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

TL;DR

This paper searches for $CP$ violation in $ ext{Lambda}_b^0$ decays using LHCb data, finding no evidence of $CP$ violation but observing parity violation with high significance.

Contribution

It applies both triple product asymmetries and the unbinned energy test to search for $CP$ violation in $ ext{Lambda}_b^0$ decays, and reports the first observation of parity violation in this decay mode.

Findings

No significant $CP$ violation observed.

Parity violation observed at over 5 sigma significance.

Results are consistent with the Standard Model expectations.

Abstract

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$\,Te\kern -0.1em V$. 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.