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

TL;DR

This paper reports a search for rare $K_{S,L}^0$ decays into $\pi^+\pi^-\mu^+\mu^-$ using LHCb data, setting the first upper limits on their branching fractions at 13 TeV collision energy.

Contribution

The study provides the first upper limits on the branching fractions of these rare decays, improving constraints on new physics models involving kaon decays.

Findings

No signals observed for the decay modes.

Upper limits on branching fractions are set at $1.4 imes 10^{-9}$ for $K_S^0$ and $6.6 imes 10^{-7}$ for $K_L^0$.

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.