, CONACYT,SEP,andUASLP-FAI(Mexico);MBIE(NewZealand);PAEC (Pakistan);MSHE andNSC(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 (UnitedKingdom);DOE andNSF(USA).

Individuals have received support from the Marie-Curie pro-gramme and the European Research Council and EPLANET (Eu-ropean Union); the Leventis Foundation; the A.P. Sloan Founda-tion; the Alexander von Humboldt Foundation; the Belgian Fed-eral 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 programmeof the Foundation for Pol-ish Science, cofinanced from European Union, Regional Develop-ment Fund; the OPUS programme of the National Science Cen-ter(Poland);the Compagnia diSan Paolo (Torino); MIURproject 20108T4XTM (Italy); the Thalis and Aristeia programmes cofi-nancedbyEU-ESFandtheGreekNSRF;theNationalPriorities Re-searchProgrambyQatarNationalResearchFund;theRachadapisek Sompot Fund for Postdoctoral Fellowship, Chulalongkorn Univer-sity(Thailand);theChulalongkorn Academicinto Its2nd Century Project Advancement Project (Thailand); and the Welch Founda-tion,contractC-1845.

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TheCMSCollaboration

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,

M. Krammer

1

,

I. Krätschmer,

D. Liko,

T. Matsushita,

I. Mikulec,

D. Rabady

2

,

B. Rahbaran,

H. Rohringer,

J. Schieck

1

,

R. Schöfbeck,

J. Strauss,

W. Treberer-Treberspurg,

W. Waltenberger,

C.-E. Wulz

1

InstitutfürHochenergiephysikderOeAW,Wien,Austria

V. Mossolov,

N. Shumeiko,

J. Suarez Gonzalez

NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus

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. Zhang

3

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. Beluffi

4

,

O. Bondu,

S. Brochet,

G. Bruno,

A. Caudron,

L. Ceard,

G.G. Da Silveira,

C. Delaere,

D. Favart,

L. Forthomme,

A. Giammanco

5

,

J. Hollar,

A. Jafari,

P. Jez,

M. Komm,

V. Lemaitre,

A. Mertens,

M. Musich,

C. Nuttens,

L. Perrini,

A. Pin,

K. Piotrzkowski,

A. Popov

6

,

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. Chinellato

7

,

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 Manganote

7

,

A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahuja

a

,

C.A. Bernardes

b

,

A. De Souza Santos

b

,

S. Dogra

a

,

T.R. Fernandez Perez Tomei

a

,

E.M. Gregores

b

,

P.G. Mercadante

b

,

C.S. Moon

a

,

8

,

S.F. Novaes

a

,

Sandra S. Padula

a

,

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

UniversityofSofia,Sofia,Bulgaria

M. Ahmad,

J.G. Bian,

G.M. Chen,

H.S. Chen,

M. Chen,

T. Cheng,

R. Du,

C.H. Jiang,

R. Plestina

9

,

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. Finger

10

,

M. Finger Jr.

10

CharlesUniversity,Prague,CzechRepublic

E. El-khateeb

11

,

T. Elkafrawy

11

,

A. Mohamed

12

,

E. Salama

13

,

11

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