New horizon in particle physics: first observation of CP violation in baryon decays

Abstract

Recently, the LHCb Collaboration achieved the observation of CP violation (CPV) in baryon decays through the process of $\hat{I}{›}_b^0\to p{K}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$, reporting an asymmetry of $(2.45\pm 0.46\pm 0.10)\%$ with a significance of 5.2$\ddot{I}ƒ$. This marks a breakthrough and a milestone in particle physics, six decades after the first observation of CPV in mesons. It will be helpful to understand the matter-antimatter asymmetry in the universe. In addition to the global CPV, local CPV is also observed by LHCb in the low mass region of $m_{p\ddot{I}{€}^{+}\ddot{I}{€}^{-}}<2.7$GeV as $(5.4\pm 0.9\pm 0.1)\%$ with a significance of 6.0$\ddot{I}ƒ$. Intriguingly, this measurement aligns well with a theoretical prediction of $(5.6-5.9)\%$ based on a CPV dynamics using the data of $N\ddot{I}€\to p\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ scatterings. Since baryons contain one more quark than mesons, the dynamics of baryon decays are significantly different from those of mesons. Therefore, the first observation of baryon CPV by LHCb opens a new horizon in the studies of dynamics of the strong interaction.

2 pages