Search for stealth supersymmetry in events with jets, either photons or leptons, and low missing transverse momentum in pp collisions at 8 TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

stealth

supersymmetry

in

events

with

jets,

either

photons

or

leptons,

and

low

missing

transverse

momentum

in

pp

collisions

at 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: Received26November2014

Receivedinrevisedform18February2015 Accepted8March2015

Availableonline10March2015 Editor:M.Doser Keywords: CMS Physics Stealth Supersymmetry Photons Leptons

Lowmissingtransverseenergy

Theresultsofasearchfornewphysicsinfinalstateswithjets,eitherphotonsorleptons,andlowmissing transversemomentumarereported.Thestudyisbasedonasampleofproton–protoncollisionscollected ata center-of-mass energy√s=8 TeV with the CMSdetector in2012. Theintegrated luminosity of the sample is 19.7 fb−1_{. Many models of new physics predict the production of events with jets,} electroweak gauge bosons, and little or nomissing transverse momentum. Examplesinclude stealth modelsofsupersymmetry(SUSY),whichpredictahiddensectorattheelectroweakenergyscaleinwhich SUSYisapproximatelyconserved.ThedataareusedtosearchforstealthSUSYsignaturesinfinalstates witheithertwophotonsoranoppositelychargedelectronandmuon.Noexcessisobservedwithrespect tothestandardmodel expectation,andtheresultsare usedtosetlimitsonsquarkpairproductionin thestealthSUSYframework.

©2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.

1. Introduction

Models of supersymmetry [1,2] (SUSY) with a stable, neutral, massive,weaklyinteracting,lightestsupersymmetricparticle(LSP) havereceivedconsiderableattentioninrecentyears becausethey simultaneously offer a solution to the hierarchy problem, allow unification of the fundamental interactions, and provide a dark mattercandidate.Many searchesforSUSY are basedon this sce-nario,whichpredictslargemissingtransversemomentum



pmiss_T as aconsequenceoftheundetectedLSPs.Nonetheless,well-motivated modelsofSUSYexistthatpredictsmallp



miss_T ,suchasmodelswith R-parity violation [3], gauge mediated SUSY breaking [4], com-pressedspectra[5,6],orhiddenvalleys [7].Manynon-SUSY mod-els ofnewphysics, including theorieswith extradimensions [8], heavy-flavor compositeness [9], or little Higgs scenarios [10,11], similarly predict low-p



miss_T final states. As the parameter space availableforhigh-



pmiss_T signaturesbecomesconstrainedbyresults fromtheCERNLHC[12–21],searchesfortheselow-



pmiss_T alterna-tivesbecomeincreasinglypertinent.

Among models of SUSY with low



pmiss

T final states, the

so-calledstealth scenario [22,23] hasreceived relatively little

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

tion. The simplest stealth SUSY models assume low-scale SUSY breaking and introduce a new hidden sector of particles at the weak scale, analogous to the SUSY-breaking sector, which expe-riencesonlyminimalSUSYbreakingthroughtheinteractionswith SMfields.BecauseitisweaklyconnectedtotheSUSY-breaking sec-tor, the hiddensector is populated with nearly mass-degenerate superpartners.Withthisaddition,theLSPofnon-stealthscenarios, takentobeagaugino(i.e.,a neutralinoorchargino),assumesthe roleofthelightest“visiblesector”SUSYparticle(LVSP)andcan de-caywithoutviolating R-parity[24]toyieldalighterhidden-sector SUSY particle.The LSPin thismodelis producedfromthe decay ofthehidden-sectorSUSYparticletoitsSM partner,andthenear massdegeneracyofthesuperpartnersresultsintheLSPbeing pro-ducedwithlow momentum. Thus, stealthSUSY models naturally producelow-



pmiss_T signatureswithneither R-parityviolationnora specialtuningofmasses.

In thisLetter we presenta search for stealth SUSY signatures involving the decayof a gauginoto a stealth-model particle and eitheraphoton(

γ

analysis)oraleptonicallydecayingW± boson (



±analysis).Thedatasample,correspondingtoanintegrated lu-minosity of19.7 fb−1 of proton–protoncollisions at

√

s

=

8 TeV, was collected withtheCMSdetectorattheLHC in2012. Forthe interpretationofresults,weassumeaminimalhiddensector com-posed of an R-parity-even scalarparticle S andits superpartner,

http://dx.doi.org/10.1016/j.physletb.2015.03.017

0370-2693/©2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

Fig. 1. Decayofasquarkq toaquarkandgauginoχ1instealthSUSY.The

subse-quentdecayofthegauginoproducesasinglinoS andaγ orW± boson,andthe singlinodecaystotwogluonsandasoftgravitinoG.

the singlino



S, both of which are singlets under all SM interac-tions. We consider singlino production in the context of squark pairproduction,withthedecayofthesquarkshownin

Fig. 1

. In the

γ

(



±)scenario,theLVSPneutralino(chargino)decaystoan



S andaphoton(W± boson),withasubsequentdecayofthe



S toan S anda gravitino,



S

→ 

GS.The S isassumedto decayto jetsvia S

→

gg.BecauseofthesmallmasssplittingbetweentheSand



S, theresultinggravitinocarriesverylittlemomentumandyieldslow



pmiss_T .

The

γ

analysisisanextensionofasimilarstudy[25]performed withasample ofproton–protoncollisions at

√

s

=

7 TeV.The



± analysisisthefirst ofits kind.Forthe

γ

analysiswe requirethe presenceoftwophotonsinthefinalstate,whileforthe



± analy-sis we requirethe presence oftwo leptons withdifferent flavors and opposite charges (e±

μ

∓). Both the

γ

and



± analyses are basedonasearchforanexcessofeventswitha largenumberof jetsNjetsandhighST,whereSTisthescalarsumofthetransverse

momenta pT ofallphysicsobjects usedinthestudy.Weperform

astatisticaltestforthepresenceofthespecificstealthSUSY mod-elsdescribed inthisLetter,andprovideadditionalinformationto allowalternativeinterpretationsofthedata.

ThisLetter isorganizedasfollows:inSection2wedescribethe data samples, trigger criteria, and object definitions used in the analysis.Thedetailsofthesimulationofthesignalandbackground samplesaredescribedinSection3.Methodsbasedoncontrol sam-ples in data for estimating the backgrounds for the

γ

and



± analysesaregiveninSections4and5.Systematicuncertaintiesare discussedin Section 6andthe results,includingexclusionlimits, arepresentedinSection7.Section8summarizesourconclusions.

