Search for $C!P$ violation and observation of $P$ violation in $Lambda_b^0 to p pi^- pi^+ pi^-$ decays

A search for $C!P$ violation in the $Lambda_b^0 to p pi^- pi^+ pi^-$ decay is performed using LHCb data corresponding to an integrated luminosity of 6.6$,fb^{-1}$ collected in $pp$ collisions at centre-of-mass energies of 7, 8 and 13$,Tekern -0.1em V$. The analysis uses both triple product asymmetries and the unbinned energy test method. The highest significances of $C!P$ asymmetry are 2.9 standard deviations from triple product asymmetries and 3.0 standard deviations for the energy test method. Once the global $p$-value is considered, all results are consistent with no $C!P$ violation. Parity violation is observed at a significance of $5.5$ standard deviations for the triple product asymmetry method and $5.3$ standard deviations for the energy test method.