Search for dark matter in events with a leptoquark and missing transverse momentum in proton-proton collisions at 13 TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

dark

matter

in

events

with

a

leptoquark

and

missing

transverse

momentum

in

proton-proton

collisions

at

13 TeV

.

The

CMS

Collaboration



CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received26November2018 Receivedinrevisedform11May2019 Accepted29May2019

Availableonline3June2019 Editor:M.Doser Keywords: CMS Physics Darkmatter Leptoquarks

A searchispresented for darkmatterinproton-protoncollisions atacenter-of-massenergy of√s₌

13 TeV usingeventswithatleastonehightransversemomentum(pT)muon,atleastonehigh-pTjet,

andlargemissingtransversemomentum.ThedatawerecollectedwiththeCMSdetectorattheCERNLHC in2016and 2017,andcorrespondtoanintegratedluminosity of77.4 fb−1_{.Intheexaminedscenario,}

a pairofscalarleptoquarks is assumedto beproduced. One leptoquark decays toamuon and ajet while the otherdecaysto dark matterand low-pTstandard model particles. Thesignature for signal

events would besignificantmissing transverse momentumfromthe darkmatterin conjunctionwith apeakattheleptoquark massintheinvariantmassdistributionofthehighestpTmuonandjet. The

data areobservedtobeconsistentwiththebackgroundpredictedbythestandardmodel.Forthefirst benchmarkscenarioconsidered,darkmattermassesupto500 GeVareexcludedforleptoquarkmasses

mLQ≈1400 GeV, and up to300 GeVfor mLQ≈1500 GeV.For the secondbenchmarkscenario, dark

mattermassesupto600 GeVareexcludedformLQ≈1400 GeV.

©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Dark matter (DM) has been a subject of intense interest for decades.ExtensiveastrophysicalevidenceforDMexists [1–3],such asfromobservationsofthedynamicsofgalaxyclustersand mea-surements of anisotropies in the cosmic microwave background. Nonetheless, the nature of DMremains unknown andit has not been observedoutside the astrophysical context. Its relic density isdeterminedtobe



DM

= (

0

.

1186

±

0

.

0020

)/

h2 [4,5],whereh is

theHubbleconstant.

Darkmattercouldpotentiallybecreatedinhigh-energy proton-proton (pp) collisions, such as at the CERN LHC. Because of its presumed weakly interacting nature, a DM particle produced at the LHC would escape unobserved, manifesting itself as missing transversemomentum



pmiss

T inthereconstructedevents.Themost

genericsignal forDMatthe LHCthusconsistsofan excess, rela-tivetothestandardmodel(SM)expectation,ofeventswithsizable



pmiss_T recoilingagainstavisibleSMobjectsuchasajet,aphoton, or an electroweak boson. Such searches have been conducted at theLHCbytheATLASandCMSCollaborations [6–14] butwithno evidence, to date,for DM [15]. The absence of a signal in these

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

genericsearchessuggeststhatalternativestrategiesshouldbe pur-sued.

In thisLetter, wepresenta search forDMatthe LHCusing a new approach, based on the coannihilation paradigm introduced inRef. [16].Thedata,correspondingtoanintegratedluminosityof 77.4 fb−1ofpp collisions,werecollectedbytheCMSCollaboration in 2016 (35.9 fb−1) and 2017 (41.5 fb−1) at a center-of-mass en-ergyof

√

s

=

13 TeV.Thecoannihilationprocessconsideredarises withinageneralclassofsimplifiedmodelsinwhichaDMparticle is eitherannihilated orproduced inconjunctionwitha so-called coannihilationpartner,denoted“X”.AttheLHC,DMcouldthusbe producedthroughareactionlikeM

→

DM

+

X,whereM isa me-diator representingeitheran SM ora beyond-the-SMparticle.To beconsistentwiththeobservedvalueof



DM,thefractionalmass

difference



X,DM

≡ (

mX

−

mDM

)/

mDMbetweentheX andDM

par-ticlesshouldbelessthan

≈

0.2 [16].

The considered coannihilation paradigm introduces many DM signaturesthatarenotcoveredbycurrentsearches.Here,we con-sider the principal case-study scenario ofRef. [16], inwhich the mediator M is a scalar leptoquark (LQ) doublet and the particle X is a new Dirac fermion. An LQ is a hypothetical color-triplet, fractionally charged boson that carries both lepton and baryon quantumnumbers.Leptoquarks appearinmanyextensionsofthe SM, such asgrand unification theories [17–20] and models with

https://doi.org/10.1016/j.physletb.2019.05.046

0370-2693/©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

compositequarksandleptons [21].Tobe consistent with experi-mentalconstraintsonflavorchangingneutralcurrents,weassume theLQtocoupletoasingle SMflavorgenerationonly [22], taken tobethesecondgenerationforthisstudy.We choosethesecond generationbecausemuonsprovideaclearexperimentalsignature. We further assume pair production of LQs, as is predominantly expectedinpp collisions.FollowingRef. [16],theDMparticleis as-sumedtobeaMajoranafermionwiththegaugegroupstructure(1, 1,0),wherethenumbersinparenthesesindicatethecolorSU(3)C,

weak isospin SU(2)L, and weak hypercharge U(1)Y multiplet

di-mensions,respectively.We usethe convention Q

=

T3

+

Y

/

2 for

theelectriccharge Q oftheparticle,withT3 thethirdcomponent

ofweak isospin andY the weak hypercharge. The corresponding assignmentsforboththeX andLQparticlesare(3,2,7/3).Forthe LQ,T3

= ±

1

/

2 and Q

=

5

/

3

,

2

/

3 forthetwomembersofthe

dou-blet,respectively. The interaction term ofthe Lagrangian forthis modelis:

L

= −(

yDXMsDM

+

yQQLMsR

+

yLuLLMcsuR

+

h.c.

)

(1) where the superscript c refers to charge conjugation. After the breaking ofelectroweak symmetry, the differentdoublet compo-nentsofX,Ms, QL,andLL taketheform:

L

= −

yDXuMus DM

−

yQuLMus

R

−

yLueL(Mus

)

cuR (2)

−

yDXdMdsDM

−

yQdLMds

R

−

yLu

ν

L(Mds

)

cuR (3) Thefirst linerepresents theinteractions ofthe upper compo-nentoftheLQdoubletMu

s,whichhaselectriccharge-5/3.Thefirst terminthefirst linedescribesthedecayoftheLQtoDMandX, withyDthecouplingstrength.Thesecondandthirdtermsofthe

first line represent the interactions, with coupling strengths yQ

and yLu,forthedifferent helicitycouplingsto theup-type quark

andthelepton. The second line describestheinteractions ofthe lowercomponentoftheleptoquarkdoubletMds,whichhaselectric charge -2/3.In the limit that yQ

=

0 and yLu

=

0,both the

up-perandlower componentsofthedoublet havethesamecollider phenomenology. The SM decays of the upper component of the

Mu

s doubletaretoup-typequarksandleptons,whilethoseofthe lowercomponentofthe Md

s doubletaretodown-typequarksand leptons.Inthelimitthat yQ

=

0 andyLu

=

0,theupperandlower

componentsofthedoublethavedifferentcolliderphenomenology. TheSMdecaysoftheuppercomponentofMu

s areagaintoup-type quarks and leptons, but the only SM decays of the lower com-ponent are to neutrinos and up-typequarks, and not to the full leptoquarksignature.Boththeupperandlowercomponentsofthe LQdoublet have been considered in this analysis. Following the exampleofRef. [16],we assume yLu

=

0. Thus itshould beborn

inmind that the limits obtainedin thisanalysis are validunder thisexplicitassumption.InthepairproductionoftheLQ,one LQ decaysto amuon anda c oran s quark, while theother decays throughthecoannihilationparadigm,toDMand X.TheX particle subsequentlydecaysthroughacrossedcoannihilationprocesstoa DMparticleandan off-shellLQ,wherethedecayproducts ofthis latterparticle,alsoamuonandac orans quark,havelow trans-versemomentum(pT)becauseofthesmallnessof



X,DM andare

potentiallyundetected.AnexampleFeynmandiagramisshownin Fig.1.