2. Triggerandobjectselection

Thecentralfeature oftheCMSapparatusisasuperconducting solenoidof6 minnerdiameterthatsurroundsasiliconpixeland striptracker,coveringthepseudorapidityregion

|

η

|

<

2

.

5,aswell asaleadtungstatecrystalelectromagneticcalorimeter(ECAL)and abrass/scintillatorhadroncalorimeter(HCAL),bothcovering

|

η

|

<

3

.

0. Muons are detected withgas-ionization detectors embedded inthesteelflux-returnyokecoveringtherange

|

η

|

<

2

.

4.A more detaileddescriptionoftheCMSdetector,togetherwithadefinition ofthecoordinatesystemusedandtherelevantkinematicvariables, canbefoundinRef.[26].

For the

γ

analysis we employ a diphoton trigger requiring two photons satisfying pT

>

36 and 22 GeV. The SM background

isstudiedwitheventsfromatriggerthatrequires HT

>

750 GeV,

where HT is the scalar sum of the pT of all jets in the event

with pT

>

40 GeV. The



± analysis is based on a single-muon

trigger, which requires the presence of at least one muon with pT

>

24 GeV and

|

η

|

<

2

.

1.

Muon candidatesare reconstructedwiththeparticle-flow (PF) algorithm[27],whichsimultaneouslyreconstructsallparticles pro-ducedinacollisionbasedoninformationfromalldetector subsys-temsandidentifies each asa chargedorneutral hadron,photon, muon,orelectron.CandidatesarerequiredtohavepT

>

15 GeV,to

be reconstructed inthefiducialvolume ofthe trigger(

|

η

|

<

2

.

1), andtohaveatransverse(longitudinal)impactparameterlessthan 2 (5) mm with respect to the primary vertex of the event. The primary vertexis definedas the vertexwith thehighest sumof p2_T oftracks associatedwithit.Toensure aprecise measurement of the transverse impact parameter of the muon track relative to the beamspot, we consider only muons with tracks contain-ing more than ten measured points in the silicontracker andat least one in the pixel detector. We ensure isolation from other activity in the event by restricting the scalar pT sum of all

PF-reconstructed photonsandchargedandneutralhadrons withina cone

R

≡



(

η

)

2

_{+ (φ)}

2

₌

₀

_.

_{4 aroundthe muon directionto}

be lessthan12% ofthecandidate pT aftersubtractingthe

contri-butionsofadditionalpp collisions(pileup)[28].

Electron candidates are reconstructed by matching an energy cluster inthe ECALbarrel(

|

η

|

<

1

.

44) witha trackreconstructed witha Gaussian sumfilter[29] inthetracking system.The ECAL endcap regions are omitted due to the low expected signal ac-ceptance in these regions. The shape ofthe matched ECAL clus-ter mustbe consistent withthat expected forelectrons, and the differenceintheinverseclusterenergyandtheinversetrack mo-mentum mustbelessthan0

.

05 GeV−1.Theelectroncandidateis requiredtobeinconsistentwiththeconversionofaphotontoan e+e− pair in the tracker. The track forthe candidate must have a longitudinal impact parameter lessthan 1 mm with respect to theprimaryvertexandfewerthantwomissinghitsinthetracker. All candidates must have pT

>

15 GeV, and the pileup-corrected

sum of the pT of all PF-reconstructed charged hadrons, neutral

hadrons, and photons in a cone of radius

R

=

0

.

3 around the candidate directionis requiredto be lessthan 10% ofthe candi-date pT.

Photoncandidatesarereconstructedfromenergyclustersinthe ECALbarrelwith

|

η

|

<

1

.

44.WerequiretheECALclustershapeto be consistentwiththatexpectedforphotons, andthe energy de-tected in theHCAL inthe directionofthe photon shower not to exceed5%oftheECALenergy.A baserequirementofpT

>

15 GeV

isimposedonallphotoncandidates.Further,thecandidatecannot be matchedto hitpatterns inthepixeldetector. Inacone of ra-dius

R

=

0

.

3 aroundthecandidatephotondirection,the pileup-correctedcharged-hadroncontributionmustbe lessthan1.5 GeV, the correctedneutral-hadroncontribution lessthan1

.

0 GeV

+

4% of thephoton pT,andthecorrected electromagneticcontribution

lessthan0

.

7 GeV

+

0

.

5% ofthephoton pT.

Jetsarereconstructedwiththeanti-kTclusteringalgorithm[30]

withadistanceparameterof0.5usingPFobjectsasinput[31].To remove jetsarising frompotential instrumentalandnon-collision backgrounds, we require the fraction of jet energy coming from chargedandneutralelectromagneticdepositstobelessthan0.99, the neutralhadronfractiontobe lessthan0.99, andthecharged hadron fraction to be greater than zero.The jet energy and mo-mentumarecorrectedforthenonlinearresponseofthe calorime-ter and the effects of pileup [32]. Jets are required to have cor-rected pT

>

30 GeV,

|

η

|

<

2

.

4, and to be isolated from photon

and lepton candidates by

R

>

0

.

5. Jets are identified as origi-nating from b-quark hadronization (b-tagged) using a combined secondary vertexalgorithmthat yields 70%signal efficiencyforb jetsand1.5%misidentificationoflightquarkjets[33].

The missingtransverse momentum vector



pmiss

T is definedas

theprojectionontheplaneperpendiculartothebeamsofthe neg-ativevector sumofthe momentaofallreconstructed particlesin an event.Itsmagnitudeisreferredtoas Emiss_T . ST isthescalar pT

sum ofall acceptedphysics objects in theanalysis: muons, elec-trons,photons,jets,andEmiss

3. Simulationofbackgroundandsignalevents

Monte Carlo (MC) simulations of signal andbackground pro-cessesareusedtooptimizeselectioncriteria,validateanalysis per-formance,determinesignalefficiencies,anddeterminesome back-groundsandsystematic uncertainties.To simulatethesesamples, weusethe MadGraph 5.1.3.30[34]leading-order(LO)event gener-atorunlessotherwisenoted.The pythia 6.426[35]eventgenerator withCTEQ6L1[36]partondistributionfunctions(PDF)and param-etersbasedonmeasurements fromtheLHC runat

√

s

=

7 TeV is usedtodescribepartonshowering,hadronization,multiple-parton interactions, andthe underlying event for MadGraph 5samples. A fullsimulation of the CMSdetector based onthe Geant4 [37]

packageisappliedtoallsamples.Eacheventissuperimposedwith asetofsimulatedminimumbiaseventstoreproducetheeffectof pileup.

