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Searching for Supersymmetry with the ATLAS Detector at the LHC

SUSY-After-Higgs Workshhop UC Davis April 22-26, 2013. Searching for Supersymmetry with the ATLAS Detector at the LHC. Bruce A. Schumm Santa Cruz Institute for Particle Physics University of California, Santa Cruz. SUSY States.

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Searching for Supersymmetry with the ATLAS Detector at the LHC

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  1. SUSY-After-Higgs Workshhop UC Davis April 22-26, 2013 Searching for Supersymmetry with the ATLAS Detector at the LHC 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 SUSY-After-Higgs; UC Davis 2013

  3. R Parity To avoid lepton/baryon number violation can require that “SUSYness” is conserved, i.e., preserves an additive “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 SUSY-After-Higgs; UC Davis 2013

  4. SUSY Breaking But we know that SUSY is broken… SUGRA: Local supersymmetry broken by supergravity interactions Phenomenology: LEP (usually 10) carries missing energy. GMSB: Explicit couplings to intermediate-scale (MEW <  < MGUT) “messenger” gauge interactions 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. SUSY-After-Higgs; UC Davis 2013

  5. The 8 TeV (2012) ATLAS Data Set A total of 20.7 fb-1 deemed to be adequate for SUSY analyses SUSY-After-Higgs; UC Davis 2013

  6. The 7 TeV (2011) ATLAS Data Set A total of 4.7 fb-1 deemed to be adequate for SUSY analyses SUSY-After-Higgs; UC Davis 2013

  7. The ATLAS Detector Non-prompt tracks Photon conversions SUSY-After-Higgs; UC Davis 2013

  8. Favorite Discriminating Variables • ETmiss: Transverse momentum imbalance • LSP escapes detection (RP conserving SUSY) meff, HT, etc: Transverse energy scale • Strong production can reach high mass scales • “Scale chasing” mt2, mCT: Generalized (under-constrained) transverse mass • When two copies of intermediate state are produced X: Minimum  separation between ETmiss vector and any object of type X. • LSP produced in intermediate-to-high mass decay • Separation between LSP and decay sibling • Jet backgrounds tend to have small separation Heavy Flavor: “Natural” preference for 3rd generation • b jets,  jets (now also c jets) SUSY-After-Higgs; UC Davis 2013

  9. Back-Up SUSY-After-Higgs; UC Davis 2013

  10. Jets + MET in Minimal (MSUGRA) Paradigm • Very basic signature • Interpreted in fully-constrained model (five fundamental parameters) • Employs “scale chasing” to limit backgrounds (high meff) • Maintains some low meff analyses 6 fb-1 at 8 TeV • Plot shows one of 12 selections (some SRs have loose, medium, tight meff cut) • Observed: 5 events; Expected: 6.3  2.1 • NP < 1.03 fb; typical for model point (best of 12 is Ctight at 0.57 fb) • At each point in MSUGRA parameter space, choose SR with best expected sensitivity… SRD SUSY-After-Higgs; UC Davis 2013

  11. Jets+MET Exclusion in MSUGRA Parameter Space • Set limits in MSUGRA parameter space • To get a handle on scale, re-cast in MSUGRA-constrained generic squark and gluino mass space • Excluded scale at mgluino = msquark is ~ 1500 GeV But many scenarios for which SUSY can still exist below 1500 GeV! mgluino= msquark SUSY-After-Higgs; UC Davis 2013

  12. Looking for the Holes The gaps in coverage arise from many different considerations. How do we identify them?  Reasoning and intuition: 3rd generation NLSP, no light strong partners, ”compressed” scenarios, etc…  Brute force: model-space carpet bombing (e.g. “pMSSM”…) SUSY-After-Higgs; UC Davis 2013

  13. The pMSSM M.W. Cahill-Rowley, J.L. Hewett, A. Ismail, T.G. Rizzo Now an ATLAS associate! SUSY-After-Higgs; UC Davis 2013

