1 / 33

Searching for Supersymmetry with the ATLAS Detector at the LHC

CIPANP 2012 St. Petersburg, FL May 29 – June 2, 2012. Searching for Supersymmetry with the ATLAS Detector at the LHC. for the ATLAS Collaboration. Bruce A. Schumm Santa Cruz Institute for Particle Physics University of California, Santa Cruz. SUSY States.

kirra
Download Presentation

Searching for Supersymmetry with the ATLAS Detector at the LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CIPANP 2012 St. Petersburg, FL May 29 – June 2, 2012 Searching for Supersymmetry with the ATLAS Detector at the LHC for the ATLAS Collaboration 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 CIPANP 2012: Searches for SUSY with ATLAS

  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 CIPANP 2012: Searches for SUSY with ATLAS

  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. CIPANP 2012: Searches for SUSY with ATLAS

  5. Classes of Models Minimal Models General Models • 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 e.g. General Gauge Mediation (GGM) CIPANP 2012: Searches for SUSY with ATLAS

  6. 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 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) CIPANP 2012: Searches for SUSY with ATLAS

  7. The ATLAS Data Set A total of 4.7 fb-1 deemed to be adequate for SUSY analyses CIPANP 2012: Searches for SUSY with ATLAS

  8. The ATLAS Detector Non-prompt tracks Photon conversions CIPANP 2012: Searches for SUSY with ATLAS

  9. 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” 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 (combinatoric) Heavy Flavor: “Natural” preference for 3rd generation • b jets,  jets CIPANP 2012: Searches for SUSY with ATLAS

  10. Synopsis of ATLAS SUSY Searches • ATLAS public results: 18 signatures analyzed with 1 fb-1 or greater • Interpretation (some signatures have more than one!) • Minimal models: 4 mSUGRA, 1 mGMSB • Simplified: 8 mSUGRA-like, 4 GMSB-like, 1 AMSB-like • Of these, three are EW production • Six R-parity-violating or non-contextual • Generic scalar top exchange (lepton flavor violation) • pMSSM (19-parameter R-parity-conserving SUSY model) • SO(10) GUTS • e- resonance • R hadrons • “BC1” R-parity-violating mSUGRA (no missing energy) Acceptance, efficiency, CLs confidence level for each analysis to be found at https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults CIPANP 2012: Searches for SUSY with ATLAS

  11. Basic signature: No leptons, several jets, ETmiss • LSP (0) undetectable • missing transverse energy ETmiss ATLAS-CONF-2012-033 5 fb-1 • Signature: ETmiss + several jets (0 leptons) • One of several “standard” signatures • Six sub-channels (based on # jets) • For each point in m0, m1/2 plane, choose channel that provides best a-priori sensitivity • In this constrained model, exclude • mgluino < ~850 GeV • msquark < ~1400 GeV CIPANP 2012: Searches for SUSY with ATLAS

  12. Lepton + jets + ETmiss Simplified Model • Same analysis “recast” in terms of a simplified model: • Two generations of squarks • Gluino octet • Massless neutralino (generic) • Everything else decoupled • Colored sparticle limits similar to those of more constrained mSUGRA interpretion : • Mgluino > 940 GeV • Msquark > 1380 GeV 5 fb-1 ATLAS-CONF-2012-033 In this case simplified model captures the generic dynamics of the more constrained model CIPANP 2012: Searches for SUSY with ATLAS

  13. Hot Signature: 0 Lepton + Multijet + ETmiss mSUGRA processes often produce many jets e.g. Exploit with multi-jet analysis (6-9 jets) Jet trigger (no ETmiss) sensitive to low ETmiss 5 fb-1 5 fb-1 ATLAS-CONF-2012-037 mSUGRA: Mgluino < 850 GeV for large m0 Simplified model only Mgluino < 880 GeV for M0 < 100 GeV CIPANP 2012: Searches for SUSY with ATLAS

