Weak decays of unstable $b$-mesons

TL;DR

This paper explores the weak decays of unstable excited $b$-mesons, particularly $B^*$ states, as probes of short-distance weak interactions, with predictions for rare decay rates and discussions on experimental detection prospects.

Contribution

It provides theoretical predictions for the decay rates of excited $b$-mesons, especially $B_s^* o ext{leptons}$, and discusses experimental strategies to measure these rare processes.

Findings

Predicted $B_s^* o ext{leptons}$ branching fraction $ o 10^{-11}$

Identified the main uncertainty from the $B_s^*$ width

Discussed potential detection at the LHC and scattering experiments

Abstract

We investigate the decays of the excited $(b\bar q)$ mesons as probes of the short-distance structure of the weak $\Delta B=1$ transitions. These states are unstable under the electromagnetic or strong interactions although their widths are typically suppressed by phase space. As compared to the pseudoscalar $B$ meson, the purely leptonic decays of the vector $B^*$ are not chirally suppressed and are sensitive to different combinations of the underlying weak effective operators. An interesting example is $B^*_s\to \ell^+\ell^-$, which has a rate that can be accurately predicted in the standard model. The branching fraction is $\mathcal{B}\sim10^{-11}$, irrespective of the lepton flavor and where the main uncertainty stems from the unmeasured and theoretically not-well known $B_s^*$ width. We discuss the prospects for producing this decay mode at the LHC and explore the possibility of measuring the $B_s^*\to\ell\ell$ amplitude, instead, through scattering experiments at the $B_s^*$ resonance peak. Finally we also discuss the charged-current $B_{u,c}^*\to\ell\nu$ decay which can provide complementary information on the $b\to u\ell\nu$ and $b\to c\ell\nu$ transitions.