Optimized predictions for $W\to B_c+\gamma$ by combining light-cone and NRQCD approaches

Abstract

The rare process of $W$ radiative decay into the $B_c$ meson can serve as an interesting play ground for testing two influential perturbative QCD approaches: non-relativistic quantum chromodynamics (NRQCD) and ligh-cone (LC) factorization. Since the $B_c$ meson is a genuine heavy quarkonium which is composed of two different species of heavy quarks, it is natural to employ NRQCD factorization to tackle this exclusive quarkonium production process; on the other hand, since the mass of the $W$ boson is much greater than that of the $B_c$, the collinear factorization is also a viable approach. To fully disentangle the contributions from several distinct scales $M_W$, $m_Q$, $m_{Q}v$ ($v$ represents the typical velocity of the $c/\bar{b}$ quarks inside $B_c$), and ${\Lambda }_{\mathrm{QCD}}$, we carry out a joint analysis that combines both light-cone and NRQCD factorization approaches, and compute the order-${\alpha }_s$ correction to $W\to B_c+\gamma$. With the aid of the celebrated Efremov-Radyushkin-Brodsky-Lepage (ERBL) evolution equation, we resum the leading collinear logarithms ${\alpha }_s\ln \frac{M_W}{m_Q}$ to all orders in ${\alpha }_s$. We also explore some phenomenological implications of our predictions.

Comments: 16 pages, 3 figures