Current LHC constraints on minimal universal extra dimensions

HAL Id: in2p3-01454835

http://hal.in2p3.fr/in2p3-01454835

Submitted on 14 Dec 2018

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Current LHC constraints on minimal universal extra

dimensions

N. Deutschmann, T. Flacke, Jong Soo Kim

To cite this version:

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Current

LHC

constraints

on

minimal

universal

extra

dimensions

Nicolas Deutschmann

a

,

b

,

Thomas Flacke

c

,

∗

,

Jong

Soo Kim

c

a_{UnivLyon,UniversiteLyon1,CNRS/IN2P3,IPNL,F-69622,Villeurbanne,France}

b_{CentreforCosmology,ParticlePhysicsandPhenomenology(CP3),UniversitecatholiquedeLouvain,CheminduCyclotron2,B-1348Louvain-la-Neuve,Belgium} c_{CenterforTheoreticalPhysicsoftheUniverse,InstituteforBasicScience(IBS),Daejeon,34051,RepublicofKorea}

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received8February2017

Receivedinrevisedform2May2017 Accepted2June2017

Availableonline7June2017 Editor:G.F.Giudice

In thisletter, wepresent LHClimits onthe minimal universal extra dimension (MUED) model from LHCRun1 dataand currentlimits fromsearches ofthe ongoingRun 2.Typicalcollider signalsofthe Kaluza–Klein(KK)statesmimicgenericdegeneratesupersymmetry(SUSY)missingtransversemomentum signatures since the KK particles cascade decayinto jets, leptons and the lightest KK particlewhich isstable duetoKKparityand evadesdetection. Wetest theparameter spaceagainst alargenumber of supersymmetry based missing energy searches implementedin the public code CheckMATE.We demonstratethe complementarityofemployingvarioussearches whichtargetalargenumber offinal statesignatures,andwederivethemostuptodatelimitsontheMUEDparameterspacefrom13 TeV SUSYsearches.

©2017TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Universalextradimensions–introductionandreview

Modelswithuniversal extra dimensions(UED)[1]representa simpleextensionoftheStandardModelwhichincludeadark mat-tercandidateandare testable attheLHC.1 _{The extra-dimensions} areuniversalinthe sensethat allStandardModel(SM) fieldsare promotedtofieldswhichpropagateonthefullspace–time

M

×

X ,

where

M

istheflat fourdimensional(4D) Minkowskispaceand

X is a compact space. As X is compact,the momenta along the extra-dimensions arediscretized. In the4D effective theory,each extra-dimensionalfieldyieldsa4Dfieldwithoutextra-dimensional momentum(thezero-modewhichistobeidentifiedwiththe4D SMfield)aswellasaKaluza–Klein(KK)towerofexcitationswhich areheavy partnerstateswiththesame quantumnumbersasthe zero-mode.The KK mass spectrum is determined by the inverse size and the geometry of the extra-dimensions. In the simplest case of only one extra dimension, – which we focus on in this letter–compactificationontheorbifoldX

=

S1

/

Z2allowstohave

chiralzero-modes offermionsand Aμ zero-mode forgaugefields withoutanadditional A5mode.2

*

Correspondingauthor.

E-mailaddresses:[email protected](N. Deutschmann),

fl[email protected](T. Flacke),[email protected](J.S. Kim).

1 _{Cf. Refs.[60,61]forearlierproposalsofTeVscaleextradimensions.ForReviews}

onUEDmodelsandtheirphenomenologycf.[62,63].

2 _{For more than one extra-dimension, the compact space is not unique. Cf.}

Ref.[64]foraclassificationofflat2Dorbifolds,Ref.[65,66]forrealizations.Models withsphericalorbifoldshavealsobeenstudied[67,68].

The 5D UED model appears to be a very simple and predic-tive model as it seems to have only one parameter beyond the StandardModel(BSM),thecompactificationradius R.However,as a 5Dtheory,the modelisinherently non-renormalizableandcan onlybeconsideredasaneffectivetheory,validbelowacutoffscale



,whichintroducesanadditionalparameterintothemodel.Naive dimensionalanalysis[2–5]andboundsfromunitarityviolationin gluonKKmodescattering[6]suggestthatthecutoffisratherlow:



R



O(

10

−

50

)

.Asaconsequence,higher-dimensionaloperators atthecutoffscalecanbephenomenologicallyrelevant.3 _Inthe5D minimalUED(MUED)model[7],allhigher-dimensionaloperators areassumedtobeabsent atthecutoffscale



,andtheyareonly induced atlower energies dueto renormalizationgroup running, thuskeepingthemodelasimpleBSMscenariowithonlytwo pa-rameters: theinversecompactification radius R−1 whichsets the massscaleofthefirstKKexcitations,i.e. ofthelightestpartnersof the SM fields,and



R,which controlsthe numberof KK modes present in the spectrum below the cutoff, and determines how muchtheKKmodemassesandcouplingsareeffectedbyone-loop running.

3 _{Theleastirrelevantoperatorsareboundarylocalizedkinetictermsandother}

SM-likeoperators.Theyareinduced byrenormalizationgrouprunningandthus genericallypresent. Theirinclusionyieldsnon-minimalUED models[69]with a muchlargerparameterspace.AnotherUEDextension–splitUED[70]–includes fermionbulkmassterms.Fermionbulkmasstermsarenotradiativelyinducedand couldthusbeabsentconsistently.

http://dx.doi.org/10.1016/j.physletb.2017.06.004

516 N. Deutschmann et al. / Physics Letters B 771 (2017) 515–520

The phenomenology of the MUED model resembles the

phe-nomenology of the minimal supersymmetric standard model

(MSSM)inmanyways.EachSMparticleisaccompaniedbya part-ner particle atthe first KK mode level (but in the case of UED, the partners have the same spin as the SM particle). Also, the MUEDmodelpossessesa geometricparity(“KKparity”),which is respected by loop corrections and corresponds to the reflection ofthe orbifold S1

_/

_Z

2 atits midpoint.4 The lightest partner state

(which in MUED is the partner of the U

(

1

)

Y gauge boson [7]) represents a darkmatter candidate [8–11] which reproduces the observed dark matter relic density if 1

.

