Multidimensional theories at TeV energies, as given in the brane world scenarios with large or compact extra spatial dimensions (ED), are discussed. One interesting feature of recent ED models is the rich low-energy phenomenology that originates from the Kaluza-Klein spectrum of various particles propagating in ED. A series of searches is addressed in the CMS experiment with different signatures

Antoniadis

Appelquist

Arkani-Hamed

Randall

Sergei Shmatov

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Search for Extra Dimensions with the CMS Detector

Shmatov, Sergei

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Available on CMS information server CMS CR 2007/032CMS Conference ReportJuly 3, 2007Search for Extra Dimensions with the CMSDetectorSergei ShmatovJoint Institute for Nuclear Research, Dubna, Russiaon behalf of the CMS collaborationAbstractMultidimensional theories at TeV energies, as given in the brane world scenarios with large or compactextra spatial dimensions (ED), are discussed. One interesting feature of recent ED models is therich low-energy phenomenology that originates from the Kaluza-Klein spectrum of various particlespropagating in ED. A series of searches is addressed in the CMS experiment with different signatures.Presented at Hadron Collider Physics Symposium,La Biodola, Isola d’Elba, Italy, 20-26 May 20071 IntroductionExtra dimension (ED) models have a rich low-energy phenomenology that originates from the Kaluza-Klein (KK)spectrum of various particles propagating in ED. In what follows we consider the ADD [1], RS1 [2], TeV−1 [3],and UED [4] models and discuss various experimental signals and the discovery potential of the CMS experiment.2 ADD ModelThe ADD model [1] gives multiple production of KK modes of the graviton that leads to violations from SMpredictions in the TeV scale region. The characteristic feature of ADD is the existence of light KK-gravitonswhich could be directly produced at colliders (real graviton production) in qq¯ → gG, gq → qG, gg → gGprocesses or observed through virtual KK-graviton exchange.Real gravitons carry away a fraction of the total energy produced in a hard collision, producing nal states withmissing energy accompanied by a mono-jet or photons. In the GADD channels a 5 σ discovery can be made withless than 1 fb−1 of data for scenarios with the fundamental Planck mass, MD in the range of 1-1.5 TeV, and lessthan 10 fb−1 for values of MD in the range of 2-2.5 TeV, largely independent of the number of extra dimensions[5]. These estimates are conservative taking into account only the events for which the graviton mass is smallerthan MD and should be considered as lower bound.Virtual gravitons interfere with the SM diagrams, as like lepton pair production or photon pair production, andproduce signicant modication to these spectra. These signatures are clear, very sensitive to new physics andcould signal the existence of extra dimensions. The reachable values of the fundamental Planck mass, MD, with5 σ for various number of extra dimensions were estimated in [6]. The uncertainties related to misalignment andtrigger systematic effects, PDFs, QCD-scale errors, EW and QCD corrections were taken into account. It showsthat even the rst LHC run with an integrated luminosity of 1 fb−1 allows exploration of the new ADD modelscale region between 3.9 and 5.5 TeV uncovered so far by other colliders. An increase of the collected luminosityup to 100 fb−1 makes it possible to probe low-scale gravity with MD in the range 5.7-8.3 TeV.3 Randall-Sundrum ModelThe distinctive feature of Randall-Sundrum (RS1) approach [2] is that the excited massive graviton states (RS1graviton). These resonance states are strongly coupled to ordinary particles and can signicantly contribute to theSM processes above the fundamental scale. Thus, the characteristic experimental signature for these processes isa pair of high-pT leptons, gammas or jets coming from the same vertex. The Figures 1 shows the LHC discoverypotential for Randall-Sundrum graviton in the both dilepton channels (dilectron and dimuon) for the different valueof integrated luminosities [7, 8]. These results were obtained with full simulation and reconstruction analyseswhich took into account systematic uncertainties. The mass region 0.8-2.3 TeV can be explored at LHC with1 fb−1 in the dimuon channel for c = 0.01-0.1. The model parameter c is dened as the ratio k/MPl, where kis the curvature of the anti-de-Sitter space, MPl is the 4-D Planck scale. For