Observation of the decay ${\Lambda }_b^0\to p{K}^{-}{\mu }^{+}{\mu }^{-}$ and a search for $CP$ violation

Abstract

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

All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-059.html

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