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Searches for 3 rd generation squarks : status and prospects

Searches for 3 rd generation squarks : status and prospects. Monica D’Onofrio University of Liverpool BSM 4 LHC UK @ IPPP, 12 th Jan 2011, Durham. Motivation. Third generation squarks might be lighter than 1 st , 2 nd generation

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Searches for 3 rd generation squarks : status and prospects

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  1. Searches for 3rd generation squarks: status and prospects Monica D’Onofrio University of Liverpool BSM 4 LHC UK @ IPPP, 12th Jan 2011, Durham

  2. Motivation • Third generation squarks might be lighter than 1st, 2nd generation • Favored by many theorists because of naturalness arguments • Gluino masses could be ~ TeV scale: • Sbottom and stop production via gluino-mediated or direct pair processes • Possibly large cross sections • Phenomenology depends on SUSY mass hierarchy ~ /t b/ ~ ~ /t b/ Monica D'Onofrio, BSM 4 LHC UK

  3. Outline • Gluino-mediated searches for sbottom: • Searches in 0-lepton final states with b-jets (ATLAS/CMS) • Gluino-mediated searches for stop: • Search in 1-lepton final states with b-jets (ATLAS) • Search in 2 SS lepton final states (CMS) • Direct sbottom pair production searches (ATLAS) • Prospects: further updates and stop pair production searches Monica D'Onofrio, BSM 4 LHC UK

  4. Gluino-mediated sbottom production ATLAS: PLB Volume 701, Issue 4, July 2011, p.398-416 (35 pb-1) ATLAS-CONF-2011-098 (2011) CMS: JHEP 1107:113, 2011 (35 pb-1) CMS-PAS-SUS-11-006 (2011) At least 4 b-jets expected (+MET)

  5. Search in b-jets+MET (ATLAS) Event selection: • Lepton-veto with pT>20 GeV(e), 10 GeV(m) • Jet pT>130,50,50 GeV • MET>130 GeV • Δφmin , minimum Δφ between any of 3 leading jets and MET, >0.4 rad • MET/meff>0.25 • Define 4-signal regions • 3JA (>=1 b-jet, meff> 500 GeV) • 3JB (>=1 b-jet, meff> 700 GeV) • 3JC (>=2 b-jets, meff> 500 GeV) • 3JD (>=2 b-jets, meff> 700 GeV) Data-set: 0.83 fb-1 Use Effective Mass as discriminant Trigger-driven selections QCD-multijet background rejection designed to enhance sensitivity in different scenarios: - low/high DM(g-b) - low/high DM(g-LSP) Monica D'Onofrio, BSM 4 LHC UK

  6. QCD-multijet background • Smear pT of jets in data events with no MET to create sample of pseudo-events with large fake MET (Jet Smearing Method) • Normalize pseudo-events to data in QCD-enriched control-region (reversal of Δфmin cut). Validated by checking Meff distributions for SM bkg and data in QCD CR  4-5% of total background depending on SR Monica D'Onofrio, BSM 4 LHC UK

  7. Non-QCD background estimates • Dominated by top pair production • MC-driven estimate: • ttbar, single top: use MC@NLO+HERWIG • W,Z+jets (light/HF): ALPGEN+HERWIG • 1-lepton control region: validated in control regions Transfer Factor 1-ele 1-muon Monica D'Onofrio, BSM 4 LHC UK

  8. Results • Good agreement between data and SM expectations within uncertainties SR 2-btags • Results translated as model • independent exclusion limits •  in N events and s 3JA 3JB 3JC 3JD Monica D'Onofrio, BSM 4 LHC UK

  9. Interpretation of the results • Two phenomenological interpretations • Gluino-sbottom decays on-shell or off-shell, sbottom in b+LSP in both cases • m(gl)>720(660) GeV excluded depending on gluino – sbottom - neutralino mass hierarchy Upper cross section limits also provided in case of simplified models Exclusions in SO10 models in back-up Monica D'Onofrio, BSM 4 LHC UK

