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Higgs Phenomenology of Minimal Universal Extra Dimensions Genevie`veBe´langer1,a,AlexanderBelyaev2,b,MatthewBrown3,c,MitsuruKakizaki4,d,andAlexanderPukhov5,e 1 LAPTH,Universite´ deSavoie,CNRS,B.P.110,F-74941Annecy-le-VieuxCedex,France 2 NExTInstitute,SchoolofPhysicsandAstronomy,UniversityofSouthampton,UK 3 SchoolofPhysicsandAstronomy,UniversityofSouthampton,UK 4 DepartmentofPhysics,UniversityofToyama,3190Gofuku,Toyama930-8555,Japan 5 SkobeltsynInstituteofNuclearPhysics,MoscowStateUniversity,Moscow119992,Russia 2 1 Abstract. TheminimalmodelofUniversalExtraDimensions(MUED)isbrieflyreviewed.Weexplainhow 0 thecross-sectionsforHiggsproductionviagluonfusionanddecayintophotonsaremodified,relativethethe 2 StandardModel(SM)values,byKKparticlesrunninginloops,leadingtoanenhancementofthegg→h→γγ n and gg → h → W+W− cross-sections. ATLAS and CMS searches for the SM Higgs in these channels are a reinterpretedinthecontextofMUEDandusedtoplacenewlimitsontheMUEDparameterspace.Onlyasmall J regionofbetween1and3GeVaroundmh = 125GeVfor500GeV < R−1 < 1600GeVremainsopenatthe 6 95%confidencelevel. 2 ] h 1 Introduction nances(thelightestnewparticlespredictedbyMUED)can p onlybepairproducedandn = 2resonancesaretypically - The idea of extra dimensions of space is conceptually in- tooheavytobeproducedon-shellatLHCenergies.How- p triguingandprovidesarichframeworkforbuildingmod- ever,KKparityensuresthatthelightestn=1KKparticle e h elsthatgobeyondtheStandardModel(SM).Oneclassof (the“LKP”inanalogytotheLSPinSUSY)isstable;for [ extra-dimensionaltheories,proposedbyAppelquist,Cheng much of the parameter space the LKP is neutral and so it andDobrescu[1]in2001,involvesuniversalextradimen- providesanexcellentDarkMatterWIMPcandidate.This 1 sions(UED).Insuchmodelsallparticlescanpropagatein isthemainmotivationforMUED. v alldimensions(i.e.inthe“bulk”),andtheextradimensions Likeallgaugetheoriesingreaterthanfourdimensions, 2 8 arehiddenbycompactifyingthemonadistancescaletoo MUEDisperturbativelynon-renormalisable;thetheorymust 5 smalltobeprobedbyourcurrentexperiments. be cut off at a momentum scale Λ above which the new 5 In this note we focus on the simplest possible UED physics of the UV completion is expected to become no- . model, Minimal UED (MUED), which has one extra di- ticeable. Discounting the mild cutoff dependence at LHC 1 0 mension compactified on a circle. The circle has transla- energyscales,MUEDhastwoparameterswithvaluesnot 2 tional symmetry and so there is conserved momentum in completelyconstrainedbyexperiment:theHiggsmassmh 1 the 5th dimension which is discretised because of the pe- andtheinversecompactificationradiusR−1. : riodicboundaryconditions;onethereforetalksaboutcon- The R−1 parameter is already bounded to be less than v served “Kaluza-Klein” (KK) number n. The extra dimen- i around1600GeVbyWMAPobservationsbecauseitsets X sion is then further compactified onto an S1/Z orbifold 2 the scale of the Dark Matter (DM): if DM were heavier r (essentially a line segment with particular boundary con- it would lead to the Universe having a measurable posi- a ditions for the fields ). This “orbifolding” is necessary to tivecurvature.Also,m isboundedfromabovebythere- h obtainchiralmatter,anditbreaksthetranslationalinvari- quirement that DM be neutral. These DM considerations ancesoKKnumberisonlyconservedattreelevel.There are discussed in detail in [2] and shown in Fig. 4 of this isaremnantreflectionsymmetryoftheorbifoldaboutits note. midpoint which leads to a KK “parity” (−1)n being con- TheHiggsmassisrequiredtobegreaterthan114.1GeV servedatallordersinperturbationtheory. bytheLEP2HiggssearchesandR−1 (cid:38) 300GeVinorder WhenMUEDisexpressedasa4Deffectivetheory,the not to conflict with electroweak precision measurements different possible KK numbers of a 5D particle manifest [3]. themselvesasatowerofprogressivelyheavierseparate4D