25 TeV



R−1

_

₁

_.

_{5 TeV}

[11], while for larger R−1_{, the Universe would be over-closed.}

Vialoopcorrections,theKK resonancescontributetoelectroweak precision observables [1,12,13] and flavor physics [14–16] which imposeaboundofR−1

_

_{750 GeV andR}−1

_>

_{600 GeV.}5

Atthe LHC,two mainsignal classes(non-SUSY-likeand SUSY-like)allow totest UEDmodels.MUEDpredicts theexistence ofa wholetowerofpartnerstatesofwhichthefirstKKlevelstatesare KK parity odd, while the second KK level states are the lightest KK parityeven BSMstates.As loop-inducedcouplings violate KK number(whilstconservingKK parity),second KKmodestatescan beresonantlyproducedattheLHCandsearchedforin Z

,

Wand coloredresonancesearches[17–19].Thecurrentlystrongestknown boundonMUEDfromthissignalclassamountstoaboundonthe secondKK photonmassofm_A(2)



1

.

4 TeV, whichcorrespondsto

R−1

_

_{715 GeV [20] andwas obtained froma recastofthe CMS}

searchforadi-leptonresonanceat8TeVwith20.6fb−1 _[21].

Complementarily,SUSYsearchesalsoprovideahigh discovery-andexclusion potential for the MUED model.The first KK mode partnersareproducedinpairsandthencascadedecaytothe light-eststateatthefirstKKlevelwhichitselfonlyleavesamissing en-ergy/momentumsignature[1,22].ATLASandCMSperformedmany SUSYsearchesat8TeVand13TeVwhicharesuitabletoconstrain theMUEDparameterspace. TheATLASsearchesRefs.[23,24] pro-videexplicitMUEDlimits,and[23]reportsthecurrentlystrongest boundofR−1



900

−

950 GeV(dependingonthevalueof



R).

Inthisletter,weprovide theMUEDboundsobtainedfrom re-casts of a large number of SUSY searches at8 and 13 TeV, per-formedwith

CheckMATE

.

2. ConstrainingMUEDwithexistingSUSYsearches

We focuson theLHC phenomenology ofthe SM andthefirst KKlevelexcitations.TheKKzeromodelevelcontainspreciselythe SMfieldcontent,includingoneHiggsdoublet.AtthefirstKKlevel, eachchiralSMfermion

(

Qi

,

ui

,

di

,

Li

,

ei

)

(i istheSMfamilyindex) has one a Dirac-fermion partner

(

Q_i(1)

,

u(_i1)

,

d_i(1)

,

L(_i1)

,

e(_i1)

)

, each SM gauge boson gμ

,

W μ

,

Bμ hasa massive gaugeboson partner

gμ(1)

,

Wμ(1)

,

Bμ ,(1) and the Higgspartner sector contains a scalar, a

pseudo-scalarandachargedpartner(h(1)

_,

_A(1)

0

,

H

(1)

± ).6Themasses

oftheSMpartnersareattree-levelgivenbymn

=



(

n

/

R

)

2

₊

_m2

S M, suggesting a very compressed mass spectrum. However, at loop level, the near-mass-degeneracy is partially lifted (with

increas-4 _{InUEDextensionswithboundarytermsandbulkfermionmasses[71],KK}

par-ityisconservedifboundarytermsarechosensymmetriconbothboundariesandif bulkfermionmassesarechosenKKparityodd.

5 _{Boundsfromotherprecisionobservables,likethemuong−2[72,73],Zbb}¯_[74],

ormodificationsofHiggscouplings[75–77]areweaker.

6 _{The KK gauge bosonsacquire their masses dominantlyfrom the scalar KK}

modes g(51),W (1) 5 ,B

(1)

5 , whichweaklymixwith thefirstKK Higgsmodesdueto

electroweaksymmetrybreaking.ThusateachKKlevel,fivescalardegreesof free-domare“eaten”whilefourphysicalscalardegreesofremainintheelectroweak sector.

Fig. 1. LoopcorrectedKKmassspectruminMUEDfor R−1_{=960GeV,R=30and} mh=125GeV.

ingsplittingsforincreased



R),makingtheKKgluontheheaviest state andthe KK partner of the U

(

1

)

Y gauge boson the lightest state ateach KK level [7,22]. A sample spectrum ofthe first KK resonances is shown inFig. 1.7 As can be seen, the mass differ-encescanreachuptoseveralhundredsofGeV.

Inthisletter,we restrictourselvesto thestrongproductionof coloredKKmodessuchasKKgluonsandKKquarks,

pp

→

g(1)g(1)

,

pp

→

Q

(1) i

Q

(1) j

,

pp

→

g (1)

_Q

(1) j

,

(1)

where

Q

(1)

₌

_Q(1)

_,

_q(1)_andQ(1)_denotestheSU

₍

₂

₎

_doubletquark partners(ortheiranti-particles)andq(1)

=

u(1)

,

d(1)aretheSU

(

2

)

singletquark partners(ortheir anti-particles)takingintoaccount all three generations. The total production cross section is fully determined viaQCD interactions andvariesbetween1(8)pband 20(480)fbforR−1

₌

_{800 GeVandR}−1

₌

_{1200 GeVwith}

_

_R

₌

₄₀

at8(13)TeV,respectively.8

The decaychaincan becomevery complicatedandinthe fol-lowing we briefly discusstypical decay modesofthe KK states.9 The KK gluonisthe heaviest particle,andit decaysintoKK dou-bletandsingletquarkswithroughlyequalbranchingratio.TheKK quarkdecaymodesmainlydependonits SU

