B\rightarrow µµ, B\rightarrow K*µµ

Masato Aoki
2016 Proceedings of Flavor Physics and CP Violation 2010 — PoS(FPCP 2010)   unpublished
Studying flavor changing neutral current transitions provides important information that helps searches for physics beyond the standard model. In this paper we report on recent measurements of these transitions using data collected by the CDF and D0 experiments at the Tevatron pp collider, including world-leading limits on the branching fraction of the decay B 0 which is consistent and competitive with best B-factories results, and the first observation of the Flavor Physics and CP Violation
more » ... CP 2010 May 25-29, 2010 Turin, Italÿ Speaker. † On behalf of the CDF and D0 Collaborations. c © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/ PoS(FPCP 2010)026 Rare B decays at the Tevatron Masato Aoki ¤ s¥ § ¦ µ¨µ © , B¨¦ K¨µ¨µ © , B 0 ¦ K 0 µ¨µ © and B 0 s ¦ φ µ¨µ © , performed by the CDF and D0 collaborations. ¦ µ¨µ © and B 0 ¦ µ¨µ © to test the Minimal Flavor Violation [2]. CDF has performed a search for B 0 ¤ s¥ ¦ µ¨µ © ¦ h¨h © decays (h¨and h © represent a charged kaon or pion), which peak in the signal invariant mass region and do not occur in the sidebands. The contribution from other heavy-flavor decays is negligible. The combinatorial background is estimated by linearly extrapolating from the sideband region to the signal region. The B ¦ h¨h © contributions are about a factor of ten smaller than the combinatorial background. The dimuon invariant mass distributions for three different NN output ranges are shown in Fig. 1. The limit on the branching fraction is computed by normalizing to the number of reconstructed B¨¦ J ¦ µ¨νD¡D ¦ µ © ¯νX sequential semileptonic decays, resulting in m µ µ predominantly below the B hadron mass. The simulated dimuon mass distributions for both background sources are parametrized using an exponential function to estimate the number of background events in the signal region after fitting the dimuon mass in the data sideband regions in each β bin. The uncertainty on this background estimate is dominated by the statistical uncertainty of the sideband sample (10% § 35%). The B ¦ h¨h © background contribution is negligible. The limit on the branching fraction is computed by normalizing to the number of reconstructed B¨¦ J ψK¨events. A ¦ sµ¨µ © decays, the exclusive channels B¨¦ K¨µ¨µ © and B 0 ¦ K 0 µ¨µ © have been observed and studied at Belle [13] and BaBar [14]. At the Tevatron it is also possible to search for analogous decays B 0 s ¦ φ µ¨µ © and Λ 0 b ¦ Λµ¨µ © . CDF reports new results on measurements of B¨¦ K¨µ¨µ © , B 0 ¦ K 0 µ¨µ © and B 0 s ¦ φ µ¨µ © decays [15]. Event selection starts from selecting two oppositely charged muon candidates with a transverse momentum greater than 1 5 GeV or 2 0 GeV depending on the trigger selection. B ¦ hµ¨µ © candidates are then reconstructed by adding h ¥ K¨, K 0 , or φ candidates to the dimuon pair. The K 0 is reconstructed in the mode K 0 ¦ K¨π © and the φ is reconstructed as φ ¦ K¨K © . The kaon and pion candidates are required to be consistent with the time-of-flight (TOF) and dE dx combined log-likelihood probability of each particle hypothesis. The muon candidates are further purified by the muon-likelihood. To enhance separation of signal from background, an Artificial Neural Network multivariate classifier is constructed. Figure 3 shows the invariant mass distribution for each rare decay. By performing an unbinned maximum log-likelihood fit of the B invariant mass distribution, 120 16 events for B¨¦ K¨µ¨µ © , 101 12 events for B 0 ¦ K 0 µ¨µ © , and 27 6 events for B 0 s ¦ φ µ¨µ © are found, with 8 5σ , 9 7σ and 6 3σ statistical significance, respectively. This is the first observation of B 0 s ¦ φ µ¨µ © decay. Using the corresponding B ¦ J ψh modes as a reference, CDF determines the following absolute branching fractions: ¢ ¡ B ¦ K¨µ¨µ © £ ¦ K 0 µ¨µ © and B¨¦ K¨µ¨µ © are also calculated as shown in © ) direction and the direction opposite to the B (B) direction in the dimuon rest-frame, and θ K is the angle between the kaon direction and the direction opposite to the B meson in the K 0 rest frame. The fit results of F L and A FB for B 0 ¦ K 0 µ¨µ © are shown in Fig. 5, as well as A FB for B¨¦ K¨µ¨µ © . Both F L and A FB are consistent with the SM expectation, and also with an example of a SUSY model [16] . These results are also consistent and competitive with the B-factories' measurements [13, 14] .
doi:10.22323/1.116.0026 fatcat:264jshtsjfexll3wlsgg2m64su