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Searching for Supersymmetry with Final- State Photons at ATLAS

UC Davis High-Energy Physics Seminar November 6, 2012. Searching for Supersymmetry with Final- State Photons at ATLAS. Bruce A. Schumm Santa Cruz Institute for Particle Physics University of California, Santa Cruz. SUSY States.

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Searching for Supersymmetry with Final- State Photons at ATLAS

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  1. UC Davis High-Energy Physics Seminar November 6, 2012 Searching for Supersymmetry with Final- State Photons at ATLAS Bruce A. Schumm Santa Cruz Institute for Particle Physics University of California, Santa Cruz

  2. SUSY States SUSY posits a complete set of mirror states with SSUSY = |SSM – ½| • Stabilize Higgs mass for GUTs • Can provide reasonable dark-matter candidate • Minimum of two Higgs doublets Searches for SUSY with photons at ATLAS

  3. R Parity To avoid lepton/baryon number violation can require that “SUSYness” is conserved, i.e., preserves a multiplicative “parity” quantum number R such that RSM = +1; RSUSY = -1 If you can’t get rid of SUSYness, then the lightest super-symmetric particle (LSP) must be stable  dark matter, missing energy LSP is typically a “neutralino” (dark matter must be neutral); admixture of , known as “10 ”, whose identity is not that relevant to phenomenology Searches for SUSY with photons at ATLAS

  4. SUSY Breaking But we know that SUSY is broken… SUGRA: Local supersymmetry broken by supergravity interactions Phenomenology: LSP (usually 10) carries missing energy. GMSB: Explicit intermediate-scale “messenger” gauge couplings to some number of “secluded” superfields mediate SUSY breaking. Phenomenology: Gravitino ( ) LSP; NLSP is 10 or . Content of 10 germane. AMSB: Higher-dimensional SUSY breaking communicated to 3+1 dimensions via “Weyl anomaly”. Phenomenology: LSP tends to be , with 1+, 10 nearly degenerate. Searches for SUSY with photons at ATLAS

  5. “Minimal” (Standard) GMSB Phenomenology Minimal GMSB has five parameters: : Scale at which SUSY “kicks in” to cure quadratic divergences Mmess: Scale of new gauge interactions Nmess: Number of fields in secluded sector tan: Ratio of <vev>s of two Higgs doublets sgn(): Sign of SUSY Higgs mass parameter Over most of GMSB parameter space, NLSP is a bino-like neuatralino, i.e., the partner of the U(1) gauge boson Searches for SUSY with photons at ATLAS

  6. Photon Signatures in GMSB If the 10 NLSP is bino-like, then it decays to -gravitino with BF  cos2W. Since SUSY states come in pairs (R-parity) this produces a striking  +  + ETMiss signature • “SPS8 Trajectory” of GMSB • Single free parameter  • tan = 15 • Mmess = 2 • Nmess = 1 •  > 0 • For minimal GMSB (SPS8) • mgluino msquark >> m • “EW production” • Associated leptons, jets Searches for SUSY with photons at ATLAS

  7. Strong vs. Electroweak Production • However: if colored states are decoupled, EW production will dominate • Dedicated EW prod. analyses • Pure-EW simplified models (new!) STRONG COUPLING •  probe high mass scale • steep mass dependence (~M-8) • beam energy vs. luminosity • lower backgrounds; “scale chasing” mGMSB ELECTROWEAK COUPLING s = 7 TeV 5 fb-1 reach EW Strong •  probe intermediate mass scales • higher backgrounds • benefit from high L.dt SUSY Breaking Scale  (TeV) Searches for SUSY with photons at ATLAS

  8. Generalized Gauge Mediation Scenarios • Preserve basic phenomen-ology (gravitino LSP and bino-like NLSP) • Decouple everything else except for one higher-mass state that governs production (total transverse energy scale) • Bino NLSP governs final decay step (ETMiss, ET scales) • For existing analyses, high-mass state is colored (gluino, squark) • Strong production • High mass scale Start w/ minimal GMSB and decouple most states Searches for SUSY with photons at ATLAS

  9. GGM Parameter Space The high-mass (strongly-coupled) state can be either gluino or squark  Set limits in gluino-bino (squark-bino) plane 7 TeV Strong-Production Cross Sections Searches for SUSY with photons at ATLAS

  10. Even-More Generalized Scenarios: Wino NLSP • Further, one can relax assumption that 10 NLSP is bino-like. • What about a wino-Like NLSP? • Degenerate triplet 1, 10 • Final state  + lepton + ETMiss • Both EW and strong production EW Production at Wino (1 10) scale Strong Production at gluino scale Searches for SUSY with photons at ATLAS

  11. And Also: Higgsino-Like NLSP If 10 is pure higgsino, no photons in final state For certain range of admixture with bino,  + bjet + MET is best channel Searches for SUSY with photons at ATLAS