  14. 1 Lepton + Jets + ETmiss New Additional discriminating variable: lepton-ETmiss transverse mass New “soft-lepton” signal region for cascades with nearly-degenerate steps ATLAS-CONF-2012-041 Backgrounds estimate: Njet distributions of ttbar, W+jets control regions times signal-region transfer functions Fit for allowed signal assuming poisson probability of control-region projections When exploring specific model, use signal meff distribution as additional constraint 5 fb-1 CIPANP 2012: Searches for SUSY with ATLAS

  15. 1 Lepton + Jets + ETmiss “One-step” simplified model: production with soft lepton channel 5 fb-1 Captures region of degeneracy 3/4 jet channels ATLAS-CONF-2012-041 Mgluino > 900 GeV for M0 < 200 GeV mSUGRA/CMSSM: Msquark, Mgluino < 1200 GeV (for Msquark = Mgluino) CIPANP 2012: Searches for SUSY with ATLAS

  16. 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 CIPANP 2012: Searches for SUSY with ATLAS

  17. EW Production See Brokk Toggerson’s talk Saturday!! • Few-hundred GeV gauginos, decoupled colored sparticles “natural”. • Multi-lepton signals • ETmiss from  and 10 • Simplified model, only gauginos and sleptons light • 3-Lepton (e,) + ETmissSearch • Require one opposite-sign, same flavor pair (0  l+l-) • ETmiss> 50 GeV • Observe 127; expect 98  13 • Limits reach 250-300 GeV 2 fb-1 arXiv:1204.5638 CIPANP 2012: Searches for SUSY with ATLAS

  18. In Search Of: Light 3rd Generation See next talk by Katerina Pajchel !! Maximal mixing for 3rd generation: naturally lightest sfermions • Look for leptons, ETmiss, b-tagged jets • Stop generally more difficult than sbottom (softer jets) • Gluino mass limits can be compromised if stop dominates decay chain • Scalar Bottom • Gluino-mediated production • Direct sbottom production 2 fb-1 CIPANP 2012: Searches for SUSY with ATLAS arXiv:1203.6193

  19. Light Stop • Stop-mediated gluino decay • Softer gluino mass limits Mgluino > 750 GeV for lower 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 CIPANP 2012: Searches for SUSY with ATLAS

  20. Disappearing Tracks!!! (+ ETmiss) • AMSB: Chargino/Neutralino naturally quasi-degenerate • Long-lived states • Asymmetric decay • Disappearing tracks • TRT is critical component Exclude 0.2 < + < 90 ns for M+ < 90 GeV Disappearing track  few TRT hits arXiv:1202.4847 5 fb-1 CIPANP 2012: Searches for SUSY with ATLAS

  21. NEW Lepton Flavor Violation in the e Continuum • R-Parity Violating (RPV) SUSY has terms in Lagrangian of form • RPV stop exchange • Search continuum (rather than for resonances) • 1 e, 1 , opposite charge • 0 jets, Meμ > 100 GeV, Δφeμ > 3.0, ETmiss < 25 GeV Observe: 39 events Expected: 44  6 events arXiv:1205.0725 2 fb-1 CIPANP 2012: Searches for SUSY with ATLAS

  22. Stau LSP: 4 Leptons • “BC1” model mSUGRA + RPV while: • Preserving proton stability • Unstable stau LSP • Strong pair production • 4 Lepton Analysis •  4 isolated leptons • Moderate ETmiss > 50 GeV Observed: 0 events Expected: 0.7  0.8 events For most favorable region, gluino mass limits approach 1.8 TeV 2 fb-1 Mstau = 200 GeV Mg = 1400 GeV ATLAS-CONF-2012-035 CIPANP 2012: Searches for SUSY with ATLAS

  23. Compendium of ATLAS SUSY Search Limits https://twiki.cern.ch/twiki/pub/AtlasPublic/CombinedSummaryPlots/AtlasSearches_susy_march12.pdf CIPANP 2012: Searches for SUSY with ATLAS

  24. 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) CIPANP 2012: Searches for SUSY with ATLAS

