We present a search for Randall-Sundrum (RS) gravitons decaying to diphotons
or dielectrons or dimuons, performed with the CDF II detector and using up to
5.7 fb-1 of integrated luminosity. The respective mass spectra are consistent
with the ones expected by the standard model. For the RS-model parameter
k/M_Pl=0.1, RS-gravitons with mass less than 1111 GeV/c^2 are excluded at 95%
CL.Comment: XIX International Workshop on Deep Inelastic Scattering and related
  subjects -- DIS11, Newport News, VA, USA Apr. 11-15, 2011 [4 pages, 4
  figures

Strologas, John

U., /New Mexico

English

arXiv

We present a search for Randall-Sundrum (RS) gravitons decaying to diphotons or dielectrons or dimuons, performed with the CDF II detector and using up to 5.7 fb{sup -1} of integrated luminosity. The respective mass spectra are consistent with the ones expected by the standard model. For the RS-model parameter k/{bar M}{sub Pl} = 0.1, RS-gravitons with mass less than 1111 GeV/c{sup 2} are excluded at 95% CL

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Search for RS-gravitons at CDFJohn StrologasDepartment of Physics and Astronomy, University of New Mexico,Albuquerque, NM 87131, USAAbstract. We present a search for Randall-Sundrum (RS) gravitons decaying to diphotons ordielectrons or dimuons, performed with the CDF II detector and using up to 5.7 fb−1 of integratedluminosity. The respective mass spectra are consistent with the ones expected by the standard model.For the RS-model parameter k/MPl = 0.1, RS-gravitons with mass less than 1111 GeV/c2 areexcluded at 95% CL.Keywords: Gravitons, dilepton resonances, diphoton resonances, collider physics, Tevatron, CDFPACS: 14.70.Kv, 13.85.Qk, 13.85.Rm, 14.70.-e, 11.25.WxINTRODUCTIONAlthough extremely successful, the standard model (SM) of particles and fields is notsufficient for solving many open physics problems including the source of the darkmatter, the incorporation of gravity, and the hierarchy problem between the weak andPlanck scales. One theory that addresses the hierarchy problem is the Randall-Sundrum(RS) graviton model [1].The RS model solves the hierarchy problem by introducing an extra compact dimen-sion accessible only to gravity. The phenomenology leads to a small number of distinctKaluza-Klein states (spin-2 gravitons) that couple with gravitational-strength to SM par-ticles and can be detected as resonances of pairs of jets, leptons, photons, or W/Z bosons.Given the considerable dijet background in a hadron-collider environment, and the lowleptonic branching fraction of the weak bosons, the prompt dilepton and diphoton fi-nal states offer the greatest sensitivity at the Tevatron. We present here the recent CDFsearches for RS-gravitons decaying to diphotons, dielectrons, or dimuons.SEARCH FOR RS-GRAVITONS DECAYING TO DIPHOTONSFor the 5.4 fb−1 diphoton search [2] a combination of two diphoton (ET > 12,18 GeV)and two single-photon (ET > 50,70 GeV) triggers is used. The two photon candidatesare required to be central and fiducial in the detector, have ET > 15 GeV and excessenergy around a cone of ∆R =√∆φ)2 +(∆η)2 = 0.4 less than 2 GeV.The expected number of RS graviton events, as a function of graviton mass, isestimated using the PYTHIA [3] Monte Carlo (MC) event generator, with CTEQ5L [4]parton distribution functions (PDF), and processed by the GEANT-based [5] CDF IIdetector simulation.The main SM diphoton background to the graviton signal is the γγ production,determined using DIPHOX [6] next-to-leading order (NLO) MC event generator, withFERMILAB-CONF-11-474Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.  )2) (GeV/cγγm(200 400 600Entries/5 GeV-310-210-110110210310-1CDF, 5.4 fbTotal backgroundJets faking photonsγγ→Search for X CDF Run II PreliminaryFIGURE 1. Diphoton mass spectrum from the CDF search for RS-gravitons.acceptance corrected using a PYTHIA SM diphoton sample passing the CDF detectorsimulation, and with the high-mass spectrum extrapolated. A secondary backgroundcomes from jet+γ or dijet events where one or two jets are misidentified as photons(fake-photon background). This background is determined with the construction of aCDF “fake diphoton” sample with looser photon identification requirements, to allowfor jet contamination. Subsequently, the actual CDF diphoton spectrum is fitted to this“fake diphoton” shape along with the MC-estimated SM diphoton spectrum, with bothcomponents varying in the fit.Systematic uncertainties arise from the luminosity determination (6%), the initialand final radiation (4-8%), and the Q2 and PDF uncertainties (20%) in the DIPHOXcalculation.Figure 1 shows the observed diphoton mass spectrum with the total background over-laid. In the region around 200 GeV/c2 there is an excess of events, with a local probabil-ity of such a fluctuation of 1.3%. This is consistent with the 1-sigma spread of minimalprobabilities in the range of 150-650 GeV/c2, as determined with pseudoexperiments.SEARCH FOR RS-GRAVITONS DECAYING TO DILEPTONSCDF completed searches for the RS-gravitons in the dielectron [7] and dimuon [8]channels using 5.7 fb−1 of integrated luminosity. Single-lepton triggers requiring anelectron or muon with transverse momentum pT > 18 GeV/c are used, in addition to atrigger that remains efficient for pT > 70 GeV/c electrons. Offline two electrons (muons)are selected, at least one with energy (pT ) above 20 GeV (GeV/c). The leptons comefrom the same primary vertex and are isolated, i.e., the excess energy in a cone ∆R = 0.4around each lepton is less than 10% of the energy (momentum) of the electron (muon).Cosmic veto and photon-conversion removal are applied; no opposite charge is enforced.Main SM dilepton background to the RS-graviton dilepton signal is the Drell-Yan(DY) process qq̄→ Z/γ∗→ `+`−. Significant background comes from QCD-originatedevents of one real lepton and one "fake" lepton, i.e., jet (track) faking an electron (muon).Minor backgrounds come from diboson (WW , WZ, ZZ, Wγ∗) and tt̄ processses with sub-sequent leptonic decays. The QCD background is determined with CDF data, with theapplication of a probability that a jet (track) fakes an electron (muon) on events with one)2Dielectron Mass (GeV/c100 200 300 400 500 600 700 800 900 1000N of events-210-110110210310410510 DATADrell-YanQCDDibosontt)-1CDF Run II (L=5.7 fb)2Dimuon Mass (GeV/c100 200 300 400 500 600 700 800 900 1000)2N of events / 5 (GeV/c-210-110110210310410510DATADrell-YanQCDDibosontt)-1CDF Run II preliminary (L=5.7 fbFIGURE 2. Dielectron and dimuon mass spectra from the CDF search for RS-gravitons.identified lepton. This probability is a function of the jet’s (track’s) transverse momen-tum and is determined by counting reconstructed electrons and muons in a jet-rich CDFdata, which is characterized by minimal leptonic content. All other backgrounds are es-timated with MC simulations (PYTHIA-generated events using CTEQ5L PDF, processedby the CDF detector simulator) abosolutely normalized to the theoretical next-to-leadingorder cross sections, data luminosity, lepton-ID scale factors and trigger efficiencies.The main sources of systematic uncertainty on the MC-estimated backgrounds arethe theoretical cross sections (an 8% effect on the event yields), the luminosity (6%),the lepton-ID efficiency (2%), the parton distribution functions (2%), and the triggerefficiency (0.5%). The total MC systematic uncertainty on the expected event yield is∼ 10%. The respective QCD-background systematic uncertainty is∼ 50%, which comesfrom the variation in the measurement of the fake probabilities using different jet-richCDF datasets triggered