  14. Minimal (constrained) vs. General Models Idea #1: Are model-dependent linkages between masses fooling us? • GUT unification: few parameters • mSUGRA/CMSSM • mGMSB • e.g. mSUGRA: • m0: GUT scale common scalar mass • m½: GUT scale common gaugino mass • tan: Ratio of Higgs doublet VEVs • A0: Common trilinear coupling • Sgn(): Higgs mass term “General” Model “Minimal” Model e.g. General Gauge Mediation (GGM) SUSY-After-Higgs; UC Davis 2013

  15. Jets+MET in a Generalized MSUGRA Scenario • Jets+MET interpreted • with simplified model • generic squark • generic gluino • 0 LSP • All other SUSY states decoupled • Standard decay of SUSY particles to accessible states mgluino= msquark • Limits in same range (scenario has at least one accessible strong partner • Again, excluded scale is ~1500 GeV for msquark = mgluino (for light 10) SUSY-After-Higgs; UC Davis 2013

  16. Compressed Scenarios Idea #2: Is visible signature too soft to see or trigger on? • Small mass splittings can lead to signature with little visible energy • Even if ETmiss is large, events can be buried in backgrounds or not even stored on disk • Requires complex triggers (object + ETmiss) and clever analyses • Important weapon: Initial state radiation • ATLAS is perfecting its modeling of ISR • Can look for events for which ISR “stiffen” the visible content of the event • Somewhat “up-and-coming” SUSY-After-Higgs; UC Davis 2013

  17. Compression and the Jets+MET Analysis Removal of meff cut for some SRs geared towards compressed scenarios Inspired by LeCompte, Martin, PRD84 (2011) 015004 SUSY-After-Higgs; UC Davis 2013

  18. 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-10) • beam energy vs. luminosity • lower backgrounds 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) SUSY-After-Higgs; UC Davis 2013

  19. EW Production Searches Next Idea: Are non-colored states the only accessible states? • Many “natural” scenarios have few-hundred GeV gauginos, decoupled colored sparticles (except perhaps 3rd generation; see next section)… • Multi-lepton signals • ETmiss from  and 10 • Simplified model, only gauginos and sleptons light • Large backgrounds to content with (smaller cross section for given mass scale) SUSY-After-Higgs; UC Davis 2013

  20. Multi-lepton + MET EW SUSY Searches • Employ simplified models with bino, wino masses as free parameters; all else decoupled • Can also have light sleptons • Example: • 1+ 20 degenerate wino NLSP, 10 bino LSP • Two cases: only gauginos light, or also with generic left-handed slepton with mass half-way between bino and wino, • Produce 1+1- or 1+20; involves opposite-sign, same-flavor lepton pair SUSY-After-Higgs; UC Davis 2013

  21. 3 Lepton + MET Weak-Production Search • Search for 3 leptons, including one same-flavor, opposite-sign pair • Signal regions consider presence (SRZ) or absence (SRnoZ) of on-shell Z • ETmiss, transverse mass SUSY-After-Higgs; UC Davis 2013

  22. 3 Lepton + MET Analysis Limits ~600 GeV when sleptons are accessible Softer limits without sleptons (vector boson BFs) Still at the ~1/2 TeV scale for now SUSY-After-Higgs; UC Davis 2013

  23. The One that Almost Got Away Exploration of non-excluded pMSSM points revealed that a Heavy chargino scenario not considered! Significant Z-mediated production of 2030 if they contain significant higgsino admixture Accessible right-handed sleptons  4-lepton final state dominant SUSY-After-Higgs; UC Davis 2013

