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SUSY using b- and  - signatures at LHC

SUSY using b- and  - signatures at LHC. Magali Gruwé CERN – Atlas Workshop on b/ t physics at the LHC 30 May – 1 June 2002. Introduction. Quite a few Susy final states with b’s and/or t ’s Good b/ t reconstruction allows full or partial reconstruction of Susy events

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SUSY using b- and  - signatures at LHC

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  1. SUSY using b- and - signatures at LHC Magali Gruwé CERN – Atlas Workshop on b/t physics at the LHC 30 May – 1 June 2002

  2. Introduction • Quite a few Susy final states with b’s and/or t’s • Good b/t reconstruction allows • full or partial reconstruction of Susy events • determination of some sparticle masses • Various cases (various Susy models): • One case will be detailed, as an example: • mSugra models with large tg b (both t and b rec. needed) • Some other cases will be briefly described: • need either t or b reconstruction • methods and ideas rather similar • expected results outlined • Some cases not shown here... • Some cases not even studied yet... • Everything presented here: • based on Atlas simulations • of course valid for CMS as well... Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  3. Layout • Reconstruction (outlined) • Some words about t reconstruction and b tagging • Using t and b reconstruction: • In mSugra models with large tg b • Using t reconstruction: • Lepton flavour violation • GMSB with t1 as the NLSP • Using b reconstruction • In mSugra models • h0 b b in cascade decays • g  b…  b l+ l-… • Conclusion Described in detail ~ Only briefly shown ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  4. Reconstruction • t finder: • Concentrate on hadronic t decays • leptonic decays not used because: • origin of lepton not clear • lepton in general carries only a small fraction of the t momentum • Performances (of t finder used for Susy) • Rejection against jets: factor of 15 • Probability for a jet to be correctly tagged as t: 66% • Probability for its charge to be correctly assigned: 92% • When tt: • invariant mass distribution • ~gaussian • peaks at M = 0.66 Mtt • s/M = 0.12 Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  5. Reconstruction • b-tagging: • Efficiency ~ 60% • Lepton identification (e or m): • Efficiency ~ 90% Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  6. Layout • Reconstruction (outlined) • Some words about t reconstruction and b tagging • Using t and b reconstruction: • In mSugra models with large tg b • Using t reconstruction: • Lepton flavour violation • GMSB with t1 as the NLSP • Using b reconstruction • In mSugra models • h0 b b in cascade decays • g  b…  b l+ l-… • Conclusion Described in detail ~ Only briefly shown ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  7. Susy at the LHC • Susy rates dominated by the production of • gg • gq • qq (depending on Susy model) • Lightest Susy particle (c01) is • stable • neutral • escapes the detector • gives missing energy • Classical signature for Susy production: • Excess of final states • with missing energy ( E ) • with 2 hard central jets arising from qq, qg,... ~~ ~~ ~~ ~ ~~ ~~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  8. Sugra models • Reminder: • Minimal Sugra has 4 parameters + a sign: • m0: common scalar mass at GUT scale • m1/2: common gaugino mass at GUT scale • A: common trilinear Higgs sfermion-sfermion coupling at GUT scale • tg b: ratio of the Higgs vacuum expectation values • sgn(m): m being the SUSY conserving Higgsino mass Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  9. Sugra models with large tg b ~ ~ • t is the lightest l • If m1/2 small enough: • c02c01 h, c01 Z not allowed • If m0 small enough: • c02 lR l not allowed • The only allowed 2-body decay is: c02t t t c01 • t decays are dominant: Final states involving t’s must be used! ~ ~ ~ Use benchmark point 6: m0 = 200 GeV m1/2 = 200 GeV A = 0 tg b = 45 sgn(m) = -1 mg = 540 GeV mb1 = 