  12. Generic Single-Photon Signature For bino/higgsino state, choice  > 1 suppresses 10  h + gravitino • Signature: • Single photon • ETmiss • Njets • Value of N under study (3?) Searches for SUSY with photons at ATLAS

  13. Prompt vs. Non-Prompt Photons • For all cases, c < 1 mm (photons point back towards origin) • A separate group is look at standard bino-like case for which c is a free parameter (not disfavored by cosmological considerations) • Requires a new photon reconstruction, more background-prone • This is an analysis for which ATLAS is particularly well-suited ( segmentation of first layer of CAL) This analysis is not included in this talk! (but…) Searches for SUSY with photons at ATLAS

  14. Summary of four signatures, and status • Overall status of SUSY searches with photons: • No 2012 (8 TeV) results yet; 7 TeV results as follows: • Diphoton + MET: 35 pb-1, • 35 pb-1, 1 fb-1 published, 5 fb-1 in press • Annecy, Argonne, DESY, La Plata, Tokyo Tech, UCSC • Photon + lepton + MET: • 5 fb-1 conference result • UCSC • Photon + bjet + MET: • 5 fb-1 conference result in preparation • UCSC, Technion • Photon + Njet + MET: • Just getting underway • La Plata, UCSC Searches for SUSY with photons at ATLAS

  15. The ATLAS Detector Non-prompt tracks Photon conversions Searches for SUSY with photons at ATLAS

  16. The 2011 ATLAS Data Set A total of 4.7 fb-1 deemed to be adequate for SUSY analyses Searches for SUSY with photons at ATLAS

  17. 2012 (8 TeV) Data is Accumulating Fast Expect 25-30 fb-1 at 8 TeV for 2012 Searches for SUSY with photons at ATLAS

  18. Diphoton + MET: Strong Production • The basic search: Strong (gluino) production, bino decay • 36 pb-1 Analysis: • Require two stiff, isolated photons (ET1 > 30 GeV, ET2 > 20 GeV) • Then ETmiss > 125 GeV separates signal from the backgrounds Searches for SUSY with photons at ATLAS

  19. Strong-Production “Scale Chasing” • With GGM gluino (squark) mass constrained to be high (> 500 GeV) a two-scale system emerges • Bino mass sets ETmiss scale Mi m = 275 GeV m = 450 GeV Searches for SUSY with photons at ATLAS

  20. Strong-Production “Scale Chasing” • Gluino mass sets total transverse energy scale ~ 1 TeV HT does not include missing energy (wanted to maintain observational independence) Electroweak production mgluino = 1000 GeV Searches for SUSY with photons at ATLAS

  21. (,ETmiss) • Jet   mireconstruction can • Introduce fake photons • Lead to large ETmiss Resulting ETmiss often in direction of  •  (Small) sensitivity improvement from cutting on (,ETmiss) (,ETmiss) > 0.5 Searches for SUSY with photons at ATLAS

  22. Diphoton + MET Singal Regions (A,B, and C) • Strong Production • HT large • High-mass bino  More ETmiss, less HT, larger (,ETmiss) • Low-mass bino  Less ETmiss, more HT, small (,ETmiss) • EW Production • HT small • Moderate ETmiss • Larger (,ETmiss) A B C Searches for SUSY with photons at ATLAS

  23. Diphoton + MET Backgrounds • “QCD” Backgrounds •  (probably not dominant) •  + jet; jet   misreconstruction • Estimate from loose-photon sample scaled to data at low ETmiss • “EW” Backgrounds • W; W  e; e  misreconstruction • tt; t  be; e   misreconstruction • Estimate from e data rate, with e   fake rate also from data • “Irreducible” Backgrounds • W; W  e • Z; Z  • Estimate directly from MC simulation Searches for SUSY with photons at ATLAS

  24. Expected Background and Observed Signal • Analysis nearly background-free in SRs A,B • 2 events in SR C, consistent with background expectation (no HT cut for EW production search) C Searches for SUSY with photons at ATLAS

  25. Estimating QCD Backgrounds • Define two control samples: • QCD: One loose-but-not-tight photon (dominated by EM-like jets) • QCD: One loose, one loose-but-not-tight photon • Normalize to diphoton sample for 0 < ETmiss < 20 GeV Normalization region 5 fb-1 control samples (no HT cut) Background estimate Searches for SUSY with photons at ATLAS

  26. Estimating Electroweak Backgrounds • Dominated by e   misidentification • ETmiss distribution from data e sample • Scale by measured fake rate from (Ze)/(Zee) 5 fb-1 e sample (no HT cut) Just a reminder! Searches for SUSY with photons at ATLAS

