A brief review of searches for physics beyond the Standard Model with photons
using the CDF detector at the Tevatron is given here. These include searches
for supersymmetry, extra dimensions, excited electrons and W/Z$+\gamma$
production, as well as anomalous photon production. Recent results from CDF Run
II experiment is presented, but some results from Run I are also reviewed.Comment: To appear in the Proceedings of SUSY 2003, held at the University of
  Arizona, Tucson, AZ, 5-10 June 200

Lee, Sung-Won

English

arXiv

A brief review of searches for physics beyond the Standard Model with photons using the CDF detector at the Tevatron is given here. These include searches for supersymmetry, extra dimensions, excited electrons and W/Z+{gamma} production, as well as anomalous photon production. Recent results from CDF Run II experiment are presented, but some results from Run I are also reviewed

Lee, Sungwon

UNT Digital Library

Fermilab FERMILAB-Conf-04/026-E  May 2004May 7, 2004 10:11 WSPC/Trim Size: 9in x 6in for Proceedings slee_susy03NEW PHYSICS SEARCHES WITH PHOTONS IN CDFSUNGWON LEE for the CDF COLLABORATIONDepartment of PhysicsTexas A&M UniversityCollege Station, TX77843, USAE-mail: slee@fnal.govA brief review of searches for physics beyond the Standard Model with photonsusing the CDF detector at the Tevatron is given here. These include searches forsupersymmetry, extra dimensions, excited electrons and W/Z+ production, aswell as anomalous photon production. Recent results from CDF Run II experimentare presented, but some results from Run I are also reviewed.1. IntroductionThere are a large number of important and well-motivated theoreticalmodels which make a strong case for looking for new physics in eventswith a photon in the nal state. These theories include Supersymme-try (SUSY), Extra Dimensions (ED), Grand Unied Theories, Compositemodels, Anomalous couplings and Higgs models. On the experimental sideCDF detected the eeE=T candidate event for which there is an a posterioribackground of rate of 10 6 events expected from the Standard Model (SM)processes 1.Besides the specic theoretical models, searching for new physics withphotons has several advantages. For example, the photon is one of the threeSU(2)U(1) gauge bosons and as such is likely to be a good probe of newinteractions since it couples to any new gauge sector. Final-state photonshave additional distinct detection advantages over W or Z0 bosons sincethey do not decay. Thus they do not suer a sensitivity loss from branch-ing ratios and momentum sharing between the decay products. There arevery few SM backgrounds which produce photons, allowing a fairly cleansignature.Talk presented by S.W. Lee at SUSY 2003: Supersymmetry in the Desert, held at theUniversity of Arizona, Tucson, AZ, June 5-10, 2003. To appear in the Proceedings.1May 7, 2004 10:11 WSPC/Trim Size: 9in x 6in for Proceedings slee_susy032In this article we summarize the current CDF experimental results ofsearches for new physics in nal states containing energetic photons at theTevatron.Chargino Mass (GeV)100 120 140 160 180 200 220 BR  (pb)× σ10-11)-1CDF Run II Preliminary (84 pb95% C.L. limitNeutralino NLSP ScenarioT+Eγγin the /Total SUSY (TeV)Λ50 55 60 65 70 75 80 85Figure 1. The 95% C.L. cross section limits from +E=T analysis, without backgroundsubtraction. Also shown is the total SUSY cross section for the neutralino NLSP as afunction of M~1and .2. Search for Supersymmetry in +E=T EventsAmong various SUSY models, two SUSY breaking mechanisms are inter-esting, which predict photons in the nal state. Supergravity models canproduce events which decay down to the second lightest neutralino via aloop into the lightest neutralino (~01) and a photon, where the ~01 is thelightest supersymmetric particle (LSP). Gauge-Mediated SUSY Breakingmodels (GMSB) with the ~01 decaying into a photon and gravitino can pro-duce a nal state of two photons and large missing transverse energy (E=T ).E=T is often used as a pointer to possible SUSY signals because it indicatesthe escape of a non-interacting SUSY particle from the detector. The LSPsignals are of particular interest as they provide a natural explanation forthe dark matter.CDF has searched for +E=T nal state within GMSB scenario using 84pb 1 of Run II data. Events are selected as having two photon candidateswith ET> 13 GeV in the central. We expect a total of 0:77+0:40 0:21 events withMay 7, 2004 10:11 WSPC/Trim Size: 9in x 6in for Proceedings slee_susy033E=T > 25 GeV and two events pass all requirements in the data. The lowermass limit on the lightest chargino derived from this analysis is M~1>113 GeV at the 95% C.L. lower limit (see Figure 1). Updated analysis isnow underway using 200 pb 1 data and new results are starting to appear.3. Searches