# Observation of the decay $\Lambda^0_b \to pK^- \mu^+ \mu^-$ and a search for $CP$ violation

LHCb Collaboration; Bernet, R; Müller, K; Serra, N; Steinkamp, O; Straumann, U; Vollhardt, A; et al (2017). Observation of the decay $\Lambda^0_b \to pK^- \mu^+ \mu^-$ and a search for $CP$ violation. Journal of High Energy Physics, 06:108.

## Abstract

A search for CP violation in the decay $\Lambda^0_b \to pK^- \mu^+ \mu^-$ is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of $CP$ 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 fb$^{−1}$. The $\Lambda^0_b \to pK^- \mu^+ \mu^-$ decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured,
$\Delta\mathcal{A}_{CP} ≡ \mathcal{A}_{CP}(\Lambda^0_b \to pK^- \mu^+ \mu^-) − \mathcal{A}_{CP}(\Lambda^0_b \to pK^−J/\psi)$ and a $\mathcal{a}^{\hat{T}-odd}_{CP}$, where the latter is based on asymmetries in the angle between the $\mu^+\mu^-$ and $pK^-$ decay planes.
These are measured to be
$\Delta\mathcal{A}_{CP} = (−3.5 \pm 5.0(stat) \pm 0.2(syst)) \times 10^{−2}$,
$\mathcal{a}^{\hat{T}-odd}_{CP} = (1.2 \pm 5.0(stat) \pm 0.7(syst)) \times 10^{−2}$,
and no evidence for CP violation is found.

## Abstract

A search for CP violation in the decay $\Lambda^0_b \to pK^- \mu^+ \mu^-$ is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of $CP$ 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 fb$^{−1}$. The $\Lambda^0_b \to pK^- \mu^+ \mu^-$ decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured,
$\Delta\mathcal{A}_{CP} ≡ \mathcal{A}_{CP}(\Lambda^0_b \to pK^- \mu^+ \mu^-) − \mathcal{A}_{CP}(\Lambda^0_b \to pK^−J/\psi)$ and a $\mathcal{a}^{\hat{T}-odd}_{CP}$, where the latter is based on asymmetries in the angle between the $\mu^+\mu^-$ and $pK^-$ decay planes.
These are measured to be
$\Delta\mathcal{A}_{CP} = (−3.5 \pm 5.0(stat) \pm 0.2(syst)) \times 10^{−2}$,
$\mathcal{a}^{\hat{T}-odd}_{CP} = (1.2 \pm 5.0(stat) \pm 0.7(syst)) \times 10^{−2}$,
and no evidence for CP violation is found.

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