Forthe

γ

analysis, SM diphoton events are generated by re-quiringexactlytwophotonswithpT

>

20 GeV andminimum

sep-aration

R

=

0

.

4. Up to fouradditional partonsare allowed. For the



±analysis, wegeneratesamplesofeventswitha topquark– antiquark(tt) pair, Drell–Yan (DY), ZZ, WW, andWZ production. The tt sample is produced with up to three additional partons, the DY sample is produced with up to four additional partons, andthedibosonsamplesare producedwithupto twoadditional partons. Single-top quark (t-, s-, and tW-channels) samples are generated with the powheg v1.0 [38–42] generator. The tt and DYsamplesarenormalizedtocrosssectionscalculatedat next-to-next-to-leading-order accuracy [43,44].The normalizations ofthe single-topquarkanddibosonsamplesarevalidto next-to-leading-order(NLO)[45]andLO[46],respectively.Thediphotonsampleis usedonlytovalidatethebackgroundestimationmethodandsoits normalizationisnotrelevant.

Wegeneratesignalsamplesforbothanalysesusingthe pythia generatorwith theCMS fastsimulation [47] of thedetector. The models are characterized by the masses of the particles in the decaychain. The small



S–S mass splitting,the central feature of stealthSUSY,istakentobe10 GeV,andweassumethe



S massto be100 GeV.Inthe



±analysis,a rangeofsquarkmasses(M_q)are

consideredfrom300to1000 GeV,andthecharginoisfixedtobe halfofM_q roundedup tothenearest100 GeV.Inthe

γ

analysis,

M_q rangesfrom200to1400 GeV andtheneutralino mass(Mχ1) ranges from 150 to 1350 GeV, withthe requirement Mχ_1

<

Mq. In both models, the gravitino mass is taken to be zero. We as-sume branching fractions of unity for the decays

χ



0

1

→ 

S

γ

and



χ

₁±

→

SW±inthe

γ

and



±analyses,respectively.

Theproductioncrosssectionsfortheseprocessesarecalculated asa function of Mq at NLO accuracy includingthe resummation

ofsoftgluon emission atnext-to-leading logarithmic (NLL) accu-racy[48–51]withuncertaintiescomputedasdescribedinRef.[52]. The



q

→

q

χ



₁±decayispossibleonlyforleft-handedsquarks,sofor consistencytheproductionprocessesarelimitedtos-channel pro-ductionofmass-degenerate,left-handedsquarks(



u,



d,



s,and



c)for bothanalyses.Themassesofthegluino,theright-handedsquarks, andtopandbottom squarks areassumed tobe toolarge to par-ticipate in the interactions. The masses of the gluino and right-handed squarks havebeen changed withrespect to the previous analysis[25],wheretheywereassumedtobe sufficientlylightto participateintheproduction.

4. The

γ

analysis

Thedominantbackgroundsforthe

γ

analysisarisefromtheSM productionofeventswithtwophotons, andwitha photonanda jet misidentified asa photon. We estimate thesebackgrounds as functionsof ST andNjets directlyfromthe dataviathe ST shape

Table 1

Selectioncriteriaforthesearch(A)andcontrol(B)regionsfortheγanalysisbased onthepTofthephotonsandtheHTintheevent.

Selection Njets (GeV) γ1pT (GeV) γ2pT (GeV) HT A ≥2 >40 >25 >60 B ≥2 <75 – >800 Table 2

Selectioncriteriadefiningthesearchandsidebandregions foreventspassingselectionAfortheγanalysisbasedon thenumberofjetsandtheSTintheevent.

Region Njets ST(GeV)

Search ≥4 >1200

STsideband ≥4 1100–1200

Njetssideband =3 >1100

invariance method [53–55,25],which relies on the empirical ob-servation that theshape ofthe ST distribution isindependent of

the number of jets in the final state above some ST threshold.

Thus, the ST shape obtainedfroma low-Njets control samplecan

beusedtopredictthebackgroundinthehigh-Njetssignalsample.

Thismethod isvalidatedwitha datacontrol sampleand simula-tion.

StartingfromthebasicobjectselectiondescribedinSection 2, the

γ

analysisimposes twosetsofselectioncriteriabasedonthe trigger used to collect the data, as indicated in Table 1. Selec-tion A,whichisappliedtothediphotonsimulationandtoevents inthedatathatsatisfythediphotontrigger,requiresaphotonwith pT

>

40 GeV,a secondphotonwithpT

>

25 GeV,andatleasttwo

jets. Selection B is applied to events passing the HT trigger and

requiresHT

>

800 GeV,exactlyonephotonwithpT

>

15 GeV,and

atleasttwojets.Additionally,werequirepT

<

75 GeV forthe

pho-ton to make this sample disjointfrom a single photon selection, not discussedhere,that was usedtotest thebackground estima-tionmethod.Eventsthatsatisfy selectionB,alongwithsimulated diphoton events, are used to validate the background estimation method. Events that satisfy selection A are further divided into threesamples,shownin

Table 2

: thesignal-enhanced“search re-gion” isdefinedaseventswith Njets

≥

4 and ST

>

1200 GeV,the

signal-depleted “ST sideband”is definedaseventswith Njets

≥

4

and 1100

<

ST

<

1200 GeV, and the signal-depleted “Njets

side-band”isdefinedaseventswithNjets

=

3 and ST

>

1100 GeV.

To verifythe assumption that the ST distribution is

indepen-dentofNjets,wepresentin

Fig. 2

theSTspectraforeventswith2,

3,4,and

≥

5jets. Theassumption ischeckedinsimulatedevents passing selection A (top) and directly in data forevents passing selectionB(bottom).Thedistributionsarenormalizedtounitarea andthelowerplotsshowtheirratioswithrespecttotheNjets

=

3

distribution. For the selection B data, the ratios are seen to be consistent with a constant function of ST within the

uncertain-ties.Forthesimulateddiphotonsample,theNjets

≥

5 eventsshow

an upwardtrendwithincreasing ST withrespectto theNjets

=

3

distribution.Theincreasecorrespondstoa15%increaseinthe ex-pected background rate for ST

>

1200 GeV and is accounted for

intheevaluationofsystematicuncertainties,asdescribedin Sec-tion6.

To obtain the shape of the ST distribution for the SM

back-ground in the search region, we fit the ST distribution in the

Njets sideband with the nominal shape 1

/x

p1ln ST, where x

≡

ST

/(

8000 GeV

)

. Two alternate functions, 1

/x

p2 and 1

/e

p3x, are

used to assess the systematic uncertainty associated with the choice of fit function. We find p1

=

1

.

