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Searches for Supersymmetry with leptons in the final state

Searches for Supersymmetry with leptons in the final state. Didar Dobur University of Florida. On behalf of the CMS Collaboration. Physics @ LHC, June 2011, Perugia Italy. Lepton production in SUSY. Many ways to produce isolated leptons at the LHC if SUSY exists

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Searches for Supersymmetry with leptons in the final state

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  1. Searches for Supersymmetry with leptons in the final state DidarDobur University of Florida On behalf of the CMS Collaboration Physics @ LHC, June 2011, Perugia Italy

  2. Lepton production in SUSY • Many ways to produce isolated leptons at the LHC if SUSY exists • Direct chargino or neutralino production (small ) • Direct squark production and subsequent decays to charginos and neutralinos • Direct gluino production and subsequent decays to squark, which decay to charginos/neutralinos DidarDobur2/21 Physics @ LHC, Perugia, 2011

  3. Signal characteristics lepton (n) q A (q) mA C mC B p mB p A: LSP [dark matter motivated; MET] B: gluino/squark[large x-sec; jets] C: chargino[leptons] • mB drives the cross section • DmBC drives hadronic activity : is arbitrary • DmCA drives lepton’s pT • MET is large as long as DmBA is large • tau’s can be “naturally” much more prolific than muons and electrons DidarDobur 3/21 Physics @ LHC, Perugia, 2011

  4. SUSY Searches with CMS • All search topologies involve MET • Categorized by number of leptons • All counting experiments at this point • Major SM backgrounds are measured from data! 2011 So far, no excess over expected SM yield is observed ! DidarDobur 4/21 Physics @ LHC, Perugia, 2011

  5. Single Lepton + Jets & MET search Signal Selection: pT(m/e)> 20 GeV , Nlep=1 ,  4 jets, HT > 500 GeV, MET > 250 GeV • Dominant bkg.: ttBar/Wjets • ABCD method • “lepton spectrum” method: Model the pT(ν) using pT(l) • Corrections to account for differences (due to W helicity) taken from theory • Use MET templates measured in multi-jet events to smear pT(l) U.L. on the signal events at 95 C.L. is 4.1 DidarDobur5/21 Physics @ LHC, Perugia, 2011

  6. OSDL: Search strategy Signal Selection: pT(m,e)> 10/20 GeV |mll-mZ | > 20 GeV HT > 300 GeV, y> 8.5 GeV½ • Background prediction: • ttBar (dominant) • ABCD method, (HT, y) • PT(ll) method • OF subtraction (not covered here) • QCD (small) : Tight-to-loose method Good agreement between Data/MC in the control region DidarDobur 6/21 Physics @ LHC, Perugia, 2011

  7. OSDL: bkg prediction ABCD method : HT and y mostly uncorrelated in ttBar ND = NA x NC/NB D: signal region PT(ll) method : • Exploits the fact that landν get the same boost in ttBar/Wjets • Model MET using pT spectrum of di-leptons • Corrections to account for differences • prediction: 2.1 ± 2.1 (stat) ± 0.6 (syst) DidarDobur 7/21 Physics @ LHC, Perugia, 2011

  8. OSDL : results in 34 pb-1 • All three methods give consistent estimation of SM backgrounds • Upper limit on the non-SM event yield in the signal region at 95% CL is 4.0 DidarDobur 8/21 Physics @ LHC, Perugia, 2011

  9. Z + Jets+ MET search with “JZB” Signal Selection: pT(m,e)> 20 GeV |mll-mZ | < 20 GeV > 1 Jet with pT> 30 GeV Dominant bkgds: Z+jets, ttbar Jet-Z-Balance (JZB): signal/background discrimination control region signal region • Use JZB< 0 to predict Z+Jets bkg. in JZB > 0 • eμ pairs to predict ttBar in JZB > 0 DidarDobur 9/21 Physics @ LHC, Perugia, 2011