Themostrestrictivelowerlimitonthemassofapair-produced second-generationLQ,assuminganLQbranchingfraction

B(

LQ

→

c

μ

)

=

100%, is currently1530 GeV [23]. However, when the de-caytoDMandX isallowed,theLQ

→

c

μ

/

s

μ

branchingfractionis reducedandthelimitonmLQbecomesweaker.Thebranching

frac-tionthenalsodependsonmDM,



X,DM,andB,whereB isdefined

Fig. 1. AnexampleFeynmandiagramforthesignalprocessconsideredinthisstudy, whereg isagluon,LQaleptoquark,DMadarkmatterparticle,anX anewDirac fermion.Thesuperscript“*”indicatesanoff-shellparticle.

as

B(

LQ

→

c

μ

/

s

μ

)

in the limit of massless X and DM particles andisrelatedtoyQandyDbythefollowingformula:

B

=

B

(

LQ

→

c

μ

/

s

μ

)

|

mDM=mX=0

=

y2

Q

y2_Q

+

2 y2_D

.

(4) FollowingRef. [16],wesetyD

=

0

.

1 and



X,DM

=

0

.

1.Weconsider

two values for B: 0.5 and 0.1. Recasting the results of Ref. [23] for the upper component of the LQ doublet, and taking mDM

=

300 GeV as a representative value, the lower limit on a second-generationLQisreducedto1340 GeVforB

=

0

.

5 andto960 GeV forB

=

0

.

1.

Inthisanalysis, thefinalstate consistsofahigh-pT muonand

a high-pT jet from the decay ofthe on-shell LQ,



pmissT from the

DM particles, andlow-pT SM objects from the decayof the

off-shell LQ. Note that, in the analysis, we do not employ c quark tagging criteriabut rather—toimprove the signal eventselection efficiency—utilize generic untagged jets asthe c quark jet candi-dates.Theexistence ofthesignalprocess isinferredbya peakat the LQ mass mLQ, in the invariant mass mμj distribution of the

high-pT muon andjet,in conjunctionwithsignificant



pmissT from

theDM.ThispeakattheLQmassprovidesastrikingexperimental signatureinthesearchforsignalprocessescontainingDM.In con-trast,genericsearchesforDM,inwhichtherearenonewparticles otherthanDMandintermediatemediatorstates,mostlyrelyona mereenhancementinthetailofthep



miss_T distribution.

Theprincipal SMbackgroundsinthissearch arisefromevents witha Wboson andjets(W +jets)orwithatop quark-antiquark (t

¯

t)pair:inbothcases,theleptonic decayofaW bosoncanyield a high-pT muon and neutrino, where the neutrino can lead to

significant



pmiss

T .Events with single top quark or diboson(W W , W Z ,and Z Z ) productionsimilarly can enterthe background, al-though atalower level.Other smallersources ofSM background arisefromquantumchromodynamics(QCD)events,namelyevents withamultijetfinalstateproducedexclusivelythroughthestrong interaction, andfrom eventswith a Zboson andjets ( Z +jets). A QCD event can enter the background if a muon and a neutrino are produced through the semileptonicdecay of a quark, or if a jetiserroneouslyidentifiedasamuon inconjunctionwith spuri-ous



pmiss

T arisingfromthemismeasurementofjet pT.Eventswith Z +jets production canenterthebackground ifone oftheleptons in Z

→ μ

+

μ

− decaysis not reconstructedor liesoutsidethe ac-ceptanceofthedetector,leadingto



p_Tmiss,orif



pmiss_T arisesbecause ofmisreconstructedjet pT.

2. The CMS detector and trigger

The central feature of the CMSdetector is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of

3.8 T.Withinthesolenoidvolumeareasiliconpixelandstrip in-ner tracker, a lead tungstate crystal electromagnetic calorimeter, andabrass andscintillatorhadron calorimeter,eachcomposedof a barrel andtwo endcapsections. Extensive forwardcalorimetry complementsthecoverage providedbythebarrelandendcap de-tectors.Muonsaredetectedingas-ionizationchambersembedded inthe steelflux-return yokeoutside thesolenoid. A detailed de-scription of the CMS detector, together with a definition of the coordinate system and the relevant kinematic variables, is given inRef. [24].

Events of interest are selected using a two-tiered trigger sys-tem [25].Thefirstlevel,composedofcustomhardwareprocessors, usesinformationfromthecalorimetersandmuondetectorsto se-lect eventsata rateof around 100 kHz.The second level,based onanarrayofmicroprocessorsrunningaversionofthefullevent reconstructionsoftwareoptimizedforfastprocessing, reducesthe eventrate to around 1 kHz before data storage. The set of trig-gersusedforthisanalysisrequireseventstocontainamuonwith

pT

>

50 GeV.

3. Event reconstruction and selection

Individual particles are reconstructed with the CMS particle-flow(PF)algorithm [26],whichidentifiesthemaschargedhadrons, neutralhadrons, muons, electrons, or photons. Muon reconstruc-tion is performedby matchinga tracksegment reconstructed in theinnertrackerwithatracksegmentreconstructedinthemuon detector and performing a global fit of the hits from the two tracksegments. The candidatemuons are required to satisfy the tight selection criteria of Ref. [27], to pass within 2 mm of the primary event vertex in the direction along the beam axis and within 0.45 mm in the plane perpendicular to that axis, andto have pT

>

60 GeV and

|

η

|

<

2

.

4, where

η

is the

pseudorapid-ity. Electrons are reconstructed by matching energy deposits in theelectromagneticcalorimeterwithtracksegments intheinner tracker [28] andare requiredto have pT

>

15 GeV and

|

η

|

<

2

.

5.

Hadronicallydecaying

τ

leptons (

τ

h) are reconstructed usingthe

hadrons-plus-strips algorithm described in Ref. [29] and are re-quired to have pT

>

20 GeV and

|

η

|

<

2

.

3. The electron and

τ

h

candidatesaremainly usedtoveto Z +jets anddibosonevents,as describedbelow,andareselectedusingloose [28,29] identification criteria.

