Measurement of matter-antimatter differences in beauty baryon decays

Differences in the behaviour of matter and antimatter have been observed in $K$ and $B$ meson decays, but not yet in any baryon decay. Such differences are associated with the non-invariance of fundamental interactions under the combined charge-conjugation and parity transformations, known as $C\text{\hspace{0.17em}⁣}P$ violation. Using data from the LHCb experiment at the Large Hadron Collider, a search is made for $C\text{\hspace{0.17em}⁣}P$-violating asymmetries in the decay angle distributions of ${\mathrm{\Lambda }}_b^0$ baryons decaying to $p{\pi }^{-}{\pi }^{+}{\pi }^{-}$ and $p{\pi }^{-}{K}^{+}{K}^{-}$ final states. These four-body hadronic decays are a promising place to search for sources of $C\text{\hspace{0.17em}⁣}P$ violation both within and beyond the Standard Model of particle physics. We find evidence for $C\text{\hspace{0.17em}⁣}P$ violation in ${\mathrm{\Lambda }}_b^0$ to $p{\pi }^{-}{\pi }^{+}{\pi }^{-}$ decays with a statistical significance corresponding to 3.3 standard deviations including systematic uncertainties. This represents the first evidence for $C\text{\hspace{0.17em}⁣}P$ violation in the baryon sector.