First evidence of $CP$ violation in beauty baryon to charmonium decays

Abstract

A study of the difference in the $CP$ asymmetries between ${\Lambda }_b^0\to J/\psi p{\pi }^{-}$ and ${\Lambda }_b^0\to J/\psi p{K}^{-}$ decays, $\Delta {\mathcal{A}}_{CP}$, is performed using proton-proton collision data collected by the LHCb experiment in the years 2015--2018, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$. This quantity is measured to be $\Delta {\mathcal{A}}_{CP}=(4.03\pm 1.18\pm 0.23)\%$, where the first uncertainty is statistical and the second is systematic. When combined with the previous LHCb result, a value of $\Delta {\mathcal{A}}_{CP}=(4.31\pm 1.06\pm 0.28)\%$ is obtained, corresponding to a significance of $3.9\sigma$ against the $CP$ symmetry hypothesis. Studies of triple-product asymmetries, which provide an additional probe of $CP$ violation, show no significant deviation from $CP$ symmetry.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3877/ (LHCb public pages)

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