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Experimental Status of SUSY Searches Henning Flaecher University of Rochester

Experimental Status of SUSY Searches Henning Flaecher University of Rochester with University of Bristol from Oct. 1 st SUSY Strategy Workshop – Imperial College. Overview. ATLAS and CMS have established their New Physics searches with missing energy

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Experimental Status of SUSY Searches Henning Flaecher University of Rochester

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  1. Experimental Status of SUSY Searches Henning Flaecher University of Rochester with University of Bristol from Oct. 1st SUSY StrategyWorkshop– Imperial College Imperial College London

  2. Overview • ATLAS and CMS have established their New Physics searches with missing energy • mostly presented in context of Supersymmetry • “2nd round” of results presented at this years summer conferences • EPS, LP, SUSY11 • All results discussed today are based on ~1fb-1 • >3 timesas much data on tape by now • In this talk: • SUSY missing energy searches • Jets + missing energy • Jets + missing energy + 1 lepton • Jets + missing energy + 2 OS/SS leptons • Jets + missing energy + photons Imperial College London

  3. There’s more… • Unfortunately no time to cover many analyses, e.g., • analyses with b-tags • analyses with taus • search with >=6 jets • search with >=3 leptons • Additional info can be found at: • ATLAS • https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults • CMS • https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS Imperial College London

  4. SUSY Searches: Overview • Search so far focused on heavy pair-produced particles that decay to SM particles and LSP • strong production of squarks and gluinos •  large cross-section • heavy squarks and gluinos •  possibility of long decay chains • direct decay of squarks or gluinos to quarks (jets) + LSP • cascade decays via charginos resulting in leptons • R-parity conservation: LSP •  missing energy • Signature: high-pT jets, leptons and missing energy • Focus on simple signatures/topologies • common to many models Imperial College London

  5. Search Strategy • 2 lepton (same sign) • A natural SUSY signature • Very small Standard Model backgrounds • Include all three generations of leptons and all cross channels • Multi-lepton • Very clean events, very low SM background • Include all three generations of leptons and all combinations • Search inclusively, on the Z peak, with and without MET • Photons • Many gauge-mediated models predict photons in final state • Di-photon searches dominated by QCD multijet and γ+jet backgrounds • 0 lepton • Very challenging due to large amount and wide range of backgrounds • However most sensitive search for strongly produced SUSY • pursue complementary strategies based on kinematics and detector understanding • 1 lepton • Lepton (electron or muon) requirement reduces background considerably • Only ttbar and W+jets left ➔ topological handles • 2 lepton (opposite sign) • Adding a second lepton (electron or muon) reduced W background • Several techniques including opposite-sign opposite-flavour subtraction • Shape information and mass edges From A. Tapper, CERN LPCC seminar

  6. Unfortunately, no signs of new physics so far… • This is why we’re here • Focus on complementary methods • Point out some maybe no so well known “peculiarities” of the event selections Imperial College London

  7. Jets + missing energy • ATLAS • Selection on jet pT and ETmiss • split by jet multiplicity • Meff = HT + ETmiss as discriminating variable • CMS • “inclusive” HT & MHT search • Complementary approaches, using kinematic variables • αT, MT2, “razor” • Different selections/variables result in different SM backgrounds Imperial College London

  8. ATLAS: Jets + MET Imperial College London

  9. “Classic” MHT search Imperial College London

  10. Classic HT & MHT • Search regions in HT & MHT • Baseline (HT>350 & MHT > 200) • loose event selection used for validation • Medium (HT>500 & MHT > 350) • generic high multiplicity and missing momentum search • High HT (HT>800 & MHT > 200) • long cascades, high particle multiplicity • High MHT (HT>800 & MHT > 500) • generic search for weakly interacting neutralparticle, good background rejection SUS-11-004 Imperial College London

  11. CMS: αT inspired by L. Randall & D. Tucker-Smith, Phys.Rev. Lett. 101 (2008) 221803 jet jet LSP LSP jet jet Requires >=2 jets with pT > 50 GeV and |η|<3.0 Leading two jets required to have pT > 100 GeV • Kinematic variable αT • Exploits QCD di-jet properties • jets are balanced in pT • back-to-back in φ • Define: HT = ΣpT(ji), MHT = |-ΣpT(ji)|, ΔHT=ET(pj1)-ET(pj2) aT for n jets: aT for dijets: (form two pseudo-jets – defined by balance in “pseudo-jet” HT = SET) Expectation for QCD: αT = 0.5 Jet mis-measurements: αT < 0.5 αT>0.55 implies MHT/HT > 40% Veto on forward jets (|η|>3.0) to “protect” MHT measurement 11 Imperial College London