Theprimaryeventvertexisdefinedtobethereconstructed in-teraction vertexwiththe largestvalue ofsummed physics-object

p2_T. The physics objects considered for this purpose are the jets foundbyclusteringthecharged-particletracksassignedtothe ver-tex,usingtheanti-kT jetfindingalgorithm [30,31] withadistance

parameter 0.4,andtheassociatedmissingtransversemomentum, takenasthenegativeofthevectorpTsumofthosejets.The

trans-versemomentumimbalance



pmiss_T inaneventiscalculatedasthe negative ofthevector pT sumofall PFcandidates.Its magnitude

isdenoted pmiss

T .EventsarerequiredtohavepmissT

>

100 GeV.

Tosuppressthecontributionsofmuonsthatarisefromhadron decays,muoncandidatesaresubjectedtoanisolationrequirement. Thescalar pT sumofchargedhadron,neutralhadron,andphoton

PF candidates within a cone of radius



R

≡



(

η

)

2

_{+ (φ)}

2

₌

0

.

4 around the muon direction, where

φ

is theazimuthal angle, iscalculated.Theexpectedcontributionsofneutralparticles from additionalpp interactionsinthesameorneighboringbunch cross-ings(pileup)aresubtracted [32].Anisolationvariable I isdefined by dividing thissumby the muon pT. The isolation requirement

isI

<

0

.

15.Atleastoneisolatedmuoncandidateisrequiredtobe presentintheevent.

Thereconstructionofjetsisperformedbyclustering PF candi-datesusingtheanti-kTalgorithmwithadistanceparameterof 0.4,

excluding charged-particletracks notassociatedwiththeprimary vertex. The jet energies are corrected forthe combined response function ofthecalorimeters [33] andto accountfortheexpected contributions ofneutralparticles frompileup [32,34].Jetsare re-quiredtoappearwithin

|

η

|

<

2

.

4.Bottom(b)quarkjetsare iden-tified (b tagged)fromthis sample usingthecombined secondary vertex (CSVv2) algorithm at the tight working point [35], which yields ab quarkjetidentificationefficiencyofapproximately40%, and a misidentification probability of about 0.1% for gluon and light-flavoredquarkjetsandofabout2%forcharmquarkjets.Jets taggedasb jetsarerequiredtohavepT

>

30 GeV.

The leading (highest pT) jet in an event is required to have pT

>

100 GeVandto beseparatedby



R

>

0

.

5 fromtheleading

isolated muon candidate.The leading isolated muon andleading jet are then combined to form the LQ candidate. Studies with simulatedsignaleventsestablishthat,forthevaluesofmodel pa-rameters used in the present study, this matching identifies the correctcombinationover98%ofthetime.

Tosuppressbackgroundfromt

¯

t production,eventsarerejected iftheycontain ab-taggedjet,anelectron candidate,ora

τ

h

can-didate. The vetoon eventswitha b-taggedjet reducesthe back-groundfromeventswitha top quarkby morethan a factorof2 while reducing thesignal efficiency by onlyaround 10%. The ve-toesonelectron and

τ

h candidatesalsosuppressthe W +jets and Z +jets background.The W +jets background isfurther suppressed byrequiringthetransversemassmT[36] formedfromthepT

vec-toroftheleadingmuon and



pmiss

T toexceed100 GeV. The Z +jets

backgroundisfurtherreducedbyeliminatingeventswithaloosely identified and isolated (I

<

0

.

25) muon candidate if that muon candidate has pT

>

10 G a dimuon masswith theleading muon

within10 GeVoftheZbosonmass

BackgroundfromQCDeventsmostlyariseswhenthepT ofone

ofthehighestpT jetsisunderestimatedorwhenahadroninajet

undergoes a semileptonicdecay,introducing



pmiss_T that isaligned withthat jet.Tosuppressthisbackground,the angulardifference

φ

between the leading jet and



pmiss

T , andbetween theleading

muonand



pmiss

T ,isrequiredtoexceed 0.5.

The above requirements are referred to as the “preselection” criteria,andformthebasisforthedefinitionofseveralcontrol re-gions usedtoevaluatebackground,asdescribed inSection 5.The final selectioncriteria, correspondingto thesignalregion, arethe same as thepreselection criteriaexcept fora morestringent re-quirement onmT,mT

>

500 GeV.This condition studies utilizing

simulated signal andSM eventsamples.FormLQ

>

800 GeV, the

signal efficiency for events satisfying the preselection criteria is around 73%,essentiallyindependentof mLQ.Forthesignal region

criteria,thesignalefficiencyvariesfrom47to63%asmLQincreases

from800to1500 GeV.

4. Event simulation

Monte Carlo (MC) simulation of signal and background pro-cesses is used tovalidate theanalysis procedures,evaluate back-ground, and determinethe signal efficiency.Simulation oft

¯

t and single top quark events is performed at next-to-leading-order (NLO) accuracy withthe powheg 2.0 [37–42] event generator.To describe W +jets andZ +jets production,the MadGraph5_amc@nlo 2.2.2 [43,44] programatleadingorder(LO)isused.AK factor, cal-culatedasdescribedinRef. [6],isappliedasafunctionofbosonpT

toaccountfornext-to-NLO(NNLO)corrections.Thestatistical pre-cisionofouravailable MadGraph5_amc@nlo W +jets sampleislow foroff-shellW bosonmassesabovearound100 GeV.Therefore,to describe W +jets production forW bosonmassesabove 100 GeV, we use the LO pythia 8.212 [45] program with the CUETP8M1 tune [46], ratherthan MadGraph5_amc@nlo, witha K factor to

accountforNNLO correctionsappliedasa functionofthe W bo-sonmass.This K factor isdeterminedusingthe fewz 3.1 [47,48] program.DibosonproductionissimulatedatNLOusingeitherthe powheg[49] or MadGraph5_amc@nlo 2.2.2generators.

SignaleventsaresimulatedatLOusing MadGraph5_amc@nlo 2.2.2.Thesignal samplesaregeneratedforLQandDMmassesin the ranges 800



mLQ



1500 GeV in 100 GeV steps and300



mDM



700 GeVin50 GeVsteps, respectively,withcrosssections

normalizedtoNLO [50,51] accuracy.

For simulated samples at LO (NLO), the NNPDF3.0LO (NNPDF3.0NLO) [52] partondistributionfunctions(PDFs)areused. All samples are interfaced to pythia 8.212 to describe parton showeringandhadronization.Pileupinteractionsaremodeled us-ingsimulatedminimumbiaseventsamplesgeneratedwith pythia, with the distribution of pp interactions per bunch crossing ad-justedtoreproducetheobservedspectrum.

TheresponseoftheCMSdetectorismodeled,forboththe sig-nalandbackgroundsamples,usingthe Geant4 [53] suiteof pro-grams.Smalldifferencesbetweenthe data andsimulationin the trigger,particleidentification, andmuonisolation efficiencies,and inthejet pT resolutionand pmissT , areaccounted forthroughthe

applicationofscalefactorcorrections.