(

2

)

charge.TheSU

(

2

)

singletKK quarkdirectlydecaystothe U

(

1

)

Y KK gaugeboson

γ

1

whichisstable.ThetopKKmode alsohassizabledecaysintothe

W_±(1) and H_±(1) astheKK top SU(2)doublet andsingletmix. The

SU

(

2

)

doubletKK quarks mainlydecayinto the SU

(

2

)

KK gauge bosons W_±(1) and Z(1)_{.The KK W and Z bosonsare lighter than} theKKquarksandthusmostlydecayintoleptonicKKstateswhich themselvesdecayfurtherinto thelighteststableKKparticle

γ

(1)_. Asa result,typicaleventshavea relativelylargelepton multiplic-ity, multiple jets andmissing transverse momentum in the final state configuration although all decay products will be relatively softduetotherelativelycompressedspectrum.

The masses and decay branching ratios are calculated with

the multi purpose Monte Carlo (MC) event generator

Her-wig++2.7.1

[25] which is also used to generate the fully hadronized MC events employing the default parton distribution function (PDF) setMRST [26].We work withthe defaultsettings

7 _{Cf. Refs.[7,22]forfullmassexpressions.}

8 _{Weclearlyseethatthecrosssectionincreasefrom8to13TeVisquite}

signifi-cantforheavyKKmassesandthusweexpectalargeincreaseinsensitivityfrom8 to13TeV.

9 _{Cf. Refs.[7,22]forexpressionsoftherelevantzero- andfirstKKmodecouplings}

Table 1

8TeVanalysesusedinourstudy.ArticlesareshownbytheirarXiv number.Themiddlecolumndenotesthetargetfinalstate,andthe thirdcolumnshowsthetotalintegratedluminosity.

Reference Final state L[fb−1_]

1403.4853 (ATLAS)[36] 2+

/

ET 20.3 1404.2500 (ATLAS)[37] SS 2or 3 20.3 1405.7875 (ATLAS)[38] jets +

/

ET 20.3 1407.0583 (ATLAS)[39] 1+(b) jets+

/

ET 20.0 1407.0608 (ATLAS)[40] monojet+

/

ET 20.3 1402.7029 (ATLAS)[41] 3+

/

ET 20.3 1501.03555 (ATLAS)[23] 1+jets+

/

ET 20.3 1303.2985 (CMS)[42] αT+b jets 11.7 1405.7570 (CMS)[43] 1, SS-OS2, 3, 4+

/

ET 20.3 Table 2

13TeVanalysesusedinourstudy.The*CONF*papersareonly publishedasconferenceproceedings.Themiddlecolumndenotes thetargetfinalstate,andthethirdcolumnshowsthetotal inte-gratedluminosity.

Reference Final state L[fb−1_]

1605.03814 (ATLAS)[44] jets+

/

ET 3.2

1605.04285 (ATLAS)[45] 1+jets+

/

ET 3.2

ATLAS-CONF-2016-054[46] 1+jets+

/

ET 14.8

ATLAS-CONF-2016-076[47] 2(stop search) 13 ATLAS-CONF-2016-078[48] jets+

/

ET 13.3

in all collider tools. We feed the truth level events to

Check-MATE2.0.2

[27–29]whichisbased onthefastdetector simula-tion

Delphes

3.4.0

[30].

Fastjet3.2.1

isused for the jet clustering [31].

CheckMATE

allows foreasy testingofwhethera modelpointisexcludedornotat95% confidencelevelagainst cur-rentATLASandCMSsearchesattheLHC.

CheckMATE

requiresan eventfileandthecorrespondingproductioncrosssectionasinput. Forthestudypresentedhere,wetaketheleadingordercross sec-tion from

Herwig++

, which yields a very conservative estimate oftheconstraintsaswedonotre-scaletheleadingorderestimate witha

K

factor.Inprinciple,MC eventsshouldbegeneratedwith atleastoneadditionalpartonatmatrixelementlevelandmatched withthe

Herwig++

partonshowersincetheMUEDparticle spec-trumisrelativelydegenerate[32–34].However,thisisbeyondthe scopeofthecurrentwork.Oursimpleapproachwillcertainly in-troduceanon-negligiblesystematicuncertaintyinourpredictions formasssplittingsmallerthan100GeV,whichinparticularoccurs inthelow



R

≤

5 region.

We have performed a grid scan in the R−1_–

_

_{R plane with}

the SM Higgs mass fixed to mh

=

125 GeV. For each grid point, 105 events havebeengenerated. Wetest each grid point against allATLASandCMSsearchesimplementedinto

CheckMATE

. How-ever,noteverysearchissensitivetoMUEDandweonlyshowthe relevant 8 and 13 TeV studies in Table 1 and 2. Most searches are validatedand the validation notescan be found on the offi-cialwebpage.10,11_{Eachanalysistypically containsalargenumber} of signal regions which target different mass hierarchies and fi-nalstatemultiplicities.Foragivensearch,thebestsignalregion for

each point in theparameter space is definedby

CheckMATE

as that with the largest expected exclusion potential. This criterium isthen repeatedtoselectthe bestsearch which isdefinedasthe searchwhosebestsignalregion hasthelargestexpectedlimit.This

10 _{https://checkmate.hepforge.org/.}

11 _{Theimplementationofthesearch[24]hasbeenonlypartiallyvalidated and}

wedidnotincludeitinoursearch.Thesearch[23]presentslimitsontheMUED parameterspaceand weplot theirlimitsinFig. 2. Theconferencenotes[46,48]

didnotprovidecutflows.However,bothsearchesarebasedon[44,45]withminor modificationsandthetwolattersearchesarevalidated.