  12. CMS: αT SUS-11-003 arXiv:1109.2352 • Uses muon and photon control samples in same kinematic region • HT distribution described over 3 orders of magnitude • αT > 0.55 • Background precision ~5% in low HT bins “Hadronic” signal sample Imperial College London

  13. Limits on CMSSM • Similar sensitivity of ATLAS and CMS searches and complementary approaches • CMSSM: 4 parameter model assuming common gaugino and scalar masses at GUT scale (m1/2, m0) Imperial College London

  14. Other searches: MT2 • MT2 is a generalization of transverse mass to a system with two semi-invisibly decaying particles • Two selections: • heavy sparticles large msq, small mgl Trigger! Imperial College London

  15. Other searches: MT2 • High MT2 Low MT2 SUS-11-005 Imperial College London

  16. Leptonic Searches • Isolated lepton requirement reduces background considerably • strong suppression of QCD • mainly W’s and tt left • Analyses typically require • leptons (el,mu) with pT>20-25 GeV • additional (>=3) jets with pT >40 GeV + ETmiss • Different discriminating variables • Missing Transverse Energy: MET • Lepton projection variable & ST= pTlep + MET • Effective Mass: HT + MHT • HT and MET • HT and y=ETmiss/√HT Imperial College London

  17. CMS 1-lepton search: 2 Methods • 1) Lepton Spectrum Method • >= 4 central jets • exploit similarity of charged lepton pT and neutrino pT (=ETmiss) spectra in W decays • correct for efficiency, acceptance and polarisation • smear lepton pT using QCD templates (ETmiss resolution) • Etmiss from LSP’s extends to much higher values • Selection: • HT>500 GeV • MHT>250 (loose) • MHT >350 (tight) SUS-11-015 Imperial College London

  18. CMS 1-lepton search: 2 Methods • 2) Lepton Projection Method • Exploit difference in correlations between lepton and ETmiss in SM (W, tt) and SUSY events • Lepton-projection variable: • Define signal and control regions and use MC to extrapolate SUS-11-015 Muons Electrons Imperial College London Signal region requires ST>250GeV and HT>500GeV

  19. ATLAS 1-lepton search • 1 lepton + 3 or 4 jets • 4 signal regions with different selections on MT, ETmiss and Meff • Low MT and ETmiss control regions for W and tt background • b-tag for tops Imperial College London

  20. CMS OS dileptons • Selection of 2 isolated leptons • strong change in SM background composition • strong QCD suppression as well as W’s • main background: tt • Analyses inside & outside Z window • Require two central, isolated opposite sign leptons • pT> 20 & 10 GeV • >= two jets with pT > 30 GeV • requirements on HT and MHT • HT > 300 and MET > 275 GeV • HT > 600 and MET > 200 GeV Imperial College London

  21. ATLAS OS dilepton • 2 opposite sign leptons • Electron pT > 20 (25 if leading) GeV • MuonpT > 10 (20 if leading) GeV • 3 signal regions: • 1) ETmiss > 250 GeV • 2) ETmiss > 220 GeV, 3 jets withpT > 80,40,40 GeV • 3) ETmiss > 100 GeV, 4 jets with pT >100,70,70,70 GeV • tt and Z background from control regions • fake leptons from “matrix method” • WW,WZ,ZZ from MC Imperial College London

  22. SS dileptons • Basically no significant SM process • apart from “fake” leptons • Natural SUSY signature through charginos in gluino cascade decays Imperial College London

  23. ATLAS SS dilepton • 2 same sign dileptons with missing energy • Electron pT > 20 (25 if leading) GeV • MuonpT > 10 (20 if leading) GeV • two search regions: • ETmiss > 100 GeV • ETmiss >80 GeV, 2 jets with pT > 50 GeV • Charge misidentification from Z events • Fake lepton with matrix method using “tight” and “loose” selection Imperial College London

  24. CMS SS dilepton search • require two isolated same sign dileptons • >= two jets with pT > 40 GeV • search in different HT & ETmissregions • Main backgrounds from fakes, various data driven methods using “tight”-”loose” selections on the leptons SUS-11-010 Imperial College London