5. Background estimation

Background from t

¯

t production is evaluated from simulation, withtheeventsreweightedtoreproducetheobserveddistribution ofthetop quark pT [54,55].The normalizationisdetermined

us-ing a data-to-simulation scale factor derived froma t

¯

t-enhanced control sample. The control sample is defined using the prese-lection criteria of Section 3 except that events are required to contain at least one b-tagged jet. The purity of t

¯

t events in the controlsample isestimatedto be 85%.The remaining15% ofthe sample is composed primarily of events with W +jets and sin-gle topquark production.The scalefactor isdefined astheratio of the number of events in the control sample from data, after subtractionofthenon-t

¯

t components, estimatedfromsimulation, to thenumber in thecorresponding simulatedt

¯

t control sample scaledtothesameintegratedluminosity.Thescalefactorisfound to be 0

.

95

±

0

.

01(stat) for the 2016 data and 1

.

16

±

0

.

01(stat) for the 2017 data and is essentially independent of the mT

se-lection requirement. The difference in the scale factors between 2016and2017arisesfromchangesintherunningconditions,the reconstruction procedures, andthe tuning ofthe simulation pro-grams.Fig.2(top)showsthedistributionofmμj inthecombined

2016+2017t

¯

t controlsamplefordataandsimulation.

The systematic uncertainty in the scale factor is derived us-ing an orthogonal t

¯

t-enhanced control sample, selected withthe preselection criteriaexceptthat eventsmust containatleast one electroncandidate,inadditiontotheexistingmuoncandidate,and the veto on the presence of a b-tagged jet is removed. The pu-rityof t

¯

t events in this control sample is around 90%, with the remainder of the events arising primarily from single top quark production.The scale factorobtained is0

.

85

±

0

.

01(stat) forthe 2016dataand1

.

00

±

0

.

01(stat) forthe2017data.Onthebasisof theseresults,asystematicuncertaintyof10% isassignedto both the 2016and 2017scale factors discussed in the previous para-graph.

ThebackgroundfromW +jets productionissimilarlyestimated fromsimulation,witha correction to thenormalizationobtained froma W +jets-dominated control sample. The control sample is definedusingthe preselection criteriaexcept withtheadditional requirement50

<

mT

<

150 GeV. The purityof W +jets events in

thissampleisabout80%.Themainremainingcontributionisfrom t

¯

t production. A data-to-simulation normalization scale factor is

Fig. 2. Themμjdistributionsindataandsimulationforthe(top)t¯t- and(bottom)

W +jets-enrichedcontrolsamplesforthecombined2016and2017datasets.The respectivedata-to-simulationnormalizationscalefactorshavebeenappliedtothe simulateddistributions.Thelowerpanelsshowtheratiooftheobservedto simu-latedresults.Theverticalerrorbarsonthedatapointsarestatistical.Thegrayband showsthetotaluncertaintyinthebackgroundprediction,includingbothstatistical andsystematicterms.

obtained by subtracting the non-W +jets contribution, estimated fromsimulation,fromthecontrolsampleindata,anddividingthe resultingnumberofeventsbythenumberofeventsinthe simu-latedcontrolregionnormalizedtothesameintegratedluminosity. The t

¯

t scale factorhas beenapplied to the t

¯

t background before subtracting itfromthecontrolsample indata.Thescale factoris found to be 1

.

02

±

0

.

01(stat) and 1

.

11

±

0

.

01(stat) for the 2016 and2017 data,respectively. The distribution of mμj inthe

com-bined2016+2017 W +jets controlsample,fordataandsimulation, isshowninFig.2(bottom).

Toverifythestability ofthescalefactorinregions withlarger

mT, corresponding to off-shell W boson production, the

data-to-simulation scale factor has been remeasured in control regions withmTintheranges150to200,200to300and300to400 GeV.

The measured scale factor is in agreement within 20% with the original scale factor. In a second test, we examine the level of agreementbetweenthedataandsimulationforthenormalization ofthemμj distributioninaZ(

→ μ

+

μ

−)+jets controlsample with

one ofthetwo muonsineacheventremoved toemulate a sam-pleofW +jets events.Thiscontrolsample isselectedby requiring two oppositely chargedisolated muonswith pT

>

30GeV,witha

other-wise similar selection criteriato those ofthe preselection. The Z bosoncandidateis boostedtoits restframe,the dimuonmassis scaledtothemassoftheWboson,andthesystemisthenboosted backtotheoriginallaboratoryframe.Oneofthetwomuonsis ran-domlyremoved to simulateaneutrinofromW boson decay.The resulting missingmomentum is addedto the



pmiss

T of the event

andthevalueofmT recalculatedbeforeapplyingthesignalregion

selectioncriteria.Thelevelofagreementintheresulting distribu-tionof mμj betweendata andsimulationis alsoaround 20%.On

the basis of thesetwo studies, a 20% uncertainty is assigned to theW +jets backgroundprediction.Inaddition,relevanttheoretical uncertainties are also taken into consideration in the shape and normalizationoftheW +jets backgroundinthesignalregions.This isdiscussedinSection6.

The background fromQCD processes is expectedto be small. However, since the QCD background primarily arises asa conse-quence of jet mismeasurement, it is not well modeled by sim-ulation. Thus, we evaluate the QCD background using a method based primarily on data. A control sample is defined using the signal region criteria of Section 3 except that muon candidates are required to fail the isolation condition. Toestimate the QCD backgroundinthesignalregion,theeventsinthecontrol sample areweighted asafunction ofmuon pT by amuon

misidentifica-tionprobability,calledthejet-to-muon misidentificationrate, de-terminedina QCD-enrichedeventsample denotedthe “low-

φ

” sample.Thelow-

φ

sampleisdefinedinthesamemannerasthe signalregion excepttheangle

φ

between



pmiss_T andtheleading jet isrequired to be

φ <

0

.

5 ratherthan

φ >

0

.

5 and we re-quiremT

>

100 GeV ratherthan mT

>

500 GeV.The jet-to-muon

misidentificationrateisdefined,fromthissample,astheratioof thenumberofeventsthat satisfythemuon relativeisolation cri-terion I

<

0

.

15 to thenumberofevents withnorequirementon theisolation,aftersubtractingthenon-QCDcomponents,evaluated withsimulation, fromboth the numeratorand denominator.The purityofQCDeventsinthenumeratorisabout25%,whilethatin thedenominator isapproximately70%. Thejet-to-muon misiden-tificationrateisparameterizedintermsofthemuon pT usingan

analytical functionand variesfrom5% formuon pT

=

60 GeV to

50%forpT

>

300 GeV.

A50%uncertaintyisassignedtotheQCDbackgroundprediction toaccountfortheuncertaintyinthejet-to-muonmisidentification rate.Thisuncertaintyprimarilyarisesfromtheuncertaintiesinthe normalizationofthe non-QCD processessubtracted fromthe nu-meratoranddenominatorincalculatingthemisidentificationrate. Other sources of uncertainty, such as the choice of the analytic function used to parameterize the jet-to-muon misidentification rate, orthe uncertainties in the valuesof the fitparameters, are negligibleincomparison.

The backgrounds from events withdiboson, single top quark, and Z +jets production are estimated from simulation. An uncer-tainty of 15% is assigned to the diboson background prediction basedon thelevel ofagreement betweendataandsimulationin a diboson-enhanced control sample selected by requiring events to contain three leptons (e or

μ

), two of which are consistent witharising fromZboson decay.Uncertaintiesof15and10%are assignedtothe single topquark and Z +jets backgrounds, respec-tively,basedontheresultsofRefs. [56] and [57].