with varied jet-energy thresholds.The dielectron and dimuon mass spectra are consistent with expectation, as can beseen in Figure 2. At the same time, the highest-dielectron-mass event ever observedat the time was detected (Mee = 960 GeV/c2). In this event, the two electrons havetransverse momenta of 482 and 468 GeV/c and are oppositely charged. The event ischaracterized by very low hadronic activity (no jets are reconstructed) and by a lowmissing transverse energy of 17 GeV – separated by 23 degrees in φ from the 468 GeV/celectron – coming most probably from the resolution of the calorimeter. The probabilitythat at least one event is observed with a mass at least that high is 4%. This probabilityis within the 1-sigma range of minimal probabilities observed anywhere in the dileptonspectrum, as determined by pseudoexperiments.COMBINED LIMITSThe measured diphoton and dilepton spectra can be used to set a limit on RS-gravitonproduction [8]. Here we parametrize the RS model using the mass of the lightest RSgraviton (m1) and the dimensionless parameter√8πk/MPl ≡ k/MPl , where k is thecurvature scale of the extra dimension and MPl is the Planck mass. RS-graviton signal)2Graviton Mass (GeV/c200 400 600 800 1000 1200)(pb)µµ/ee/γγ→Br(G×σ -310-210 = 0.01PlMk/0.0250.05 0.07 0.1)-1CDF Run II Preliminary (L=5.7 fbRS model, NLO cross sectionObserved 95% CL upper limitExpected limitσ 1±Expected limit σ 2±Expected limit FIGURE 3. The 95% CL upper limit on the lightest RS-graviton production cross section, shown withtheoretical cross sections for five values of k/MPl .MC events are generated using PYTHIA and values of m1 from 200 to 1100 GeV/c2. Thesignal-MC events are generated and normalized in the same manner as the background-MC events. The leading-order PYTHIA cross section is multiplied by a scale (“K-factor”)to correct for next-to-leading-order effects [9].Figure 3 shows the combined 95% CL cross-section (σ × Br(G → γγ/ee/µµ))upper limit as a function of m1 along with five theoretical cross-section curves fork/MPl = 0.01 to 0.1, a theoretically interesting range that would provide a solutionto the hierarchy problem. The limits are set using a frequentist method that comparesthe background-only with the signal+background hypotheses, taking into account corre-lated background systematic uncertainties across the channels [10]. The intersection ofthe cross-section exclusion limit with the theoretical cross-section curves gives the 95%CL lower limit on m1 for the respective coupling. For k/MPl = 0.1, the m1 lower limit is1111 GeV/c2, if we use proper mass-dependent RS-graviton K-factors, and 1141 GeV/c2assuming a fixed K-factor of 1.54, for comparisons with previous Tevatron results. Form1 > 1 TeV/c2, cross sections greater than 0.6 fb are excluded at the 95% CL. At thetime of release, these results were the most strigent in the world.REFERENCES1. L. Randall and R. Sundrum, Phys. Rev. Lett. 83, 3370 (1999).2. T. Aaltonen et al. (CDF Collaboration), Phys. Rev. D 83, 011102(R) (2011).3. T. Sjöstrand, L. Lönnblad, and S. Mrenna, PYTHIA 6.2, arXiv:hep-ph/0108264.4. H. Lai et al, (CTEQ Collaboration), Eur. Phys. J. C 12, 375 (2000).5. R. Brun, R. Hagelberg, M. Hansrou, and J. Lasalle, CERN report CERN-DD-78-2-REV (1978).6. T. Binoth et al., Eur. Phys. J. C 16, 311 (2000).7. T. Aaltonen et al. (CDF Collaboration), Phys. Rev. Lett. 107, 191806 (2011).8. T. Aaltonen et al. (CDF Collaboration), CDF public note 10479 (2011).9. P. Mathews, V. Ravindran, K. Sridhar, J. High Energy Phys. 10(2005)031, and private communica-tion; M. C. Kumar, P. Mathews, and V. Ravindran, Eur. Phys. J. C 49, 599 (2007).10. T. Junk, Nucl. Instrum. Methods A 434, 435 (1999); A. Read, J. Phys. G 28, 2693 (2002).

Search for RS-gravitons at CDF

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