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 PP PP 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 - BK*l+l-BK*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