6. Systematic uncertainties

Weevaluatesystematicuncertaintiesthataffectthe normaliza-tion orshape of themμj spectrum, either inthe signal or

back-groundpredictions.Uncertaintiesspecifictoindividualbackground componentswerepresentedinSection5.

Table 1

Systematicuncertaintiesaffectingthenormalizationofsignaland back-grounddistributions.ThePDFuncertaintyaffectsthesignaldistribution only,while the otheruncertaintiesaffectboth the signaland back-grounddistributions.

Item Relative uncertainty (%)

Trigger efficiency 5.0

Muon identification efficiency 5.0 Electron identification (veto) efficiency 2.0

τhlepton identification (veto) efficiency 2.0 b jet identification (veto) efficiency 1.0

Pileup modeling 1.0

Integrated luminosity 2.5 (2016), 2.3 (2017)

PDF 3.0

Renormalization and factorization scales 1.0

t¯t normalization 10

W +jets normalization 20

The uncertainty in the trigger efficiency is 5%. Those in the muon reconstruction and isolation efficiency [58], the electron reconstruction efficiency [58], and the

τ

h reconstruction

effi-ciency [59,60] are 5,2, and 2%, respectively. The uncertainty re-latedtotheb-taggingmisidentificationis 1% [35].Theuncertainty inthe pileupdescriptioninsimulationisassessed byvarying the totalinelasticcrosssectionby4.6% [61],andisfoundtobe1%. Sta-tisticaluncertaintiesrelatedtothelimitednumberofeventsinthe data control samples are accountedforas described in Ref. [62], while those related to the limited number of events in simula-tion areaccountedforby allowingthe contentineachbinofthe simulated distributions to vary within its statistical uncertainty. The uncertainty in the integratedluminosity is 2.5% [63] for the 2016dataand2.3% [64] forthe2017data.Uncertaintiesassociated withthejet energyscale,thejet energyresolution,andpmiss

T are

also evaluated [65,66]. These uncertainties affect both the shape andnormalizationofthe simulatedsignal andbackground distri-butions. Uncertaintiesrelatedto the topquark pT reweighting in

simulated t

¯

t eventsare evaluated by varyingthe reweighting pa-rameters between zero and twice their nominal values [54,55]. Uncertaintiesrelated tothe PDFs,evaluated forthe signal accep-tance,aredeterminedfollowingthePDF4LHCprescription [67] and are foundtobe3%. Thoserelatedtotherenormalizationand fac-torizationscales,evaluatedforthesignalyieldsandforthet

¯

t and

W +jets backgrounds,areestimatedbyvaryingeachscale indepen-dently, andalsocoherently,bya factorof2.0and 0.5.Thelargest variationsupwardanddownwardintheresultsareusedtodefine anuncertaintyenvelope.Thisuncertaintyamountsto1%forsignal events,independentof theLQmass.Forthet

¯

t and W +jets

back-grounds,thisuncertaintyvariesbetween5and15% dependingon

mLQ andthus accountsfora systematicuncertainty inthe shape

of the distribution. The uncertainty associated with the method chosentodeterminetheK factorfortheW +jets background eval-uationisestimatedtobe 5%.

Table 1 summarizes thesystematic uncertainties affecting the normalizationofdistributions.

7. Results

TheobserveddistributionofmμjispresentedinFig.3.The

re-sults are shownincomparison tothe post-fit predictions forthe SM background,where“post-fit”meansthat theconstraintsfrom themaximumlikelihoodfitareincorporated.Forpurposesof illus-tration,thepredictionsoftwosignalmodelswithmLQ

=

1000 GeV

and mDM

=

400 GeVare alsoshown: one with B

=

0

.

5 and the

other with B

=

0

.

1.The difference isjustan overall relative nor-malizationof about2forthe lattercompared tothe former. Nu-mericalvaluesaregiveninTable2.

Fig. 3. Theobserveddistributionofmμj incomparisontothepost-fit SM back-groundpredictionsforthecombined2016and2017data“Post-fit”meansthatthe constraintsfromthemaximumlikelihoodfitareincorporated.Theunstacked pre-dictionsfortwosignalmodelswithmLQ=1000 GeVandmDM=400 GeVarealso shownwith B=0.5 andtheotherwithB=0.1.Thedifferenceisjustanoveral relativenormalizationofabout2forthelattercomparedtotheformer.Theratio oftheobservedresultstothetotalSMpredictionisshowninthelowerpanel.The verticalerrorbarsonthedatapointsarestatistical.Thegrayshowsthetotal uncer-taintyinthebackgroundprediction,includingbothstatisticalandsystematicterms.

Table 2

Observednumberofevents,post-fitSMbackgroundpredictionsand post-fit uncertaintiesforthe combined2016 and2017datasets. “Electroweak”referstothesumofexpectedeventsfromthesingle topquark,Z boson,dibosonbackgroundprocesses.Thepredictions fortwosignalmodelswithmLQ=1000 GeVandmDM=400 GeV arealsoshown:onewithB=0.5 andtheotherwithB=0.1.The uncertaintiesrepresentthestatisticalandsystematictermsadded inquadrature. Process Events W +jets 911±55 t¯t 185±25 Electroweak 241±26 QCD 63±26 Total SM background 1401±40 Signal; B=0.5, mLQ=1000 GeV, mDM=400 GeV 96±8 Signal; B=0.1, mLQ=1000 GeV, mDM=400 GeV 195±16

Observed 1390

The data are found to be consistent with the SM predictions within theuncertainties. There is a smallexcess ofevents above theSMpredictioninthemμj regionbetween1600and1900 GeV,

consistentwithastatisticalfluctuation.Thisexcesscorrespondsto a statistical significance of around 1.5 standard deviations. Thus, wedonotobtainevidenceforDMorLQproduction.

Abinned maximumlikelihoodfit isappliedto themμj

distri-butioninthesignalregion.Thefittedparametersaretheyieldsof theindividualbackgroundcomponentslistedinTable2,thesignal yield,and various nuisanceparameters. The nuisance parameters areintroducedtotreatsystematicuncertainties.Log-normal proba-bilitydistributionsareusedfornuisanceparametersthataffectthe normalizationsofthesignalandbackgroundyields.Gaussian prob-abilitydistributions are used for nuisance parameters that affect theshapeof themμj distribution.All normalizationuncertainties

aretaken tobe fullycorrelated acrossbins exceptthose that are statistical in origin, which are assumed to be uncorrelated. The overallpostfituncertaintyinthe dominantW +jets background is substantially smaller than the prefit value shown in Table 1 be-cause the normalization and shape of this background is highly constrainedbythelowersideofthemassdistribution.

Fig. 4. Observed95%CL upperlimitsontheproductofcrosssectionandbranching fractionforthesignalmodelofFig.1assumingB= B(LQ→cμ/sμ)|mDM=mX=0to be(top)0.5or(bottom) 0.1.Thesolidanddashedblackcurvesshowtheobserved andexpected95%CL exclusioncurves,takingintoaccountbothupperandlower componentsoftheLQdoublet.Thesolidbluecurveshowstheobservedexclusion limitfortheuppercomponentoftheLQdoublet,i.e.toamuonandac quark.The dottedbluecurveshowsthecorrespondingobservedlimitsfromtherecastofthe resultsfromasearchforpairproducedsecond-generationLQs [23].