  27. Assembling GGM Cross-section limits Signal Acceptance (%) • For example: SRB, low-mass Bino: • Acceptance ~20% • For background-free analysis, 95% CL is 3 events • 3/0.2  less than 15 events produced, or for 5 fb-1,  < 3 fb Searches for SUSY with photons at ATLAS

  28. Derived GGM Cross-Section Limits And sure enough… Searches for SUSY with photons at ATLAS

  29. GGM Mass Limits 3 fb corresponds to production of ~1100 GeV gluino  scale of limit Choice of signal region (A or B) based on best expected limit (depends only on expectation from data-driven backgrounds and signal MC) Searches for SUSY with photons at ATLAS

  30. Gluino-bino and Squark-bino Mass Limits 300 GeV (35%) limit increase from 1 fb-1  5 fb-1 (New signal regions, plus greater rejection of e fakes) Squark limits somewhat lower (lower cross-section) Searches for SUSY with photons at ATLAS

  31. SPS8 Limits and Electroweak Production • SPS8: Similar efficiency but higher background:  < 5 fb-1 • NNLSP/NLSP scale 550/300 GeV • Hard to glean general sense from constrained model • 2012 analysis will include “EW grid” with Wino NNLSP and bino NLSP • Grid strategy developed with David Shih (Rutgers theory) • Optimization underway; will likely include to SRs (C,D) for high/low mass bino Searches for SUSY with photons at ATLAS

  32. Photon + Lepton + MET Analysis • Single selection geared towards both EW and strong production • Make use of “transverse mass” (similar role to HT) • High ET photon: ET > (100,85) GeV for (e,) channel • Lepton with pT > 25 GeV Searches for SUSY with photons at ATLAS

  33. Photon + Lepton + MET Event Rates Electron Channel • Most backgrounds estimable from MC constrained by independent measurements (W, tt, tt, …). • Misreconstruction (jet,e  ) plays smaller role • 15e, 11 channel events observed • 13e, 15 channel events expected • BFs less favorable • Acceptance smaller (~5%) • Backgrounds higher •  Significantly weaker limits! Muon Channel Searches for SUSY with photons at ATLAS

  34. Lepton +  + MET Signal Region Distributions Muon Channel Electron Channel Electroweak Production Strong Production Searches for SUSY with photons at ATLAS

  35. Lepton +  + MET Mass Limits (Wino NLSP) Mi Electroweak Production Strong Production Searches for SUSY with photons at ATLAS

  36. Wrap-up (Page 1) • Other two analyses still under development… • Photon + bjet + MET: Nearing completion for conference result • Photon + Njet + MET: Still exploring • Plan to have complete slate of analyses for 2012 analysis • Diphoton + MET: Moriond 2013, including EW grid (underway) • Photon + lepton + MET: Moriond 2013; multiple SRs • Photon + bjet + MET: Summer 2013 • Photon + Njet + MET: Summer 2013 Searches for SUSY with photons at ATLAS

  37. Wrap-Up (Page 2) • Naïve Projection for Diphoton + MET (25 fb-1 @ 8 TeV) • 8 TeV / 7 TeV = 1.14  10% improvement in limit? •  ~ M-8 x5 statistical gain  22% gain in limit? • Overall 30% gain in limit (???) would push gluino to ~1500 GeV and squarks to ~1250 GeV (seems a little optimistic?) • But clearly an interesting step forward. • For 14 (13?) TeV running • Include c as third experimental parameter (along with production scale mass and NLSP mass) • ??? Searches for SUSY with photons at ATLAS

  38. Back-Up Searches for SUSY with photons at ATLAS

  39. “ Mi Searches for SUSY with photons at ATLAS

  40. GGM (General GMSB): Diphoton Search • GGM and the Diphoton+ETmiss Analysis • Everything decoupled except • Gluino octet • Bino-like NLSP; B(0  G) ~ 1 •  Require two photons, ETmiss > 125 GeV Observe: 5 events Expect: 4.1  0.6 (syst.) events Mgluino > 805 GeV for 50 < M0 < Mgluino 1 fb-1 Phys Lett. B 710 (2012), 519 Searches for SUSY with photons at ATLAS

  41. Wrap-Up • Vibrant and expanding program of SUSY searches • No discoveries claimed • At 5 fb-1, colored sparticle limits above 1 TeV for some contexts • Non-colored partner limits in 300-400 GeV range • Increased consideration of “simplified” models (especially EW) • Many analyses have yet to update to 5 fb-1 Speculation about 2012 reach (assume 20 fb-1 at s = 8 TeV) • ~10% gain from increased s • colored  M-8 ~10% gain from statistics (background-limited) • Somewhat better for EW production (not on PDF tails) • Ingenuity, “scale-chasing” • Guesstimate: ~25% increase in sensitive range (e.g. 1000 GeV limits increase to 1250 GeV if SUSY doesn’t exist at that scale) Searches for SUSY with photons at ATLAS

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