Fig. 2. 95%confidence levellimiton the R−1_{–R planefrom ATLAS and CMS}

searchesperformedatthecenterofmassenergy√s=8 TeV.Thesolidanddashed linedenotes the observedand expected95%confidencelevel limit,respectively fromthesearchesemployedinourpaper.Thetotalintegratedluminosityusedby thevarioussearchesaresummarizedinTable 1.Theblacksolidlinedenotesthe bestlimitexcludingRef.[23]andtheshadedareacorrespondstoourtheoretical uncertainty.WefixedtheSMHiggsmasstomh=125GeV.

means thatthe bestobserved limitis notalways used butit en-suresthat theresultislesssensitive todownwardfluctuationsin thedata thatare bound tobe presentwhenscanningover many searchesandmanysignalregions.Onceabestsearch isselectedfor agivenpointinparameterspace,thesignalyieldinourmodelis thencomparedtotheobservedlimitat95%confidencelevel[35],

r

=

S

−

1

.

96

· 

S S95exp

(2) where S,



S, and S95

exp denotes the number ofsignal events,its

theoretical uncertainty and the experimentally determined 95% confidence level limit on thenumber of signal events S, respec-tively.Weonlyconsiderthestatisticaluncertaintyduetothefinite MonteCarlosamplewith



S

=

√

S.ThequantityS

−

1

.

96

·

S

cor-respondstothe95%lowerboundonourpredictionforthenumber ofsignalevent,whichensuresthatthelimitswesetare conserva-tive[29].Ther valueisonlycalculatedfortheexpectedbestsignal region.

CheckMATE

doesnotcombinesignalregions noranalyses inordertooptimizeexclusionsincethiswouldrequireknowledge fromtheexperimental collaborations.Weconsider amodelpoint as excluded if r is larger than one. However, due to theoretical uncertainties wecannot evaluatedirectly suchasmissingnext to leadingordercalculations, PDFuncertainties,detailsoftheparton shower andthefinite MCeventsample,we assigna conservative uncertaintytooursignal prediction.Asaresultwedefineapoint as definitively allowed for r

<

2

/

3 and definitively excluded for

r

>

3

/

2,which should be large enough to account forthe afore-mentionedeffects.

3. Results

OurnumericalresultsareshowninFig. 2 and3.Wefirstgive a briefsummary ofthe 8TeV results.Then we presentthemost up todatelimitsonthetwodimensionalMUED parameterspace from13TeVdata.

518 N. Deutschmann et al. / Physics Letters B 771 (2017) 515–520

Fig. 3. 95%confidencelevel limiton the R−1_{–R plane from ATLAS and CMS}

searchesperformedatthecenterofmassenergy√s=13 TeV.Thesolidanddashed linedenotes theobserved and expected95%confidencelevellimit, respectively fromthesearchesemployedinourpaper.Thetotalintegratedluminosityusedby thevarioussearchesaresummarisedinTable 2.Theblacksolidlinedenotesthe bestlimitandtheshadedareacorrespondstoourtheoreticaluncertainty.Wefixed theSMHiggsmasstomh=125GeV.

Ref. [23] hasan explicitMUED search included,andwe show their results for reference. As can be seen, the search Ref. [23]

providesthebestsensitivitytotheMUEDparameterspace.In par-ticular its dilepton signal regions targeting soft as well as hard leptons provide strong constraints. It should be pointed out that the observed limit of [23] is actually much better than the ex-pected one due to mild down fluctuations in the observed data. As a consequence, a compactification scale up to 950 GeV for



R=30 is excluded. Now,we wantto investigate how the other SUSYsearchesperformincomparisonandweexplorethe sensitiv-ityonMUEDexcludingRef.[23].ThelimitsofotherSUSYsearches, asobtainedwith

CheckMATE

are showningreen,turquoise and brown. We only show results of searches out of the list pro-vided in Table 1 which yield the best expected bound (shown as dashed lines) on R−1 for some value of



R. The recast ob-servedboundsoftheindividualsearchesareshownassolidlines. The blacksolid curve denotes the95% confidencelevel bound as determined from Eq. (2) for r

=

1,12 and the grey shaded area is our estimate forthe uncertainty and denotes the region with 0

.

67

<

r

<

1

.

5.ConsideringsearchesotherthanRef.[23],thelimit ismainlydriven by[38,41,43].[38] isthe ‘vanilla’ATLAS multijet and large missing transverse momentum search which performs well forsizable



R.For small



R

∼

5 GeV, the massdifference between the KK gluon g1 and the lightest KK mode

γ

1

dimin-ishesquite rapidlywitha splittingof

∼

100 GeV. Inthisregime, monojetsearchescanbecomecompetitive.However,sincewe did not generate matched event samples,the systematic uncertainty ontheexclusionlimitinthisregionofparameterspacewouldbe too large and thus the results should be interpreted with great care. Ref. [41] and [43] are dedicated multi-lepton and missing transversemomentumsearches.Multipleleptonsinthefinalstate areveryhandy insuppressingtheSM background.Itisclearthat for small



R values, the leptons become too soft and thus the multi-lepton searches loose their sensitivity very quickly. Again, dedicatedstudiestargetingsoftleptonssuchasRef. [23]and

pos-12 _{Theapparentdiscrepancybetweenthelimitshownbythislineandtryingto}

followtheindividuallimitsisaresultoftheinterpolationweperformedtoproduce thisfigure.Inparticular,thedisplayedexpectedlimitfortheCMSsearchisin re-alitybrieflythebestsearcharoundR=20,whichisnotdisplayedbecausethe interpolationsmoothedthecurve.Thisexplainstheoutwardbulgeofthelimitin thatregion.

siblymonojet searcheswillimprovesensitivityinthisdegenerate region.

