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Exploring Physics with Photons and Missing Energy at ATLAS: Models, Analyses, and Production Mechanisms

Discover the physics of photons and missing energy in the ATLAS experiment, featuring analyses like Monojets, Zero-Lepton, and Multi-Lepton. Explore models such as mSUGRA and Generic GMSB to understand production mechanisms like strong and weak production. Learn about the 2010 data sample, Tevatron analyses, and General Gauge Mediation. Find out about the 2011 analysis plans and improvements, including different channels like Photon + (b)jet + MET and Non-pointing photons. Stay updated on SCIPP's role in SUSY analysis and ongoing research endeavors.

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Exploring Physics with Photons and Missing Energy at ATLAS: Models, Analyses, and Production Mechanisms

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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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