Measurement of Forward-Backward Asymmetry in B→K(*)&mu+&mu- and Search for Bs0→&phi&mu+&mu-

Primary authors: Hideki Miyake, Shinhong Kim, Fumihiko Ukegawa

This page summarizes analysis results for rare B decays dominated by FCNC b→s&mu+&mu- transition ; B0→K*0(892)&mu+&mu-, B+→K+&mu+&mu- and Bs0→&phi&mu+&mu-.
In addition to BR, we measured differential BR, kaon longitudinal polarization (FL), and muon forward-backward asymmetry (AFB) with respect to square of dimuon mass.
This analysis is based on a dataset of 4.4fb-1 and previous CDF analysis was performed by 924pb-1( Phys. Rev. D79, 011104(R) (2009), web page).
The results have been approved by B group as of Nov. 12th, 2009. Details are described in CDF Note 10047.
Update: In Apr. 8th, 2010, BR measurements and angular analyses in 1 &le q2 < 6 (GeV2/c2) were approved.

Analysis outline:


We start from the rare B di-muon (RAREB_LXY) trigger, which reqires Pt> 1.5 or 2.0 GeV/c muon pairs.
After several pre-selection cuts, final selection is performed by Neural Network that is trained by Pythia+EvtGen signal MC and sideband data.
NN cut is optimized to maximize S=S/sqrt(S+B) for B0→K*0(K+&pi-)&mu+&mu- and B+→K+&mu+&mu-, while Bs0→&phi(K+K-)&mu+&mu- is optimized to maximize S=S/(5*0.5+sqrt(B)) since the channel is the first observation stage.
We extract the signal yield from B mass distribution, with using unbinned maximum log likelihood.
Signal PDF is parameterized by double Gaussian that have different means, and background are first order polynomial.
Signal shape is determined from the signal MC except the signal fraction and mean of narrow Gaussian (mean difference is fixed).
During the yield fit, parameters above and slope of the background are floated.
For B0→K*0(K+&pi-)&mu+&mu- and B+→K+&mu+&mu-, there are significant physics backgrounds that consist of partially reconstructed b hadrons including feed-down from the rare B decays, in the lower sideband. We excluded these sideband from the fit region.
Signal yield is obtained from ±2&sigma window from the B PDG mass, where &sigma=20Mev/c2.


Branching Ratio is measured as relative BR to control channel, where control channels are corresponding J/&psi h decay.

Differential BR

After event selection, we divide dimuon mass spectrum into five or six q2 bin, where q2 is square of dimuon mass. Differential BR is measured in each q2 bin.

Angular Analysis (FL and AFB)

AFB is measured from muon angular distribution in dimuon restframe. We employ unbinned maximum likelihood method to extract AFB and use same q2 binning as differential BR. Angular acceptances are taken from signal MC and considered in the fit. In case of B0→K*0&mu+&mu-, we measure kaon longitudinal polarization FL from kaon angular distribution in K*0 restframe prior to measure AFB.

Blessed plots:

B mass distribution

B0→K*0(K+&pi-)&mu+&mu- unblinded yield: (png) (eps)
B+→K+&mu+&mu- unblinded yield: (png) (eps)
Bs0→&phi(K+K-)&mu+&mu- unblinded yield: (png) (eps)

Differential BR

B0→K*0(K+&pi-)&mu+&mu- Differential BR: (png) (eps)
B+→K+&mu+&mu- Differential BR: (png) (eps)

Angular Analysis (6 bin)

B0→K*0(K+&pi-)&mu+&mu- FL: (png) (eps)
B0→K*0(K+&pi-)&mu+&mu- AFB: (png) (eps)
B+→K+&mu+&mu- AFB: (png) (eps)

Angular Analysis (5 bin)

B0→K*0(K+&pi-)&mu+&mu- FL (5bin): (png) (eps)
B0→K*0(K+&pi-)&mu+&mu- AFB (5bin): (png) (eps)
B+→K+&mu+&mu- AFB (5bin): (png) (eps)

Angular Distributions

B0→K*0(K+&pi-)&mu+&mu- kaon angular distributions: (png) (eps)
B0→K*0(K+&pi-)&mu+&mu- muon angular distributions: (png) (eps)

Blessed numbers:

Signal yield :

Significance is deterimined from the likelihood ratio to a null signal hypothesis.

Relative BR

Absolute BR

Differential BR, FL, and AFB