To summarize, we have demonstratedthat a large number of searchescanprovidecomplementaryconstraintsontheMUED pa-rameter space. Thestrongestconstraints from8TeV searches are obtained from the dedicated MUED motivated signal region of Ref. [23],butsignal regions ofother SUSY searches yieldbounds whichare notsubstantially weaker.Other 8TeV searchessuchas

[49]couldbesensitivetothesignalsweconsider,butarecurrently notimplementedorvalidatedin

CheckMATE

.

Now,weturnourattentiontoLHCsearchesat

√

s

=

13 TeV.So far,ATLAS andCMSdidnotpresentdedicatedMUED resultsfrom Run 2. InFig. 3, we display the excluded region from the ongo-ing Run 2 asobtained from our recast studywith

CheckMATE

. We includetwo published searches [44,45]from theearly Run2 dataandthreeconferencenoteswithroughly14fb−1 ofcollected data[48,47,46].Othersearchessuchas[50–58]couldalsobe sen-sitive tothe signalsweconsider, butare notyet implementedor validatedin

CheckMATE

.Weobserveaclearimprovementofthe limitsascomparedtoRun1.ThemassscaleuptoR−1

₌

_{1500 GeV}

canbeexcludedat95% confidencelevel.Thesearch[46]requiring oneisolatedleptonperformsbetterthanthecorrespondingsearch withaleptonveto[48].Forbothsearches,thelimitsbecomemuch weaker for increasing



R. This might be quite surprising since naivelyonewouldexpectthatforincreasingmasssplitting,the ef-ficiencyinthesignal regions wouldincrease. However,increasing



R raisesalsotheoverallmassscaleofthehardprocesswhich re-sultsinalargereductionofthehadroniccrosssection.Inaddition, thebestsignal regionofRef.[46] isGG2Jwhichtargetsrelatively heavy andcompressedspectra. Sensitivityisenhanced forevents withrelatively largejet recoilsagainst thepairproduced KK par-tons whichresults in largemissing transverse momentum. How-ever,forincreasingmasssplitting,themissingtransverseenergyis reducedandthus weobserve thatthe bestlimitsarederived for relatively small



R.Onthe other hand,thedileptonstop search

[47] performs very well even forlarge



R values. Here, a large mass splitting results in more energetic leptons which improves the sensitivity. However, the response degrades very quickly for verysmall



R asinthisregion,theleptonstendtobetoosoftto bedetected.

4. Conclusions

WehavedeterminedthecurrentlimitsontheMUEDparameter spacefromLHCsupersymmetrysearchesat8and13TeV.Afterthe endofRun1,alargenumberofsupersymmetrysearchestargeting a vast number offinal state topologieshave beenpublished. We demonstratedthe complementarityofusingall available searches inordertoconstrain MUED.Run2isongoing andthenumberof searchesisquiterestrictedcomparedtoRun1.However,thelarge gain in parton luminosity allows for impressive improvement in the exclusion of parameter space. The dilepton stop search per-formsverywell,andwehavederivedthemoststringentlimitson theMUEDparameterspacesofarwithR−1

≈

1400 GeV excluded for



R

∼

10.Thislimitisconservativeinthesensethatitdoesnot includeand

K

factor.Fora

K

factorof1.5,thelimit wouldbe in-creasedtoR−1

_≈

_{1500 GeV.MUEDyieldstheobserveddarkmatter}

relicdensityifco-annihilationandsecondKKmoderesonant(co-) annihilation are taken into account if 1

.

25 TeV



R−1

_

₁

_.

_{5 TeV}

5. Noteadded

While we were finishing thisletter, we becameaware of the complementarystudyRef.[59],whichstudiesMUEDboundsfrom SUSYsearches withanMUED implementationin

Pythia

6

and

Pythia

8

foreventgeneration and

CheckMATE

.We thankthe authorsofRef. [59]forcommunicationandformakinga prelimi-narydraftoftheirpaperavailabletous.Intheoverlappingregions of the two studies, the results were found to be in reasonable agreement.

Acknowledgements

WethankKyoungchulKongandSeongChanParkfortheir con-tributionandcollaboration in thebeginning of thiswork aswell asformanyhelpful comments.Wealsothank SimonPlatzerand PeterRichardsonforinformationanddetails ontheMUED imple-mentationin

Herwig

.TheworkofJ.S.KandT.F.wassupportedby IBSundertheprojectcode,IBS-R018-D1.N.D.andT.F.acknowledge thePartenariatHubertCurien(PHC)STARprojectno.34299VE,and partialsupportfromtheCNRSLIAFKPPL.

References

[1]T.Appelquist,H.-C.Cheng,B.A.Dobrescu,Boundsonuniversalextra dimen-sions,Phys.Rev.D64(2001)035002,arXiv:hep-ph/0012100.

[2]R.Barbieri,A.Strumia,WhatisthelimitontheHiggsmass?,Phys.Lett.B462 (1999)144–149,arXiv:hep-ph/9905281.

[3]M. Papucci, NDA and perturbativity in Higgsless models, arXiv:hep-ph/ 0408058.

[4]Z.Chacko,M.A.Luty,E.Ponton,Massivehigherdimensional gaugefieldsas messengersofsupersymmetrybreaking,J.HighEnergyPhys.07(2000)036, arXiv:hep-ph/9909248.

[5]G.Bhattacharyya,A.Datta,S.K.Majee,A.Raychaudhuri,Powerlawblitzkrieg inuniversal extra dimension scenarios, Nucl. Phys. B760(2007) 117–127, arXiv:hep-ph/0608208.

[6]R.S.Chivukula,D.A.Dicus,H.-J.He,Unitarityofcompactifiedfive-dimensional Yang–Millstheory,Phys.Lett.B525(2002)175–182,arXiv:hep-ph/0111016.

[7]H.-C.Cheng,K.T.Matchev,M.Schmaltz,RadiativecorrectionstoKaluza–Klein masses,Phys.Rev.D66(2002)036005,arXiv:hep-ph/0204342.

