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Search for B s  μμ and B d  μμ with 2 fb -1 of data

Search for B s  μμ and B d  μμ with 2 fb -1 of data. CDF 8925. blessed on Aug 09. Slava Krutelyov UCSB with D.Glenzinski, H.Held (KIT), C.-J.Lin (FNAL) T.Kamon, M.Weinberger (TAMU) M.Herndon (UWisconsin) SUSY-Group Meeting 08/29/2007. Motivation and history

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Search for B s  μμ and B d  μμ with 2 fb -1 of data

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  1. Search for Bsμμ and Bdμμ with 2 fb-1 of data CDF 8925 blessed on Aug 09 Slava Krutelyov UCSB with D.Glenzinski, H.Held (KIT), C.-J.Lin (FNAL) T.Kamon, M.Weinberger (TAMU) M.Herndon (UWisconsin) SUSY-Group Meeting 08/29/2007 • Motivation and history • Analysis • Setup • Event selection: signal discriminants • muon ID with LH • Neural Net • (optimized) Expectations and results • Effects on SUSY

  2. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  3. b m ~ n l’i23 l i22 m s Motivations: Models • MSSM • With RPV: can proceed at tree level • couplings not constrained much otherwise • In general case has a diagram ~ tan6b/MH4 • tan4b/MH4 come from MSSM is a 2HDM • remaining tan2b is from SUSY (stop L-R mixing) • Just need large tanb, not too-high MH, some stop mixing • SO(10) with Yukawa unification tanb~50 ! • mSUGRA with large tanb • Other BSM: with no extra flavor structure the enhancement < ~ a factor of 2 • With improving limits start asking any theorist “Is it allowed by Bsμμ?” • More in the end of the talk EXCLUDED Bsmm appears to get into the “model exclusion hall of fame” • Near 200 citations (combined for CDF/DØ RunII) in the past ~3 years S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  4. Bits of history • Search for Bsmm is as old as hadron colliders • First looked at by UA1 • Recent limits are all from Tevatron • DØ is often close to CDF Prior S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  5. Bs(d)m+m- Ingredients • Normalize to B+J/y K+ decays • Construct discriminant to select Bs and suppress bgd • MC sim for signal • Data mass sidebands for bgd estimate • Minimize expected 90% C.L. upper limit Signal sample (baseline) Normalization mode Bd Bs N(UU+UX) ~ 3×104 S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  6. Improving sensitivity: muon ID • Dx c2 cut  use muon LH (LH>0.1) • Combined dX, dPhi, dZ, EM, HAD • add dE/dX cut • Z>-0.2 • Suppress combinatorics • ~x2 less events (after preselection) • Bring Bhh below the horizon • Bhh fakes are ~0.05 for Bs and ~0.5 for Bd windows • cf. ~ 0.3 (Bs) and ~2 (Bd) with Dx c2cut S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  7. Normalization mode • B+J/ψK+ + c.c. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  8. l/s μ l pmm pTmm pTm R=1 μ a l pTm Bs a Discriminating variables • Used as inputs to Neural Net S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  9. Preselections: signal+sidebands • Vertex Requirements: • c2(vtx) < 15 • s(L3D) < 150 mm • L3D < 1 cm • 0 < l < 3 mm • (l = proper decay length) • l/s(l) > 2 • pT(B)>4 GeV && |y(B)|<1 • 4669 < M(mm) < 5969 MeV • In addition: • Isolation>0.5 • Pointing angle Da<0.7 Bsmm Search Sample: N(CMU-CMU) = 15594 N(CMU-CMX) = 15072 (completely Bgd dominated) Note: without muon LH & dE/dX ~x2 more backgrounds here S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  10. Signal MC • Use Pythia • BGen for systematics • Reweigh to follow pT distributionfrom data • Compare using B+ data and MC S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  11. NN: inputs • After applying pre-selections use sidebands (bgd) and signal MC to train NN • 6 inputs to NN training • λ – lifetime • λ/σ – lifetime significance • Δα – 3D poining (vtx vs momentum) • Iso • pT(B) • pT(μ) min – lower of the pair S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  12. NN inputs: x-check w data B+ plots • Input variables are well-modeled • including pT(μ) high used in the trial NN S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  13. NN: output • Compared to LH (used previously) get a better (~2 times) rejection at the same efficiency • LH had 3 vars: Iso, P(λ), Δα • 5 var NN: add λ/σ and pT(B) • 7 var NN includes both pT(μ) • introduces mass biasnot used