Observation of $D^0$ meson decays to $\pi^+\pi^-\mu^+\mu^-$ and $K^+K^-\mu^+\mu^-$ final states

Abstract

The first observation of the $D^0 \to \pi^+\pi^-\mu^+\mu^-$ and $D^0 \to K^+K^-\mu^+\mu^-$ decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to 2  fb$^{−1}$ of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay $D^0 \to K^−\pi^+[\mu^+\mu^−]_{\rho^0 / \omega}$, where the two muons are consistent with coming from the decay of a ${\rho}^0$ or $\omega$ meson. The results are
$\mathscr{B}(D^0 \to \pi^+\pi^−\mu^+\mu^−) = (9.64 \pm 0.48 \pm 0.51 \pm 0.97) \times 10^{−7}$ and
$\mathscr{B}(D^0 \to K^+K^−\mu^+\mu^−) = (1.54 \pm 0.27\pm 0.09 \pm 0.16) \times 10^{−7}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.