B_s->D_s/B->D Semileptonic Form-Factor Ratios and Their Application to BR(B^0_s->\mu^+\mu^-)

TL;DR

This paper uses lattice QCD to calculate form-factor ratios between specific B meson decays, providing crucial inputs for accurately determining the B_s to mu+ mu- decay rate, with results showing no significant U-spin symmetry breaking.

Contribution

The study presents the first lattice QCD calculation of semileptonic form-factor ratios relevant for B_s and B decays, improving the theoretical precision in B physics measurements.

Findings

Form-factor ratios are approximately 1.046 and 1.054 with uncertainties.

No significant U-spin symmetry breaking observed.

Results differ from previous QCD sum-rule calculations.

Abstract

We calculate form-factor ratios between the semileptonic decays \bar{B}->D^+\ell^-\bar{\nu} and \bar{B}_s->D_s^+\ell^-\bar{\nu} with lattice QCD. These ratios are a key theoretical input in a new strategy to determine the fragmentation fractions of the neutral B decays, which are needed for measurements of BR(B^0_s-> \mu^+\mu^-). We use the MILC ensembles of gauge configurations with 2+1 flavors of sea quarks at two lattice spacings of approximately 0.12 fm and 0.09 fm. We use the model-independent z-parametrization to extrapolate our simulation results at small recoil toward maximum recoil. Our results for the form-factor ratios are $f_0^{(s)}(M^2_\pi)/f_0^{(d)}(M^2_K) =1.046(44)_{stat.}(15)_{syst.}$ and $f_0^{(s)}(M^2_\pi)/f_0^{(d)}(M^2_\pi)=1.054(47)_{stat.}(17)_{syst.}$. In contrast to a QCD sum-rule calculation, no significant departure from U-spin (d<->s) symmetry is observed.