  10. “JZB”: closure test Predicted and observed JZB distribution in MC in the presence of signal ( x 20) : excess of signal is well above predicted bkg. Predicted and observed JZB distribution in MC , no signal : very good agreement DidarDobur 10/21 Physics @ LHC, Perugia, 2011

  11. “JZB”: results with 34 pb-1 signal region DidarDobur 11/21 Physics @ LHC, Perugia, 2011

  12. “JZB”: results with 191 pb-1 2011 signal region U.L. on the signal yield 6.6 is set with 95% C.L. Bayesian interference & profile likelihood model for uncertainty DidarDobur 12/21 Physics @ LHC, Perugia, 2011

  13. SSDL: Search strategy • ğğ production would give SS:0S = 1:1 • OS squark-squark can give SS di-leptons via multi-leptons • SS squark-squark production -> SS:0S = 2:1 SM background is very small for SSDL Search regions to maximize the sensitivity to different mass splittings • Low pT leptons & lower hadronic activity • Hadronic Triggers • High pT leptons & lower hadronic activity • LeptonicTriggers (ee/ mm / em / et / mt / tt) pT(m , e, t )> 5, 10, 15GeV HT > 300 (350) (2 jets) MET > 30 (50) GeV (ee / mm / em ) pT(e, m) > 20/10 GeV HT > 60 (2 jets) , MET > 80 HT > 200 (2 jets) , MET > 30(20) GeV DidarDobur 13/21 Physics @ LHC, Perugia, 2011

  14. SSDL: bgk. prediction strategy • SS prompt leptons (WW,ZZ,WZ) • small contribution • reasonably well understood take from MC : < 0.1 • charge mis-identification (electrons only) • small contributionderive from data : 0.012 ± 0.006 • Use SS/OS ee events within the Z mass window to estimate the charge mis-id rate : 0.0007 • non-prompt leptons from jets (ttBar/W+jets/QCD) • dominant contributionderive from data (next two slides) DidarDobur 14/21 Physics @ LHC, Perugia, 2011

  15. b-tag-and-probe for ttBar/V+jets • Lepton isolation is the main handle for controlling the prompt+fake • Measure Isolation templates in a bbBar enriched control sample • Fix the normalization of the measured isolation templates with Sideband events • Sideband: events passing all analysis cuts, except for one lepton failing the isolation cut • Prediction :0.52±0.24 (stat) ~50% syst DidarDobur 15/21 Physics @ LHC, Perugia, 2011

  16. Factorization method for QCD • Exploit the fact that some selection cuts are uncorrelated: Isolation of μ1, Isolation of μ2, MET Npred= Npreselected. εIsoμ1.εIsoμ2 .εMET See the poster by: R.Remington • Npreselected: all cuts, except for isolation and MET εIsoμ1μ2= ε2Isoμ1 Prediction: 0.18±0.12 (stat) , ~65% syst uncertainty DidarDobur 16/21 Physics @ LHC, Perugia, 2011

  17. “Tight-to-loose” for fake tau bkg. • The dominant background is due to “fake” taus: “Tight-to-Loose” method • eT/L : probability of loosely identified taus to pass the tight id-cuts • Measure eT/L(pT,h)in multi-jet sample, <eT/L > ≈0.1 • Sideband: all analysis cuts but one or two taus pass the loose id and fail tight-id • Reweight the observed events in the sideband events by efficiencieseT/L(pT,h) Closure test of the method: Prediction : 0.28±0.14 (stat) ~32% systematic uncertainty DidarDobur 17/21 Physics @ LHC, Perugia, 2011

  18. SSDL : results with 35 pb-1 Summary of the predicted SM background and observed events in each search region We set 95 % CL upper limits onevent yields in each search region : 3.1 , 4.3 , 4.4, 3.4 • Bayesian with a flat prior on signal strength • Lognormal pdf for systematic errors DidarDobur 18/21 Physics @ LHC, Perugia, 2011