  10. Searches with b-jets (CMS) Event selection • Veto on isolated leptons (e,m) • ≥4 jets (MT2 analysis) • ≥3 jets (MET analysis) • Df(jet-MET) cut to reject QCD bkg • SR MT2: HT>650 GeV, MT2>150 GeV, ≥ 1 b-tags • SR MET: HT>350(500) GeV, MET>200(300) GeV, ≥ 1/2 b-tags Data-set: 1.1 fb-1 Two different analyses based on: (MET,HT) and (MT2,HT) One of the two SR of a more general analysis based on MT2 (the other optimized for high gluino/1st 2nd generation squarks mass) 2 signal regions, optimized to enhance sensitivity for different DM(gl-LSP) Monica D'Onofrio, BSM 4 LHC UK

  11. MT2 + bjets • QCD background extrapolated from pre-tag samples • Validated using an extrapolation method from low Df (jet-MET) region (<0.2) • For ttbar background • use1-lepton CR and apply transfer factor (MC correction)  0-lepton • Validate in 100<MT2<150 GeV region • For all other backgrounds, use MC estimates Results SM: 10.6 ± 1.9(stat) ± 4.8(stat) Data: 19 events Monica D'Onofrio, BSM 4 LHC UK CR SR

  12. Search in MET+bjets: QCD • In addition to standard event selection (>=3 jets with pT>50 GeV, at least 1 btag), consider • DfNmin > 4.0, defined as minimum Df (jet-MET) corrected by the resolution • Strongly reduce correlations with MET Important for data-driven estimate of residual QCD background estimate Monica D'Onofrio, BSM 4 LHC UK

  13. Non QCD background • ttbar, single top and W+jets: • Use 1-lepton CR to extract MET shape • Template normalized in 150-200 GeV MET range (SB) • Z nn+ (b)jets: • use dilepton CR and remove recoe,m • Correct for efficiency and acceptance 2 btags 1 btag Ex. Tight SR: HT>500 GeV Monica D'Onofrio, BSM 4 LHC UK

  14. Results • Good agreement data and SM predictions HT > 350 GeV >= 2 btags SM bkg contributions obtained also with a global likelihood fit  simultaneous estimate of different sources Monica D'Onofrio, BSM 4 LHC UK

  15. Interpretation of the results • Consider gluino bb+LSP production for MET+bjets analysis Exclude gluino masses up to 800 GeV for LSP masses up to 350 GeV Exclusion in mSUGRA models (tan b 10 and 40) in back-up slides Monica D'Onofrio, BSM 4 LHC UK

  16. Gluino-mediated stop production ATLAS: PLB Volume 701, Issue 4, July 2011, p.398-416 (35 pb-1) ATLAS-CONF-2011-130 (2011) CMS: reinterpretation of results in CMS-PAS-SUS-11-010 (2011) or At least 2 tops and b-jets expected, or 4 tops

  17. Search in jets+MET+1-lepton Event selection: • Exactly one lepton (electron or muon): • Electron: pT>25 GeV, track isolation • Muon : pT>20 GeV, track isolation • 4 Jets with pT>50 GeV • MET > 80 GeV • At least 1 b-jet Trigger-driven selections Signal region: mT>100 GeV and meff>600 GeV Main background: top production, W+jets QCD background almost negligible (see back-up) Monica D'Onofrio, BSM 4 LHC UK

  18. Non-QCD background • ttbar and single top estimated using a semi-data-driven estimation • Define mTvsmeff plane • Obtain Transfer Factor (T) in control region (CR) defined by 40 GeV < mT< 100 GeV and meff> 600 GeV (CR1). SR (used as cross checks) Good agreement between data and MC in CR1 and other CRs Monica D'Onofrio, BSM 4 LHC UK

  19. Results Good agreement between data and MC within uncertainties Model independent upper cross section limits: Exp: 31 fb Obs: 46 fb Monica D'Onofrio, BSM 4 LHC UK