higher statistics, 10 fb−1, a RS1graviton can be observed with a 5 σ limit up to the mass values of 1.2-3.1 TeV and 1.35-3.3 TeV in the dimuon anddielectron channel, respectively. The overall 5 σ limit for diphoton channel with a 30 fb−1 integrated luminosityis 1.61 TeV for low coupling c = 0.01, and 3.95 TeV for high coupling c= 0.1 [9].Once a new resonance has been discovered, its properties have to be determined, in order to establish its identity.A characteristic feature of the graviton is its spin-2 nature. Other particles usually considered which give a similarsignature are spin-1 Z0 extra gauge bosons or Kaluza-Klein excitations of a Z boson. Angular disributions of thedecay products in the center of mass frame provide a measurement of the spin of the resonance. For an integratedluminosity of Lint = 100 fb−1, the spin-1 and spin-2 hypotheses can be discriminated at 2 σ level for gravitondecay into a muon pair with mass up to 1.1 TeV for c = 0.01 and 2.5 TeV for c = 0.1 [9].4 TeV−1 Extra Dimension ModelThe gravitons are not the only particles possibly sensitive to extra dimensions. For example, gauge bosons couldpropagate in TeV−1-sized extra dimensions [3]. The phenomenological consequence of this scenario is the appear-ance of the KK tower of states of gauge boson elds. The LHC will provide sufciently high energy in the centreof mass to search for the direct production of new heavy resonances. The main discovery channel is the decay ofa heavy particle into electrons and muons pairs (ZKK decays), which presents a clear resonance signature over awell controlled Drell-Yan background.2Figure 1: Theoretical and CMS constraints on the RS1 scenario parameter in the k = MPl and m1 = mG planefor dielectrons (left) [7] and dimuons (right) [8].For Kaluza-Klein excitations of Z decaying into an electron-positron pair, a 5 σ discovery limit is achieved forcompactication scales up to MD = 4.97 TeV for an integrated luminosity of 10 fb−1, MD = 5.53 TeV for 30fb−1 and MD = 5.88 TeV for 60 fb−1.5 Universal Extra DimensionsThe Universal Extra Dimensions model (UED) [4] is a multidimensional eld theory in which all the StandardModel (SM) elds, fermions as well as bosons, propagate in the bulk, so that each SM particle has its innite towerof Kaluza-Klein (KK) partners. In particular, the minimal UED (mUED) assumes that the elds can propagate ina single extra dimension. In this case the 1st KK states must be pair produced. The lightest massive KK particle(LKP) is the KK photon and it is stable. The experimental signatures for KK modes production at hadron collidersare the missing energy carried away by the LKPs in addition to soft leptons radiated in the cascade decay process.In Figure 2, the required integrated luminosity for a 5 σ (reference value and value including systematics) is shown.A discovery of mUED physics with R−1 = 300 and 500 GeV will be possible with a luminosity below 1 fb−1,which corresponds roughly to three months LHC running at L = 1033 cm−2 s−1. The highest signicance levelsare achieved for the channels with muons because the trigger and reconstruction efciencies are larger than forelectrons, specially for low transverse momentum. For R−1 = 300 GeV the lepton spectrum is quite soft and the 4channel is the most effective. Above R−1 600 GeV the 2e2µ channel becomes the most sensitive because its crosssection is two times larger than for the 4µ channel and it is not signicantly affected by the trigger inefciency forlow momentum electrons.Figure 2: Discovery potential of UED signals in 4l channel. The dotted lines show the inuence of experimentaluncertainties and the background cross-section uncertainty [10].3References[1] N. Arkani-Hamed, S. Dimopoulos, and G. Dvali, Phys. Lett. B429 263 (1998); Phys. Rev. D59, 086004(1999). I. Antoniadis et al., Phys. Lett. B436, 257 (1998).[2] L. Randall and R. Sundrum, Phys. Rev. Lett. 83, 3370 (1999). Phys. Rev. Lett. 83, 4690 (1999).[3] I.Antoniadis, Phys. Lett. B377, 246 (1990). I. Antoniadis and K. Benakli, Phys. Lett. B326, 69 (1994);I.Antoniadis, K. Benakli, and M. Quiros, Phys. Lett. B331, 313 (1994).[4] T.Appelquist, H.-Ch. Cheng, and B. A. Dobrescu, Phys. Rev. D64, 035002 (2001).[5] J. Weng et al., CMS NOTE 2006/129.[6] I. Belotelov et al., CMS NOTE 2006/076.[7] B. Clerbaux et al., CMS NOTE 2006/083.[8] I. Belotelov et al., CMS NOTE 2006/104.[9] M.-C. Lemaire, V. Litvin, H. Newman, CMS NOTE 2006/051.[10] M. Kazana, CMS CR 2006/062.4

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