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 f0(s)(Mπ2)/f0(d)(MK2)=1.046(44)stat.(15)syst. and f0(s)(Mπ2)/f0(d)(Mπ2)=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.
@article{arxiv.1202.6346,
title = {B_s->D_s/B->D Semileptonic Form-Factor Ratios and Their Application to BR(B^0_s->\mu^+\mu^-)},
author = {Jon A. Bailey and A. Bazavov and C. Bernard and C. M. Bouchard and C. DeTar and Daping Du and A. X. El-Khadra and J. Foley and E. D. Freeland and E. Gamiz and Steven Gottlieb and U. M. Heller and Jongjeong Kim and A. S. Kronfeld and J. Laiho and L. Levkova and P. B. Mackenzie and Y. Meurice and E. Neil and M. B. Oktay and Si-Wei Qiu and J. N. Simone and R. Sugar and D. Toussaint and R. S. Van de Water and Ran Zhou},
journal= {arXiv preprint arXiv:1202.6346},
year = {2012}
}
Comments
30 pages, 11 figures. Fig. 1 updated. Table II added. Conforms with version published in Physical Review D, except typos fixed, as in the PRD Erratum, in Table V (previously Table IV in arXiv v1). Results unchanged