The light invisible boson in FCNC decays of $B$ and $B_c$ mesons

TL;DR

This paper investigates flavor-changing neutral current decays of B and Bc mesons involving an invisible light boson, deriving constraints on couplings and predicting branching ratios of rare decays within a model-independent framework.

Contribution

It introduces a model-independent effective Lagrangian for light invisible bosons in meson decays and provides new bounds and predictions for decay branching ratios.

Findings

Branching ratios of Bc decays are predicted to be around 10^{-6} or 10^{-5}.

Maximum decay rates occur when the invisible particle mass is approximately 3.5-4 GeV.

Constraints on coupling coefficients are derived from experimental missing energy limits.

Abstract

In this paper, we study the FCNC decay processes of $B$ and $B_c$ meson, in which one invisible particle is emitted. Both the spin-0 and spin-1 cases are considered. The model-independent effective Lagrangian is introduced to describe the coupling between the light invisible boson and quarks. The constraints of the coupling coefficients are extracted by experimental upper limits of the missing energy in $B$ meson decays. The bounds are used to predict the upper limits of branching fractions of corresponding $B_c$ decays, which are of the order of $10^{-6}$ or $10^{-5}$ when final meson is pseudoscalar or vector, respectively. The maximum branch ratios are achieved when $m_\chi\approx3.5- 4$~GeV, where $m_\chi$ is the mass of the invisible particle.