[8]G.Servant,T.M.P.Tait,IsthelightestKaluza–Kleinparticleaviabledarkmatter candidate?,Nucl.Phys.B650(2003)391–419,arXiv:hep-ph/0206071.

[9]K.Kong,K.T.Matchev,PrecisecalculationoftherelicdensityofKaluza–Klein darkmatterinuniversalextradimensions,J.HighEnergyPhys.01(2006)038, arXiv:hep-ph/0509119.

[10]F.Burnell,G.D.Kribs,TheabundanceofKaluza–Kleindarkmatterwith coanni-hilation,Phys.Rev.D73(2006)015001,arXiv:hep-ph/0509118.

[11]G.Belanger,M.Kakizaki,A.Pukhov,DarkmatterinUED:theroleofthesecond KKlevel,J.Cosmol.Astropart.Phys.1102(2011)009,arXiv:1012.2577 [hep-ph].

[12]T.Appelquist,H.-U.Yee,UniversalextradimensionsandtheHiggsbosonmass, Phys.Rev.D67(2003)055002,arXiv:hep-ph/0211023.

[13]M.Baak,M.Goebel,J.Haller,A.Hoecker,D.Ludwig,K.Moenig,M.Schott,J. Stelzer,Updatedstatusoftheglobalelectroweakfitandconstraintsonnew physics,Eur.Phys.J.C72(2012)2003,arXiv:1107.0975[hep-ph].

[14]A.J.Buras,M.Spranger,A.Weiler,Theimpactofuniversalextra dimensions ontheunitaritytriangleandrareKand Bdecays,Nucl.Phys.B660(2003) 225–268,arXiv:hep-ph/0212143.

[15]A.J.Buras,A.Poschenrieder,M.Spranger,A.Weiler,Theimpact ofuniversal extradimensionsonB→Xsγ,B→Xs g,B→Xsμ+ μ−,KL→π0e+e−

and/,Nucl.Phys.B678(2004)455–490,arXiv:hep-ph/0306158.

[16]U.Haisch,A.Weiler,BoundonminimaluniversalextradimensionsfromB¯→

Xsγ,Phys.Rev.D76(2007)034014,arXiv:hep-ph/0703064.

[17]A.Datta,K. Kong, K.T. Matchev, Discriminationofsupersymmetry and uni-versalextradimensionsathadroncolliders,Phys.Rev.D72(2005)096006, arXiv:hep-ph/0509246,Phys.Rev.D72(2005)119901(Erratum).

[18]T.Flacke,A.Menon,Z.Sullivan,ConstraintsonUEDfromW’searches,Phys. Rev.D86(2012)093006,arXiv:1207.4472[hep-ph].

[19]S.Chang,S.Y.Shim,J.Song,Directboundontheminimaluniversalextra di-mensionmodelfromthet¯t resonancesearchatthetevatron,Phys.Rev.D86 (2012)117503,arXiv:1207.6876[hep-ph].

[20]L.Edelhauser,T.Flacke,M.Kramer,Constraintsonmodelswithuniversalextra dimensionsfromdileptonsearchesattheLHC,J.HighEnergyPhys.08(2013) 091,arXiv:1302.6076[hep-ph].

[21] CMSCollaboration,Searchforresonancesinthedileptonmassdistributionin ppcollisionsat√s=8TeV,CMS-PAS-EXO-12-061.

[22]H.-C. Cheng, K.T. Matchev, M. Schmaltz, Bosonic supersymmetry? Getting fooledattheCERNLHC,Phys.Rev.D66(2002)056006,arXiv:hep-ph/0205314.

[23]ATLAS Collaboration,G.Aad,etal.,Searchforsquarksandgluinosinevents withisolatedleptons,jetsandmissingtransversemomentumat√s=8 TeV withtheATLASdetector,J.HighEnergyPhys.04(2015)116,arXiv:1501.03555 [hep-ex].

[24] ATLASCollaboration,Searchfor squarksand gluinosineventswithisolated leptons, jets and missing transverse momentum at √s=8 TeV with the ATLAS detector, Tech. Rep.ATLAS-CONF-2013-062, CERN,Geneva, Jun 2013,

https://cds.cern.ch/record/1557779.

[25]J.Bellm,etal.,Herwig++2.7releasenote,arXiv:1310.6877[hep-ph].

[26]A.D.Martin,R.G.Roberts,W.J.Stirling,R.S.Thorne,NNLOglobalpartonanalysis, Phys.Lett.B531(2002)216–224,arXiv:hep-ph/0201127.

[27]D.Dercks,N.Desai,J.S.Kim,K.Rolbiecki,J.Tattersall,T.Weber,CheckMATE2: fromthemodeltothelimit,arXiv:1611.09856[hep-ph].

[28]J.S. Kim, D.Schmeier,J.Tattersall,K. Rolbiecki,A frameworktocreate cus-tomisedLHCanalyseswithinCheckMATE,Comput.Phys.Commun.196(2015) 535–562,arXiv:1503.01123[hep-ph].

[29]M. Drees, H. Dreiner, D. Schmeier,J. Tattersall, J.S. Kim, CheckMATE: con-frontingyourfavouritenewphysicsmodelwithLHCdata,Comput.Phys. Com-mun.187(2015)227–265,arXiv:1312.2591[hep-ph].

[30]DELPHES3Collaboration,J.deFavereau,C.Delaere,P.Demin,A.Giammanco, V.Lemaître,A.Mertens,M.Selvaggi,DELPHES3,amodularframeworkforfast simulationofagenericcolliderexperiment,J.HighEnergyPhys.02(2014)057, arXiv:1307.6346[hep-ex].

[31]M.Cacciari,G.P.Salam,G.Soyez,FastJetusermanual,Eur.Phys.J.C72(2012) 1896,arXiv:1111.6097[hep-ph].

