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 B s(d)   +  - Status and Prospects Non-resonant Rare Decays: - B d   K *0 - B +   K + - B s   Conclusion

3 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 (B 0, B +, B s,  b …) Dataset: Di-muon sample, easy to trigger on with good purity level in hadronic environment Analyses presented today use to 1 fb -1 of data TEVATRON & CDF Tevatron Integrated Luminosity Projection Baseline Design We are here Tevatron is expected to deliver 8 fb -1 /exp for Run II Monte Carlo CDF: Excellent silicon vertex detector Good particle identification (K,  ) Good momentum and track impact parameter resolutions M(B s )-M(B d )~90MeV CDF can distinguish B s and B d   decays

4 Trigger is the lifeline of B physics in a hadron environment !!! Rare B “Di-Muon” triggers: Low single muon thresholds Require Sum p T or outer muon chambers Di-muon trigger is the primary trigger for the CDF B s      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 B Triggers at CDF CDF

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

6 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      h : B +   K + B 0   K * B s    Rare processes: predicted BR(B s    )=16.1x fb-1 di-muon trigger data C. Geng and C. Liu, J. Phys. G 29, 1103 (2003)   s s s b s b s s   B u,d,s       K + /K*/ 

7 B   +   : 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/  K + normalization mode Step 4: open the box  compute branching ratio or set limit

8 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/  K + normalization mode Step 4: open the box  compute branching ratio or set limit B   +   : Analysis Overview 9.8 X 10 7 B + events (produced)

9  +  - mass ~±2.5  mass window B vertex displacement: CDF  Isolation (Iso): (fraction of p T from B   within  R=(  2 +  2 ) 1/2 cone of 1) “pointing (  )”:  (angle between B s momentum and decay axis) P  PP PP L 3D  x y B s    R < 1 (  < 57 o )     z B      SIGNAL VS BKG DISCRIMINATION

10 CDF OPTIMIZATION CDF constructs a likelihood ratio using discriminating variables  Iso P s/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 L R (optimized)>0.99

11 Background Estimate CDF signal region is also contaminated by B  h + h - (e.g. B  K + K -, K +  ,     ) - K   muon fake rates measured from data Assume linear background shape extrapolate # of background events sidebands to signal region ± 60 MeV signal window Decay B  hh Background Combinatoric Background Total Background BsBs 0.19± ± ±0.36 BdBd 1.37± ± ±0.39 L R > 0.99

12 L R > 0.99 CMU-CMU Channel: Expect Observed Prob B s 0.88± % B d 1.86± % CMU-CMX Channel: Expect Observed Prob B s 0.39± % B d 0.59± % Now Look in the Bs and Bd Signal Windows B s Limits (combine both channels): Br(B s   )<8.0×10 90%CL Br(B s   )<1.0×10 95%CL B d Limits (combine both channels): Br(B d   )<2.3×10 90%CL Br(B d   )<3.0×10 95%CL

13 CDF B s   176 pb ×10 -7 Published DØ B s   240 pb ×10 -7 Published DØ B s   300 pb ×10 -7 Prelim. DØ <B s   700 pb -1 Prelim. Sensitivity CDF B s   364 pb ×10 -7 Published CDF B s   780 pb ×10 -7 Prelim. Branching Ratio Limits Evolution of limits (in 95%CL): World’s best limits Babar B d   111 fb ×10 -8 Published CDF B d   364 pb ×10 -8 Published CDF B d   780 pb ×10 -8 Prelim. 90% CL Conservative projection based on our current (780pb -1 ) performance Latest improvements Sensitivity enhanced ~15-20% Use NN over Likelihood dE/dx for muon ID to reduce K/  fake rate Factor of 4 improvement at 8 fb -1 ?

14 B      h DECAYS AT THE TEVATRON

15 METHODOLOGY Experimental method similar to B s   analysis Measure branching ratio (or set limit) relative to the reference B  J/  h resonance decay Exclude  and  ’ 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

16 NORMALIZATION MODES Clean samples of norm events Apply similar pre-selection requirements as B   analysis N B+ = 6246 N B0 = 2346 N Bs = 421 J/ψ K J/ψ φ J/ψ K *

17 Use three similar variables to B   Decay length significance 2D Pointing |  B –  vtx | Isolation B      h SIGNAL VS BKG DISCRIMINATION Optimization: Using data sidebands and MC to avoid introducing biases f.o.m. = N sig / sqrt(N sig +N bkg ) optimized for Branching Ratio Cut

18 UNBLINDED B 0 AND B + RESULTS B +   K + : N obs = 107 = 51.6 ± 6.1 Significance = 5.2  B 0   K* 0 : N obs = 35 = 16.5 ± 3.6 Significance = 2.9  CDF B s    : N obs = 9 = 3.5 ± 1.5 Significance = 1.8 

19 B  J/  h RESULTS CDF 1fb -1 B    B    B s  Rel BR± stat ± syst ± 0.15 ± ± 0.23 ± ± 0.55 ± 0.11 Abs BR ± stat ± syst ± 0.15 ± ± 0.31 ± ± 0.51 ± 0.31 Rel BR 95% CL Limit x Rel BR 90% CL limit x B  Kl + l - BK*l+l-BK*l+l- BaBar (208 fb -1 ) ± ±0.12 PRD 73, (2006) Belle (253 fb -1 ) ± ±0.11 preliminary, hep- ex/ D0 (0.45 fb -1 )hep-ex/ x10 -3

20 Conclusions CDF is a very rich environment to do B, and especially Rare B, physics. It has measured B s   and B d   with the worlds best limits, and will make significant improvements to the next update It has measured the branching ratios for B     B    0  and set a limit for B s  Future updates are planned which will utlize the large data sets being taken at the Tevatron

21 Back up Slides

22 Pre-Selection cuts: < m  < GeV/c 2 muon quality cuts p T (  )>2.0 (2.2) GeV/c CMU (CMX) p T (B s cand.)>4.0 GeV/c |y(B s )| < 1 good vertex 3D displacement L 3D between primary and secondary vertex  (L 3D )<150  m proper decay length 0 < < 0.3cm CDF PRE-SELECTION Bkg substantially reduced but still sizeable at this stage