  24. Compressed Scenarios in Weak Production (Anadi Canepa, ATLAS) SUSY-After-Higgs; UC Davis 2013

  25. Higgs in EW SUSY Decay Chains SUSY-After-Higgs; UC Davis 2013

  26. In Search Of: Light 3rd Generation Maximal mixing for 3rd generation: naturally lightest sfermions Naturalness suggests they might well be accessible Low cross-section to single chiral state (e.g. stop-L  1/20 gluino) Challenging signatures with high backgrounds • Look for leptons, ETmiss, b-tagged jets • Make use of kinematic variables (jet,MET, mT2,…) • Stop can be more difficult than sbottom (softer jets) • Gluino mass limits can be compromised if stop dominates decay chain SUSY-After-Higgs; UC Davis 2013

  27. Direct Stop Production • Assume left-handed stop only accessible colored state. Look for decays through • t 10 • b 1+ with 1+  W(*) 10 ; assume some 1+ mass (e.g. 150 GeV) Some lack of coverage in “compressed” zones. Limits around 600 GeV for t10; 500 GeV for b1+ SUSY-After-Higgs; UC Davis 2013

  28. Summary of Light-Stop Results Reach for b1+ analysis very dependent on 1+ mass, but some sensitivity to regions not probed by t10 mass (avoid top in decay chain) SUSY-After-Higgs; UC Davis 2013

  29. Light Stop • Stop-mediated gluino decay • Softer gluino mass limits Mgluino > 750 GeV for any 10 mass • Gluino-mediated stop production • production with • Mgluino > 650 GeV; Mstop > Mgluino- Mtop • Direct search (dilepton) imminent 2 fb-1 arXiv:1203.6193 arXiv:1203.5763 2 fb-1 SUSY-After-Higgs; UC Davis 2013

  30. Back-Up SUSY-After-Higgs; UC Davis 2013

  31. Gluino-Mediated Stop/Sbottom Gluino lower limits soften to ~1300 GeV if decay chain forced to go through sbottom, stop N.B.: No lower limits on stau from direct stau production (look for 1-2 taus plus ETmiss SUSY-After-Higgs; UC Davis 2013

  32. The One that Got Away SUSY-After-Higgs; UC Davis 2013

  33. Final State with Photons Arise from bino-like NLSP GMSB has 10 NLSP over much of parameter space Pure bino NLSP: BR(10  G) = cos2W = 78% Consider both pure bino-NLSP case as well as admixture “Minimal” GMSB Signatures Considered: Pure bino-like NLSP: Diphoton + MET (including non-pointing photons) Higgsino Admixtue: Photon + bjet(s) + MET Pure Wino NLSP (BR(10  G) = sin2W = 22%): Photon + lepton + MET SUSY-After-Higgs; UC Davis 2013

  34. Back-Up SUSY-After-Higgs; UC Davis 2013

  35. Back-Up SUSY-After-Higgs; UC Davis 2013

  36. Back-Up SUSY-After-Higgs; UC Davis 2013

  37. Disappearing Tracks!!! (+ ETmiss) • AMSB: Chargino/Neutralino naturally quasi-degenerate • Long-lived states • Asymmetric decay • Disappearing tracks • TRT is critical component Exclude 0.2 < M+ < 90 ns for M+ < 90 GeV Disappearing track  few TRT hits arXiv:1202.4847 5 fb-1 SUSY-After-Higgs; UC Davis 2013

  38. Back-Up SUSY-After-Higgs; UC Davis 2013

  39. Back-Up Mantis shrimp analysis; compressed SUSY: Koutsman Sbottom production compressed scenario: Suruliz and following two talks; Note use of ISR jet for compressed sceanarios and Mt2, AMt2 variables! Stop with Z + bjets? [Probably not; doesn’t seem to open up new parameter space, esp compressed scenario Mono-X searches? Higgs in EW production scenarios RPV: Disappearing tracks? Non-prompt photons!! [WE NEED TO DO PROMPT-ANALYSIS STUDY] SUSY-After-Higgs; UC Davis 2013

  40. 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) SUSY-After-Higgs; UC Davis 2013

  41. Back-Up SUSY-After-Higgs; UC Davis 2013

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