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Rare B Decays At CDF Michael Weinberger (Texas A&M University ) For the CDF Collaboration DPF 2006

Rare B Decays At CDF Michael Weinberger (Texas A&M University ) For the CDF Collaboration DPF 2006 November 1, 2006. OUTLINE. Experimental Issues For Rare Decay Searches B s(d)  m + m - Status and Prospects Non-resonant Rare Decays: - B d  mm K *0 - B +  mm K +

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Rare B Decays At CDF Michael Weinberger (Texas A&M University ) For the CDF Collaboration DPF 2006

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  1. Rare B Decays At CDF Michael Weinberger (Texas A&M University) For the CDF Collaboration DPF 2006 November 1, 2006

  2. OUTLINE • Experimental Issues For Rare Decay Searches • Bs(d)m+m- Status and Prospects • Non-resonant Rare Decays: • - Bd  mmK*0 • - B+  mmK+ • - Bs  mmf

  3. TEVATRON & CDF Monte Carlo • Tevatron is gold mine for rare B decay searches: • Enormous b production cross section, • x1000 times larger than e+e- B factories • All B species are produced (B0, B+, Bs, Lb…) • Dataset: • Di-muon sample, easy to trigger on with good purity level in hadronic environment • Analyses presented today use • 0.450 to 1 fb-1 of data • Tevatron is expected to deliver 8 fb-1/exp for Run II Design We are here Baseline Tevatron Integrated Luminosity Projection • CDF can distinguish Bs • and Bdmm decays M(Bs)-M(Bd)~90MeV • CDF: • Excellent silicon vertex detector • Good particle identification (K,p) • Good momentum and track • impact parameter resolutions

  4. B Triggers at CDF CDF • Trigger is the lifeline of B physics in a hadron environment !!! • Rare B “Di-Muon” triggers: • Low single muon thresholds • Require Sum pT or outer muon chambers • Di-muon trigger is the primary trigger • for the CDF Bsm+m- search • SVT “Hadronic” triggers using silicon vertex detectors: • exploit long lifetime of heavy quarks • Two-track trigger (CDF) – • Two oppositely charged tracks • with large impact parameters

  5. BRIEF MOTIVATION • In the Standard Model, the FCNC decay of B m+m- is heavily suppressed SM prediction  (Buchalla & Buras, Misiak & Urban) • Bdmm is further suppressed by CKM factor (vtd/vts)2 • SM prediction is below the sensitivity of current experiments • SM  Expect to see 0 events at the Tevatron Any signal at the Tevatron would indicate new physics!!

  6. Bu,d,sm+m-K+/K*/f s s s s s s b b m- m+ m- m+ • Penguin or box processes in the Standard Model • New physics could interfere with the SM amplitudes • Can look for new physics via decay rates and decay kinematics • B Rare Decays Bm+m- h : • B+ mm K+ • B0mm K* • Bsmmf • Rare processes: predicted BR(Bsmmf)=16.1x10-7 • 1 fb-1 di-muon trigger data C. Geng and C. Liu, J. Phys. G 29, 1103 (2003)

  7. Analysis Overview Motto: reduce background and keep signal eff high Step 1: pre-selection cuts to reject obvious background Step 2: optimization (need to know signal efficiency and expected background) Step 3: reconstruct B+J/y K+ normalization mode Step 4: open the box  compute branching ratio or set limit

  8. Analysis Overview Motto: reduce background and keep signal eff high Step 1: pre-selection cuts to reject obvious background Step 2: optimization (need to know signal efficiency and expected background) Step 3: reconstruct B+J/y K+ normalization mode Step 4: open the box  compute branching ratio or set limit

  9. Analysis Overview 9.8 X 107B+ events Motto: reduce background and keep signal eff high Step 1: pre-selection cuts to reject obvious background Step 2: optimization (need to know signal efficiency and expected background) Step 3: reconstruct B+J/y K+ normalization mode Step 4: open the box  compute branching ratio or set limit

