Radiative Decays of Heavy-light Mesons and the $f_{H,H^{\ast },H_1}^{(T)}$ Decay Constants

Abstract

The on-shell matrix elements, or couplings $g_{H{H}^{\ast }(H_1)\gamma }$, describing the $B(D{)}_q^{\ast }\to B(D{)}_q\gamma$ and $B_{1q}\to B_q\gamma$ ($q=u,d,s$) radiative decays, are determined from light-cone sum rules at next-to-leading order for the first time. Two different interpolating operators are used for the vector meson, providing additional robustness to our results. For the $D^{\ast }$-meson, where some rates are experimentally known, agreement is found. The couplings are of additional interest as they govern the lowest pole residue in the $B(D)\to \gamma$ form factors which in turn are connected to QED-corrections in leptonic decays $B(D)\to \ell \bar{\nu }$. Since the couplings and residues are related by the decay constants $f_{H^{\ast }(H_1)}$ and $f_{H^{\ast }(H_1)}^T$ respectively, we determine them at next-leading order as a by-product. The quantities $\{f_{H^{\ast }}^T,f_{H_1},f_{H_1}^T\}$ have not previously been subjected to a QCD sum rule determination. All results are compared with the existing experimental and theoretical literature.

Comments: 34 pp (plus refs) and 6 figs, version to appear in JHEP (colouring removed)