Form Factors for $B_c^*\to \eta_c+l\nu_l$ at NLO in QCD

TL;DR

This paper calculates the form factors for the decay $B_c^* o a_c + l u_l$ at NLO in QCD using NRQCD, providing analytical expressions, asymptotic forms, and predictions for decay widths and branching fractions.

Contribution

It offers the first complete NLO NRQCD calculations of multiple form factors for $B_c^* o a_c$ decays, including analytical and asymptotic expressions, and combines them with lattice and $z$-series methods for full $q^2$ coverage.

Findings

NLO corrections are sizable and well-behaved at low $q^2$.

Provided analytical expressions and asymptotic forms for form factors.

Predicted decay widths and branching fractions for $B_c^* o a_c + l u_l$.

Abstract

We present the Non-Relativistic QCD (NRQCD) calculations at the next-to-leading order (NLO) of $\alpha_s$ for $B_c^*\to \eta_c$ vector, axial-vector, tensor and axial-tensor form factors, and obtain complete analytical expressions for the form factors, along with their asymptotic forms in the hierarchical heavy quark limit. Our results show that the NLO corrections are both sizable and well-behaved in the low squared transfer momentum $(q^2)$ region. Using the NRQCD + lattice + $z$-series method, we further provide theoretical predictions for $B_c^*\to \eta_c$ form factors across the full physical $q^2$ range. Based on these predicted form factors, we finally compute the decay widths and branching fractions for the semileptonic decays $B_c^*\to \eta_c+l{\nu_l}$.