New extraction of CP violation in b-baryon decays

Abstract

We study CP violation in b-baryon decays of $\Xi_b^- \to \Xi^- D$ with $D = D^0, \bar{D}^0$ and $D_i~(i=1,2)$. We find that these baryonic decay processes provide an ideal opportunity to measure the weak phase due to the absence of the relative strong phase. Explicitly, we relate $\bar{\rho}$ and $\bar{\eta}$ the CKM elements with the decay rate ratios of $R_i= \Gamma(\Xi_b^- \to \Xi^-D_{i} ) / \Gamma( \Xi_b^- \to \Xi^-D^0 )$ without the charge conjugate states. As a complementary, we also examine the decay distributions of $\Lambda_b \to \Lambda(\to p \pi^- ) D$. There are in total 32 decay observables, which can be parameterized by 9 real parameters, allowing the experiments to extract the angle $\gamma\equiv \arg(-V_{ud}V_{ub}^*/V_{cd}V_{cb}^*)$ in the CKM unitarity triangle. In addition, the feasibilities of the experimental measurements are discussed. We find that $\bar{\rho}$ and $\bar{\eta}$ can be extracted at LHCb Run3 from $\Xi_b^- \to \Xi^- D$, and a full analysis of $\Lambda_b \to \Lambda(\to p \pi^-)D$ is available at LHCb Run4.