Weak decays of Heavy mesons

TL;DR

This paper investigates heavy meson decays as potential probes for flavor-changing neutral currents, predicting decay contributions within the standard model and exploring their sensitivity to new physics, with emphasis on rare decay modes like $B_c\to B_u^*\gamma$.

Contribution

It provides detailed predictions of heavy meson decay rates within the standard model and assesses their potential to reveal physics beyond the standard model, especially through rare decay channels.

Findings

Long distance contributions dominate charm meson decay probabilities.

Detection of $B_c\to B_u^*\gamma$ at branching ratios above $10^{-8}$ indicates new physics.

High di-lepton mass region in $D\to \pi l^+l^-$ is promising for probing $c\to ul^+l^-$ transition.

Abstract

I explore the possibility of using heavy meson decays as probes for flavour changing neutral transitions (FCNC) $c\to u\gamma$ and $c\to ul^+l^-$. In the standard model, these are the most frequent FCN transitions among the quarks with charge $2/3e_0$. I predict the short and long distance contributions to the relevant heavy meson decays within the standard model and explore their sensitivity to different scenarios of physics beyond the standard model. The rare $B_c\to B_u^*\gamma$ decay is proposed as the most suitable case study of the $c\to u\gamma$ transition and is studied with the ISGW model. Its detection at the branching ratio much higher than $10^{-8}$ would signal new physics. Weak decays of charm mesons to a light meson and a photon or a charged lepton pair are also studied for this purpose. Their probabilities are found to be dominated by the long distance contributions and raise our hopes that they may be detected soon. A window of opportunity to probe the $c\to ul^+l^-$ transition is found in the decay $D\to \pi l^+l^-$, at the kinematical region of high di-lepton mass. In order to study the charm meson decays, I adapt the Heavy Meson Chiral Lagrangian approach and demonstrate for its applicability by predicting the charm meson nonleptonic decay rates.