01

±

0

.

19. The

Fig. 2. ST distributionsusedintheγ analysisasafunctionofNjetsforsimulated

diphotoneventspassingselectionA(top)andfordataeventspassingselectionB (bottom).Thedistributionsarenormalizedtounitarea.Thelowerplotsshowratios withrespecttotheNjets=3 distribution.

5. The



±analysis

For the



± analysis, the signal region is defined in terms of Njets, the number Nb-jets of b-tagged jets, and the lepton flavors

andcharges.ToreducethemultijetandW

+

jets backgrounds,we requirethatboth W bosonsdecayleptonicallyresultinginexactly two oppositely charged leptons in the final state with no addi-tional lepton that satisfies loosened isolation criteria. To reduce the large DY contribution to the background, we require one of theseleptons to be a muon and the other to be an electron. To ensure optimal trigger efficiency, the muon is required to have pT

>

30 GeV.Finally,tosuppressthett background,signal events

are required to have Nb-jets

=

0. The principal requirements for

the signal event selection are listed in the top row of Table 3. To enhance the statisticalsignificance of a potential observation, we dividethe signalsample into fourexclusive regions basedon Njets (4, 5, 6, and

≥

7) and divide each Njets bin into three

in-clusive samples with ST thresholds of 300, 700, and 1200 GeV.

Thesethresholdvaluesweredeterminedthroughaprocedurethat optimizes sensitivity to stealth SUSY production via examination ofthe ZBi variable [56], whichis the ratio ofthe Poissonmeans

Table 3

Summaryofsearchandcontrolsampledefinitionsforthe±analysisbasedonthe numberofjets,numberofb-taggedjets,leptonflavor,andleptoncharge.

Sample Leptons Njets Nb-jets

Search e±,μ∓ ≥4 0

Top shape e±,μ∓ ≥2 ≥2

Top normalization e±,μ∓ <4 0

Drell–Yan μ±,μ∓ ≥2 0

Non-prompt e±,μ± ≥2 0

Fig. 3. DistributionofNjetsfordataandsimulation,forthetop-shapecontrolregion

usedinthe±analysis.Thelowerplotshowstheratioofdataandsimulation,with systematicuncertaintiesshownbytheshadedbands.The(negligible)signal contri-butiontothiscontrolsampleisshownasadashedlinethatappearstocoincide withthehorizontalaxis.

of the expected signal andbackground given the systematic un-certainty in theexpectedbackground.We findthat thresholds of Smin_T

=

300

,

700

,

700

,

and 1200 GeV are optimalforsquark mass valuesof300,400,500,and600 GeV,respectively.

The largestSM backgroundcontributions inthe signalregions arefromtt andsingle-topquarkevents,whichwecollectivelyrefer toasthe“top-quarkbackground”.Dependingonthe STthreshold,

approximately 1–10% of the background arises from Z

→

τ

+

τ

−, diboson,andnon-promptlepton production,where“non-prompt” refers to leptons from hadron decay and to hadrons that are misidentified as leptons. The estimate of the SM background is based on four data control regions, defined in the bottom four rows of Table 3 in terms of Njets, Nb-jets, and the lepton flavors

andcharges.

The top-quark background isestimated fromsimulation, with correctionstotheshapeoftheNjetsdistributionobtainedby

com-paringdata andsimulationin the“top shape” control region de-fined in Table 3. A comparison of data and simulation in this control region isshownin

Fig. 3

withthesystematicuncertainty inthe topquark background,estimatedbyvarying the renormal-izationandfactorizationscaleup anddownby afactorof2. The small corrections, which are derived fromthe lowest ST bin, are

consistent withunity forall valuesof Njets. The top-quark

simu-lation is then normalized to the data in the “top normalization” control region defined in Table 3. Before obtaining the normal-ization correctionfactor fromthissample,we usethe simulation to subtract contributions from the DY, diboson, and non-prompt backgrounds,whichcollectivelyaccountfor20%ofthetotal back-ground. We then determine the correction factor from events with ST

>

200 GeV as the ratioof the number of eventsin this

background-subtracteddatasampletothenumberofeventsinthe simulated top-quark background, finding 0

.

97

±

0

.

02, where the uncertaintyisstatistical.

Similarly,thesmallDYbackground(about10%ofthetotal back-ground)isevaluatedfromsimulation,withacorrection factorfor thenormalization derived from the DY control sample (Table 3), which requirestwo oppositely charged muons. Because the con-tributionof signal eventsto the DY control sample is potentially significant at large Njets, we perform a fit to the dimuon mass

spectrumusingtemplates fromsimulation todescribetheshapes of the DY and diboson components, with a first-order polyno-mialusedtodescribe thecombinedshape ofpotential signaland remaining (non-peaking) background events. The number of DY events NDY, polynomial normalization, and polynomial slope are

determinedinthefit.Thecorrectionfactor,definedastheratioof NDY to the number ofevents in the DY simulation, ranges from

1

.

02

±

0

.

01 for Njets

=

2 to 1

.

56

±

0

.

25 for Njets

≥

6,where the

uncertaintiesarestatistical.

Toestimate thesmallbackgroundassociatedwithnon-prompt leptons(about2%ofthetotalbackground)weusethenon-prompt control sample (Table 3), defined using same charge (SC) e

μ

events.After subtracting the simulatedcontribution to this sam-plefromSMtop-quarkanddibosonevents,wetaketheremaining dataastheestimate ofthe non-promptbackgroundinthesearch region.BecauseofthelownumberofSCeventswithhighNjetsand

highST,wefittheNjetsdistributiontoanexponentialfunctionfor

ST

>

300 GeV.Thenormalizationoftheexponentialdistributionis

determined foreach ST thresholdby thetotal number ofevents

passingtheselection.

To estimate the diboson background (about 10% of the total background)weusethepredictionfromsimulation.

6. Systematicuncertainties

Weevaluatethesystematicuncertaintiesinthebackground ex-pectation,signalefficiency,andluminosity.Foreachsourceof un-certainty,wedescribebelowtheuncertaintyvalueandthemethod usedforitsestimation.

