Hot topics from Belle experiment

TL;DR

This paper reports the first evidence of the B- --> tau- nu_tau-bar decay with a significant detection and measures its branching fraction, along with studies of various Bs meson decays and production mechanisms at the Belle experiment.

Contribution

It provides the first evidence for B- --> tau- nu_tau-bar decay and detailed analysis of Bs meson decay modes and production at Belle, including setting upper limits on rare decays.

Findings

Evidence of B- --> tau- nu_tau-bar decay with 4.2 sigma significance.

Measured branching fraction of (1.06 +0.34-0.28(stat) +0.22-0.25(syst))*10^-4.

Dominant production of Bs mesons via Bs^* Bsbar^* pairs.

Abstract

We present the first evidence of the decay B- --> tau- nu_tau-bar using 414 fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We detect the signal with a significance of 4.2 standard deviations including systematics, and measure the branching fraction to be Br(B- --> tau- nu_tau-bar) = (1.06 +0.34-0.28(stat) +0.22-0.25(syst))*10^-4. We also report results based on 1.86 fb^-1 data collected by the Belle detector at the Upsilon(5S) resonance. Several exclusive Bs decays Bs --> Ds^{(*)+} pi- (rho-) and Bs --> J/psi phi(eta) are studied. The Bs meson production is found to proceed predominantly through the creation of Bs^* Bsbar^* pairs. Upper limits on Bs --> K+K-, Bs --> phi gamma, Bs --> gamma gamma and Bs --> Ds^{(*)+} Ds^{(*)-} decays are also reported.