Dispersive Analysis of $B\to K^{(\ast )}$ and $B_s\to \varphi$ Form Factors

Abstract

We perform the first simultaneous dispersive analysis of the $B\to K$, $B\to K^{\ast }$, and $B_s\to \varphi$ form factors. By means of an improved parametrization, we take into account the form factors' below-threshold branch cuts arising from on-shell ${\bar{B}}_s{\pi }^0$ and ${\bar{B}}_s{\pi }^0{\pi }^0$ states, which so far have been ignored in the literature. In this way, we eliminate a source of hard-to-quantify systematic uncertainties. We provide machine-readable files to obtain the full set of the $\bar{B}\to {\bar{K}}^{(\ast )}$ and ${\bar{B}}_s\to \varphi$ form factors in and beyond the entire semileptonic phase space.

Comments: v4: We have corrected the application of the unitarity bounds, which were ill-defined in the previous versions. Ancillary material at https://zenodo.org/record/13981091