For the

γ

analysis, the largest systematic uncertainty in the background prediction arises from the statistical uncertainty in thenormalizationofthebackgroundshapefromthe ST sideband,

which is 30% (38%) for Njets

=

4 (

≥

5). The largest uncertainty

in the assumed shape of the ST distribution is due to the

sta-tistical uncertainty in the estimation of the fitted parameter p1

(Section4), which results in a systematic uncertaintyof 31% for ST

>

1200 GeV.Thesecondlargestuncertaintyassociatedwiththe

shapearisesfromtheassumptionthattheSTshapeisindependent

ofNjets.Weestimatethisuncertaintybyfirstseparatelyfittingthe

ST distributions for Njets

=

4 and Njets

≥

5 to thenominal

func-tion,forthediphotonsimulationintheselectionAregionandfor the datain the selection B region.We then compare the result-ingfittedparametervalueswiththenominalresultsfor Njets

=

3

inthecorrespondingsampleandtakethelargestdifferenceasthe systematicuncertaintyinthevaluesoftheparameters.Thelargest differenceis observedfor Njets

≥

5 and correspondsto a

system-aticuncertaintyof15%inthebackgroundprediction.Thesmallest shapeuncertainty,whichisrelatedtothechoiceofthefitfunction, is evaluated by constructing the envelope formed by the nomi-nal fit function and the two alternate fit functions described in Section 4 andresults in a 12% variation in the total background predictionforST

>

1200 GeV.

Thedominantsystematicuncertaintyinthe



±analysisis asso-ciatedwiththetop-quarkbackground.TheuncertaintyintheNjets

shape correctionsfor the top-quarkbackground is dominated by thestatisticaluncertaintyinthecontrolsampleandisestimatedto

be2–25%dependingonNjets.Theuncertaintyinthenormalization

isdetermined by findingthecorrection asdescribed inSection 5

for300

<

ST

<

700 GeV andST

>

700 GeV separately.Wefind

cor-rectionsof0

.

97

±

0

.

02 and0

.

86

±

0

.

12 respectively, andtake the difference summed in quadrature withthe statistical uncertainty asthesystematicterm, which resultsina systematicuncertainty of15% inthebackgroundprediction.Anadditionaluncertainty is obtainedbysimultaneouslychangingtherenormalizationand fac-torizationscalesinthesimulationbyafactorof2andbyafactor of0.5,resultingina10%systematicuncertaintyinthebackground prediction.Wevary theb-taggingefficiencyandmisidentification ratesbytheiruncertainties[57]andfindthattheeffectonthetop backgroundpredictionvariesby1–3%dependingonNjets.

Forthe DY background,the uncertaintyis takento be half of thecorrection appliedto thesimulation,andconstitutesa2–28% uncertainty depending on Njets. For the diboson prediction the

uncertaintyisgivenbythesuminquadratureofthedifference be-tweentheCMSmeasurement[58] andtheNLO calculationofthe W+W−crosssection[46]andthe Njets-dependentDYuncertainty.

Finally, the uncertainty in the non-prompt dilepton background comes fromthe statistical uncertaintyin the control sample and is50–120%dependingonthe STthreshold.

Thesignalefficiencyuncertaintiesforthe

γ

analysisarerelated to the statistical uncertainty from the finite size of signal simu-lationsamples (2–15%,depending on Njets), knowledge ofthejet

energyscale(1–7%,depending onthe



q–



χ

1 massdifference), and

photon identificationand reconstruction efficiencies (3%).Forthe



± analysis, theuncertaintyduetothejetenergyscaleis5%.We assign an uncertaintyof 1% to account forthemuon trigger and reconstruction efficiencies, 3% to account for the electron recon-structionefficiency,and0–7%(dependingontheST thresholdand

Njets)toaccountforthefinitesizeofthesimulatedeventsamples.

For both analyses the uncertaintyrelated to thesize of the data sample is 2.6% [59], while the uncertainties related to the PDFs andpileupinteractionsarefoundtobenegligible.

7. Results

For the

γ

analysis, the measured ST distribution and

corre-spondingbackgroundpredictionsareshownin

Fig. 4

.Weobserve 19 (6) events for Njets

=

4 (

≥

5), comparedto an expected

back-ground of 22

.

5

±

11

.

5 (14

.

3

±

8

.

1) events.The data are seen to agreewiththebackgroundestimatewithintheuncertainties.

Fig. 5showsthecorrespondingresultsforthe



± analysis.The eventyieldsforST

>

1200 GeV arelistedin

Table 4

withthetotal

(stat.

+

syst.)uncertainties. The data are seen to agreewith the backgroundexpectations.

We determine 95% confidence level (CL) upper limits on the squarkpairproductioncrosssectioninthestealthSUSYframework describedabove.WeusethemodifiedfrequentistCLSmethod[60, 61] based on a log-likelihood ratio test statistic that compares the likelihoodof theSM-only hypothesis to thelikelihood ofthe presenceof signalinaddition totheSM contributions.Forthe

γ

analysis, the likelihood functions for Njets

=

4 and Njets

≥

5 are

basedontheexpectedshapesoftheSTdistributionsforsignaland

background,andthetotallikelihoodfunctionistheproductofthe two.Forthe



±analysisweperformasimultaneouscomparisonof thenumberofsignalandbackgroundeventspassingtheoptimized Smin

T thresholddefinedin Section5inthe Njets

=

4

,

5

,

6

,

and

≥

7

samples,withthelikelihoodfunctiongivenbytheproductof Pois-sonlikelihoodtermsfromeachoftheNjetsregions.

Systematicuncertaintiesareincorporatedintothetest statistic as nuisance parameters, with gamma distributions for the prob-abilitydensityfunctionsforthe backgroundnormalization uncer-taintyinthe

γ

analysisandthetop-quarkbackground

normaliza-Fig. 4. Measured ST distribution incomparisonwith the backgroundprediction

inthesignalregionofthe γ analysisfor Njets=4 (top)and Njets≥5 (bottom).

Thesystematicuncertaintyofthebackgroundpredictionandtheexpected distribu-tionofsignaleventsforMq=900 GeV andeitherM_χ0

1=450 or850 GeV arealso

shown.

tionin the



± analysis. Theprobability distributions forall other uncertainties are takento be log-normal. For the

γ

analysis, the backgroundshapeuncertaintiesareincludedwithfullcorrelations in ST. For the



± analysis, all uncertainties except those arising

fromstatistical uncertainties in the control samples are takento becorrelatedacrosstheNjetsbins.

