Search for a low-mass pseudoscalar Higgs boson produced in association with a b(b)over-bar pair in pp collisions at root s=8 TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

a

low-mass

pseudoscalar

Higgs

boson

produced

in association

with

a

bb pair

in

pp

collisions

at

√

s

=

8 TeV

.

CMS

Collaboration



CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received11November2015 Receivedinrevisedform21April2016 Accepted2May2016

Availableonline6May2016 Editor:M.Doser

Keywords:

CMS Physics Higgs

AsearchisreportedforalightpseudoscalarHiggsbosondecayingtoapairof

τ

leptons,producedin

association with abb pair,in thecontext oftwo-Higgs-doublet models.The results are basedonpp

collision data atacentre-of-mass energyof 8 TeVcollected bythe CMS experiment atthe LHCand

corresponding to an integratedluminosity of19.7 fb−1_{.Pseudoscalar boson massesbetween 25 and}

80 GeVareprobed.Noevidenceforapseudoscalarbosonisfoundandupperlimitsaresetontheproduct ofcrosssectionandbranchingfractionto

τ

pairsbetween7and39 pbatthe95%confidencelevel.This

excludespseudoscalarAbosonswithmassesbetween25and80 GeV,withSM-likeHiggsbosonnegative

couplingstodown-typefermions,producedinassociationwithbb pairs, inType II,two-Higgs-doublet

models.

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

1. Introduction

The discovery of a newboson with a mass closeto 125 GeV

[1–3], consistentwiththe standard model(SM) Higgsboson,has shedlightononeofthemostimportantquestionsofphysics:the originofthemassofelementaryparticles. Althoughallthe mea-surementsmadeuptonowareinimpressiveagreementwiththe predictionsoftheSM[4,5],theSMcannot addressseveralcrucial issues such as the hierarchy problem, the origin of the matter-antimatterasymmetry andthenatureofdarkmatter[6–9]. Theo-riespredictingnewphysicsbeyondthestandardmodelhavebeen proposed toaddress theseopen questions.Manyof thempredict theexistenceofmorethanoneHiggsboson.

Two-Higgs-doublet models (2HDM) [10–14] are a particularly simpleextension ofthe SM. Starting withthe two doubletfields



1 and



2 andassumingan absenceofCPviolationintheHiggs sector, after SU

(

2

)

L symmetry breaking five physical states are

left: two CP-even (h and H), one CP-odd (A), and two charged (H±)bosons.Toavoidtree-levelflavourchangingneutralcurrents, one imposes a Z2 symmetry according to which the Lagrangian is requiredto be invariant under



1

→ 

1,



2

→ −

2.The re-sultis four distinct classes ofmodels, corresponding to different patternsofquarkandleptoncouplings.Themostcommonly con-sideredare Type I and Type II.In Type I, all quarks andleptons

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

obtain masses from



1



. In Type II, up-type quarks masses are derived from



1



≡

v1 anddown-typequarks andcharged lep-tonsmassesare derived from



2



≡

v2.In thelimit ofan exact Z2symmetry[15],theHiggssectorofa2HDMcanbedescribedby sixparameters:fourHiggsboson masses(mh,mH,mA,andmH±), the ratio of the vacuum expectation values of the two doublets (tan

β

≡

v2

/

v1)andthemixingangle

α

ofthetwoneutralCP-even Higgs states.Allowing a softbreaking of theZ2 symmetry intro-ducesanewHiggsmixingparameterm2₁₂[11].Inthe“decoupling limit”of2HDMs

[16,17]

,themassesmH,mA,andmH± arealllarge, cos

(β

−

α

)



1, andh is the observed bosonat 125 GeV andis SM-like.AnSM-likeh orH at125 GeV canalsobeobtainedinthe “alignment limit” [16,17] without the other bosons being heavy. ThisisaninterestingcaseandcanbecompatiblewiththeSM-like Higgs boson total width measurements and branching fractions evenifoneormoreofthelightHiggsbosonshave amassbelow halfof125 GeV providedoneadjuststhemodelparameterssothat thebranchingfractionoftheSMHiggsbosontopairsoflightHiggs bosonsisverysmall.ThisscenariocanbetestedattheCERNLHC bysearchingforsinglyproducedlightbosonsdecayingtoapairof

τ

leptonswithlargecrosssections.InType II2HDMs,iftheHiggs couplingtothethirdgenerationofquarksisenhanced,ashappens atlargetan

β

,alargeproductioncrosssectionisexpectedforthe production ofthe low-mass A boson in association withbb. The crosssection isoftheorderof1 pbforregionsofthe2HDM pa-rameterspacewithsin

(β

−

α

)

≈

1,cos

(β

−

α

)

>

0 andsmallm2₁₂. The cross section can be much larger, between 10 and 100 pb,

http://dx.doi.org/10.1016/j.physletb.2016.05.003

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

forsomeotherregionsoftheparameterspace,i.e. sin

(β

±

α

)

≈

1, cos

(β

−

α

)

<

0 and tan

β >

5 [18,19], wherethe coupling ofthe SM-likehbosontodown-typefermionsisnegative(“wrongsign” Yukawacoupling).Consequently, giventhelarge productioncross sectionoftheA bosoninsuchscenarios,theLHCdataaresensitive toitspresenceforsomecombinationsofmodelparameters.

Previoussearches fordi-τ resonances [20,21]have mainly fo-cusedonmassesgreaterthanthemassoftheZ boson,for exam-pleinthecontextoftheminimalsupersymmetricstandardmodel (MSSM)[22–24],whichisahighlyconstrained2HDMofType II.In fact,alightpseudoscalarHiggsbosonisexcludedintheMSSM,but anA bosoncanstillhavequitealowmassingeneral2HDMs,even givenalltheconstraintsfromLEP,TevatronandLHCdata[18,19].

