20–27 juil. 2011
Alpes Congrès - Alpexpo
Fuseau horaire Europe/Paris

Bs decays at Belle

21 juil. 2011, 15:00
15m
Oisans (Alpes Congrès - Alpexpo)

Oisans

Alpes Congrès - Alpexpo

Parallel session talk Flavour Physics and Fundamental Symmetries Flavour Physics and Fundamental Symmetries

Orateur

Dr Remi Louvot (EPFL, Lausanne)

Description

Using fully reconstructed Bs mesons, we measure the branching fractions for the decays of BsDs()+Ds() exclusively. Assuming these decay modes saturate decays to CP-even final states, the branching fraction determines the relative width difference between the CP-odd and CP-even Bs states. We study the decay Bs0J/ψϕ, ϕK+K. In this sample Bs0 mesons are produced in three Υ(5S) decays: Υ(5S)BsBs, BsBs and BsBs, where the Bs mesons decay to Bsγ. We determine the absolute branching fraction of the decay Bs0J/ψϕ, which is an important mode for measuring the CP violating phase βs in the BsBs mixing. The latter is of particular interest as it is sensitive to physics beyond the Standard Model. We also report the first observation of Bs0J/ψf0(980) and first evidence for Bs0J/ψf0(1370), which are CP-eigenstate decay modes. We measure the branching fractions B(Bs0J/ψf0(980);f0(980)π+π)=(1.160.19+0.31(stat.)0.17+0.15(syst.)0.18+0.26(NBs()B¯s()))×104 with a significance of 8.4σ, and B(Bs0J/ψf0(1370);f0(1370)π+π)=(0.340.14+0.11(stat.)0.02+0.03(syst.)0.05+0.08(NBs()B¯s()))×104 with a significance of 4.2σ. The last error listed is due to uncertainty in the number of produced Bs()B¯s() pairs. We have also performed the first search for charmed baryonic Bs0 decay, B¯s0Λc+πΛ¯. The measurement precision of the Bs0 branching fraction at Belle is limited by the poor knowledge of the Bs0 production fraction, fs=σ(Bs()B¯s())/σ(bb¯). We present the status of the current measurements and discuss their main limitations. Using dilepton events, a new independent measurement of fs is presented, together with its impact on the precision of Belle's Bs0 measurements. We present a measurement of the CP violation parameter sin2ϕ1 at the Υ(5S) resonance using a new tagging method called the B-π tagging. This method in general uses a Υ(5S) decay to a charged B meson, a neutral B meson, and a charged pion. The neutral B meson decays to a CP eigenstate, and the charged B meson is reconstructed as missing mass of the neutral B meson and the charged pion. The initial flavor of the neutral B meson is determined by the charge of the pion at the moment of the Υ(5S) decay. CP violating parameters can be derived from asymmetry of the number of BBπ+ and BBπ events without measuring decay time. Since the B-π tagging method have different systematic errors from the analyses on the Υ(4S) resonance and thus complementary. In this analysis, the neutral B meson is reconstructed as J/ψKS. All these results are based on a data sample collected with the Belle detector at the Υ(5S) resonance with an integrated luminosity of 121.4 fb1 at the KEKB asymmetric-energy e+e collider.

Auteur principal

Dr Remi Louvot (EPFL, Lausanne)

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