# Observation of the decay $\Lambda^0_b \to p K^- \mu^+ \mu^-$ and a search for $C\!P$ violation

## TL;DR

This paper reports the first observation of the decay $
Lambda^0_b o p K^- ^+ ^-$ and measures $C ext{P}$ violation observables, finding no significant evidence for $C ext{P}$ violation in this decay mode.

## Contribution

The study presents the first observation of the decay $
Lambda^0_b o p K^- ^+ ^-$ and measures $C ext{P}$ violation observables using LHCb data, providing new insights into flavor-changing neutral-current processes.

## Key findings

- Decay $
Lambda^0_b o p K^- ^+ ^-$ observed for the first time.
- Measured $C ext{P}$ violation observables show no significant $C ext{P}$ violation.
- Results are consistent with Standard Model predictions.

## Abstract

A search for $C\!P$ violation in the decay $\Lambda^0_b \to p K^- \mu^+ \mu^-$ is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of $C\!P$ violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of $3$ $\mathrm{fb}^{-1}$. The $\Lambda^0_b \to p K^- \mu^+ \mu^-$ decay is observed for the first time, and two observables that are sensitive to different manifestations of $C\!P$ violation are measured, $\Delta\mathcal{A}_{C\!P} \equiv \mathcal{A}_{C\!P}(\Lambda^0_b \to p K^- \mu^+ \mu^-)-\mathcal{A}_{C\!P}(\Lambda^0_b\to pK^- J/\psi)$ and $a_{C\!P}^{\widehat{T}-odd}$, where the latter is based on asymmetries in the angle between the $\mu^+\mu^-$ and $p K^-$ decay planes. These are measured to be $\Delta\mathcal{A}_{C\!P} = (-3.5 \pm 5.0(stat) \pm 0.2(syst))\times 10^{-2}$, $a_{C\!P}^{\widehat{T}-odd} = (1.2 \pm 5.0(stat) \pm 0.7(syst))\times 10^{-2}$, and no evidence for $C\!P$ violation is found.