Thisletterpresentsasearchforalow-masspseudoscalarHiggs boson produced in association with a bb pair and decaying to a pair of

τ

leptons. Associated production of the A boson with a bb pair has the advantage that there is a higher signal over backgroundratio relative togluon–gluon fusionproduction. Such a signature is also relevant in the context of light pseudoscalar mediatorsandcoydarksectors[25].The analysisisbasedon pp collisiondataatacentre-of-massenergyof8 TeV recordedbythe CMS experiment at the LHC in 2012. The integrated luminosity amounts to 19.7 fb−1_.The

_τ

_{leptons are reconstructed via their} muon, electron andhadronic decays.In the following, the terms leptonsrefer toelectronsandmuons, whereas

τ

s thatdecayinto hadrons

+

ν

τ aredenoted by

τ

h.The invariant massdistributions ofthe

τ

pairsinallthreechannelsareusedtosearchfor pseudo-scalarbosonswithmassesbetween25and80 GeV.

2. TheCMSdetectorandeventsamples

The central feature of the CMS apparatus is a superconduct-ingsolenoidof 6 minternal diameter,providing amagnetic field of3.8 T.Withinthesolenoidvolumeare asilicon pixelandstrip tracker,aleadtungstatecrystalelectromagneticcalorimeter(ECAL), andabrassandscintillatorhadroncalorimeter(HCAL),each com-posed of a barrel and two endcap sections. Muons are detected ingas-ionisation detectorsembeddedinthesteelflux-returnyoke outsidethesolenoid. Extensive forward calorimetrycomplements thecoverage provided by the barrelandendcap detectors.A de-taileddescription ofthe CMSdetector,together withadefinition ofthecoordinatesystemusedandtherelevantkinematicvariables, canbefoundinRef.[26].

The first level of the CMS triggering system (Level-1), com-posedofcustom hardware processors, uses informationfromthe calorimetersandthemuonsdetectorstoselectthemost interest-ingeventsinafixedtimeintervaloflessthan4 μs.Thehigh-level trigger(HLT)processorfarmfurtherdecreasestheeventratefrom around100 kHztolessthan1 kHz,beforedatastorage.

Asetof MonteCarlo(MC) simulatedevents isused tomodel thesignalandbackgrounds.Drell–Yan, Wbosonproduction asso-ciated to additional jets, production of top quark pairs (tt), and diboson(WW, WZ and ZZ) backgrounds are generatedusing the leading order (LO) MadGraph 5.1 package [27]. Single top quark samplesareproduced usingthenext-to-leading-order (NLO) gen-erator powheg (v1.0) [28]. Simulatedsamplesof gluon–gluon fu-sion to bbA signal events are generated with pythia 6.426 [29]

formassesbetween25and80 GeV in5 GeV steps.As noloopis involvedatleadingorderinthebbA productionprocess,the prod-uct of acceptance and efficiency for signal only depends on the A boson mass, withno dependence on other model parameters. The simulated samples are produced using the CTEQ6L1 parton distributionfunction (PDF) set [30]. All thegenerated signal and backgroundsamplesareprocessedwiththesimulationoftheCMS detectorbasedon geant 4[31].

Additional eventsareadded tothe MC-simulatedevents,with weights corresponding totheluminosity profile indata,to simu-lateLHCconditionsandthepresenceofother softppinteractions (pileup)inthesameorneighbouringbunchcrossingsofthemain interaction. Finally, identical algorithms and procedures are used toreconstructbothsimulatedeventsandthecollecteddata.

3. Eventreconstruction

Event reconstruction is based on the particle-flow (PF) algo-rithm[32,33],whichaimstoexploittheinformationfromall sub-detectors to identifyindividual particles (PF candidates): charged andneutralhadrons, muons,electrons,andphotons. Complex ob-jects, such as

τ

leptons that decayinto hadronsand a neutrino, jets,andtheimbalanceinthetransversemomentumintheevent arereconstructedfromPFcandidates.

Thedeterministicannealingalgorithm

[34,35]

isusedto recon-structthecollisionvertices.Thevertexwiththemaximumsumof squaredtransversemomenta(p2

T)ofallassociatedtracksis consid-eredastheprimaryvertex.Muons,electrons,and

τ

hsarerequired tooriginatefromtheprimarycollisionvertex.

Muon reconstruction starts by matching tracks in the silicon trackerwithtracksintheoutermuonspectrometer[36].A global muontrackisfittedtothehitsfrombothtracks.A preselectionis appliedto thesemuon tracksthat includesrequirementsontheir impact parameters, to distinguish genuine prompt muons from spurious muonsor muons fromcosmic rays. In addition, muons are required to pass isolation criteriato separate prompt muons from those associated witha jet, usually from the semi-leptonic decaysofheavy quarks.The muonrelative isolation isdefinedas thefollowing[26]: Irel

=

⎡

⎣



charged pT

+

max

⎛

⎝

0

,



neutral pT

+



γ pT

−

1 2



charged,PU pT

⎞

⎠

⎤

⎦ /

pμ_T

,

(1)

where all sums are over the scalar pT ofparticles inside a cone with size of

R

=



(

η

)

2

_{+ ( φ)}

2

₌

₀

_.

_{4 relative to the muon} direction, where

η

is the pseudorapidity and

φ

is the azimuthal angle (in radians) in theplane transverse to the beamaxis, and “charged” corresponds to charged hadrons, muons, andelectrons originating from the primary vertex, “neutral” refers to neutral hadronsand“charged, PU”refers to chargedhadrons,muons, and electronsoriginatingfromotherreconstructedvertices.Thelastof thesesumsisusedtosubtracttheneutralpileupcomponentinthe computation, andthefactorof1

/

2 reflectsthe approximateratio ofneutraltochargedparticlesinjets[37].