  20. Interpretation of the results • Two phenomenological interpretations depending on mass hierarchy and stop decay mode gluino-stop plane: m(~g)>m(~t1). Lightest neutralino mass  60 GeV, m(chargino) ~ 2 * m(neut) gluino masses below 520 GeV is excluded @ 95% CL. gluino masses below 570 GeV (and up to LSP mass 40 GeV) excluded @ 95% CL. Monica D'Onofrio, BSM 4 LHC UK

  21. Same-sign leptons search • Gluino pair production with subsequent stop-top decay and stopt+LSP leads to a signature with 4 tops + Missing Energy • Same-sign dilepton (+MET) final states • Advantage: low SM background Event Selection: 3 baseline selections 2-inclusive: ee, em, mm pT(e/m)>10/5 GeV, HT>200 GeV 2-high pT: ee, em, mm pT(lead l)>20 GeV, HT>80 GeV t-dilepton: tt, et, mtpT(t)>15 GeV, HT>350 GeV, MET>80 GeV 4 Final SRs selection based on MET, HT cuts 1. 2. 3. Monica D'Onofrio, BSM 4 LHC UK

  22. Background estimates • SM processes: ttbar+W, WZ, ZZ, W-strahlung, Wg …  from MC • Fake leptons (e,m,t misidentified by jets)  data-driven procedures based on ‘tight-to-loose’ methods: • Loosen identification criteria on leptons (mostly isolation requirements) • Estimate ‘fake’ rate in multijet samples • Estimate background contributions from data sample with one well identified lepton (tight) and one ‘loose’ lepton (for e/m, methods labeled as A1,A2, B). • Similar for taus (rate of e and mmisidentified as taus negligible) • Lepton Charge misreconstruction rate measured in Z-dominated data samples, mostly from electrons (~10-3) and taus (~7%) (10% to 40% of the total background depending on SR) Fake rate t jet Monica D'Onofrio, BSM 4 LHC UK

  23. Results • Good agreement between data and SM prediction in • baseline • Signal regions Inclusive and t High pTdileptons Monica D'Onofrio, BSM 4 LHC UK SS prompt  SM MC predictions OS prompt  charge misidentification

  24. Interpretation of the results • Results interpreted in several simplified scenarios. For third generation: Monica D'Onofrio, BSM 4 LHC UK

  25. Sbottom direct pair production ATLAS ArXiv:1112.3832

  26. Event selection • Use exclusive selection for baseline analysis: • pT(1st jet) > 130 GeV, pT(2nd jet) > 50 GeV; pT (3rd jet) < 50 GeV; • Inclusive selection considered as cross check • Additional selections: • Df(ETMiss- jet1,2)>0.4 ; Df(ETMiss- jet3)>0.2 (30 < pT< 50 GeV) • ETMiss/(pTjet1 + pTjet2 + ETMiss)>0.25 • Leading jets b-tagged • Boost corrected contransverse mass (mCT) of the two b-jets used to further discriminate sbottom pair production from SM background. • Contransverse mass: • Boost-corrected version to account for boosts in the transverse plane due to ISR and hence protects expected endpoint • Offers hard reduction of top background (kinematic endpoint ~ 138 GeV) Retain 3 mCT selections to increase sensitivity across the sbottom-neutralino mass plane: mCT> 100, 150, 200 GeV SR To reject QCD-multijet background G. Polesello and D. Tovey, JHEP 03, 030 (2010) D. Tovey, JHEP 04, 034 (2008) ( )1/2 Monica D'Onofrio, BSM 4 LHC UK

  27. Background estimate (I) • Composition changes with varying mCT: • top dominating for mCT>100 GeV • W+hfand Z(nn)+hfdominating at mCT>150 GeV and > 200 GeV • QCD estimated with Jet Smearing Method (<5%) • Semi-data driven estimate for top & W+hfbackground using 1-lepton CR D Estimate as function of mct cut Monica D'Onofrio, BSM 4 LHC UK