  25. CMS CMSSM Summary Similar for ATLAS Imperial College London

  26. Alternative Interpretation: Simplified Models • Working with theorists in context of LPCC • Models proposed at: http://www.lhcnewphysics.org • Agreed on reference topologies for early searches • Cover what one might see in the early running phase, all initiated by strong production • So far considered • pair produced squarks, where each squark decays to quark (jet) and LSP • gluino decoupled at high scale • pair produced gluinos, where each gluino decays directly to two light quarks (jets) and LSP • squarks decoupled at high scale • Study 2D parameter space in msq (mgl) and mLSP • Set limits on production cross section Imperial College London

  27. Variable mass splittings! efficiency maps • αT: Example: Assume only light stop with mass splitting such that decay to top forbidden and stop->c chi0 dominant. Reference cross sections are for degenerate L/R first two generations => need to divide by 8 => currently no exclusion cross-section limit Imperial College London

  28. Models with leptons: SS and OS • Same-sign dilepton Opposite sign dilepton Remember: exclusion assumes BF of 1! Imperial College London

  29. ALTAS Simplified Models 3 different mass splittings Imperial College London

  30. Simplified Model Summary Similar for ATLAS Remember: exclusion assumes BF of 1! Imperial College London

  31. MET Searches with Photons • Neutralino NLSP in General Gauge Mediation • decay to photon + gravitino Imperial College London

  32. MET Searches involving Photons Imperial College London

  33. Photon (+lepton) + MET • Photon + Jets • MET > 200 GeV • 7 events observed, 7.4 +-2.6 stat +-1.5syst expected from SM • Photon + Lepton • MET > 110 GeV • 2 events compared to 3.3+-0.8 expected SM Imperial College London

  34. Diphoton + (jets) + MET • ATLAS diphoton • CMS diphoton + >=1 jet SM Imperial College London

  35. Summary • Searches categorized by topology • Some things to think about: • hadronic searches • leading jet pT cuts • forward jet vetoes • should we worry about these (ISR)? • dominated by 2-4 jet events • what about high jet multiplicities? • leptonic searches • pT threshold ~20 GeV • lowered to ~10GeV in case of second lepton • typically require jets (>=2) with a few 100 HT • for OS dileptons: analyses inside & outside Z window • multileptons (>=3)? • searches with photons • requirement of hadronic activity? • More diversification to third generation • b-tags, taus? Imperial College London

  36. BACKUP Imperial College London

  37. αT: CLS Imperial College London

  38. ATLAS Limits Imperial College London

  39. Imperial College London

  40. CMS: αT • αT as “QCD killer” • exploit RαT = N(αT>0.55)/N(αT<0.55) independence of HT • photon+jets control sample for Zνν + jets • muon control sample for W/tt • combined fit to photon, muon and hadronic signal sample mu control sample (possible “signal contamination” considered) Imperial College London

  41. Jets + missing energy • Analysis strategy • Define control regions or control samples for different types of background • W, Z, tt, QCD multijet events • Obtained by reversing a signal region cut, or requiring leptons or photons • defined in a kinematically similar environment to signal region • MC transfer factors used to extrapolate from control region/sample to signal region • takes care of efficiency, acceptance etc. Imperial College London

  42. ATLAS: Jets + missing energy • Example • Zνν + jets: use Zμμ + jets and photon+jets control samples • for photon pT >> mZ, process is kinematically similar • W and tt background: require well reconstructed lepton • use b-tag (veto) to separate W’s from tt • QCD background • reverse cut on min(ΔΦ) between ETmiss and 3 leading jets • select badly measured jets that align with ETmiss QCD tt Imperial College London

  43. ATLAS: control distributions photon +jets Zμμ W+jets Imperial College London

  44. Interpretation in CMSSM • Single lepton analyses of CMS and ATLAS Imperial College London

  45. CMS OS dilepton search • 2 methods for background estimation • 1) Lepton Spectrum method • use the observed pT(ll) distribution to model the pT(vv) distribution, which is identified with ETmiss • 2) “Matrix method” • two uncorrelated variables, each with signal and control region, HT and y=ETmiss/√HT SUS-11-011 Imperial College London

  46. CMS SS dilepton • Data yields compared with different background estimation metods SUS-11-011 inclusive dilepton high-pTdilepton tau dilepton Imperial College London

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