Electron reconstruction starts from ECAL superclusters, which aregroupsofoneormoreassociatedclustersofenergydeposited intheECAL.Superclustersarematchedtotrackseedsintheinner tracker(the closest layers ofthe trackerto theinteraction point) andelectrontracksare formedfromthose.Trajectoriesare recon-structed based on the modelling of electron energy loss due to bremsstrahlung,andarefittedusingtheGaussian sumfilter algo-rithm[38].Electronidentificationisbasedonamultivariate(MVA) boosteddecisiontreetechnique[39] todiscriminategenuine elec-tronsfromjetsmisidentifiedaselectrons[40].The mostpowerful variables for thediscrimination of

τ

h candidates are the ratio of energydepositions inthe ECALandHCAL,the angulardifference betweenthetrackandsupercluster,andthedistributionofenergy depositionsintheelectronshower.Relativeisolationisdefinedin

an analogous way to that of Eq. (1) and is used to distinguish promptelectronsfromelectronswithinajet.

JetsarereconstructedfromPFcandidatesusingtheanti-kT[41] algorithm witha distanceparameter of 0.5, in the FastJet pack-age [42]. Several corrections are applied to the jet energies to reducetheeffectofpileupandcorrectforthenonlinearresponse of the calorimeters [37]. To identify and reject jets from pileup, an MVA discriminator is defined based on information fromthe vertexand the jet distribution [43].Jets identified as originating fromabquark,calledb-taggedjets,areidentifiedusingthe com-binedsecondaryvertex(CSV)algorithm[44],whichisbasedona likelihoodtechnique, andexploitsinformationsuchastheimpact parametersofcharged-particle tracksandthepropertiesof recon-structeddecayvertices.

The hadron-plus-strips (HPS) algorithm [45,46] is used to re-constructthe

τ

h candidates.It starts froma jet,andsearches for candidatesproduced bythemain hadronicdecaymodesofthe

τ

lepton:eitherdirectlytoone chargedhadron,orviaintermediate

ρ

anda1

(

1280

)

mesons to one chargedhadron plus one ortwo neutral pions, or three charged hadrons with up to one neutral pion.Thechargedhadronsare usuallylong-livedpions,whilethe neutralpions decayrapidlyintotwo photons. The HPSalgorithm takesinto account the possible conversion ofphotons into e+e− pairs in material in front of the ECAL, and their corresponding bremsstrahlunginthemagneticfieldwithconsequent broadening ofthe distribution of theshower. Strips are formed from energy depositionsin the ECAL arising from electrons and photons. The stripsizes inECALare0

.

05

×

0

.

20 in

η

× φ

.The

τ

hdecaymodes are reconstructed by combining the charged hadrons with ECAL strips.Neutrinos producedin

τ

hdecaysarenot reconstructedbut contributetoEmiss_T .IsolationrequirementsbasedonanMVA tech-nique take into account the pT of PF candidates around the

τ

leptondirectionandinformationrelatedtoitslifetime,suchasthe transverse impact parameter ofthe leading track of the

τ

h can-didate and its significance for decays to one charged hadron or thedistancebetweenthe

τ

hproductionanddecayverticesandits significancefordecaystothreechargedhadrons.Electronscanbe misidentified as

τ

h candidates withonetrackandECAL strip.An MVAdiscriminatorbasedon propertiesofthereconstructed elec-tron, such asthe distributionof theshower and theratio ofthe ECALandHCALdepositedenergies, isusedto improve pion/elec-tronseparation.Finally,anotherMVAdiscriminatorisusedto sup-pressmuonsreconstructedas

τ

hcandidateswithonetrack.It ex-ploitsinformationabouttheenergydepositedinthecalorimeters with

τ

hcandidates,aswell ashitsandsegmentsreconstructedin themuon spectrometersthatcan bematched tothecomponents ofthe

τ

h.

The missing transverse momentum vector

pmiss_T is defined as theprojectionontheplaneperpendiculartothebeamsofthe neg-ativevectorsumofthemomentaofall reconstructedparticles in anevent.ItsmagnitudeisreferredtoasE_Tmiss.Toimprovethe res-olution,andreduce theeffectofpileup,a

pmiss_T basedonanMVA regressiontechnique[47]isused,whichtakesintoaccountseveral collectionsofparticlesfromdifferentvertices.

Theinvariantmassofthe

τ

pair(mττ )isusedastheobservable for the statistical interpretation of results in all channels andis reconstructedusingthe SVFit algorithm[48].The SVFit algorithm usesa maximumlikelihood techniquewhere thelikelihoodtakes asinputthefour-momentaofthevisibledecayproducts ofthe

τ

, the projection of

pmiss_T along the x- and y-axes, as well as the covariancematrixofthecomponentsof

pmiss_T .

The relative mττ resolution obtained through the SVFit algo-rithmisabout15%overthewholemassrange.Itisslightlyhigher fortheeμchannelbecauseofthepresenceofoneadditional neu-trino.

4. Eventselection

Three di-τ final states are considered:

μτ

h, eτh,and eμ. The

μμ

andee finalstatesarediscardedbecauseoftheirsmall branch-ing fractionsandlargebackgrounds,while

τ

h

τ

h isnot considered becauseofinefficienciesduetothetriggerthreshold.

The selection of events in the

μτ

h or eτh final state starts from a trigger that requires a combination of a muon or elec-tronwithpT

>

17 or22 GeV,respectively,andanisolated

τ

hwith pT

>

20 GeV.Thiscombinedtriggerisseededbyasinglemuonor electron, withpT

>

16 or20 GeV atLevel-1. Theoffline selection requires a muon or electron with pT

>

18 or 24 GeV, respec-tively,and

|

η

|

<

2

.

1,andanoppositelycharged

τ

h candidatewith pT

>

22 GeV and

|

η

|

<

2

.

3.Leptons are requiredto pass a tight identification[36,40] andhavea relativeisolation, Irel,

<

0

.