Inthispaperweplacenewconstraintsontheparameter particles, one for each KK number. The zero mode parti- space using data from the latest ATLAS and CMS Higgs clesareidentifiedwithSMparticles. searches.Thisideahasbeenattemptedbefore[4],butwith- KKparityconservationmakesMUEDparticularlyhard outtakingintoaccounttheeffectofMUEDonHiggsde- to observe at the LHC because it means that n = 1 reso- cay to two photons.1 This is explained more fully in the a e-mail:[email protected] followingsections. b e-mail:[email protected] c e-mail:[email protected] 1 Whilstwehavebeenpreparingtheseproceedings,Nishiwaki d e-mail:[email protected] etalhaveproducednewworkthatincludesKKsuppressionof e e-mail:[email protected] theh→γγvertex[9]. EPJWebofConferences 2 Higgs production and decay vertices that can be as large as 50 % of the leading order values,althoughthesecancelintheratiosplottedinFig.2. For low and intermediate m , the most important Higgs h productionprocessattheLHCisgluon-gluonfusion.The lowestorderFeynmandiagramcontributingtothisprocess 1.30 istheoneshowninFig.1(top),withquarksrunninginthe gg h triangle loop. For low m , Higgs decay to two photons is 1.25 → h themostimportantchannelduetoitssmallbackground.In 1.20 Fig.1(bottom),twoleadingordercontributionsareshown. | h Thereareactuallymanyotherone-loopdiagramsinvolving gg 1.15 W± bosonsthatarenotshown;forthefulldetailssee[5]. R But essentially there is tension between the quark/lepton |1.10 (dominated by the top quark) and the W contributions to 1.05 the decay, with the W contribution being dominant in the SM. 1.00 100 150 200 250 300 350 400 450 500 g mh [GeV] 1.20 R 1 =500 GeV h γγ − q h 1.15 R−1 =750 GeV → R 1 =1000 GeV − |1.10 R−1 =1250 GeV hγγ R−1 =1500 GeV g R 1.05 γ γ | 1.00 h W± h q,(cid:96)± 0.95 100 150 200 250 300 350 400 450 500 m [GeV] h γ γ 1.40 1.35 gg h γγ → → Fig.1.RepresentativediagramsinvolvedinHiggsproductionby |1.30 γ gluonfusion(top)andsubsequentdecaytophotons(bottom). γ h 1.25 R ×1.20 In MUED, KK particles can also flow in the loops. gh 1.15 g These enhance each of the diagrams shown. The rate of R 1.10 | HiggsproductionisthereforeincreasedrelativetotheSM. 1.05 TheopposingfermionandWcontributionstothediphoton decayareeachenhanced,butthefermionenhancementis 1.00 100 150 200 250 300 350 400 450 500 greater than the W and so the partial decay width to pho- m [GeV] tonsisdecreasedformostoftherelevant(m ,R−1)param- h h eterspace.Thematrixelementsforproductionanddecay bothtaketheform Fig. 2. Ratios of the scalar parts of matrix elements for Higgs productionanddecay,whereR=M˜ /M˜ .Foreachgraph, MUED SM M=M˜ ×m2hgµν−pνqµ(cid:15)µ(cid:15)ν, oofn5th0e0,R7H50S,,1fr0o0m0,t1o2p5t0oabnodtt1o5m0,0thGeecVu.rvesrepresentR−1values 2 wherethe(cid:15)four-vectorsaregluonorphotonpolarisations. Wehaveapproximatedexternalparticlesasbeingonshell. Overall,theenhancementoftheHiggsproductionam- ThescalarpartsM˜ ofthematrixelementsforg,g→hand plitude is greater than the suppression of the Higgs de- h→γ,γareplottedinFig.2(topandmiddle)asmultiples cay to two photons and so the MUED cross-section for oftheSMvaluesforvariousvaluesofm andR−1. gg → h → γγisalwaysenhancedrelativetotheStandard h WeusedourownimplementationoftheMUEDmodel Model’s. This is shown the bottom graph in Fig. 2. This intheLanHEPandCalcHEPsoftwarepackagesinorderto meansthatourmodelismoresensitivetoexperimentally- calculate these matrix elements and, later, cross-sections. determined Higgs mass limits that the SM and this sensi- Unlikeotherimplementations,oursincludestheeffectsof tivitycanbeusedtoconstraintheparameterspacefurther. radiativecorrectionstoKKparticlemassesatone-loopbe- Inadditiontogg → h → γγ,wealsolookedatgg → causethesecorrectionsplayavitalroleduetothehighly- h → W+W−, which is particularly important in the inter- degeneratetree-levelMUEDmassspectrum[6].Ourmodel mediate Higgs mass range. The gluon fusion part of the alsoincludestwo-loopSMcorrectionstothegghandhγγ process is