Upper limits at 95% confidence level (CL) are determined on the productof thesignal production crosssection andbranching fraction. These limitsare calculated usinga modified frequentist approachwiththeCLscriterion [68,69] andanasymptotic

approx-imationfortheteststatistic [70,71].Thelimitsaredeterminedas afunctionofmLQand mDM.

Fig.4(top) presentstheresultsfor B

=

0

.

5.The regionto the rightand belowthe diagonalline is whereLQdecay to DMand X is allowed. The solid and dashed black curves show the ob-served andexpectedexclusionlimits,respectively, takinginto ac-countcontributionsfrombothupperandlowercomponentsofthe LQdoublet.Combinations ofmLQ andmDM to theleft andbelow

the solid curve are excluded. It can be seen that the signal sce-nario ofFig. 1 isexcluded for valuesof mDM up to 500 GeV for mLQ

≈

1400 GeVandupto300GeVformLQ

≈

1500 GeV.

This is the first test of the co-annihilation process proposed in [16],thus it isnot possibleto makea direct comparisonwith other results.Togivean indicationoftheextenttowhichour

re-sults explore untested regions of the mLQ-mDM parameter space

wehavethereforeperformedarecastoftheresultsfromasearch forpairproducedsecond-generationLQs,eachdecayingtoamuon anda c quark [23]. The recastis performedin two steps. Inthe firststep,thechangeinthebranchingfractionoftheLQtoa lep-tonandaquarkiscalculatedoncethedecayoftheLQtoDMand X isallowed.Thechangedependsontheparametersofthemodel including



X,DM, B,LQandDMmass [16].Thealteredbranching

fractionisthenusedtofindtheexclusioncontourintheplane of

mLQ and mDM. The resultant limit contour is shownas the

dot-tedbluecurve.Thislimitcontourmaybecomparedwiththesolid bluecurve, whichshowstheobservedexclusionlimit that would beobtainedfromthepresentanalysisifonlytheuppercomponent oftheLQdoublet,decayingtoamuonandac quark,contributed tothepotentialsignal.

Fig.4(bottom)showsresultsobtainedassumingthesomewhat smaller value of 0.1 for B. In this case, the upper limit of ex-cluded DM mass is extended significantly, reaching a maximum of

≈

600 GeVformLQ

≈

1400 GeV.

8. Summary

A search has been performedfor dark matter in events con-tainingamuon, ajet, andsignificantmissingtransverse momen-tum.Thestudyisconductedusingproton-protoncollisiondataat

√

s

=

13 TeVrecordedwiththeCMSdetector,correspondingtoan integratedluminosityof77.4 fb−1.Itis assumedthatdarkmatter isproducedthroughtheproductionofaleptoquarkpair,withone leptoquark decaying to a muon and a jet, andthe other to dark matter andlow-pT standard modelparticles. The analysisis

per-formedbysearchingforapeakintheleptoquarkcandidate invari-antmassmμj distributionformedfromthehighest pT muon and

jetinanevent,withtherequirementofsignificantmissing trans-versemomentum,asisexpectedfromthepresenceofdarkmatter. The observation of such a peak in this novel search would pro-videstrongevidencefortheexistenceofbothdarkmatterparticles andleptoquarks.Thedataareobservedtoagreewiththestandard modelbackgroundpredictionswithintheuncertainties.Upper lim-itsonthe productofthecrosssectionandbranchingfractionare obtainedat 95% confidencelevel asa function of the leptoquark and dark matter particle masses. For the first benchmark sce-narioconsidered,darkmattermassesupto500 GeVareexcluded for leptoquark massesmLQ

≈

1400 GeV, and up to 300 GeV for mLQ

≈

1500 GeV.Forthesecondbenchmarkscenario,darkmatter

massesupto600 GeVareexcludedformLQ

≈

1400 GeV. Acknowledgements

We congratulate our colleagues in the CERN accelerator de-partments for the excellent performance of the LHC and thank thetechnicalandadministrativestaffs atCERN andatother CMS institutes for their contributions to the success of the CMS ef-fort.Inaddition,wegratefullyacknowledgethecomputingcenters and personnel of the Worldwide LHC Computing Grid for deliv-eringso effectively the computinginfrastructure essential to our analyses. Finally, we acknowledge the enduring support for the constructionandoperationoftheLHCandtheCMSdetector pro-videdby thefollowingfundingagencies: BMWFWandFWF (Aus-tria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, FAPERGS, andFAPESP(Brazil); MES (Bulgaria);CERN; CAS, MoST,andNSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus);SENESCYT(Ecuador);MoER,ERCIUT,andERDF(Estonia); AcademyofFinland,MEC,andHIP(Finland);CEAandCNRS/IN2P3 (France); BMBF,DFG, andHGF (Germany); GSRT (Greece);NKFIA (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN

(Italy); MSIP andNRF (Republic ofKorea); LAS (Lithuania);MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI(Mexico);MBIE(New Zealand);PAEC(Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS,RFBR,andNRCKI(Russia);MESTD(Serbia);SEIDI,CPAN,PCTI, and FEDER (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, andNSTDA (Thailand); TUBITAK andTAEK(Turkey);NASUandSFFR(Ukraine);STFC(United King-dom);DOEandNSF(USA).

Individuals have received support from the Marie-Curie pro-gramme and the European Research Council and Horizon 2020 Grant, contractNo. 675440 (EuropeanUnion); theLeventis Foun-dation; the A. P. Sloan Foundation; the Alexander von Hum-boldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the F.R.S.-FNRS and FWO (Belgium) under the “Excellence of Science - EOS” - be.h projectn. 30820817;the MinistryofEducation,YouthandSports (MEYS) of the Czech Republic; the Lendület (“Momentum”) Pro-gramme and the János Bolyai Research Scholarship of the Hun-garian Academy of Sciences, the New National Excellence Pro-gram ÚNKP, the NKFIA research grants 123842, 123959, 124845, 124850 and 125105 (Hungary); the Council of Science and In-dustrial Research, India; the HOMING PLUS programme of the Foundation for Polish Science, cofinanced from European Union, Regional Development Fund,the MobilityPlus programmeofthe Ministry of Science and Higher Education, the National Science Center (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus 2014/13/B/ST2/02543, 2014/15/B/ST2/03998, and 2015/19/B/ST2/ 02861,Sonata-bis2012/07/E/ST2/01406;theNationalPriorities Re-search Program by Qatar National Research Fund; the Programa Estatalde Fomentode laInvestigación CientíficayTécnica de Ex-celencia María de Maeztu, grant MDM-2015-0509 and the Pro-grama Severo Ochoa del Principado de Asturias; the Thalis and Aristeia programmes cofinanced by EU-ESF and the Greek NSRF; theRachadapisekSompotFundforPostdoctoralFellowship, Chula-longkornUniversityandtheChulalongkornAcademic intoIts2nd CenturyProject AdvancementProject(Thailand);theWelch Foun-dation,contractC-1845;andtheWestonHavensFoundation(USA).