1. The

τ

hcandidateshavetopassatightworkingpointoftheMVA dis-criminantthatcombinesisolationandlifetimeinformation (result-ingina

τ

hreconstructionandisolationefficiencyofabout30%and ajetto

τ

hmisidentificationratebetween0.5and1.0 per mille),as well as the requirements to suppress electron and muon candi-dates misidentified as

τ

h, described inSection 3. Leptonsand

τ

h candidatesarerequiredtobeseparatedby

R

>

0

.

5.Eventswith additionalidentifiedandisolatedelectronsormuonsarediscarded. TosuppressW

+

jets andtt backgrounds,thetransversemass be-tween thelepton transversemomentum

p

T and

pmissT ,definedin Eq.(2),isrequiredtobesmallerthan30 GeV,

MT

( ,

p

missT

)

=



2p _TEmiss_T

(

1

−

cos

φ),

(2)

where

φ

is the azimuthal angle betweenthe lepton transverse momentumandthep

miss

T vectors.

Events selected in the eμ channel must pass a trigger that requires a combination of an electron and a muon, with pT

>

17

(

8

)

GeV forthe leading (subleading)lepton. Dependingon the flavour of the leading lepton that passes the trigger selection, events are required to have either a muon with pT

>

18 GeV andan electronwith pT

>

10 GeV,ora muonwith pT

>

10 GeV andanelectronwithpT

>

20 GeV.Thefiducialregionsformuons (electrons)aredefinedby

|

η

|

<

2

.

1

(

2

.

3

)

.Additionally,leptonswith oppositechargeareselectedandrequiredtobespatiallyseparated by

R

>

0

.

5.

The muonsandelectronsarerequiredtobe isolated,with rel-ative isolation lessthan 0

.

15 in thebarrel(

|

η

|

<

1

.

479) andless than0

.

1 intheendcaps(

|

η

|

>

1

.

479).Inaddition,bothmuonsand electrons are required to pass the tight identification criteria as describedinSection3.Eventshavingadditionalidentifiedand iso-latedleptonsarevetoed,similarlytothe

μτ

handeτhchannels.To reducethelargett backgroundintheeμfinalstate,alinear com-binationofthe Pζ andPvis_ζ variables[49]isused.Pζ and P_ζvisare

definedasfollows: Pζ

=

pμ_T

+

pe_T

+

pmiss_T



· ˆζ

and Pvis_ζ

=



pμ_T

+

pe_T



· ˆζ,

(3)

where

ˆζ

is the unit vector of the axis bisecting the angle be-tween

pμ_T and

pe

T of the muon and electron candidates, respec-tively.Thesevariablestakeintoaccountthefactthattheneutrinos producedin

τ

decaysaremostlycollinearwiththevisible

τ

decay products,butthisisnottrueforneutrinosfromtheothersources, nor for misidentified

τ

h candidates from background. The linear combination Pζ

−

α

Pvisζ isrequiredto be greater than

−

40 GeV,

withanoptimalvalueof

α

of1.85,determinedintheCMSsearch foraMSSM Higgsboson inthe

τ τ

final state [21].Tofurther re-ducett andelectroweakbackgroundsintheeμfinalstate,theMT

betweenthedileptontransversemomentumand

pmiss_T ,definedas inEq.(2),isrequiredtobelessthan25 GeV.

Inaddition to theabove selections, events inall channels are alsorequiredtohaveatleastone b-taggedjet withpT

>

20 GeV and

|

η

|

<

2

.

4,whichpassestheworkingpointoftheCSVb-tagging discriminant (corresponding to b-tagging efficiencyof about 65% and light-jet misidentification rate of about 1%) and the pileup MVAdiscriminant forjets,andis separatedby atleast

R

=

0

.

5 fromthesignalleptons.

5. Backgroundestimation

Oneofthemainbackgrounds inall threechannelsis Z

/

γ

∗

→

τ τ

.Drell–Yaneventswithinvariant masslarger than50 GeV are modelled using “embedded” eventsamples, as follows: Z

→

μμ

events are selected in data with an invariant mass larger than 50 GeVtoremovethemassrangebiasedbyatriggerrequirement. Thereconstructedmuonsarereplacedbysimulated

τ

leptonsthat aresubsequently decayedvia tauola [50].To modelthe detector responsetothe

τ

decayproducts theGEANTbaseddetector sim-ulation is used.Jets,

pmiss_T , and

τ

h are then reconstructed, while lepton isolations are recomputed [51]. This substantially reduces theuncertaintiesrelatedtothemodellingofthe Emiss

T ,thejet en-ergyscale,andtheb jetefficiency.Low-mass Z

/

γ

∗

→

τ τ

events, whichcannot becoveredbytheembedded samples,aretaken di-rectlyfromasimulatedsample.

Multijeteventsoriginatedby QCD processescompriseanother majorbackground,especiallyatlowdi-τ mass.Thecontributionof theQCDmultijetbackgroundarisesfromjet

→

τ

hmisidentification and to a lesser extent from jet

→

μ

and jet

→

e misidentifica-tion,depending onthefinal state.Other contributions aredueto the presence of muons or electrons from the semi-leptonic de-cays of heavy flavour quarks.This background is estimatedfrom data.

Multijet background normalisation in the

μτ

h and eτh final statesis determined from a sample definedin the same wayas the signal selection described in Section 4, except that the lep-ton andthe

τ

h candidateare required to have electriccharge of samesign(SS).TheeventswiththeSSselectionaredominatedby multijets,andthelimitedcontributionfromtheother processesis subtracted using predictions from simulatedevents. To take into accountthe difference inthe multijetnormalisation betweenthe SS andopposite-sign (OS) regions, an OS/SS extrapolation factor isused to multiply themultijet yield in the SS region. This fac-torismeasuredinsignal-freeeventsselectedwithinvertedlepton isolations(0

.

2

<

Irel

<

0

.