  25. Back-Up CIPANP 2012: Searches for SUSY with ATLAS

  26. Scalar Bottom Searches: bjets + ETmiss (+ lepton) Maximal mixing for 3rd generation: naturally lightest squark. Direct sbottom Gluino-mediated sbottom • 2 bjets • ETmiss > 130 GeV • jet > 0.4 Then look for kinematic endpoint via “contransverse mass”, defined as ETmiss > 130 GeV 0 LEPTON 1 LEPTON, 1 b jet 2 fb-1 • Sbottom/gluino simplified plane: • Gluon-mediated production • Direct production • In all cases • Mass limits: 400-700 GeV range CIPANP 2012: Searches for SUSY with ATLAS

  27. SUSY with Light(est) Scalar Top: Part I SUSY processes involving stop more challenging (softer jets) • Stop-mediated gluino decay • Lepton + bjet + ETmiss (SR1-D, SR1-E from previous slide) Lepton signs need not be correlated • 2 same-sign leptons, 4 jets, ETmiss > 150 GeV Softer gluino mass limits: Mgluino < 750 GeV for any 0 mass 2 fb-1 2 fb-1 CIPANP 2012: Searches for SUSY with ATLAS

  28. SUSY with Light(est) Stop: Part II Gluon-mediated Stop production production followed by As above: 2 same-sign leptons, 4 jets, ETmiss > 150 GeV; also > (100 GeV)2 Mgluino > 650 GeV; Mstop > Mgluino - Mtop 2 fb-1 • Direct Stop production • GMSB: NLSP decay provides additional handle: • Light higgsino  B(10  ZG) ~ 1 • Two jets, one b-tagged • Reconstructed Z  l+l- • ETmiss > 50 (80) GeV for Signal Region A (B) Stop limits in the ~ 300 GeV range. 2 fb-1 CIPANP 2012: Searches for SUSY with ATLAS

  29. Stau LSP/NLSP Similarly, 3rd generation sleptons are naturally light mGMSB: Multiple messenger fields, high tan  NLSP Strong production  Busy decay chain Mgluino = 1000 GeV • 2 + jets + ETmiss Analysis • Exactly two hadronic  • Two jets; (ET1, ET2) > (130,30) GeV • ETmiss > 130 GeV • Meff > 700 GeV • Efficiency 0.2 – 3%; lowest in non-stau NLSP region of course. • Observed: 3 • Expected: 5.3 +- 1.3 +- 2.2 • Probe strong scales  1000 GeV Tau jets MET 2 fb 2 taus jets MET 2 fb Dilepton jet MET 1 fb 4 leptons + mET 2 fb (BC1) Mgluino = 600 GeV Mgluino = 1000 GeV 2 fb-1 CIPANP 2012: Searches for SUSY with ATLAS

  30. mGMSB • “SPS8” trajectory has single free parameter  • EW production (+0, +-) • Bino NLSP  • Two photons; ETmiss > 125GeV • Observed: 5 events • Expected: 4.1  0.6  1.6 •   > 145 TeV at 95% CL • 145 TeV UL on  implies • M10 > 205 GeV • M1+ > 390 GeV • Mgluino > 1170 GeV • Although gluino scale is artificial… Two photons; ETmiss > 125 GeV 1 fb-1 CIPANP 2012: Searches for SUSY with ATLAS

  31. Late-Breaking: Dilepton Light Stop Search Include if approved!! • Two leptons • At least one jet • ETmiss CIPANP 2012: Searches for SUSY with ATLAS

  32. Simplified Models • Simplified/Pheno Models • focus on small set of parameters • “Pheno” models maintain basic flavor of underlying minimal model • e.g. General Gauge Mediation (GGM) • Bino NLSP from mGMSB • Gluino octet only other light states • All other states decoupled • Yield general constraints on, e.g., gluino mass under assumption of bino/gravitino NLSP/LSP D. Shih, J. Ruderman arXiv:1103.6083 Also, non-contextual (ad-hoc) searches: light stop, generic resonances, etc. CIPANP 2012: Searches for SUSY with ATLAS

  33. Back-Up CIPANP 2012: Searches for SUSY with ATLAS

More Related