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Physics with Photons and Missing Energy at ATLAS

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. ATLAS MET-Based Analyses.

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Physics with Photons and Missing Energy at ATLAS

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  1. 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

  2. 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)

  3. 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

  4. Gauge Mediation Hidden gauge sector breaks SUSY via weakly-coupled messenger interactions LSP is light (< 1 GeV) gravitino NLSP is typically Bino-like neutralino 01, which decays with ~75% BF to photon-gravitino  Two photons + missing transverse energy (MET) is effective signature.

  5. Production Mechanisms • Strong production: • gluino/gluino or squark/squark • dominates when colored sparticles are accessible • Weak production: • 1 20 or 1 1 • dominates when only EW-charged particles are accessible • In both cases, decay proceeds through NLSP 10 •  Little additional activity in limit that produced state is degenerate with NLSP.

  6. Tevatron (2 TeV) Analyses • Based on “minimal” SPS8 model designed for ‘Snowmass’-type comparitive studies • Essentially one single phenomenological parameter, often cast as MBino • Strong partner mass tied to 10 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

  7. General Gauge Mediation (GGM) • 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 10 masses:

  8. Thanks to Shih/Ruderman, ArXiv 0911.4130 Production cross-section (7TeV) Bino - like Neutralino: |M1| <<  and |M1| < |M2|; M of Neultralino NLSP ~ M1, Neultralino NLSP   + Gravitino (76%) SPS8 Trajectory No visible jet activity when Mg ~ M D0 Limit For Bino-like neutralino, two photons + MET is most promising but lose coverage if hadronic activity is required (jets, HT, etc.)

  9. GGM Reach: Tevatron vs. LHC “Recast” D0 result in terms of GGM; compare to expected LHC reach (Ruderman & Shih, arXiv:1103.6083) 2010 analysis (36 pb-1) breaks significant new ground

  10. 2010 (36 pb-1) Analysis • Avoid inefficiencies with very simple selection: • One photon with Et > 30 GeV • Another photon with Et > 20 GeV • MET > 125 GeV Signal Region MET

  11. Data-Driven Background Estimate • 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

  12. ISO: New Physics! Signal region Nothing there with 36 pb-1, so we set limits…

  13. Observed, Expected Limits ATLAS has better photon reconstruction than CMS (conversions)

  14. 7/25/11: Accepted (pending small revisions)

  15. 2011 (~1 fb-1) Analysis • More selective trigger (2g20) forces higher Pt cuts • Two photons with Et > 25 GeV • MET > 125 GeV still • Estimated backgrounds above MET=125: • QCD 2.3  0.9 • EW 2.4  1.3 • Total 4.8  1.5

  16. Observed in Signal Region vs. Expected Background

  17. 20101 (~1 fb-1) Analysis 2011 30x increase in data sample size  12x improvement in cross-section limit 2010 But:   1/M9 for Mgluino~ 900 GeV!

  18. 2011 Analysis: What Next? • 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

  19. Photon(s) + MET Summary • 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)

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