Searches for 25 rare and forbidden decays of $D^+$ and $D_s^+$ mesons

TL;DR

This paper reports a search for 25 rare and forbidden charm meson decays using LHCb data, setting new upper limits on their branching fractions, with no evidence of these decays observed.

Contribution

The study provides the first comprehensive search for these specific charm decays and significantly improves the upper limits on their branching fractions.

Findings

No evidence of the 25 decay modes was observed.

Upper limits on branching fractions range from 1.4×10⁻⁸ to 6.4×10⁻⁶.

Most limits are 10 to 100 times more stringent than previous results.

Abstract

A search is performed for rare and forbidden charm decays of the form $D_{(s)}^+ \to h^\pm \ell^+ \ell^{(\prime)\mp}$, where $h^\pm$ is a pion or kaon and $\ell^{(')\pm}$ is an electron or muon. The measurements are performed using proton-proton collision data, corresponding to an integrated luminosity of $1.6\text{fb}^{-1}$, collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and $90\%$ confidence level limits on the branching fractions are set between $1.4\times10^{-8}$ and $6.4\times10^{-6}$. In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.