Fig. 6 showsthecross section upperlimitsforthe

γ

analysis asafunction ofthe squarkandneutralinomasses. The predicted NLO

+

NLLcrosssectionisusedtoplaceconstraintsonthemasses of the squarks and neutralinos under the assumption of stealth SUSY. We show the observed (median expected) mass exclusion witha bandcorrespondingtothevariationofthetheoretical (ex-perimental) uncertainties by one standard deviation. For higher neutralinomasses, we excludesquark massesbelow 1050 GeV at a 95% CL for the

γ

analysis. At low masses the neutralino be-comes more boosted, andthe resulting decayproducts are more tightly collimated, spoiling the isolation of the photon. As a re-sultthelimitdegradesforneutralinomassesbelow300 GeV.

Fig. 7

showstheobservedandmedianexpectedcrosssectionupper lim-itsforthe



±analysisasafunctionofsquarkmassforthemodel

Fig. 5. MeasuredNjetsdistributionsincomparisonwiththebackgroundpredictions

inthesignalregionsofthe±analysis.Thelowerplotsshowtheratioofthedata tothebackgroundprediction,withthesystematicuncertaintyinthebackground predictionderivedfromcontrolsamplesindata.

Table 4

Eventyieldsobservedindataandtheexpectedcontributionsfrombackgroundsin the searchregionofthe± analysisfor ST>1200 GeV.Thetotal(stat.+syst.)

uncertaintiesarealsoshown.

Njets=4 Njets=5 Njets=6 Njets≥7

Observed events 5 2 1 1 Total background 4.14±0.68 2.95±0.48 1.45±0.33 0.66±0.19 Top 2.96±0.55 2.22±0.43 1.30±0.30 0.56±0.17 DY 0.31±0.02 0.22±0.02 0.00±0.02 0.00±0.02 Diboson 0.58±0.18 0.36±0.12 0.08±0.03 0.06±0.02 Non-prompt 0.30±0.36 0.15±0.18 0.08±0.09 0.04±0.05 Signal (Mq=600 GeV) 0.9±0.1 1.3±0.1 1.3±0.1 1.4±0.1

Fig. 6. The95%confidencelevelupperlimitsonthesquarkpairproductioncross sectionasafunctionofsquarkandneutralinomassesfromtheγanalysis.The con-toursshowtheobservedandmedianexpectedexclusionsassumingtheNLO+NLL crosssections,withtheironestandarddeviationuncertainties.

Fig. 7. Observedandmedianexpectedcrosssectionupperlimitsasafunctionof squarkmassfromthe±analysis.Thebandabouttheexpectedlimitindicatesthe onestandarddeviationexperimentaluncertainty.TheNLO+NLLcrosssectionwith itsonestandarddeviationuncertaintyisalsoshown.

choicesdescribedinSection 3,aswellasthepredictedcross sec-tionfromstealthSUSY.Based ontheintersectionoftheobserved limit andthe predicted cross section, we exclude squark masses below550 GeV ata95%CL.

8. Summary

Weperform asearch fornewphenomena ineventswithfour ormore jets, low missingtransverse momentum,andeither two photons(

γ

analysis) or one electron and one muon of opposite charge(



± analysis),basedona datasamplecorresponding toan integratedluminosity of19.7 fb−1 _{ofpp collisions at}

√

_s

₌

_{8 TeV.}

Using background estimation methods based on control samples indata,we determinelimitson thesquark pairproductioncross section,andwe usethose limitsinconjunctionwithNLO

+

NLL crosssection calculationsto constrain themassesof squarksand neutralinosin theframework ofstealthSUSY. Wedonot observe a significant excess of events above the standard model expec-tation in any search region. In the

γ

analysis we establish 95% confidencelevellower limitsonsquarkmassesbetween700and 1050 GeV,depending on the neutralino mass. In the



± analysis we excludesquark massesbelow550 GeV at the95% confidence level.Themasslimitsforthe

γ

analysissupersedethosefromour previousstudy[25].Ourresultsforthe



± analysisrepresentthe firstlimitsforthischannel.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrativestaffs atCERN andatother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso 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 ofFinland,MEC,andHIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); CINVESTAV, CONACYT,SEP,andUASLP-FAI(Mexico);MBIE(NewZealand);PAEC (Pakistan);MSHEandNSC (Poland);FCT(Portugal);JINR(Dubna); MON,RosAtom,RASandRFBR(Russia);MESTD(Serbia);SEIDIand CPAN(Spain);SwissFundingAgencies(Switzerland);MST(Taipei); ThEPCenter,IPST, STARandNSTDA(Thailand);TÜBITAK andTAEK (Turkey);NASUandSFFR(Ukraine); STFC(United Kingdom);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); theMinistry ofEducation, YouthandSports (MEYS) of theCzechRepublic;theCouncilofScienceandIndustrialResearch, India; the HOMING PLUS programme of Foundation For Polish Science, cofinanced from European Union, Regional Development Fund;the CompagniadiSan Paolo(Torino); the Consorzioper la Fisica (Trieste); MIURproject20108T4XTM (Italy);the Thalisand Aristeia programmes cofinanced by EU-ESF andthe Greek NSRF; andtheNationalPrioritiesResearchProgrambyQatarNational Re-searchFund.