  19. Signal efficiency parameterization • Acceptance model is defined with respect to stable particles at generator level • Lepton efficiencies: • Isolation corrections: • MET : smear by 7-25% (depending on HT) • HT : smear by 20-30% (depending on HT) DidarDobur 19/21 Physics @ LHC, Perugia, 2011

  20. Summary • CMS performed searches for SUSY in various leptonic final states using integrated luminosities 35- 191 pb-1 • Multiple data-driven techniques to measure SM bkg are developed • No evidence beyond SM expectations found, set limits on new physics event yields • 2011 will be ( the most ?) an exciting year for SUSY searches DidarDobur 20/21 Physics @ LHC, Perugia, 2011

  21. Bibliography Search for new physics with opposite-sign di-leptons at the LHC, CMS PAS SUS-10-007 , Accepted by JHEP Search for new physics with same-sign di-leptons at the LHC, CMS PAS SUS-10-004 , Accepted by JHEP Search for new physics with single-leptons at the LHC, CMS PAS SUS-10-006 Search for new physics with multileptons at the LHC, CMS SUS-10-008 see also: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResults DidarDobur21/21 Physics @ LHC, Perugia, 2011

  22. BackUp

  23. Supersymmetry (SUSY) • Theory introduces a spin-based symmetry between fermions and bossons ; result in each fermion having a bosonic super-partner and vica versa gaugino/Higgsino mixing • Provides solution to the Hierarchy Problem • Allows unification of the gauge couplings at high scales • Defines a new quantum number R-parity=(-1)3(B-L)+2S and if conserved, provides Dark Matter candidate, Lightest SupersymmetricParticle(LSP) • How to search for SUSY signature ? • Difficult without making assumptions, production x-sections and the details of the decay chains depend on the SUSY model • Most popular ones R-parity conserving scenarios -> Missing Transverse Energy(MET) , large squark/gluino masses -> long decay chains, jets, leptons DidarDobur23/21 Physics @ LHC, Perugia, 2011

  24. SS di-leptons: Trigger strategy • Lepton triggers • all un-prescaled lepton and di-lepton triggers not relying on isolation • High-pT leptons (pT1>20/10 GeV) • Can allow for low HT • Trigger efficiency in signal region: 99±1% (T&P) • HT* triggers • High HT (>300 GeV) • low-pT leptons including tau’s • Efficiency in signal region: 94±5% (measured in an unbiased dataset) * HT: scalar sum of the pT of the jets with pT > 30 GeV DidarDobur24/21 Physics @ LHC, Perugia, 2011

  25. Same Sign prompt leptons Double W-strahlung Double-parton scattering Di-boson production Contribution is very small and taken from simulation: ≤ 0.1 event for all search regions DidarDobur25/21 Physics @ LHC, Perugia, 2011

  26. Isolation templates isolation template for muons isolation template for muons • Gray(QCD MC) and red(ttBar) form the closure of the method, black: data • Observe total 24 events in sidebands of ee,mm, emchannels: • Prediction (Signal Region C):0.52±0.24 (stat) ~50% syst DidarDobur26/21 Physics @ LHC, Perugia, 2011

  27. Charge mis-identification • Methodology • Map charge-flip probability e(pT,h) using e-gun MC • Direct SS Zee yield in Z MC: 7.9±0.9 • Expected yield in Z MC using e(pT,h): 4.9±0.1 • <e>data= N(SS Zee)/( OS Zee)= 5/3642=0.0007 Option 1: apply the MC-based e(pT,h) to the observed isolated OS ee/em events (+HT, +MET) Option 2: use<e>datainstead of MC • Both options give self-consistent results: • 50% : stat uncertainty of the data-driven validation DidarDobur27/21 Physics @ LHC, Perugia, 2011

  28. Summary of bkg and observed yields A B C D • Limits: • Bayesian with a flat prior on signal strength • Lognormal pdf for systematic errors • Errors on background rates and signal acceptance are not correlated DidarDobur28/21 Physics @ LHC, Perugia, 2011

  29. Signal acceptance uncertainties DidarDobur1/18 Physics @ LHC, Perugia, 2011

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