Search for $D^0$ meson decays to $\pi^+ \pi^- e^+ e^-$ and $K^+ K^- e^+ e^-$ final states

TL;DR

This paper reports the first observation of the decay $D^0 ightarrow \pi^+\pi^- e^+ e^-$, measures its branching fraction, sets limits on $D^0 ightarrow K^+K^- e^+ e^-$, and confirms lepton universality using LHCb data.

Contribution

First observation of $D^0 ightarrow \pi^+\pi^- e^+ e^-$ decay and measurement of its branching fraction, with new limits on $D^0 ightarrow K^+K^- e^+ e^-$, confirming lepton universality.

Findings

Observed $D^0 ightarrow \pi^+\pi^- e^+ e^-$ decay for the first time.

Set world-best limits on $D^0 ightarrow K^+K^- e^+ e^-$ branching fraction.

Results are consistent with lepton universality.

Abstract

A search for $D^0$ meson decays to the $\pi^+\pi^-e^+e^-$ and $K^+K^-e^+e^-$ final states is reported using a sample of proton-proton collisions collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb$^{-1}$. The decay $D^0 \rightarrow \pi^+\pi^-e^+e^-$ is observed for the first time when requiring that the two electrons are consistent with coming from the decay of a $\phi$ or $\rho^0/\omega$ meson. The corresponding branching fractions are measured relative to the $D^0 \rightarrow K^-\pi^-[e^+e^-]_{\rho^0/\omega}$ decay, where the two electrons are consistent with coming from the decay of a $\rho^0$ or $\omega$ meson. No evidence is found for the $D^0 \rightarrow K^+K^-e^+e^-$ decay and world-best limits are set on its branching fraction. The results are compared to, and found to be consistent with, the branching fractions of the $D^0 \rightarrow \pi^+\pi^-\mu^+\mu^-$ and $D^0 \rightarrow K^+K^-\mu^+\mu^-$ decays recently measured by LHCb and confirm lepton universality at the current precision.