Precise measurement of the branching fractions for Bs->Ds(*)+ Ds(*)- and first measurement of the Ds*+ Ds*- polarization using e+e- collisions

TL;DR

This paper precisely measures the branching fractions of Bs decays to Ds(*)+ Ds(*)- and reports the first measurement of Ds*+ Ds*- polarization, providing insights into Bs mixing and CP violation.

Contribution

It provides the first measurement of Ds*+ Ds*- polarization and precise branching fractions for Bs decays, constraining Bs mixing parameters.

Findings

Branching fraction B(Bs0->Ds+ Ds-) = (0.58 +0.11 -0.09 +-0.13)%

First measurement of Ds*+ Ds*- polarization: 0.12 +0.30 -0.28 +0.04 -0.05

Constraint on Bs mixing parameter Delta(Gamma_s)/cos(phi_s) with results for phi_s=0

Abstract

We have made a precise measurement of the absolute branching fractions of Bs->Ds(*)+ Ds(*)- decays using 121.4 fb-1 of data recorded by the Belle experiment running on the Upsilon(5S) resonance. The results are B(Bs0->Ds+ Ds-) = (0.58 +0.11 -0.09 +-0.13)%, B(Bs0->Ds*+- Ds-+) = (1.8 +-0.2 +-0.4)%, and B(Bs0->Ds*+ Ds*-) = (2.0 +-0.3 +-0.5)%; the sum is B(Bs0->Ds(*)+ Ds(*)- = (4.3 +-0.4 +-1.0)%. Assuming Bs->Ds(*)+ Ds(*)- saturates decays to CP-even final states, the branching fraction constrains the ratio Delta(Gamma_s)/cos(phi_s), where Delta(Gamma_s) is the difference in widths between the two Bs0-Bs0bar mass eigenstates, and phi_s is the CP-violating phase in Bs0-Bs0bar mixing. For phi_s=0 we obtain Delta(Gamma_s)/Gamma_s = 0.090 +-0.009 (stat.) +-0.023 (syst.), where Gamma_s is the mean decay width. We also measure for the first time the longitudinal polarization fraction of Bs->Ds*+ Ds*-; the result is 0.12 +0.30 -0.28 +0.04 -0.05.