for Anomalous  productionCDF has searched for new physics in the Run II diphoton sample. Twoisolated photons, each with ET > 25 GeV, are required in the analysis.The main background comes from jets which fake photons. No evidence fornew physics was found in this sample. CDF has also performed a searchin the diphoton sample for events with an additional lepton (e or ) andestimate the backgrounds to each of these measurements. All data are welldescribed by the SM expectations.4. Searches for Anomalous l productionCDF has performed a model independent search for anomalous productionof events with a high ET photon and a lepton (e or ) in the nal stateusing Run I data 2. Several nal states were dened, based on the presenceof leptons, photons, and E=T . All data sets are consistent with the SMexpectations with a possible exception of l+E=T were 7.6  0.7 events areexpected while 16 events are observed. The CDF experiment continues forsearch the anomalous l production using Run II data for hints of newphysics.5. Searches for Extra DimensionsRecent theories postulate the existence of new space-time dimensions. Suchextra dimensions might be found by studying the emission of the electro-magnetic radiation in Graviton (G) into the EDs, together with single pho-ton or diphoton emitted into the normal dimensions.CDF has searched for direct G production in the G nal state usingRun II data. The analysis required a photon with ET> 47 GeV, E=T > 42GeV, and no jets with ET> 10 GeV in the event. The main backgrounds arefrom cosmic rays and Z ! . Total 19.8  2.3 events are expected fromthe backgrounds, and 18 events are observed. No deviation from the SMexpectation is observed, and the limit is derived as a ratio to the expectedbackground from the irreducible SM process qq ! Z ! . The limit isMay 7, 2004 10:11 WSPC/Trim Size: 9in x 6in for Proceedings slee_susy0342 times the expected Z signal. This is a signicant improvement over theRun I, which obtained a limit 3.1 times the Z signal.Another way to search for the ED is to look for G exchange processesin the diphoton nal state and looking for an excess in the invariant massdistribution. In Run I CDF found no evidence of a signal, and the 95%C.L. lower limit on the eective Plank scale in the ED, MS , were set at989 (853) GeV for the Hewett convention, Hewett = -1 (+1). A search fora Randall-Sundrum graviton in the diphoton decay mode is now underwayusing Run II data and preliminary results are starting to appear.6. Searches for excited electrons with e + e EventsCDF uses 72 pb 1 of Run II data to search for the production of excitedelectrons (e) using the reaction pp! e+ e! e+ e. This is a signature-based search for a central ee nal state with a resonance in the e channel.This analysis required two high pT electrons with an additional photon inthe nal state. CDF observed no candidate events in the data after makingall selections, and set 95% C.L. limit on the production cross section timesBR(e ! e), and on the e mass for various choices of the compositenessscale  in the e model. For Me=, the mass limit is 785 GeV.7. Searches for W/Z+ productionThe associated production of a vector boson and a photon is an ideal testof the triple gauge couplings which are precisely predicted by the SM. Anydeviation from the SM could indicate new physics. Several measurementare preformed by the CDF using 73 pb 1 of Run II data. All availablelepton triggers are used to select W and Z candidates inclusively and theadditional photon is then selected.The cross section for W/Z production are measured for Rl>0.7and ET>7 GeV and the kinematic distributions are compared to the SMprediction. The W cross section is measured to be 18.2  2.9(stat) 2.3(sys)  1.1(lumi) pb compared to the SM expectation of 18.7  1.3(the-ory) pb. The Z cross section is found to be 5.8  1.3(stat)  0.7(sys) 0.3(lumi) pb compared to the theoretical prediction of 5.3  0.4(theory) pb.The results are in excellent agreement with the SM expectations.8. ConclusionSince the photon is a clean and well measured electromagnetic object, newphysics searches with photons are particularly interesting. The CDF ex-May 7, 2004 10:11 WSPC/Trim Size: 9in x 6in for Proceedings slee_susy035periment is taking data actively since 2001 and larger samples are beingcollected for new physics searches based on the photon signature. High lu-minosity data with photons will provide a good opportunity for new physicsdiscoveries, and will give experimental guidance to a better theoretical mod-eling of new physics production with photons in the nal states.References1. CDF Collaboration, Phys. Rev. Lett. 81, 1791 (1998).2. CDF Collaboration, Phys. Rev. Lett. 89, 041802 (2002).

New Physics Searches with Photons in CDF

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