391 GeV mc02 = 152 GeV mc01 = 81 GeV ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  10. Decay chains ~ ~ g b b (55%) c02 b t1t (100%) c01tg b b t t c01 qLc02 q (30%) t1t (100%) c01t q q t t c01 • Significant production of c02 significant production of t pairs from the decay of qL or g • Significant production of b’s (from g) ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  11. Analysis procedure • Select Susy events • Select tt final states • infer information on mt • Conjunction with one b-jet • reconstruct b  get mb • Conjunction with two b-jets • reconstruct g  get mg • Extract other sparticle masses (q, c04) • Constrain underlying model parameters ~ Described here ~ ~ ~ ~ ~ ~ Not shown here Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  12. Selection of events • Select Susy events (reject SM background) • Typical cuts: • ET> 100 GeV •  4 jets with pT> 50 GeV, pT1 > 100 GeV • ST> 0.2 (transverse sphericity) • No m or isolated e with pT > 20 GeV, || < 2.5 • ET > 0.2 Meff with Meff = ET + pT (sum over 4 hardest jets) • Find tt final states • In addition: • at least 2 jets identified as hadronic taus • Meff > 500 GeV Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  13. Pair of t’s ~ ~ ~ Aim: reconstruct c02t tt+ t- c01 Search for 2 t’s decaying hadronically: Reconstruct tt invariant mass In a real experiment: observation is the sum of the two histograms Combinations of two real t‘s Combinations of one real t and one fake t Peak:  infer position of the endpoint arising from c02t tt+ t- c01: Mmax = fn (mc02, mc01, mt) (mt)2 (mc02)2 Mmax =mc02 1 - 1 - (mc02)2 (mt)2 = 59.6 GeV (expected) ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ tt invariant mass Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  14. Pair of t’s Previous plot: all t charge combinations Now: subtracted distribution: t+ t- - t- t- - t+ t+  eliminates background (also from fake t’s because their charges are not correlated) Peak, allowing to reconstruct Mmax = fn (mc02, mc01, mt) ~ ~ ~ Real excess (due to c03 or c04 decays) ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  15. Pair of t’s + tagged b jets • Aim: reconstruct g bb  bbc02 bbttbbt+t-c01 • Other g decays possible... • But concentrate on final states with b quarks as • BR larger (55%) • combinatorial background lower • In addition to previous cuts: • Require two tagged b-jets, each with pT> 25 GeV • Select events with a Mtt within 10 GeV of the peak ~ ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  16. Pair of t’s + one tagged b jet First: reconstruct b bc02 bttbt+t-c01 Form invariant mass of the t pair and b-jet: Mttb Edge expected at Mmax ~ mb1 – mc01 = 310 GeV Edge not sharp because: • 3 particles lost: • 2 neutrinos • 1 c01 • distribution contaminated by decays from c03 and c04 ~ ~ ~ ~ There should be an edge at ~ mb1 – mc01 = 310 GeV ~ ~ ~ ~ ~ ttb invariant mass ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  17. Pair of t’s + 2 tagged b jets Partial reconstruction technique: • Infer momentum of c02 assuming nominal mc01 mc01 pc02 = 1 + pt+t- mt+t- • Combine with momenta of 2 measured b jets • Get: mc02bmc02bb related to mbrelated to mg as b  bc02as g  bb  bbc02 ~ ~ ~ ~ ~ ~ ~ 450 GeV exp. mg = 540 GeV ~ ~ ~ ~ 120 GeV exp. mg-mb = 150 GeV ~ ~ ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  18. Layout • Reconstruction (outlined) • Some words about t reconstruction and b tagging • Using t and b reconstruction: • In mSugra models with large tg b • Using t reconstruction: • Lepton flavour violation • GMSB with t1 as the NLSP • Using b reconstruction • In mSugra models • h0 b b in cascade decays • g  b…  b l+ l-… • Conclusion Described in detail ~ Only briefly shown ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  19. Lepton Flavour Violation • Motivation: nm to nt oscillations • mixing of the two mass eigenstates • requires LFV • Susy can accomodate LFV • For nm/nt mixing, significant mixing needed in m/t sector • Search for direct signals from LFV in Susy sector ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  20. Decays • Use: • an mSugra point • some modifications to get slepton mass matrix (with mixing terms in the m/t sector) • Decays: c02c01 Z 7%  eR e 13%  mRm 13%  t1t 66% g  q ... 