  10. B m+m-SIGNAL VS BKG DISCRIMINATION  Pmm Bs mm DR < 1 (a <57o) Da   Pm Pm y  L3D x z • m+m- mass ~±2.5s mass window • B vertex displacement: CDF  • Isolation (Iso): (fraction of pT from Bmm within DR=(Dh2+Df2)1/2 cone of 1) • “pointing (Da)”: (angle between Bs momentum and decay axis)

  11. CDF OPTIMIZATION • CDF constructs a likelihood ratio • using discriminating variables l, Da, Iso Ps/b is the probability for a given sig/bkg to have a value of x, where i runs over all variables. • Optimize on expected upper limit • LR(optimized)>0.99

  12. Background Estimate • Assume linear background shape • extrapolate # of background events sidebands to signal region • ± 60 MeV signal window • CDF signal region is also contaminated • by Bh+h- (e.g. BK+K-, K+p-, p+p-) • - K,p muon fake rates measured from data LR > 0.99

  13. Now Look in the Bs and Bd Signal Windows LR > 0.99 Bs Limits (combine both channels): Br(Bsmm)<8.0×10-8 @ 90%CL Br(Bsmm)<1.0×10-7 @ 95%CL Bd Limits (combine both channels): Br(Bdmm)<2.3×10-8 @ 90%CL Br(Bdmm)<3.0×10-8 @ 95%CL CMU-CMU Channel: Expect Observed Prob Bs0.88±0.30 1 67% Bd1.86±0.34 2 63% CMU-CMX Channel: Expect Observed Prob Bs0.39±0.21 0 68% Bd0.59±0.21 0 55%

  14. Branching Ratio Limits • Evolution of limits (in 95%CL): • Conservative projection • based on our current (780pb-1) performance • Latest improvements • sensitivity enhanced ~15-20% • Use NN over Likelihood • Uses correlations between variables • dE/dx for muon identification • Reduce K/pi fake rate • Factor of 4 improvement at 8 fb-1? World’s best limits 90% CL

  15. B m+m- h DECAYS AT THE TEVATRON

  16. METHODOLOGY • Experimental method similar to Bsmm analysis • Measure branching ratio (or set limit) relative to the • reference BJ/y h resonance decay • Exclude y and y’ invariant mass regions for • non-resonant decays • Relative efficiency determined from a combination of • data and Monte Carlo • Bkg estimated from mass side-band(s). Feed-down • contribution estimated from MC

  17. NORMALIZATION MODES NB+ = 6246 NB0 = 2346 NBs = 421 Apply similar pre-selection requirements as Bmm analysis J/ψ K Clean samples of norm events J/ψφ J/ψ K*

  18. B m+m-hSIGNAL VS BKG DISCRIMINATION • Use three similar variables to B • Decay length significance • 2D Pointing |fB – fvtx| • Isolation Cut Cut Optimization: Using data sidebands and MC to avoid introducing biases f.o.m. = Nsig / sqrt(Nsig+Nbkg) optimized for Branching Ratio Cut

  19. UNBLINDED B0 AND B+ RESULTS B+ mm K+ : Nobs = 107 <bkg> = 51.6 ± 6.1 Significance = 5.2s B0 mm K*0 : Nobs = 35 <bkg> = 16.5 ± 3.6 Significance = 2.9s

  20. UNBLINDED Bs RESULTS CDF Bs mmf : Nobs = 9 <bkg> = 3.5 ± 1.5 Significance = 1.8s

  21. BJ/yh RESULTS

  22. Conclusions

  23. Back up Slides

  24. CDF PRE-SELECTION • Pre-Selection cuts: • 4.669 < mmm < 5.969 GeV/c2 • muon quality cuts • pT(m)>2.0 (2.2) GeV/c CMU (CMX) • pT(Bs cand.)>4.0 GeV/c • |y(Bs)| < 1 • good vertex • 3D displacement L3D between primary and secondary vertex • (L3D)<150 mm • proper decay length 0 < l < 0.3cm Bkg substantially reduced but still sizeable at this stage

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