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Physics with Photons and Missing Energy at ATLAS DOE Site Visit Wednesday July 27, 2011 Bangert *, Damiani, Kim, Kuhl, Litke, Mitrevski, Nielsen, Schumm (convener) In collaboration with Liverpool, DESY, Annecy, Tokyo Tech, La Plata * Ph.D. June 2011
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ATLAS MET-Based Analyses Analyses are signature-based: Monojets * Zero-Lepton One-Lepton Two-Lepton Multi-Lepton Photon(s) * (our focus) Inclusive B Jet(s) * Co-analysis with Exotics group (that’s a different physics group altogether) Red indicates some form of public result available on full 2010 data sample (36 pb -1 )
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Models Used (for inspiration and/or analysis) mSUGRA / Constrained MSSM “24-parameter” MSSM Generic MSSM parameter space (four degenerate light quarks, gluino octet, LSP) Generic GMSB (“GGM”) space (light gluino octet, light Bino NLSP, gravitino) Non-contextual SUSY partners (tau sneutrino, stop+sbottom, hadronizing scolored particles) Largely redundant model spaces Independent; may appear only in photons+MET
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Hidden gauge sector breaks SUSY via weakly- coupled messenger interactions LSP is light (< 1 GeV) gravitino NLSP is typically Bino-like neutralino 0 1, which decays with ~75% BF to photon-gravitino Two photons + missing transverse energy (MET) is effective signature. Gauge Mediation
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Strong production: gluino/gluino or squark/squark dominates when colored sparticles are accessible Weak production: 1 2 0 or 1 1 dominates when only EW-charged particles are accessible In both cases, decay proceeds through NLSP 1 0 Little additional activity in limit that produced state is degenerate with NLSP. Production Mechanisms
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Based on “minimal” SPS8 model designed for ‘Snowmass’-type comparitive studies Essentially one single phenomenological parameter, often cast as M Bino Strong partner mass tied to 1 0 scale, and is high (~ TeV) Luminosity (lower-mass EW states) trumps energy for SPS8 analyses For 6.3 fb -1, D0 finds M > 170 GeV at 95% CL, out of reach of 36 fb -1 2010 ATLAS sample Tevatron (2 TeV) Analyses
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The “minimal” SPS8 model is ad hoc, selected somewhat arbitrarily as a concrete model for which different facilities could be compared In particular, no reason why EW and colored partner scales need be coupled Generalize model so that one strong partner, one EW partner are light, all other partner masses are high (~1.5 TeV) Free parameters are gluino, Bino-like 1 0 masses: General Gauge Mediation (GGM)
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Production cross-section (7TeV) Bino - like Neutralino: |M1| << and |M1| < |M2|; M of Neultralino NLSP ~ M1, Neultralino NLSP + Gravitino (76%) For Bino-like neutralino, two photons + MET is most promising but lose coverage if hadronic activity is required (jets, HT, etc.) No visible jet activity when M g ~ M Thanks to Shih/Ruderman, ArXiv 0911.4130 SPS8 Trajectory D0 Limit
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“Recast” D0 result in terms of GGM; compare to expected LHC reach (Ruderman & Shih, arXiv:1103.6083) GGM Reach: Tevatron vs. LHC 2010 analysis (36 pb -1 ) breaks significant new ground
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Avoid inefficiencies with very simple selection: One photon with E t > 30 GeV Another photon with E t > 20 GeV MET > 125 GeV 2010 (36 pb -1 ) Analysis Signal Region MET
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Two major sources: MET Distribution from QCD Sources Loose photon control sample Z e + e - to model events MET from EW Sources (Ws, ttbar) e control sample from data, MC Scale to contribution with e fake rate from Z ee studies Data-Driven Background Estimate
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Nothing there with 36 pb -1, so we set limits… ISO: New Physics! Signal region
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ATLAS has better photon reconstruction than CMS (conversions) Observed, Expected Limits
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7/25/11: Accepted (pending small revisions)
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More selective trigger (2g20) forces higher P t cuts Two photons with E t > 25 GeV MET > 125 GeV still Estimated backgrounds above MET=125: QCD2.3 0.9 EW2.4 1.3 Total4.8 1.5 2011 (~1 fb -1 ) Analysis
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Observed in Signal Region vs. Expected Background
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20101 (~1 fb -1 ) Analysis 2010 2011 30x increase in data sample size 12x improvement in cross-section limit But: 1/M 9 for M gluino ~ 900 GeV!
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1 fb -1 paper in preparation 3-4 fb -1 (full 2011 run) analysis will follow But, progress with 2 +MET to be incremental Background limited (re-optimization?) Steep mass dependence Explore other channels Photon + (b)jet + MET (Kuhl) Photon + MET (Kim; dedicated trigger) Photon + lepton + MET Non-pointing photons 2011 Analysis: What Next?
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SCIPP playing leadership (and major technical) role in central SUSY analysis One +MET paper in press (36 pb -1 ), one in preparation (1 fb -1 ), a third in planning (3-4 fb -1 ). Beginning to explore/develop complementary single-photon channels Talks by Bangert (Cargese 2010) Mitrevski (West-Cost Forum, SLAC) and Schumm (SUSY Recast, Davis) Photon(s) + MET Summary
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