100% qL c02 ... 30% • Most copious source of dileptons: • c02 l l , with c02 coming from q decay Use mSugra point: m0 = 100 GeV m1/2 = 300 GeV A = 300 GeV tg b = 10 sgn(m) = +1 with: ML = 236.0 GeV MtL = 235.2 GeV MR = 153.3 GeV MtR = 150.7 GeV m = 360.2 GeV At = 94.9 GeV ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  21. Effects of Lepton Flavour Violation • Main effect of LFV: • add a component of mL in t1 • decays c02t1m t1 m c01 are allowed • add m+ t- /m- t+ and m+ m- signals • asymmetry between m+t-/m-t+ and e+t-/e-t+ final states ~ ~ ~ BR( c02 c01 mt ) through t1 ~ ~ ~ ~ ~ ~ ~ ~ ~ BR( c02 c01 mm ) through t1 mixing parameter Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  22. Counting events l+ t-/l- t+ Again: • cuts to remove SM bkgd • selection of events with • a hadronic t • an isolated lepton in final state • reconstruct lt invariant mass Count events around expected signal (between 50 and 100 GeV): • For 10 fb-1: N(e+t-/e-t+) = 501 N(m-t+/m+t-) = 977 N(m-t+/m+t-) - N(e+t-/e-t+) = 476 ± 39 = 12.2% excess Could get limit on BR(c02 c01 mt) l+ t+/l- t- m+ t-/m- t+ LFV with BR = 10% SM: l+ t-/l- t+/l+ t+/l- t- ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  23. Layout • Reconstruction (outlined) • Some words about t reconstruction and b tagging • Using t and b reconstruction: • In mSugra models with large tg b • Using t reconstruction: • Lepton flavour violation • GMSB with t1 as the NLSP • Using b reconstruction • In mSugra models • h0 b b in cascade decays • g  b…  b l+ l-… • Conclusion Described in detail ~ Only briefly shown ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  24. GMSB • Reminder: • Parameters of the minimal GMSB models: • L = Fm / Mm : effective Susy breaking scale (30 TeV) • Mm : messenger scale (250 TeV) • N5 : parametrization of the SU(5) messenger fields (3) • tg b : ratio of the Higgs vacuum expectation values (12) • sgn(m) : m being the Higgsino mass term (+) • Cgrav : gravitino mass scaling factor (1) Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  25. Hard Soft but detectable (~ 10 GeV) Due to limited phase space in the decay: this t is very soft and undetectable Missing energy Very hard t ~ GMSB with t1 as the NLSP ~ • For large tg b,t1 becomes the NLSP (tg b = 12, here) • Decay chain: q c01,2q l-l+ t1l-(t) tG • Very clear same flavour opposite charge dilepton signal with a hard t ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  26. Analysis procedure • Selection: • Again cuts to remove SM background • Require same flavour opposite charge dilepton • One hard hadronic t (pT > 75 GeV) • Slepton reconstruction • Select lt combinations either with • soft lepton (pT< 15 GeV): lepton from l decay • hard lepton (pT> 15 GeV): lepton from c01 decay • Get invariant mass of lt system • Neutralino reconstruction • Get invariant mass of ll system (one hard and one soft leptons) • Squark reconstruction • Get invariant mass of llj system ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  27. tl system Invariant mass of tl system: with soft lepton: with hard lepton: Mmax = (mlR)2 – (mt1 + mt)2 = 29.0 GeV Mmax = (mc01)2 –(mlR)2 = 51.7 GeV ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  28. ll system Invariant mass of ll system: (mlR)2 (mt1+mt)2 Mmax =mc01 1 - 1 - (mc01)2 (mlR)2 = 14.5 GeV (expected) ~ ~ ~ ~ ~ (mlR)2 (mt1+mt)2 Mmax =mc02 1 - 1 - (mc02)2 (mlR)2 = 46.8 GeV (expected) ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  29. llj system ~ ~ ~ ~ Invariant mass of llj system: with Mll < 15 GeV: with 15 GeV < Mll< 46 GeV: (enhances contribution from (enhances contribution from qR c01 q ) qLc02 q ) (mc01)2 (mt1+mt)2 Mmax =mqR 1 - 1 - (mqR)2 (mc01)2 (mc02)2 (mt1+mt)2 Mmax =mqL 1 - 1 - (mqL)2 (mc02)2 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  30. Fit Enough mass relations to solve for 6 unknown masses: Mmax(tl, l