S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  14. NN output: x-check for biases • The correlation is negligible • No evidence of a bias here or in other x-checks • checked w/ control samples, trained on part of sidebands, bootstrap • use of sidebands is justifiable S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  15. NN outputs: x-check w data B+ • Good agreement S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  16. Control Samples • Independent bkg control samples to cross check bkg estimate procedure • OS - : Opposite-sign dimuon sample with ct<0 • SS+ : Same-sign dimuon sample with ct>0 • SS- : Same-sign dimuon sample with ct<0 • FM : Fake muon sample ct>0 • (require at least one muon leg to fail our muon likelihood and dE/dX requirement) S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  17. Control Samples: NN x-checks • NN performance: observation is consistent with expectations • Using a wider ± 150 MeV signal window for cross-check • For obsv<pred, prob= probability for making an observation ≤ obsv S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  18. Applying NN: getting expected bgd CMU-CMX CMU-CMU • Shape in sidebands give contribution of combinatorial bgd to signal bins • Separate fit in each NN bin: pol1 in bins 1, 2; pol0 in bin 3 S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  19. Inputs to the (exp./obs.) limit • Inputs to be used in the “main” formula • The biggest uncertainty is from fu/fs (after bgd stat) S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  20. Optimization: choice of NN bins • Relative (unnormalized) numbers are shown • The choice (of 3 bins) is • [0.8, 0.95]U(0.95, 0.995]U(0.995, 1] S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  21. Bhh contributions Contribution to Bdμμ • The contribution to Bs is small, considerable for Bd Contribution to Bsμμ S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  22. Expectations and observations: Bs S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  23. Expectations and observations: Bd S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  24. Results: limits • New world-best result S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  25. Results: 2D plots • P-value with bgd-only hypothesis, 10K pseudoexperiments CMU-CMU CMU-CMX Bsmm16% 67% Bdmm7% 58% • Observed events are consistent with expectation S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  26. Results: 2D plot combined S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  27. Results: 1D plots • Bs • 2 events in CMU-CMU channel • 1 event in CMU-CMX channel S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  28. Limits history • Getting better and better • faster than 1/sqrt(Lumi), slower than 1/Lumi • Unofficial Tevatron combination: Br(Bsμμ) < 4.5x10-8 @ 95% S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  29. S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  30. [easy model to exclude] SO(10) R. Dermisek et al., hep-ph/0507233 (2005) SUSY contemplations (1) • The importance of Bsμμ grows with tanβ • SUSY with large tanβ becomes more popular • driven by a more significant aμ now at ~3.4 σ away from SM • The SO(10) scenario by Raby et al. is practically excluded now S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  31. SUSY contemplations (2) • Light MSSM Higgs scenario is next in line for significant exclusion. Belyaev et al. SUSY07 S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  32. CDF Limit 5.8x10-8 2 fb-1 SUSY contemplations (3) • The limit eats further into the mSUGRA space now • not as significant with bsγ constraint considered S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  33. SUSY contemplations (4) • Start getting beyond bsγ at high tanβ • Still a way to go  2x10-8 will be way more noticeable S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  34. Summary • We have updated the Bmm analysis with 2 fb-1 • The limits improved significantly: • Br(Bsmm)<5.8×10-8 @ 95%CL • Br(Bdmm)<1.8×10-8 @ 95%CL • Both limits are the best in the world!!!! • Plan to prepare/publish in PRL • draft in progress ( to GPs this week?) S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

  35. backup S. Krutelyov Search for Bs,d-->mumu with 2 fb-1

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