Measurement of matter–antimatter di erences in beauty baryon decays

Di erences in the behaviour of matter and antimatter have been observed in K and B meson decays, but not yet in any baryon decay. Such di erences are associatedwith the non-invariance of fundamental interactions under the combined chargeconjugation and parity transformations, known as CP violation. Here, using data from the LHCb experiment at the LargeHadron Collider, we search for CP-violating asymmetries in the decay angle distributions of Λb baryons decaying to pπ ππ and pπKK final states. These four-body hadronic decays are a promising place to search for sources of CP violation both within and beyond the standard model of particle physics. We find evidence for CP violation in Λb to pπ ππ decays with a statistical significance corresponding to 3.3 standard deviations including systematic uncertainties. This represents the first evidence for CP violation in the baryon sector.