soft) = fn (mlR, mt1) Mmax(tl, l hard) = fn (mc01, mlR) Mmax(ll, 1st edge) = fn (mc01, mlR, mt1) Mmax(ll, 2nd edge) = fn (mc02, mlR, mt1) Mmax(llj, Mll< 15 GeV) = fn (mqR, mc01, mt1) Mmax(llj, Mll [15,46] GeV) = fn (mqL, mc02, mt1) ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  31. Layout • Reconstruction (outlined) • Some words about t reconstruction and b tagging • Using t and b reconstruction: • In mSugra models with large tg b • Using t reconstruction: • Lepton flavour violation • GMSB with t1 as the NLSP • Using b reconstruction • In mSugra models • h0 b b in cascade decays • g  b…  b l+ l-… • Conclusion Described in detail ~ Only briefly shown ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  32. h  bb in cascade decays • Decay chain qLc02 q (~30%) h c01(70 to 90%) b b (80 to 90%) • Analysis procedure: • Get clean sample of h  bb • Reconstruction of h  bb decay • Get mh • Partial reconstruction of qL c02 q  h c01 q • Get invariant mass of jbb system • sensitive to mqL • Get pT distribution of 2nd hardest jet • sensitive to mqL or mqR Use benchmark points 1, 2 and 5 ~ ~ ~ ~ ~ ~ ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  33. Reconstruction of h  bb decays • Expected events: • About 20% of Susy events contain h  bb • About 90% of these contain only 1 h boson, with <pT>~ 200 GeV • Selection: • Remove SM background: • ET> 300 GeV • Require 2 tagged b-jets with pT> 50 GeV • Enhance signal purity (for more detailed studies on the structure of the Susy signal events) • No additional b-jet with pT> 50 GeV • DRbb = (Dh)2 + (Dq)2< 2 • Lepton veto • 2 additional jets with pT> 100 GeV • One of them at least within |h|< 2.0 Enough for clear h  bb signal over bkgd Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  34. SM bkgd + Susy bkgd + Signal SM bkgd + Susy bkgd SM bkgd Pair of b’s Invariant mass of bb system: • Select events with Mbb within  25 GeV of peak: • SM bkgd < 10% of signal • Susy bkgd < 20% of signal • Fit of peak: Dmh ~ 1 GeV Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  35. ~ ~ ~ ~ Rec. of qL c02 q  c01 h q  c01b b q ~ ~ ~ ~ ~ Combination giving minimal Mjjb mc02 = 325 GeV ~ Reconstruct jbb in final state: pT distribution of the bb pair:Mjjb invariant mass: sensitive to qL and c02 massessensitive to qL, c01 and c02 masses Both combinations (2 entries per event) mc02 = 425 GeV ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  36. Observability of the h  bb channel Observability 5s-contours of h  bb from Susy cascade: For: tg b = 2 sgn(m) = + A0 = 0 Areas for S/B > 5 Contours of expected # of signal events ~ ~ BR(c02 h c01) = 0.5 (opening of the channel) Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  37. Layout • Reconstruction (outlined) • Some words about t reconstruction and b tagging • Using t and b reconstruction: • In mSugra models with large tg b • Using t reconstruction: • Lepton flavour violation • GMSB with t1 as the NLSP • Using b reconstruction • In mSugra models • h0 b b in cascade decays • g  b…  b l+ l-… • Conclusion Described in detail ~ Only briefly shown ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  38. Multi-lepton / multi-b channels mc02bb – mc02b • mSugra models in which • q heavier than g • g  b b predominantly • Topology: q g b bL b c1 q c01 ln c02 b c01 l+ l- • Analysis: • Selection, get invariant masses, partial reconstruction, etc... Get masses of sparticles ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ mg – mb ~ ~ ~ mg ~ mc02b Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

  39. Conclusions • Many Susy models predict topologies containing b’s and/or t’s in the final state • These are used in many ways: • for selection of signal events • as starting point of analysis chain in cascades • to reconstruct sparticle masses • to constrain Susy models • More possibilities than the ones presented here: • for example: • g  t t, b b  t b… • tau polarization studies ~ ~ ~ Workshop on b/t physics at the LHC – 30 May 2002 Magali Gruwé CERN - Atlas

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