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CMSCollaboration

V. Khachatryan,

A.M. Sirunyan,

A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam,

T. Bergauer,

M. Dragicevic,

J. Erö,

M. Friedl,

R. Frühwirth

1

,

V.M. Ghete,

C. Hartl,

N. Hörmann,

J. Hrubec,

M. Jeitler

1

,

W. Kiesenhofer,

V. Knünz,

M. Krammer

1

,

I. Krätschmer,

D. Liko,

I. Mikulec,

D. Rabady

2

,

B. Rahbaran,

H. Rohringer,

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,

S. Bansal,

T. Cornelis,

E.A. De Wolf,

X. Janssen,

A. Knutsson,

J. Lauwers,

S. Luyckx,

S. Ochesanu,

R. Rougny,

M. Van De Klundert,

H. Van Haevermaet,

P. Van Mechelen,

N. Van Remortel,

A. Van Spilbeeck

UniversiteitAntwerpen,Antwerpen,Belgium

F. Blekman,

S. Blyweert,

J. D’Hondt,

N. Daci,

N. Heracleous,

J. Keaveney,

S. Lowette,

M. Maes,

A. Olbrechts,

Q. Python,

D. Strom,

S. Tavernier,

W. Van Doninck,

P. Van Mulders,

G.P. Van Onsem,

I. Villella

VrijeUniversiteitBrussel,Brussel,Belgium

C. Caillol,

B. Clerbaux,

G. De Lentdecker,

D. Dobur,

L. Favart,

A.P.R. Gay,

A. Grebenyuk,

A. Léonard,

A. Mohammadi,

L. Perniè

2

,

A. Randle-conde,

T. Reis,

T. Seva,

L. Thomas,

C. Vander Velde,

P. Vanlaer,

J. Wang,

F. Zenoni

UniversitéLibredeBruxelles,Bruxelles,Belgium

V. Adler,

K. Beernaert,

L. Benucci,

A. Cimmino,

S. Costantini,

S. Crucy,

S. Dildick,

A. Fagot,

G. Garcia,

J. Mccartin,

A.A. Ocampo Rios,

D. Poyraz,

D. Ryckbosch,

S. Salva Diblen,

M. Sigamani,

N. Strobbe,

F. Thyssen,

M. Tytgat,

E. Yazgan,

N. Zaganidis

GhentUniversity,Ghent,Belgium

S. Basegmez,

C. Beluffi

3

,

G. Bruno,

R. Castello,

A. Caudron,

L. Ceard,

G.G. Da Silveira,

C. Delaere,

T. du Pree,

D. Favart,

L. Forthomme,

A. Giammanco

4

,

J. Hollar,

A. Jafari,

P. Jez,

M. Komm,

V. Lemaitre,

C. Nuttens,

L. Perrini,

A. Pin,

K. Piotrzkowski,

A. Popov

5

,

L. Quertenmont,

M. Selvaggi,

M. Vidal Marono,

J.M. Vizan Garcia

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

N. Beliy,

T. Caebergs,

E. Daubie,

G.H. Hammad

UniversitédeMons,Mons,Belgium

W.L. Aldá Júnior,

G.A. Alves,

L. Brito,

M. Correa Martins Junior,

T. Dos Reis Martins,

J. Molina,

C. Mora Herrera,

M.E. Pol,

P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

W. Carvalho,

J. Chinellato

6

,

A. Custódio,

E.M. Da Costa,

D. De Jesus Damiao,

C. De Oliveira Martins,

S. Fonseca De Souza,

H. Malbouisson,

D. Matos Figueiredo,

L. Mundim,

H. Nogima,

W.L. Prado Da Silva,

J. Santaolalla,

A. Santoro,

A. Sznajder,

E.J. Tonelli Manganote

6

,

A. Vilela Pereira

C.A. Bernardes

b

,

S. Dogra

a

,

T.R. Fernandez Perez Tomei

a

,

E.M. Gregores

b

,

P.G. Mercadante

b

,

S.F. Novaes

a

,

Sandra S. Padula

a

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

A. Aleksandrov,

V. Genchev

2

,

R. Hadjiiska,

P. Iaydjiev,

A. Marinov,

S. Piperov,

M. Rodozov,

S. Stoykova,

G. Sultanov,

M. Vutova

InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria

A. Dimitrov,

I. Glushkov,

L. Litov,

B. Pavlov,

P. Petkov

UniversityofSofia,Sofia,Bulgaria

J.G. Bian,

G.M. Chen,

H.S. Chen,

M. Chen,

T. Cheng,

R. Du,

C.H. Jiang,

R. Plestina

7

,

F. Romeo,

J. Tao,

Z. Wang

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,

D. Polic,

I. Puljak

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,

M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,

K. Kadija,

J. Luetic,

D. Mekterovic,

L. Sudic

InstituteRudjerBoskovic,Zagreb,Croatia

A. Attikis,

G. Mavromanolakis,

J. Mousa,

C. Nicolaou,

F. Ptochos,

P.A. Razis

UniversityofCyprus,Nicosia,Cyprus

M. Bodlak,

M. Finger,

M. Finger Jr.

8 CharlesUniversity,Prague,CzechRepublic

Y. Assran

9

,

A. Ellithi Kamel

10

,

M.A. Mahmoud

11

,

A. Radi

12,13

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

M. Kadastik,

M. Murumaa,

M. Raidal,

A. Tiko

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,

M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Härkönen,

V. Karimäki,

R. Kinnunen,

M.J. Kortelainen,

T. Lampén,

K. Lassila-Perini,

S. Lehti,

T. Lindén,

P. Luukka,

T. Mäenpää,

T. Peltola,

E. Tuominen,

J. Tuominiemi,

E. Tuovinen,

L. Wendland

HelsinkiInstituteofPhysics,Helsinki,Finland

J. Talvitie,

T. Tuuva

M. Besancon,

F. Couderc,

M. Dejardin,

D. Denegri,

B. Fabbro,

J.L. Faure,

C. Favaro,

F. Ferri,

S. Ganjour,

A. Givernaud,

P. Gras,

G. Hamel de Monchenault,

P. Jarry,

E. Locci,

J. Malcles,

J. Rander,

A. Rosowsky,

M. Titov

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

S. Baffioni,

F. Beaudette,

P. Busson,

E. Chapon,

C. Charlot,

T. Dahms,

M. Dalchenko,

L. Dobrzynski,

N. Filipovic,

A. Florent,

R. Granier de Cassagnac,

L. Mastrolorenzo,

P. Miné,

I.N. Naranjo,

M. Nguyen,

C. Ochando,

G. Ortona,

P. Paganini,

S. Regnard,

R. Salerno,

J.B. Sauvan,

Y. Sirois,

C. Veelken,

Y. Yilmaz,

A. Zabi

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

J.-L. Agram

14

,

J. Andrea,

A. Aubin,

D. Bloch,

J.-M. Brom,

E.C. Chabert,

C. Collard,

E. Conte

14

,

J.-C. Fontaine

14

,

D. Gelé,

U. Goerlach,

C. Goetzmann,

A.-C. Le Bihan,

K. Skovpen,

P. Van Hove

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

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,

N. Beaupere,

C. Bernet

7

,

G. Boudoul

2

,

E. Bouvier,

S. Brochet,

C.A. Carrillo Montoya,

J. Chasserat,

R. Chierici,

D. Contardo

2

,

P. Depasse,

H. El Mamouni,

J. Fan,

J. Fay,

S. Gascon,

M. Gouzevitch,

B. Ille,

T. Kurca,

M. Lethuillier,

L. Mirabito,

S. Perries,

J.D. Ruiz Alvarez,

D. Sabes,

L. Sgandurra,

V. Sordini,

M. Vander Donckt,

P. Verdier,

S. Viret,

H. Xiao

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

Z. Tsamalaidze

8

InstituteofHighEnergyPhysicsandInformatization,TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann,

