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Exploring Supersymmetry with Final-State Photons at ATLAS

Delve into the search for supersymmetric particles with photon signatures at ATLAS, focusing on SUSY breaking, GMSB, AMSB, and GGM scenarios, with detailed insights into photon signatures and production mechanisms.

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Exploring 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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