5) and arelaxed

τ

h isolation. TheOS/SS extrapolation factor is parameterised as a function of mττ , and fittedwithan exponentiallydecreasing function.Thisratiois ap-proximatelyequalto1.2fordi-τ massesof20 GeV,anddecreases toabout1.1formassesabove50 GeV.

The mττ distribution for the QCD multijet background is ob-tainedfroma control region in databy inverting the lepton iso-lationandrelaxing the

τ

h isolation. These two selectionsare re-quired to attain a control region populated with QCD multijet eventsandobtainasufficientlysmoothmττ distribution.A correc-tionhasbeenapplied toaccount forthedifferencesbetweenthe nominalselectionandtheselectionusedtoestimatetheQCD mul-tijetmττ distribution.The correctiondependsonthe

τ

h misiden-tification rate (the probability fora

τ

h,that passes a looser iso-lationrequirement, topassthetight isolationselection). Thisrate isparameterised asa function of the pT of the

τ

h in three bins ofpseudorapidity. It was checked that the mττ distributions ob-tainedwhen thelepton isolation is invertedandthe

τ

h isolation isrelaxed, are consistent within statistical uncertainties withthe normalsearchprocedure.

Intheeμfinalstate,theQCDmultijetbackgroundismeasured simultaneouslywithotherbackgroundsusingmisidentifiedleptons indata,througha“misidentified-lepton” method[51],and requir-ing atleast one jet misidentified asa lepton. The probability for loosely preselected leptons, mainly dominated by leptons within jets, tobe identified asgoodleptons is measuredin samples de-pletedofisolated leptons asa functionofthe pT and

η

.Weights obtainedfromthismeasurementareappliedtoeventsindatawith electrons and muons passing the loose preselection but not the nominalselectioncriteria,toextracttheQCDmultijetbackground contribution.

Inthe

μτ

handeτhfinalstates,theW

+

jets backgroundarises from events with a genuine isolated and identified lepton from the leptonic decayofa W boson andajet misidentified asa

τ

h. Its contributionis highly suppressed by requiring the MT of the lepton and

pmiss_T of Eq.(2)to be

<

30 GeV (low-MT region). The W

+

jets normalisationisdeterminedfromcollisiondatausingthe yield in the high-MT (

>

70 GeV) sideband, multiplied by an ex-trapolation factor that is the ratio of the W

+

jets events in the high- andlow-MT regions in simulatedevents. The small contri-bution from other backgrounds in events selected with high-MT selection issubtractedusingthepredictionfromsimulations.The distribution of mττ for the W

+

jets background is taken from simulation. A correction to the distribution, measured in a sam-pleenrichedinW

+

jets andasafunctionofthepTofthelepton originatingfromtheW boson,isappliedtocorrectthedifferences betweenobservedandsimulatedevents.Intheeμfinal state,the W

+

jets background isestimated together withthebackgrounds thatcontainatleastonejetmisidentifiedasalepton,suchasQCD multijets,aspreviouslydescribed.

The Z

/

γ

∗

→

μμ

andZ

/

γ

∗

→

ee processes contribute, respec-tively,tothe

μτ

h andeτh finalstates,becauseofthe misidentifi-cationofalepton asa

τ

h.The normalisationandthe distribution ofmττ forthesebackgroundsareobtainedfromsimulation.

The presence of genuine b jetsfrom top quark decays makes the tt background contributionimportant.The tt background has true

τ

h

≈

70% of the times and misidentified

τ

h in

≈

30% of the times. The distribution of mττ for tt events is taken from simulation, but normalised to the measurement of the tt cross section [52]. A reweighting is applied to generated tt events to improve the modelling of the top quark pT spectrum. This reweighting only depends on the simulated pT of top and anti-top quarks [52], andhasa negligible impacton the final results. Inaddition,themττ distributions observedindataandpredicted byMCsimulationsarecomparedinaregionwithhighpurityoftt events,anddepletedinsignal,obtainedbyraisingthepTthreshold oftheleptonsand

τ

h,andrequiringatleasttwob-taggedjetswith ahigherpT thresholdthanthatusedineventselectionsdescribed in Section 4. Good agreement is found between distributions in dataandMCsimulation.

Single top quark,diboson (WW, WZ, ZZ),andSM Higgs back-grounds represent a small fraction of the total background, and are takenfromsimulations andnormalisedtotheNLO cross sec-tions[51,53,54].

Scalefactorstocorrectforresidualdiscrepanciesbetweendata andMC simulationrelatedtothelepton triggering,identification, and isolation are applied to the signal and the backgrounds es-timated fromMC simulations. These correction factors are deter-minedusingthe“tag-and-probe”technique

[45,46,55]

,whichrelies onthepresenceoftwoleptonsfromZ bosondecays.Nocorrection factoris appliedto the

τ

hcandidate nortothe selectedb jet,as thecorrections arefound tobe consistent withunity.The uncer-taintiesrelatedtothesescalefactorsaredescribedinSection6.

Table 1

Systematicuncertaintiesthataffectthenormalisation.

Systematic source Systematic uncertainty

μτh eτh eμ N o rmalisation Integrated luminosity 2.6% 2.6% 2.6% Muon ID/trigger 2% — 2% Electron ID/trigger — 2% 2% τhID/trigger 8% 8% —

Muon toτhmisidentification rate 30% — —

Electron toτhmisidentification rate — 30% —

b tagging efficiency 1–4% 1–4% 1–4% b mistag rate 1–9% 1–9% 1–9% Emiss T scale 1–2% 1–2% 1–2% Z/γ∗→τ τnormalisation 3% 3% 3% Z/γ∗→τ τlow-mass normalisation 10% 10% 10% QCD multijet normalisation 20% 20% — Reducible background normalisation — — 30% W+jets normalisation 30% 30% —

tt cross section 10% 10% 10%

Diboson cross section 15% 15% 15% H→τ τsignal strength 30% 30% 30%

Theor

y Underlying event and parton shower 1–5% 1–5% 1–5%

Scales for A boson production 10% 10% 10% PDF for generating signal 10% 10% 10%

NLO vs. LO 20% 20% 20%

6. Systematicuncertainties

The results of the analysis are extracted from a fit based on themττ distributionsineachfinalstate,asdiscussedinSection7. Systematicuncertainties inthefit affectthenormalisationorthe shapeofthemττ distributionforthesignalandbackgrounds.The normalisationuncertaintiesaresummarisedin

Table 1

.