S. Beranek,

M. Bontenackels,

M. Edelhoff,

L. Feld,

A. Heister,

K. Klein,

M. Lipinski,

A. Ostapchuk,

M. Preuten,

F. Raupach,

J. Sammet,

S. Schael,

J.F. Schulte,

H. Weber,

B. Wittmer,

V. Zhukov

5

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Ata,

M. Brodski,

E. Dietz-Laursonn,

D. Duchardt,

M. Erdmann,

R. Fischer,

A. Güth,

T. Hebbeker,

C. Heidemann,

K. Hoepfner,

D. Klingebiel,

S. Knutzen,

P. Kreuzer,

M. Merschmeyer,

A. Meyer,

P. Millet,

M. Olschewski,

K. Padeken,

P. Papacz,

H. Reithler,

S.A. Schmitz,

L. Sonnenschein,

D. Teyssier,

S. Thüer,

M. Weber

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

V. Cherepanov,

Y. Erdogan,

G. Flügge,

H. Geenen,

M. Geisler,

W. Haj Ahmad,

F. Hoehle,

B. Kargoll,

T. Kress,

Y. Kuessel,

A. Künsken,

J. Lingemann

2

,

A. Nowack,

I.M. Nugent,

O. Pooth,

A. Stahl

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,

I. Asin,

N. Bartosik,

J. Behr,

U. Behrens,

A.J. Bell,

A. Bethani,

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,

J. Garay Garcia,

A. Geiser,

A. Gizhko,

P. Gunnellini,

J. Hauk,

M. Hempel

15

,

H. Jung,

A. Kalogeropoulos,

M. Kasemann,

P. Katsas,

J. Kieseler,

C. Kleinwort,

I. Korol,

D. Krücker,

W. Lange,

J. Leonard,

K. Lipka,

A. Lobanov,

W. Lohmann

15

,

B. Lutz,

R. Mankel,

I. Marfin

15

,

I.-A. Melzer-Pellmann,

A.B. Meyer,

G. Mittag,

J. Mnich,

A. Mussgiller,

S. Naumann-Emme,

A. Nayak,

E. Ntomari,

H. Perrey,

D. Pitzl,

R. Placakyte,

A. Raspereza,

P.M. Ribeiro Cipriano,

B. Roland,

E. Ron,

M.Ö. Sahin,

J. Salfeld-Nebgen,

P. Saxena,

T. Schoerner-Sadenius,

M. Schröder,

C. Seitz,

S. Spannagel,

A.D.R. Vargas Trevino,

R. Walsh,

C. Wissing

V. Blobel,

M. Centis Vignali,

A.R. Draeger,

J. Erfle,

E. Garutti,

K. Goebel,

M. Görner,

J. Haller,

M. Hoffmann,

R.S. Höing,

A. Junkes,

H. Kirschenmann,

R. Klanner,

R. Kogler,

J. Lange,

T. Lapsien,

T. Lenz,

I. Marchesini,

J. Ott,

T. Peiffer,

A. Perieanu,

N. Pietsch,

J. Poehlsen,

T. Poehlsen,

D. Rathjens,

C. Sander,

H. Schettler,

P. Schleper,

E. Schlieckau,

A. Schmidt,

M. Seidel,

V. Sola,

H. Stadie,

G. Steinbrück,

D. Troendle,

E. Usai,

L. Vanelderen,

A. Vanhoefer

UniversityofHamburg,Hamburg,Germany

C. Barth,

C. Baus,

J. Berger,

C. Böser,

E. Butz,

T. Chwalek,

W. De Boer,

A. Descroix,

A. Dierlamm,

M. Feindt,

F. Frensch,

M. Giffels,

A. Gilbert,

F. Hartmann

2

,

T. Hauth,

U. Husemann,

I. Katkov

5

,

A. Kornmayer

2

,

P. Lobelle Pardo,

M.U. Mozer,

T. Müller,

Th. Müller,

A. Nürnberg,

G. Quast,

K. Rabbertz,

S. Röcker,

H.J. Simonis,

F.M. Stober,

R. Ulrich,

J. Wagner-Kuhr,

S. Wayand,

T. Weiler,

R. Wolf

InstitutfürExperimentelleKernphysik,Karlsruhe,Germany

G. Anagnostou,

G. Daskalakis,

T. Geralis,

V.A. Giakoumopoulou,

A. Kyriakis,

D. Loukas,

A. Markou,

C. Markou,

A. Psallidas,

I. Topsis-Giotis

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

A. Agapitos,

S. Kesisoglou,

A. Panagiotou,

N. Saoulidou,

E. Stiliaris

UniversityofAthens,Athens,Greece

X. Aslanoglou,

I. Evangelou,

G. Flouris,

C. Foudas,

P. Kokkas,

N. Manthos,

I. Papadopoulos,

E. Paradas,

J. Strologas

UniversityofIoánnina,Ioánnina,Greece

G. Bencze,

C. Hajdu,

P. Hidas,

D. Horvath

16

,

F. Sikler,

V. Veszpremi,

G. Vesztergombi

17

,

A.J. Zsigmond

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,

S. Czellar,

J. Karancsi

18

,

J. Molnar,

J. Palinkas,

Z. Szillasi

InstituteofNuclearResearchATOMKI,Debrecen,Hungary

A. Makovec,

P. Raics,

Z.L. Trocsanyi,

B. Ujvari

UniversityofDebrecen,Debrecen,Hungary

S.K. Swain

NationalInstituteofScienceEducationandResearch,Bhubaneswar,India

S.B. Beri,

V. Bhatnagar,

R. Gupta,

U. Bhawandeep,

A.K. Kalsi,

M. Kaur,

R. Kumar,

M. Mittal,

N. Nishu,

J.B. Singh

PanjabUniversity,Chandigarh,India

Ashok Kumar,

Arun Kumar,

S. Ahuja,

A. Bhardwaj,

B.C. Choudhary,

A. Kumar,

S. Malhotra,

M. Naimuddin,

K. Ranjan,

V. Sharma

UniversityofDelhi,Delhi,India

S. Banerjee,

S. Bhattacharya,

K. Chatterjee,

S. Dutta,

B. Gomber,

Sa. Jain,

Sh. Jain,

R. Khurana,

A. Modak,

S. Mukherjee,

D. Roy,

S. Sarkar,

M. Sharan

SahaInstituteofNuclearPhysics,Kolkata,India

A. Abdulsalam,

D. Dutta,

V. Kumar,

A.K. Mohanty

2

,

L.M. Pant,

P. Shukla,

A. Topkar

BhabhaAtomicResearchCentre,Mumbai,India