Constraints on B--->pi,K transition form factors from exclusive semileptonic D-meson decays

Abstract

According to the heavy-quark flavour symmetry, the $B\to \pi ,K$ transition form factors could be related to the corresponding ones of D-meson decays near the zero recoil point. With the recent precisely measured exclusive semileptonic decays $D\to \pi \ell \nu$ and $D\to K\ell \nu$, we perform a phenomenological study of $B\to \pi ,K$ transition form factors based on this symmetry. Using BK, BZ and Series Expansion parameterizations of the form factor slope, we extrapolate $B\to \pi ,K$ transition form factors from $q_{max}^2$ to $q^2=0$. It is found that, although being consistent with each other within error bars, the central values of our results for $B\to \pi ,K$ form factors at $q^2=0$, $f_{+}^{B\to \pi ,K}(0)$, are much smaller than predictions of the QCD light-cone sum rules, but are in good agreements with the ones extracted from hadronic B-meson decays within the SCET framework. Moreover, smaller form factors are also favored by the QCD factorization approach for hadronic B-meson decays.

Comments: 19 pages, no figure, 5 tables