The uncertainty in normalisation that affects the signal and mostofthesimulatedbackgroundsisrelatedtotheintegrated lu-minosityat8 TeV,whichismeasuredwithaprecisionof2.6%[56]. Uncertaintiesinmuon andelectronidentificationandtrigger effi-ciency,aswellasinthe

τ

hidentificationefficiency,aredetermined using the “tag-and-probe” technique [45,46,55]. These uncertain-tiesareabout2%formuonandelectronand8%for

τ

h.Changesin acceptanceduetotheuncertaintyinthe btaggingefficiencyand the bmistag raterange from1to 9% depending onthe process. ToestimatetheuncertaintyintheW

+

jets normalisation,the un-certaintyintheextrapolationfactorfromthehigh-MTsidebandto thesignalregionisobtainedbyvaryingEmiss

T anditsresolutionby their uncertainties, leading to a 30% uncertainty. The uncertainty in the normalisation of QCD multijet background is obtained by addingthestatisticaluncertaintyrelatedtothesamplesizeofthe QCDmultijet-dominatedcontrolregioninquadraturewiththe un-certaintyintheextrapolationfactorfromthecontrolregiontothe signalregion; thisamountsto20%.The normalisationuncertainty for the tt background amounts to 10%; it is determined from a controlregionwherebothWbosons originatingfromthetopand antitopquarksdecayto

τ

leptons

[51]

.Uncertaintiesrelatedtothe dibosonbackgroundcrosssectionamountto15%

[57]

.

A30% uncertainty inthe signal strength(ratio ofobserved to expectedcross sections) for the SM Higgs boson is applied [51]. Theoretical uncertainties arising from the underlying event and parton showering matching scale, PDF [58] and the dependence onfactorisationandnormalisationscalesareconsideredforsignal. ThePDFuncertaintyistakenasthedifferenceinthesignal accep-tanceforthesignalsimulationwithCTEQ6L1,MSTW2008NLO[59], and NNPDF2.3NLO [60] PDF sets, leading to a 10% uncertainty. A 20% uncertainty in the signal normalisation is applied to take intoaccount the possibledifference inthe productofacceptance andefficiencybetween theLOsample generatedwith PYTHIA6.4 andtheNLOsamplegeneratedbythe MadGraph5_aMC@NLO gen-erator[61].

The

τ

h and electron energy scales are among the systematic uncertainties affecting the mττ distributions.To estimate the ef-fects ofthese uncertainties, the electron energyscale is changed by1% orby2

.

5% forelectronsreconstructedinthebarrelorinthe endcapregionsoftheECAL[40],respectively,whilethe

τ

henergy scaleisvariedby3%[46].ThetopquarkpTreweightingcorrection, used forsimulatedtt events to matchtheobserved pT spectrum ina dedicatedcontrolregion,ischangedbetweenzeroandtwice thenominalvalue[52,62].Theuncertaintyinthe

τ

h misidentifica-tion ratecorrection ofthe QCDmultijetandW

+

jets background distributions hasbeentakenintoaccount.Toestimate this uncer-tainty, the

τ

h misidentificationrate correction has been changed betweenzeroandtwiceitsvalue.Anadditionaltriggeruncertainty isappliedtothe

μτ

h andeτhfinal statestocoverpossible differ-ences betweencollisiondata andsimulatedeventsinthe low-pT lepton region,wherethetriggerefficiencyhasnotyetreachedits plateau. These low-pT leptons are attributed an uncertainty that corresponds to halfof the difference betweenthe measured and the plateau efficiencies. Finally, uncertainties due to the limited numberofsimulatedevents,orthenumberofeventsinthe con-trolregionsindata,aretakenintoaccount.Theseuncertaintiesare uncorrelatedacrossthebinsineachbackgrounddistribution[63].

Among all systematic uncertainties, the ones that have the largest impact on theresults are the

τ

h energy scale, the uncer-taintiesrelatedtothejettomuon,electronor

τ

hmisidentification rates,andtheuncertaintiesfromthelimitednumberofsimulated events (or the observed events indata control regions).The im-pact of theseindividual uncertainties on the combined expected limitrangesbetween5and10%dependingonmττ .

7. Results

The mass distributions for the

μτ

h,eτh and eμ channels are shown inFig. 1. No significant excessof dataisobserved on top oftheSMbackgrounds.A binnedmaximumlikelihoodfithasbeen applied simultaneously to all three distributions, taking into ac-count thesystematicuncertaintiesasnuisanceparameters.A log-normal probability distribution function is assumed for the nui-sanceparameters thataffecttheeventyields ofthevarious back-ground contributions. Systematic uncertainties affecting the mττ

distributions areassumedtohaveaGaussian probability distribu-tionfunction.

Fig. 1. Observedandpredictedmτ τ distributionsintheμτh (top),eτh (middle), andeμ(bottom)channels.Theplotsontheleftarethezoomed-inversions formτ τ distributionsbelow50 GeV.A signalforamassofmA=35 GeV isshownforacrosssectionof40 pb.Inμτhandeτhfinalstates,theelectroweakbackgroundiscomposed

ofZ→ee, Z→μμ, W+jets,diboson,andsingletopquarkcontributions.Inthe eμfinalstate, theelectroweak backgroundiscomposedofdibosonandsingletop backgrounds,whilethemisidentifiede/μbackgroundisduetoQCDmultijetandW+jets events.ThecontributionfromtheSMHiggsbosonisnegligibleandtherefore notshown.Expectedbackgroundcontributionsareshownforthevaluesofnuisanceparameters(systematicuncertainties)obtainedafterfittingthesignal+background hypothesistothedata.