[32]H.K.Dreiner,M.Kramer,J.Tattersall,HowlowcanSUSYgo?Matching, mono-jetsandcompressedspectra,Europhys.Lett.99(2012)61001,arXiv:1207.1613 [hep-ph].

[33]H. Dreiner, M.Krämer, J.Tattersall, Exploring QCDuncertainties when set-tinglimitsoncompressedsupersymmetricspectra,Phys.Rev.D87 (3)(2013) 035006,arXiv:1211.4981[hep-ph].

[34]M.Drees,M.Hanussek,J.S.Kim,LightstopsearchesattheLHCwithmonojet events,Phys.Rev.D86(2012)035024,arXiv:1201.5714[hep-ph].

[35]A.L.Read,Presentation ofsearchresults:the CL(s)technique,J.Phys. G28 (2002)2693–2704.

[36]ATLASCollaboration,G.Aad,etal.,Searchfordirecttop-squarkpairproduction infinalstateswithtwoleptonsinppcollisionsat√s=8TeVwiththeATLAS detector,J.HighEnergyPhys.06(2014)124,arXiv:1403.4853[hep-ex].

[37]ATLASCollaboration,G.Aad,etal.,Searchforsupersymmetryat√s =8TeV infinalstateswithjetsandtwosame-signleptonsorthreeleptonswiththe ATLASdetector,J.HighEnergyPhys.06(2014)035,arXiv:1404.2500[hep-ex].

[38]ATLASCollaboration,G.Aad,etal.,Searchforsquarksandgluinoswiththe AT-LASdetectorinfinalstateswithjetsandmissingtransversemomentumusing √

s=8 TeVproton–protoncollisiondata,J.HighEnergyPhys.09(2014)176, arXiv:1405.7875[hep-ex].

[39]ATLAS Collaboration,G.Aad,et al.,Searchfor topsquarkpairproductionin finalstateswithoneisolatedlepton,jets,andmissingtransversemomentum in√s=8TeVpp collisionswiththeATLASdetector,J.HighEnergyPhys.11 (2014)118,arXiv:1407.0583[hep-ex].

[40]ATLASCollaboration,G.Aad,etal.,Searchforpair-producedthird-generation squarksdecayingviacharmquarksorincompressedsupersymmetricscenarios in pp collisionsat√s=8 TeVwiththeATLASdetector,Phys.Rev.D90 (5) (2014)052008,arXiv:1407.0608[hep-ex].

[41]ATLASCollaboration,G.Aad,etal.,Searchfordirectproductionofcharginos andneutralinosineventswiththreeleptonsandmissingtransverse momen-tumin√s=8TeVpp collisionswiththeATLASdetector,J.HighEnergyPhys. 04(2014)169,arXiv:1402.7029[hep-ex].

[42]CMSCollaboration,S.Chatrchyan,etal.,Searchforsupersymmetryinhadronic finalstateswithmissingtransverseenergyusingthevariablesαTandb-quark multiplicityinppcollisionsat√s=8 TeV,Eur.Phys.J.C73 (9)(2013)2568, arXiv:1303.2985[hep-ex].

[43]CMSCollaboration, V.Khachatryan,et al.,Searches forelectroweak produc-tionofcharginos,neutralinos,andsleptonsdecayingtoleptonsandW,Z,and Higgsbosonsinpp collisionsat 8TeV, Eur.Phys.J. C74 (9)(2014)3036, arXiv:1405.7570[hep-ex].

[44]ATLASCollaboration,M.Aaboud,etal.,Searchforsquarksandgluinosinfinal stateswithjetsandmissingtransversemomentumat√s=13TeVwiththe ATLASdetector,Eur.Phys.J.C76 (7)(2016)392,arXiv:1605.03814[hep-ex].

[45]ATLASCollaboration,G.Aad,etal.,Searchforgluinosineventswithanisolated lepton,jetsandmissingtransversemomentumat√s =13TeVwiththeATLAS detector,Eur.Phys.J.C76 (10)(2016)565,arXiv:1605.04285[hep-ex].

[46] ATLASCollaboration, Searchforsquarksand gluinosineventswithan iso-lated lepton,jetsand missingtransversemomentum at√s =13TeVwith theATLASdetector,Tech.Rep.ATLAS-CONF-2016-054,CERN,Geneva,Aug2016,

520 N. Deutschmann et al. / Physics Letters B 771 (2017) 515–520

[47] ATLASCollaboration, Searchfor directtopsquark pair productionand dark matterproductioninfinalstateswithtwoleptonsin√s=13 TeVpp

colli-sionsusing13.3fb−1 _{ofATLASdata,Tech.Rep.ATLAS-CONF-2016-076,CERN,}

Geneva,Aug2016,http://cds.cern.ch/record/2206249.

[48] ATLASCollaboration,Furthersearchesforsquarksandgluinosinfinalstates with jetsand missing transversemomentumat √s =13TeV with the AT-LAS detector, Tech. Rep. ATLAS-CONF-2016-078, CERN, Geneva, Aug 2016,

http://cds.cern.ch/record/2206252.

[49] ATLASCollaboration, Searches for direct scalar toppair production infinal stateswithtwoleptonsusingthestransversemassvariableandamultivariate analysistechniquein√s=8 TeVppcollisionsusing20.3fb−1_ofATLASdata,

Tech.Rep.ATLAS-CONF-2013-065,Geneva,https://cds.cern.ch/record/1562840, 2013.

[50]ATLASCollaboration,M.Aaboud,etal.,Searchfornewphenomenainevents containingasame-flavouropposite-signdileptonpair,jets,andlargemissing transversemomentumin√s=13pp collisionswiththeATLASdetector,Eur. Phys.J.C77 (3)(2017)144,arXiv:1611.05791[hep-ex].

[51] ATLAS Collaboration, Search for supersymmetry with two same-sign lep-tons or three leptons using 13.2 fb?1 _of √_{s=13 TeV pp collision data}

collectedby the ATLAS detector, Tech. Rep.ATLAS-CONF-2016-037, Geneva,

https://cds.cern.ch/record/2205745,2016.

