Probing $c\to u\gamma$ in $B_c\to B_u^*\gamma$ decay

TL;DR

This paper investigates rare flavor-changing neutral current decays involving charm quarks, proposing specific decay channels like $B_c o B_u^*\gamma$ as sensitive probes for new physics beyond the Standard Model.

Contribution

It identifies promising decay modes for detecting $c o u\gamma$ transitions and analyzes the impact of long-distance effects on these rare processes.

Findings

$B_c o B_u^*\gamma$ decay could signal new physics if observed above $10^{-8}$ branching ratio.

High $m_{ll}$ region in $D o \pi l^+l^-$ is suitable for probing $c o ul^+l^-$ transition.

Decays like $D o V\gamma$ are less effective due to dominance of long-distance effects.

Abstract

Flavour changing neutral current (FCNC) transitions $c\to u\gamma$ and $c\to ul^+l^-$ are very rare in the standard model and present an interesting probe for the physics beyond it. We study long distance contamination to these short distance processes in different hadron decays. As the most suitable probe for $c\to u\gamma$ transition we propose $B_c\to B_u^*\gamma$ decay. Its detection at the branching ratio well above $10^{-8}$ would signal new physics. The $c\to ul^+l^-$ transition may be probed at high $m_{ll}$ in $D\to \pi l^+l^-$. The decays $D\to V\gamma$ and $D\to Vl^+l^-$ ($V$ is a light vector meson) are less suitable, since they are dominated by the long distance effects.