Fig. 2. Observedandexpectedupperlimitsat95%CLontheproductofcrosssectionandbranchingfractionforalightpseudoscalarHiggsbosonproducedinassociation withtwobquarks,thatdecaystotwoτ leptons,intheμτh(left),eτh(middle),andeμ(right)channels.The1σ and2σ bandsrepresentthe1and2standarddeviation

uncertaintiesontheexpectedlimits.

Upper limits on the product of cross section and branching fraction of the pseudoscalar Higgs boson to

τ τ

are set at 95% confidence level (CL) usingthe modified frequentist construction CLs [64,65] and the procedure is described in Refs. [66,67]. The observedandexpectedlimitsonthebbA

→

bbτ τ processandthe oneandtwostandarddeviationuncertaintiesontheexpected lim-its are shown in Fig. 2. Among the three channels,

μτ

h is the mostsensitiveonefortheentiremassrangebecauseofthehigher branchingfractionrelativetotheeμchannel,lowertriggerand of-flinethresholds onthelepton pT relativetotheeτh channel,and highermuonthanelectronidentificationefficiency.Although back-groundyields increase sharply with the mass, the acceptance of thesignalgrowsfaster,providingtherebymorestringentlimitson the cross section at highermasses. The product of signal accep-tanceandefficiencyinthe

μτ

hchannel changesfrom1

.

5

×

10−5 atan A boson mass of25 GeV to 6

×

10−4 _atm

A

=

80 GeV. In theeτhchannelitrangesfrom3

×

10−6 at25 GeV to2

×

10−4 at 80 GeV,andfinallyintheeμchannel,itrangesfrom1

.

3

×

10−5 _at 25 GeV to3

.

5

×

10−4 at80 GeV.Thetriggerrequirementsandthe

pTthresholdoftheleptonsand

τ

hsarethemainfactorsindriving thesignalacceptanceandefficiency,especiallyatlowmasses.

The upper limits from the combination of all final states are presentedin

Fig. 3

,withexactvaluesquotedin

Table 2

.Theyrange from7to39 pbforAbosonmassesbetween25and80 GeV.In ad-dition,superimposedin

Fig. 3

areseveraltypicalproductioncross sectionsforthepseudoscalarHiggsbosonproducedinassociation witha pairofbquarksinType II2HDM,formA lessthanhalfof the125 GeV Higgsboson(h), andfor

B(

h

→

AA

)

<

0

.

3 [19].The points are obtainedfrom a series of scans inthe 2HDM param-eterspace. Points withSM-like Yukawacoupling andsmalltan

β

have sin

(β

−

α

)

≈

1, cos

(β

−

α

)

>

0,and low m2

12, while points with “wrong sign” Yukawa coupling have sin

(β

±

α

)

≈

1, small cos

(β

−

α

)

<

0,andtan

β >

5.Whilethecombinedresultsofthe currentanalysisarenotsensitivetotheSM-likeYukawacoupling, they exclude the “wrong sign” Yukawa coupling for almost the entiremass range, and moregenerally for tan

β >

5. For masses greater than mh

/

2, where the constraint on

B(

h

→

AA

)

<

0

.

3 is automaticallysatisfied,theproductioncrosssectionofthe pseudo-scalarHiggsbosoninassociationwitha pairofbquarksismuch larger[18];consequently,theexclusionlimitextendstomassesup to80 GeV.

8. Summary

AsearchbytheCMSexperimentforalightpseudoscalarHiggs boson produced in association witha bb pair anddecaying to a

Fig. 3. ExpectedcrosssectionsforType II2HDM,superimposedontheexpectedand observedcombinedlimitsfromthissearch.Cyanandgreenpoints,indicatingsmall valuesoftanβasshowninthecolourscale,havesin(β−α)≈1,cos(β−α)>0, andlowm2

12,andcorrespondtomodelswithSM-likeYukawacoupling,whilered

and orangepoints,withlargetanβ,havesin(β+α)≈1,smallcos(β−α)<0, andtanβ >5,andcorrespondtothemodelswitha“wrongsign”Yukawacoupling. TheoreticallyviablepointsareshownonlyuptomA=mh/2[19].(Forinterpretation

ofthereferencestocolourinthisfigurelegend,thereaderisreferredtotheweb versionofthisarticle.)

pairof

τ

leptons isreported.Threefinalstates:

μτ

h,eτh,andeμ, are usedwhere

τ

h representsahadronic

τ

decay.The resultsare basedonproton–protoncollisiondataaccumulatedata centre-of-massenergyof8 TeV,correspondingtoanintegratedluminosityof 19.7 fb−1_{.Pseudoscalarbosonmassesbetween25and80 GeV are} probed.No evidenceforapseudoscalarbosonisfound andupper limitsare setontheproductofcross sectionandbranching frac-tionto

τ

pairsbetween7and39 pbatthe95%confidencelevel. ThisexcludespseudoscalarAbosonswithmassesbetween25and 80 GeV, with SM-like Higgs boson negative couplings to down-type fermion, produced in association with bb pairs, in Type II, two-Higgs-doubletmodels.

