# Search for rare or forbidden decays of the $D^{0}$ meson

## TL;DR

This study searches for rare lepton-number- and lepton-flavor-violating decays of the $D^0$ meson using BaBar data, setting new upper limits that improve upon previous constraints by up to three orders of magnitude.

## Contribution

First comprehensive search for multiple lepton-number- and lepton-flavor-violating $D^0$ decays with significantly improved upper limits using BaBar data.

## Key findings

- No significant signals observed in any decay mode.
- Established upper limits on branching fractions between $1.0$ and $30.6 imes 10^{-7}$.
- Limits are 10 to 1000 times more stringent than previous results.

## Abstract

We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type $D^0\rightarrow h^{\prime -} h^{-}\ell^{\prime +} \ell^{+}$ and $D^0\rightarrow h^{\prime -} h^{+}\ell^{\prime\pm} \ell^{\mp}$, where $h$ and $h^{\prime}$ represent a $K$ or $\pi$ meson and $\ell$ and $\ell^{\prime}$ an electron or muon. The analysis is based on $468$ fb$^{-1}$ of $e^+e^-$ annihilation data collected at or close to the $Y(4S)$ resonance with the BaBar detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes and we establish 90% confidence level upper limits on the branching fractions in the range $(1.0 - 30.6)\times 10^{-7}$. The limits are between one and three orders of magnitude times more stringent than previous measurements.