[52] ATLASCollaboration, Searchfor squarksandgluinosinfinalstateswithjets and missingtransversemomentum using36 fb?1 _of√_{s=13 TeVpp}

colli-siondatawiththeATLASdetector,Tech.Rep.ATLAS-CONF-2017-022,Geneva,

https://cds.cern.ch/record/2258145,2017.

[53]CMS Collaboration, V. Khachatryan, et al., Search for supersymmetry with multiplechargedleptonsinproton–protoncollisionsat√s=13TeV,arXiv: 1701.06940[hep-ex].

[54]CMSCollaboration,A.M.Sirunyan,etal.,Searchesforpairproductionfor third-generationsquarksin√s=13 TeVppcollisions,arXiv:1612.03877[hep-ex].

[55]CMSCollaboration,V.Khachatryan,etal.,Searchfornewphysicsinfinalstates withtwoopposite-sign,same-flavorleptons,jets,andmissingtransverse mo-mentuminppcollisionsat√s=13 TeV,J.HighEnergyPhys.12(2016)013, arXiv:1607.00915[hep-ex].

[56]CMSCollaboration, V.Khachatryan,et al., Searchfor supersymmetryinthe multijetandmissingtransversemomentumfinalstateinppcollisionsat13 TeV,Phys.Lett.B758(2016)152–180,arXiv:1602.06581[hep-ex].

[57] CMSCollaboration,Searchforsupersymmetryinppcollisionsat√s=13 TeV inthesingle-leptonfinalstateusingthesumofmassesoflarge-radiusjets, Tech. Rep.CMS-PAS-SUS-16-037, Geneva,https://cds.cern.ch/record/2256652, 2017.

[58] CMS Collaboration, Search for new physics with multileptons and jets in 35.9 fb−1_{ofppcollisiondataat}√_{s=13 TeV,Tech.Rep.CMS-PAS-SUS-16-041,}

Geneva,https://cds.cern.ch/record/2256435,2017.

[59]J.Beuria,A.Datta,D.Debnath,K.T.Matchev,LHCcolliderphenomenologyof minimaluniversalextradimensions,arXiv:1702.00413[hep-ph].

[60]I.Antoniadis,ApossiblenewdimensionatafewTeV,Phys.Lett.B246(1990) 377–384.

[61]I.Antoniadis,N.Arkani-Hamed,S.Dimopoulos,G.R.Dvali,Newdimensionsat amillimetertoaFermi andsuperstringsat aTeV, Phys.Lett.B436(1998) 257–263,arXiv:hep-ph/9804398.

[62]D.Hooper,S.Profumo,Darkmatterandcolliderphenomenologyofuniversal extradimensions,Phys.Rep.453(2007)29–115,arXiv:hep-ph/0701197.

[63]G.Servant,StatusreportonuniversalextradimensionsafterLHC8,Mod.Phys. Lett.A30 (15)(2015)1540011,arXiv:1401.4176[hep-ph].

[64]L. Nilse, Classification of1D and 2D orbifolds, AIPConf. Proc. 903(2007) 411–414,arXiv:hep-ph/0601015.

[65]B.A.Dobrescu,E.Ponton,Chiralcompactificationonasquare,J.HighEnergy Phys.03(2004)071,arXiv:hep-th/0401032.

[66]G.Cacciapaglia, A.Deandrea, J.Llodra-Perez, A darkmattercandidatefrom Lorentzinvariancein6D,J.HighEnergyPhys.03(2010)083,arXiv:0907.4993 [hep-ph].

[67]G. Cacciapaglia, A. Deandrea, N. Deutschmann, Dark matter and localised fermions from spherical orbifolds?, J. High Energy Phys. 04 (2016) 083, arXiv:1601.00081[hep-ph].

[68]N. Maru, T. Nomura, J. Sato, M. Yamanaka, The universal extra dimen-sional model with S2

/Z2 extra-space, Nucl. Phys. B 830 (2010) 414–433,

arXiv:0904.1909[hep-ph].

[69]T.Flacke,A.Menon,D.J.Phalen,Non-minimaluniversalextradimensions,Phys. Rev.D79(2009)056009,arXiv:0811.1598[hep-ph].

[70]S.C.Park,J.Shu,Splituniversalextradimensionsanddarkmatter,Phys.Rev.D 79(2009)091702,arXiv:0901.0720[hep-ph].

[71]T.Flacke,K.Kong,S.C.Park,Phenomenologyofuniversalextradimensionswith bulk-massesand brane-localizedterms,J. HighEnergyPhys. 05(2013)111, arXiv:1303.0872[hep-ph].

[72]P.Nath,M.Yamaguchi,EffectsofKaluza–Kleinexcitationson(gμ−2),Phys. Rev.D60(1999)116006,arXiv:hep-ph/9903298.

[73]K.Agashe,N.G.Deshpande,G.H.Wu,Canextradimensionsaccessibletothe SMexplainthe recentmeasurementofanomalousmagneticmomentofthe muon?,Phys.Lett.B511(2001)85–91,arXiv:hep-ph/0103235.

[74]J.F.Oliver,J.Papavassiliou,A.Santamaria,UniversalextradimensionsandZ→ ¯

bb,Phys.Rev.D67(2003)056002,arXiv:hep-ph/0212391.

[75]U.K.Dey,T.S.Ray,Constrainingminimaland nonminimaluniversalextra di-mensionmodels withHiggscouplings,Phys. Rev.D88 (5) (2013) 056016, arXiv:1305.1016[hep-ph].

[76]T.Kakuda,K.Nishiwaki,K.-y. Oda,R.Watanabe, Universalextradimensions afterHiggsdiscovery,Phys.Rev.D88(2013)035007,arXiv:1305.1686[hep-ph].