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,wegratefullyacknowledgethecomputingcentresand

Table 2

Expectedand observedcombinedupper limitsat95% CLinpb,along withtheir1and2standard deviationuncertainties,intheproductofcrosssectionandbranchingfractionforpseudoscalarHiggs bosonsproducedinassociationwithbb pairs.

mA(GeV) Expected limit (pb) Observed limit (pb) −2σ −1σ Median +1σ +2σ 25 20.4 28.1 41.3 63.1 95.5 35.8 30 14.6 20.0 29.1 44.3 66.3 38.7 35 12.2 16.6 24.3 36.7 55.1 37.4 40 10.3 14.1 20.6 31.1 46.5 31.3 45 8.4 11.6 16.8 25.3 37.9 20.3 50 7.0 9.5 13.7 20.7 30.8 13.2 55 6.7 9.2 13.3 20.1 29.9 10.5 60 6.1 8.2 12.0 18.0 26.7 10.6 65 5.6 7.7 11.2 17.0 25.4 8.3 70 5.1 7.0 10.2 15.6 23.3 7.1 75 5.3 7.2 10.5 15.9 23.8 7.9 80 5.5 7.5 10.9 16.6 25.0 8.0 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); AcademyofFinland,MEC, andHIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic ofKorea); 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);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 SompotFundforPostdoctoralFellowship,ChulalongkornUniversity (Thailand);andtheWelchFoundation,contractC-1845.

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CMSCollaboration

V. Khachatryan,

A.M. Sirunyan,

A. Tumasyan

W. Adam,

E. Asilar,

T. Bergauer,

J. Brandstetter,

E. Brondolin,

M. Dragicevic,

J. Erö,

M. Flechl,

M. Friedl,

R. Frühwirth

1

,

V.M. Ghete,

C. Hartl,

N. Hörmann,

J. Hrubec,

M. Jeitler

1

,

V. Knünz,

A. König,

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,

R. Rougny,

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. Reis,

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,

N. Strobbe,

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,

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,

G.A. Alves,

L. Brito,

M. Correa Martins Junior,

M. Hamer,

C. Hensel,

C. Mora Herrera,

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,

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

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,

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,

W. Zou

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

A.A. Abdelalim

11

,

12

,

A. Awad,

A. Mahrous

11

,

A. Radi

13

,

14

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. Mäenpää,

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

I. Antropov,

S. Baffioni,

F. Beaudette,

P. Busson,

L. Cadamuro,

E. Chapon,

C. Charlot,

T. Dahms,

O. Davignon,

N. Filipovic,

A. Florent,

R. Granier de Cassagnac,

S. Lisniak,

L. Mastrolorenzo,

P. Miné,

I.N. Naranjo,

M. Nguyen,

C. Ochando,

G. Ortona,

P. Paganini,

P. Pigard,

S. Regnard,

R. Salerno,

J.B. Sauvan,

Y. Sirois,

T. Strebler,

Y. Yilmaz,

A. Zabi

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

J.-L. Agram

15

,

J. Andrea,

A. Aubin,

D. Bloch,

J.-M. Brom,

M. Buttignol,

E.C. Chabert,

N. Chanon,

C. Collard,

E. Conte

15

,

X. Coubez,

J.-C. Fontaine

15

,

D. Gelé,

U. Goerlach,

C. Goetzmann,

A.-C. Le Bihan,

J.A. Merlin

2

,

K. Skovpen,

P. Van Hove

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

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,

C. Bernet,

G. Boudoul,

E. Bouvier,

C.A. Carrillo Montoya,

R. Chierici,

D. Contardo,

B. Courbon,

P. Depasse,

H. El Mamouni,

J. Fan,

J. Fay,

S. Gascon,

M. Gouzevitch,

B. Ille,

F. Lagarde,

I.B. Laktineh,

M. Lethuillier,

L. Mirabito,

A.L. Pequegnot,

S. Perries,

J.D. Ruiz Alvarez,

D. Sabes,

L. Sgandurra,

V. Sordini,

M. Vander Donckt,

P. Verdier,

S. Viret

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

T. Toriashvili

16

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze

10

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann,

S. Beranek,

M. Edelhoff,

L. Feld,

A. Heister,

M.K. Kiesel,

K. Klein,

M. Lipinski,

A. Ostapchuk,

M. Preuten,

F. Raupach,

S. Schael,

J.F. Schulte,

T. Verlage,

H. Weber,

B. Wittmer,

V. Zhukov

6

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Ata,

M. Brodski,

E. Dietz-Laursonn,

D. Duchardt,

M. Endres,

M. Erdmann,

S. Erdweg,

T. Esch,

R. Fischer,

A. Güth,

T. Hebbeker,

C. Heidemann,

K. Hoepfner,

D. Klingebiel,

S. Knutzen,

P. Kreuzer,

M. Merschmeyer,

A. Meyer,

P. Millet,

M. Olschewski,

K. Padeken,

P. Papacz,

T. Pook,

M. Radziej,

H. Reithler,

M. Rieger,

F. Scheuch,

L. Sonnenschein,

D. Teyssier,

S. Thüer

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

V. Cherepanov,

Y. Erdogan,

G. Flügge,

H. Geenen,

M. Geisler,

F. Hoehle,

B. Kargoll,

T. Kress,

Y. Kuessel,

A. Künsken,

J. Lingemann

2

,

A. Nehrkorn,

A. Nowack,

I.M. Nugent,

C. Pistone,

O. Pooth,

A. Stahl

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,

I. Asin,

N. Bartosik,

O. Behnke,

U. Behrens,

A.J. Bell,

K. Borras,

A. Burgmeier,

A. Cakir,

L. Calligaris,

A. Campbell,

S. Choudhury,

F. Costanza,

C. Diez Pardos,

G. Dolinska,

S. Dooling,

T. Dorland,

G. Eckerlin,

D. Eckstein,

T. Eichhorn,

G. Flucke,

E. Gallo

17

,

J. Garay Garcia,

A. Geiser,

A. Gizhko,

P. Gunnellini,

J. Hauk,

M. Hempel

18

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H. Jung,

A. Kalogeropoulos,

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18

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P. Katsas,

J. Kieseler,

C. Kleinwort,

I. Korol,

W. Lange,

J. Leonard,

K. Lipka,

A. Lobanov,

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18

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A.B. Meyer,

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