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Register a new userSemi-inclusive studies of semileptonic $B_s$ decays at Belle
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We present an analysis of the semi-inclusive decays $B_s to D_s^- X ell^+ u$ and $B_s to D_s^{*-} X ell^+ u$, where $X$ denotes a final state that may consist of additional hadrons or photons and $ell$ is an electron or muon. The studied $B_s$ decays are contained in the $121.4~{rm fb}^{-1}$ $Upsilon(5S)$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The branching fractions of the decays are measured to be $mathcal{B}(B_s to D_s^- X ell^+ u) = [8.2 pm 0.2 (text{stat}) pm 0.6 (text{syst}) pm 1.4 (text{ext})]%$ and $mathcal{B}(B_s to D_s^{*-} X ell^+ u) = [5.4 pm 0.4 (text{stat}) pm 0.4 (text{syst}) pm 0.9 (text{ext})]%$, where the first two uncertainties are statistical and systematic and the last is due to external parameters. The measurement also provides an estimate of the $B_s^{(*)}bar{B}_s^{(*)}$ production cross-section, $sigma(e^+e^- to B_s^{(*)}bar{B}_s^{(*)}) = (53.8 pm 1.4 (text{stat}) pm 4.0 (text{syst}) pm 3.4 (text{ext})),{rm pb}$, at the center-of-mass energy $sqrt{s} = 10.86,{rm GeV}$.
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We report recent results obtained with the Belle detector using a 23.6 fb^{-1} data sample collected on the Y(5S) resonance at the KEKB asymmetric energy e^+ e^- collider. Inclusive semileptonic B_s^0 -> X^+ l^- u decays are studied for the first time and the branching fraction is measured. Combining the electron and muon channels, we obtain Bf(B_s^0 -> X^+ l^- u) = (10.2 pm 0.8 pm 0.9)%. Also, the radiative penguin decay B_s^0 -> phi gamma is observed for the first time, and an improved upper limit for the decay B_s^0 to gamma gamma is obtained.
Recent results obtained using the data sample of 23.6 fb^-1 collected on the Y(5S) resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider are discussed. Measurements of several B_s^0 decay branching fractions are reported. Studies of the Y(5S) decays to the channels with B^+ and B^0 mesons or bottomonium states are discussed.
We report a measurement of the inclusive semileptonic $B_s^0$ branching fraction in a $121~fb^{-1}$ data sample collected near the $Upsilon(5S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. Events containing $B_s^0$ pairs are selected by reconstructing a tag side $D_s^+$ and identifying a signal side lepton $ell^+$ ($ell = e, mu$) that is required to have the same-sign charge to ensure that both originate from different $B_s^0$ mesons. The $B_s^0 rightarrow X^- ell^+ u_ell$ branching fraction is extracted from the ratio of the measured yields of $D_s^+$ mesons and $D_s^+ ell^+$ pairs and the known production and branching fractions. The inclusive semileptonic branching fraction is measured to be $[9.6 pm 0.4text{(stat)} pm 0.7text{(syst)}]~%$.
A search for mixing in the neutral D meson system has been performed using semileptonic D0 -> K(*)- e+ u and D0 -> K(*)- mu+ u decays. Neutral D mesons from D*+ -> D0 pi_s^+ decays are used and the flavor at production is tagged by the charge of the slow pion. The measurement is performed using 492 fb^-1 of data recorded by the Belle detector. From the yield of right-sign and wrong-sign decays arising from non-mixed and mixed events, respectively, we measure the ratio of the time-integrated mixing rate to the unmixed rate to be R_M = (1.3 +- 2.2 +- 2.0) x 10^-4. This corresponds to an upper limit of R_M < 6.1 x 10^-4 at the 90% C.L.
The $b rightarrow s gamma$, $b rightarrow d gamma$ and $b rightarrow s ell^+ ell^-$ processes are allowed at higher order via the electroweak loop or box diagrams in the Standard model. It is sensitive probe to search for new physics beyond the Standard model because new particles might enter in the loop. We present preliminary results of branching fraction of the $bar{B} rightarrow X_s gamma$, $CP$ asymmetry in the $bar{B} rightarrow X_{s+d} gamma$, and the forward-backward asymmetry in the $bar{B} rightarrow X_s ell^+ ell^-$. The results are based on a data sample containing $772 times 10^6 Bbar{B}$ pairs recorded at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider.
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