enhanced as before, but decay to two Ws can HadronColliderPhysicsSymposium2011 proceed via a tree-level diagram so KK particles have no ) leadingordereffectonthedecaypart. eV 2000 G ( 1800 WMAP excluded 1 -R 3 Limits on parameter space 1600 n 1400 sio Charged DM WelookedatthelatestATLASandCMSSMHiggssearches clu and reinterpreted the analyses for MUED. The results of 1200 ex ed the searches are expressed in terms of µ ≡ σ95%/σSM, 1000 arch allow AEWllo wpreedc ibsyion fits wduhcetrieonσ9a5n%didsethcaeycrporsosc-seescstitohnatfohrasapcuarrtriecnutllayrbHeiegngsruplreod- 800 ggs se EHxigcglusd LeHdC b ys ecaormchbeinsed outatthe95%confidencelevel,andσSMistheSMcross- 600 2 Hi P sectionforthatsameprocess. E OnecanplacelimitsonMUEDbycalculatingµ = 400 L σ /σ for different values of (m ,R−1) andMsUeEeDing 100 120 140 160 180 200 220 240 260 280 300 MUED SM h whether it is larger than the existing limit. We used the MH (GeV) latest limits shown in Fig. 3 of [7] for ATLAS and Fig. 6 Fig.4.ConstraintsonMUEDparameterspace.Purpleandpink (top)of[8]forCMS.Wecombinedthelimitsfromthetwo showregionsruledoutbyDMconsiderations.Golddenotesthe experiments statistically for each of channels of interest regionexcludedbytheHiggssearchanalysispresentedhereand (diphotonandW+W−)using also the existing LEP2 limit. Points between the blue hyper-  −1 boloidsagreewithLEPEWprecisionfitstoa95%CL. µcomb =µ21 + µ21  2 . ATLAS CMS 4 Conclusions This does not take into account systematic errors but it does give a good estimate of the combination in lieu of We have used the latest ATLAS and CMS Higgs search theofficialcombinationfromATLASandCMS. datatoconstraintheparameterspaceofMUED.Wehave improvedonanearlieranalysisbyincludingtheeffectsof theKKmodesontheHiggsdecaytotwophotonsandby 1600 alsoincludingtheradiativecorrectionstotheKKmasses. Fulldetailswillbegivenin[5]. 1400 We eagerly await the official limit combination from ATLASandCMS,althoughdetailsofthecombinationwill 1200 el become moot (for our purposes!) if the 125 GeV excess n V] an goesawaywhenextradataiscollectedin2012.Ifthishap- Ge 1000 ch Ruled out by pens,wewillbeabletoruleoutMUEDcompletelyatthe 1[ γγ W+W− channel 3σlimitbytheendoftheyear.Iftheexcessremainsand − R 800 by wediscovertheHiggsthere,thisshouldallowustomake t apredictionastothevalueofR−1. u o 600 d e ul R References 400 100 150 200 250 300 1. T.Appelquist,H.-C.Cheng,andB.A.Dobrescu,Phys.Rev. m [GeV] D64no.3,(2001)035002 h 2. G.Belanger,M.Kakizaki,andA.Pukhov, arXiv:1012.2577 [hep-ph] Fig.3.RegionsofMUEDparameterspaceruledoutatthe95% 3. I.GogoladzeandC.Macesanu,Phys.Rev.D74(2006) confidence level by combination of ATLAS and CMS Higgs 093012,arXiv:hep-ph/0605207 searchesusingthediphoton(red)andW+W−(blue)channels. 4. K.Nishiwaki,K.-y.Oda,N.Okuda,andR.Watanabe, arXiv:1108.1764v1 [hep-ph] 5. G.Belanger,A.Belyaev,M.Brown,M.Kakizaki,and TheparameterspaceruledoutbytheHiggssearchdata A.Pukhov,“Inpreparation” is shown in Fig. 3. All of the parameter space for m > 6. H.-C.Cheng,K.T.Matchev,andM.Schmaltz,Phys.Rev. h 111 GeV is ruled out except for a small region around D66(2002)036005,arXiv:hep-ph/0204342 125 GeV – this is due to the excess of events observed 7. TheATLASCollaboration,Tech.Rep. byATLASandCMSrecentlyinthisregion. ATLAS-CONF-2011-163,(December2011) Forcompleteness,inFig.4weshowthelimitsonthe 8. TheCMSCollaboration,CMS-PAS-HIG-11-032,(December 2011) MUEDparameterspacefromtheHiggsanalysispresented 9. K.Nishiwaki,K.-y.Oda,N.Okuda,andR.Watanabe, heretogetherwithexistinglimitsfromotherconstraints.In Phys.Lett. B707(2012)506–511 addition to those constraints described in Section 1, elec- troweakprecisionfitsfromLEPpreferaHiggswithamass inthewindowdelineatedonthegraphbythetwobluehy- perboloids. Acknowledgements Whatisleftisaverynarrowregionofparameterspace ABandMBthankRoyalSocietyforpartialfinancialsupport.AB withm around125GeVand700GeV<R−1 <1600GeV. alsodoessowiththeNExTInstituteandSEPnet. h