Search for $K_{\mathrm{S(L)}}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}$ decays at LHCb

Abstract

A search for $K_{\mathrm{S(L)}}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}$ decays is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $13\,\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4\,\mathrm{fb^{-1}}$. No $K_{\mathrm{S(L)}}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}$ signals are found and upper limits are set for the first time on the branching fractions $\mathcal{B}(K_\text{S}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}) < 1.4 \times 10^{-9}$ and $\mathcal{B}(K_\text{L}^{0} \rightarrow \pi^{+}\pi^{-}\mu^{+}\mu^{-}) < 6.6 \times 10^{-7}$, at the 90% confidence level.