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The CMS Collaboration

A.M. Sirunyan,

A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam,

F. Ambrogi,

E. Asilar,

T. Bergauer,

J. Brandstetter,

M. Dragicevic,

J. Erö,

A. Escalante Del Valle,

M. Flechl,

R. Frühwirth

1

,

V.M. Ghete,

J. Hrubec,

M. Jeitler

1

,

N. Krammer,

I. Krätschmer,

D. Liko,

T. Madlener,

I. Mikulec,

N. Rad,

H. Rohringer,

J. Schieck

1

,

R. Schöfbeck,

M. Spanring,

D. Spitzbart,

A. Taurok,

W. Waltenberger,

J. Wittmann,

C.-E. Wulz

1

,

M. Zarucki

InstitutfürHochenergiephysik,Wien,Austria

V. Chekhovsky,

V. Mossolov,

J. Suarez Gonzalez

InstituteforNuclearProblems,Minsk,Belarus

E.A. De Wolf,

D. Di Croce,

X. Janssen,

J. Lauwers,

M. Pieters,

H. Van Haevermaet,

P. Van Mechelen,

N. Van Remortel

UniversiteitAntwerpen,Antwerpen,Belgium

S. Abu Zeid,

F. Blekman,

J. D’Hondt,

J. De Clercq,

K. Deroover,

G. Flouris,

D. Lontkovskyi,

S. Lowette,

I. Marchesini,

S. Moortgat,

L. Moreels,

Q. Python,

K. Skovpen,

S. Tavernier,

W. Van Doninck,

P. Van Mulders,

I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

D. Beghin,

B. Bilin,

H. Brun,

B. Clerbaux,

G. De Lentdecker,

H. Delannoy,

B. Dorney,

G. Fasanella,

L. Favart,

R. Goldouzian,

A. Grebenyuk,

A.K. Kalsi,

T. Lenzi,

J. Luetic,

N. Postiau,

E. Starling,

L. Thomas,

C. Vander Velde,

P. Vanlaer,

D. Vannerom,

Q. Wang

UniversitéLibredeBruxelles,Bruxelles,Belgium

T. Cornelis,

D. Dobur,

A. Fagot,

M. Gul,

I. Khvastunov

2

,

D. Poyraz,

C. Roskas,

D. Trocino,

M. Tytgat,

W. Verbeke,

B. Vermassen,

M. Vit,

N. Zaganidis

GhentUniversity,Ghent,Belgium

H. Bakhshiansohi,

O. Bondu,

S. Brochet,

G. Bruno,

C. Caputo,

P. David,

C. Delaere,

M. Delcourt,

A. Giammanco,

G. Krintiras,

V. Lemaitre,

A. Magitteri,

K. Piotrzkowski,

A. Saggio,

M. Vidal Marono,

S. Wertz,

J. Zobec

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

F.L. Alves,

G.A. Alves,

M. Correa Martins Junior,

G. Correia Silva,

C. Hensel,

A. Moraes,

M.E. Pol,

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas,

W. Carvalho,

J. Chinellato

3

,

E. Coelho,

E.M. Da Costa,

G.G. Da Silveira

4

,

D. De Jesus Damiao,

C. De Oliveira Martins,

S. Fonseca De Souza,

H. Malbouisson,

D. Matos Figueiredo,

M. Melo De Almeida,

C. Mora Herrera,

L. Mundim,

H. Nogima,

W.L. Prado Da Silva,

L.J. Sanchez Rosas,

A. Santoro,

A. Sznajder,

M. Thiel,

E.J. Tonelli Manganote

3

,

F. Torres Da Silva De Araujo,

A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahuja

a

,

C.A. Bernardes

a

,

L. Calligaris

a

,

T.R. Fernandez Perez Tomei

a

,

E.M. Gregores

b

,

P.G. Mercadante

b

,

S.F. Novaes

a

,

S. Padula

a

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

A. Aleksandrov,

R. Hadjiiska,

P. Iaydjiev,

A. Marinov,

M. Misheva,

M. Rodozov,

M. Shopova,

G. Sultanov

InstituteforNuclearResearchandNuclearEnergy,BulgarianAcademyofSciences,Sofia,Bulgaria

A. Dimitrov,

L. Litov,

B. Pavlov,

P. Petkov

UniversityofSofia,Sofia,Bulgaria

W. Fang

5

,

X. Gao

5

,

L. Yuan

BeihangUniversity,Beijing,China

M. Ahmad,

J.G. Bian,

G.M. Chen,

H.S. Chen,

M. Chen,

Y. Chen,

C.H. Jiang,

D. Leggat,

H. Liao,

Z. Liu,

F. Romeo,

S.M. Shaheen

6

,

A. Spiezia,

J. Tao,

Z. Wang,

E. Yazgan,

H. Zhang,

S. Zhang

6

,

J. Zhao

InstituteofHighEnergyPhysics,Beijing,China

Y. Ban,

G. Chen,

A. Levin,

J. Li,

L. Li,

Q. Li,

Y. Mao,

S.J. Qian,

D. Wang

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

Y. Wang

TsinghuaUniversity,Beijing,China

C. Avila,

A. Cabrera,

C.A. Carrillo Montoya,

L.F. Chaparro Sierra,

C. Florez,

C.F. González Hernández,

M.A. Segura Delgado

UniversidaddeLosAndes,Bogota,Colombia

B. Courbon,

N. Godinovic,

D. Lelas,

I. Puljak,

T. Sculac

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,

M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,

D. Ferencek,

K. Kadija,

B. Mesic,

A. Starodumov

7

,

T. Susa

InstituteRudjerBoskovic,Zagreb,Croatia

M.W. Ather,

A. Attikis,

M. Kolosova,

G. Mavromanolakis,

J. Mousa,

C. Nicolaou,

F. Ptochos,

P.A. Razis,

H. Rykaczewski

UniversityofCyprus,Nicosia,Cyprus

M. Finger

8

,

M. Finger Jr.

8

E. Ayala

EscuelaPolitecnicaNacional,Quito,Ecuador

E. Carrera Jarrin

UniversidadSanFranciscodeQuito,Quito,Ecuador

H. Abdalla

9

,

A.A. Abdelalim

10

,

11

,

S. Elgammal

12

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

S. Bhowmik,

A. Carvalho Antunes De Oliveira,

R.K. Dewanjee,

K. Ehataht,

M. Kadastik,

M. Raidal,

C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,

H. Kirschenmann,

J. Pekkanen,

M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Havukainen,

J.K. Heikkilä,

T. Järvinen,

V. Karimäki,

R. Kinnunen,

T. Lampén,

K. Lassila-Perini,

S. Laurila,

S. Lehti,

T. Lindén,

P. Luukka,

T. Mäenpää,

H. Siikonen,

E. Tuominen,

J. Tuominiemi

HelsinkiInstituteofPhysics,Helsinki,Finland

T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

M. Besancon,

F. Couderc,

M. Dejardin,

D. Denegri,

J.L. Faure,

F. Ferri,

S. Ganjour,

A. Givernaud,

P. Gras,

G. Hamel de Monchenault,

P. Jarry,

C. Leloup,

E. Locci,

J. Malcles,

G. Negro,

J. Rander,

A. Rosowsky,

M.Ö. Sahin,

M. Titov

IRFU,CEA,UniversitéParis-Saclay,Gif-sur-Yvette,France

A. Abdulsalam

13

,

C. Amendola,

I. Antropov,

F. Beaudette,

P. Busson,

C. Charlot,

R. Granier de Cassagnac,

I. Kucher,

A. Lobanov,

J. Martin Blanco,

C. Martin Perez,

M. Nguyen,

C. Ochando,

G. Ortona,

P. Paganini,

P. Pigard,

J. Rembser,

R. Salerno,

J.B. Sauvan,

Y. Sirois,

A.G. Stahl Leiton,

A. Zabi,

A. Zghiche

LaboratoireLeprince-Ringuet,Ecolepolytechnique,CNRS/IN2P3,UniversitéParis-Saclay,Palaiseau,France

