1. 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

2. Third generation squarks might be lighter than 1 st, 2 nd 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 Motivation 1/12/20122Monica D'Onofrio, BSM 4 LHC UK b/ ~ ~ /t ~

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 1/12/2012Monica D'Onofrio, BSM 4 LHC UK3

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 p T >20 GeV(e), 10 GeV(  ) Jet p T >130,50,50 GeV MET>130 GeV Δφ min, minimum Δφ between any of 3 leading jets and MET, >0.4 rad MET/m eff >0.25 Define 4-signal regions ◦ 3JA (>=1 b-jet, m eff > 500 GeV) ◦ 3JB (>=1 b-jet, m eff > 700 GeV) ◦ 3JC (>=2 b-jets, m eff > 500 GeV) ◦ 3JD (>=2 b-jets, m eff > 700 GeV) 1/12/2012Monica D'Onofrio, BSM 4 LHC UK5 Trigger-driven selections QCD-multijet background rejection designed to enhance sensitivity in different scenarios: - low/high  M(g-b) - low/high  M(g-LSP) Data-set: 0.83 fb -1 Use Effective Mass as discriminant

6. QCD-multijet background Smear p T 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 Δф min cut). 1/12/2012Monica D'Onofrio, BSM 4 LHC UK6  4-5% of total background depending on SR Validated by checking Meff distributions for SM bkg and data in QCD CR

7. 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: 1/12/2012Monica D'Onofrio, BSM 4 LHC UK7 validated in control regions 1-ele 1-muon Transfer Factor Non-QCD background estimates

8. Results Good agreement between data and SM expectations within uncertainties 1/12/2012Monica D'Onofrio, BSM 4 LHC UK8 3JA 3JB 3JC 3JD Results translated as model independent exclusion limits  in N events and  SR 2-btags

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 1/12/20129Monica D'Onofrio, BSM 4 LHC UK Upper cross section limits also provided in case of simplified models Exclusions in SO10 models in back-up

10. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK10 Event selection Veto on isolated leptons (e,  ) ≥4 jets (M T2 analysis) ≥3 jets (MET analysis)  (jet-MET) cut to reject QCD bkg SR M T2 : H T >650 GeV, M T2 >150 GeV, ≥ 1 b-tags SR MET: H T >350(500) GeV, MET>200(300) GeV, ≥ 1/2 b-tags Searches with b-jets (CMS) Data-set: 1.1 fb -1 Two different analyses based on: (MET,H T ) and (M T2,H T ) One of the two SR of a more general analysis based on M T2 (the other optimized for high gluino/1 st 2 nd generation squarks mass) 2 signal regions, optimized to enhance sensitivity for different  M(gl-LSP)

11. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK11 QCD background extrapolated from pre-tag samples ◦ Validated using an extrapolation method from low  (jet-MET) region (<0.2) For ttbar background ◦ use1-lepton CR and apply transfer factor (MC correction)  0-lepton ◦ Validate in 100<M T2 <150 GeV region For all other backgrounds, use MC estimates M T2 + bjets CR SR Results SM: 10.6 ± 1.9(stat) ± 4.8(stat) Data: 19 events

12. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK12 In addition to standard event selection (>=3 jets with p T >50 GeV, at least 1 btag), consider ◦  N min > 4.0, defined as minimum  (jet-MET) corrected by the resolution ◦ Strongly reduce correlations with MET Search in MET+bjets: QCD Important for data-driven estimate of residual QCD background estimate

13. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK13 ttbar, single top and W+jets: ◦ Use 1-lepton CR to extract MET shape ◦ Template normalized in 150-200 GeV MET range (SB) Z  + (b)jets: ◦ use dilepton CR and remove reco e,  ◦ Correct for efficiency and acceptance Non QCD background 1 btag 2 btags Ex. Tight SR: HT>500 GeV

14. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK14 Good agreement data and SM predictions Results HT > 350 GeV >= 2 btags SM bkg contributions obtained also with a global likelihood fit  simultaneous estimate of different sources

15. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK15 Consider gluino  bb+LSP production for MET+bjets analysis Interpretation of the results Exclude gluino masses up to 800 GeV for LSP masses up to 350 GeV Exclusion in mSUGRA models (tan  10 and 40) in back- up slides

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) At least 2 tops and b-jets expected, or 4 tops or

17. Search in jets+MET+1-lepton Event selection: Exactly one lepton (electron or muon): ◦ Electron: p T >25 GeV, track isolation ◦ Muon : p T >20 GeV, track isolation 4 Jets with p T >50 GeV MET > 80 GeV At least 1 b-jet 1/12/2012Monica D'Onofrio, BSM 4 LHC UK17 Trigger-driven selections Signal region: m T >100 GeV and m eff >600 GeV Main background: top production, W+jets QCD background almost negligible (see back-up)

18. Non-QCD background ttbar and single top estimated using a semi-data-driven estimation Define m T vs m eff plane ◦ Obtain Transfer Factor (T) in control region (CR) defined by 40 GeV 600 GeV (CR1). 1/12/2012Monica D'Onofrio, BSM 4 LHC UK18 Good agreement between data and MC in CR1 and other CRs SR (used as cross checks)

19. Results 1/12/2012Monica D'Onofrio, BSM 4 LHC UK19 Good agreement between data and MC within uncertainties Model independent upper cross section limits: Exp: 31 fb Obs: 46 fb

20. Interpretation of the results Two phenomenological interpretations depending on mass hierarchy and stop decay mode 1/12/201220Monica D'Onofrio, BSM 4 LHC UK 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.

21. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK21 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 Same-sign leptons search Event Selection: 3 baseline selections 1. 2-inclusive: ee, e ,  p T (e/  )>10/5 GeV, H T >200 GeV 2. 2-high p T : ee, e ,  p T (lead l)>20 GeV, H T >80 GeV  -dilepton:  e ,  p T (  )>15 GeV, H T >350 GeV, MET>80 GeV 4 Final SRs selection based on MET, H T cuts 1.2.3.

22. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK22 SM processes: ttbar+W, WZ, ZZ, W-strahlung, W  …  from MC Fake leptons (e,  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/ , methods labeled as A1,A2, B). ◦ Similar for taus (rate of e and  misidentified as taus negligible) Lepton Charge misreconstruction  rate measured in Z-dominated data samples, mostly from electrons (~10 -3 ) and taus (~7%) Background estimates Fake rate   jet (10% to 40% of the total background depending on SR)

23. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK23 Good agreement between data and SM prediction in ◦ baseline ◦ Signal regions Results Inclusive and  High p T dileptons SS prompt  SM MC predictions OS prompt  charge misidentification

24. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK24 Results interpreted in several simplified scenarios. For third generation: Interpretation of the results

25. Sbottom direct pair production ArXiv:1112.3832 ATLAS

26. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK26 Use exclusive selection for baseline analysis: ◦ p T (1 st jet) > 130 GeV, p T (2 nd jet) > 50 GeV; p T (3 rd jet) < 50 GeV;  Inclusive selection considered as cross check Additional selections: ◦ (E T Miss - jet 1,2 )>0.4 ;  (E T Miss - jet 3 )>0.2 (30 < p T < 50 GeV) ◦ E T Miss /(p T jet1 + p T jet2 + E T Miss )>0.25 Leading jets b-tagged Boost corrected contransverse mass (m CT ) 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 m CT selections to increase sensitivity across the sbottom-neutralino mass plane: m CT > 100, 150, 200 GeV SR Event selection To reject QCD- multijet background () 1/2 G. Polesello and D. Tovey, JHEP 03, 030 (2010) D. Tovey, JHEP 04, 034 (2008)

27. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK27 Composition changes with varying m CT : ◦ top dominating for m CT >100 GeV ◦ W+hf and Z(  )+hf dominating at m CT >150 GeV and > 200 GeV ◦ QCD estimated with Jet Smearing Method (<5%) Semi-data driven estimate for top & W+hf background using 1-lepton CR Background estimate (I) D Estimate as function of m ct cut

28. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK28 Define a 2-lep CR with E T Miss corrected for leptons p T ◦ Exactly 2, OS leptons (e/ μ, p T > 25/20 GeV) ◦ Lepton-corrected E T Miss > 50 GeV ◦ At least 2 jets (p T > 80, 50 GeV); 2 b-jets (== leading jets) Predicted yield in SR is MC TF × 2l-CR yield for 81 < M(ll) < 101 GeV Background estimate (II) Contamination of top background in 2L-CR (~ 50% ) estimate using M(ll) sidebands

29. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK29 Good agreement between data and SM expectations. Results presented for all SR and before m CT selection Results

30. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK30 Exclude sbottom masses below 390 GeV for neutralino masses up to 60 GeV, with maximum reach in neutralino mass ~ 130 GeV Interpretation of the results Exclusion limit on sbottom masses increase to 405 GeV if nominal NLO cross section is used

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

32. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK32 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 What we know so far … …covered by direct sbottom search

33. .. A long way to go 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 General MSSM GMSB..or if sneutrino LSP..and more complex 1/12/201233Monica D'Onofrio, BSM 4 LHC UK

34. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK34 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 Conclusions Stay tuned !! …

35. Back-up

36. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK36 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%) Systematic uncertainties (ATLAS)

37. Results (ATLAS 0-lepton) 1/12/2012Monica D'Onofrio, BSM 4 LHC UK37

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. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK38 DR3 (  0 2 for HS) Theoretical BR

39. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK39 Consider mSUGRA with tan  = 10 and 40 B-jet enriched selection relevant for high m 0 region Interpretation of the results (II) M T2 MET+bjets Best expected sensitivity given by the tight >=1 bjet SR

40. 1/12/2012Monica D'Onofrio, BSM 4 LHC UK40 Max Chertok (LBL wrkshop)

41. Monica D'Onofrio, BSM 4 LHC UK41 Results SS dilepton (baseline) inclusive High pT Tau dileptons 1/12/2012

42. Monica D'Onofrio, BSM 4 LHC UK42 Inclusive High p T Tau-region Results (II)

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). 1/12/2012Monica D'Onofrio, BSM 4 LHC UK43 m T distributions for QCD control region