  28. Background estimate (II) • Define a 2-lep CR with ETMiss corrected for leptons pT • Exactly 2, OS leptons (e/μ, pT > 25/20 GeV) • Lepton-corrected ETMiss > 50 GeV • At least 2 jets (pT > 80, 50 GeV); 2 b-jets (== leading jets) • Predicted yield in SR is MC TF × 2l-CR yield for 81 < M(ll) < 101 GeV Contamination of top background in 2L-CR (~ 50% ) estimate using M(ll) sidebands Monica D'Onofrio, BSM 4 LHC UK

  29. Results • Good agreement between data and SM expectations. Results presented for all SR and before mCTselection Monica D'Onofrio, BSM 4 LHC UK

  30. Interpretation of the results Exclude sbottom masses below 390 GeVfor neutralino masses up to 60 GeV, with maximum reach in neutralino mass ~ 130 GeV Exclusion limit on sbottom masses increase to 405 GeV if nominal NLO cross section is used Monica D'Onofrio, BSM 4 LHC UK

  31. Before concluding … STOP ! (one of) the ‘hot’ topic of 2012

  32. What we know so far … • Can exclude some important scenarios if gluino masses are accessible • Can reinterpret current results in terms of stop for certain scenarios • F.i. done in arXiV 1110.6926 …covered by direct sbottom search Monica D'Onofrio, BSM 4 LHC UK

  33. .. A long way to go General MSSM • Targeted searches fundamental • Very important to have a focused program ready to cover several scenarios (even mixing different final states)  Unfortunately too early to show results in a public meeting  ..or if sneutrino LSP GMSB ..and more complex Monica D'Onofrio, BSM 4 LHC UK

  34. Conclusions • Extensive searches for sbottom and stop delivered by ATLAS and CMS • No sign for SUSY yet, exclusion limits largely exceed previous ones • Much more to be done especially in the stop sector, • Use at max 2 fb-1 for these searches, 2011 dataset ~ 5fb-1 per exp.! • Many data ready to be analyzed are waiting for us … Stay tuned !! Monica D'Onofrio, BSM 4 LHC UK

  35. Back-up

  36. Systematic uncertainties (ATLAS) • Systematic uncertainties dominated by: • Jet energy scale and resolution • B-tagging (especially for 2-btags case) • Theoretical uncertainties • Top pair cross section, ISR/FSR variation, generator dependence, Parton shower and fragmentation models • W/Z+jets: uncertainties on N jets (√N×24% and HF rescale • SUSY signals: renormalization/factorization scale (20-30%), PDF(10-20%) Monica D'Onofrio, BSM 4 LHC UK

  37. Results (ATLAS 0-lepton) Monica D'Onofrio, BSM 4 LHC UK

  38. Interpretation of the results (II) • Interpretation in GUT based on the gauge group SO(10), D-term splitting model, DR3 and Higgs splitting model, HS (H. Baer, S. Kraml, A. Lessa, S. Sekmen, JHEP 1002 (2010) 055) • In these models, squarks (~10 TeV) much heavier than gluino. • Third generation squarks (~1 TeV), gluino 3-body decay to bb+LSP/NLSP is enhanced. Theoretical BR DR3 (c02 for HS) Monica D'Onofrio, BSM 4 LHC UK

  39. Interpretation of the results (II) • Consider mSUGRA with tanb = 10 and 40 • B-jet enriched selection relevant for high m0 region MT2 MET+bjets Best expected sensitivity given by the tight >=1 bjet SR Monica D'Onofrio, BSM 4 LHC UK

  40. Monica D'Onofrio, BSM 4 LHC UK Max Chertok (LBL wrkshop)

  41. Results SS dilepton (baseline) High pT inclusive Tau dileptons Monica D'Onofrio, BSM 4 LHC UK

  42. Results (II) • Inclusive • High pT • Tau-region Monica D'Onofrio, BSM 4 LHC UK

  43. QCD-multijet background • QCD multi-jet data-driven estimation • So-called Matrix Method : decompose “loose” and “tight” selected leptons into real (EW) and fake (QCD). mT distributions for QCD control region Monica D'Onofrio, BSM 4 LHC UK

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