J.-L. Agram

14

,

J. Andrea,

D. Bloch,

J.-M. Brom,

E.C. Chabert,

V. Cherepanov,

C. Collard,

E. Conte

14

,

J.-C. Fontaine

14

,

D. Gelé,

U. Goerlach,

M. Jansová,

A.-C. Le Bihan,

N. Tonon,

P. Van Hove

UniversitédeStrasbourg,CNRS,IPHCUMR7178,Strasbourg,France

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,

C. Bernet,

G. Boudoul,

N. Chanon,

R. Chierici,

D. Contardo,

P. Depasse,

H. El Mamouni,

J. Fay,

L. Finco,

S. Gascon,

M. Gouzevitch,

G. Grenier,

B. Ille,

F. Lagarde,

I.B. Laktineh,

H. Lattaud,

M. Lethuillier,

L. Mirabito,

S. Perries,

A. Popov

15

,

V. Sordini,

G. Touquet,

M. Vander Donckt,

S. Viret

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

T. Toriashvili

16

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze

8

C. Autermann,

L. Feld,

M.K. Kiesel,

K. Klein,

M. Lipinski,

M. Preuten,

M.P. Rauch,

C. Schomakers,

J. Schulz,

M. Teroerde,

B. Wittmer

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

A. Albert,

D. Duchardt,

M. Erdmann,

S. Erdweg,

T. Esch,

R. Fischer,

S. Ghosh,

A. Güth,

T. Hebbeker,

C. Heidemann,

K. Hoepfner,

H. Keller,

L. Mastrolorenzo,

M. Merschmeyer,

A. Meyer,

P. Millet,

S. Mukherjee,

T. Pook,

M. Radziej,

H. Reithler,

M. Rieger,

A. Schmidt,

D. Teyssier,

S. Thüer

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

G. Flügge,

O. Hlushchenko,

T. Kress,

T. Müller,

A. Nehrkorn,

A. Nowack,

C. Pistone,

O. Pooth,

D. Roy,

H. Sert,

A. Stahl

17

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,

T. Arndt,

C. Asawatangtrakuldee,

I. Babounikau,

K. Beernaert,

O. Behnke,

U. Behrens,

A. Bermúdez Martínez,

D. Bertsche,

A.A. Bin Anuar,

K. Borras

18

,

V. Botta,

A. Campbell,

P. Connor,

C. Contreras-Campana,

V. Danilov,

A. De Wit,

M.M. Defranchis,

C. Diez Pardos,

D. Domínguez Damiani,

G. Eckerlin,

T. Eichhorn,

A. Elwood,

E. Eren,

E. Gallo

19

,

A. Geiser,

J.M. Grados Luyando,

A. Grohsjean,

M. Guthoff,

M. Haranko,

A. Harb,

J. Hauk,

H. Jung,

M. Kasemann,

J. Keaveney,

C. Kleinwort,

J. Knolle,

D. Krücker,

W. Lange,

A. Lelek,

T. Lenz,

J. Leonard,

K. Lipka,

W. Lohmann

20

,

R. Mankel,

I.-A. Melzer-Pellmann,

A.B. Meyer,

M. Meyer,

M. Missiroli,

G. Mittag,

J. Mnich,

V. Myronenko,

S.K. Pflitsch,

D. Pitzl,

A. Raspereza,

M. Savitskyi,

P. Saxena,

P. Schütze,

C. Schwanenberger,

R. Shevchenko,

A. Singh,

H. Tholen,

O. Turkot,

A. Vagnerini,

G.P. Van Onsem,

R. Walsh,

Y. Wen,

K. Wichmann,

C. Wissing,

O. Zenaiev

DeutschesElektronen-Synchrotron,Hamburg,Germany

R. Aggleton,

S. Bein,

L. Benato,

A. Benecke,

V. Blobel,

T. Dreyer,

A. Ebrahimi,

E. Garutti,

D. Gonzalez,

P. Gunnellini,

J. Haller,

A. Hinzmann,

A. Karavdina,

G. Kasieczka,

R. Klanner,

R. Kogler,

N. Kovalchuk,

S. Kurz,

V. Kutzner,

J. Lange,

D. Marconi,

J. Multhaup,

M. Niedziela,

C.E.N. Niemeyer,

D. Nowatschin,

A. Perieanu,

A. Reimers,

O. Rieger,

C. Scharf,

P. Schleper,

S. Schumann,

J. Schwandt,

J. Sonneveld,

H. Stadie,

G. Steinbrück,

F.M. Stober,

M. Stöver,

A. Vanhoefer,

B. Vormwald,

I. Zoi

UniversityofHamburg,Hamburg,Germany

M. Akbiyik,

C. Barth,

M. Baselga,

S. Baur,

E. Butz,

R. Caspart,

T. Chwalek,

F. Colombo,

W. De Boer,

A. Dierlamm,

K. El Morabit,

N. Faltermann,

B. Freund,

M. Giffels,

M.A. Harrendorf,

F. Hartmann

17

,

S.M. Heindl,

U. Husemann,

I. Katkov

15

,

S. Kudella,

S. Mitra,

M.U. Mozer,

Th. Müller,

M. Musich,

M. Plagge,

G. Quast,

K. Rabbertz,

M. Schröder,

I. Shvetsov,

H.J. Simonis,

R. Ulrich,

S. Wayand,

M. Weber,

T. Weiler,

C. Wöhrmann,

R. Wolf

KarlsruherInstitutfuerTechnologie,Karlsruhe,Germany

G. Anagnostou,

G. Daskalakis,

T. Geralis,

A. Kyriakis,

D. Loukas,

G. Paspalaki

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

G. Karathanasis,

P. Kontaxakis,

A. Panagiotou,

I. Papavergou,

N. Saoulidou,

E. Tziaferi,

K. Vellidis

NationalandKapodistrianUniversityofAthens,Athens,Greece

K. Kousouris,

I. Papakrivopoulos,

G. Tsipolitis

NationalTechnicalUniversityofAthens,Athens,Greece

I. Evangelou,

C. Foudas,

P. Gianneios,

P. Katsoulis,

P. Kokkas,

S. Mallios,

N. Manthos,

I. Papadopoulos,

E. Paradas,

J. Strologas,

F.A. Triantis,

D. Tsitsonis