New extraction of CP violation in b-baryon decays

Abstract

We study CP violation in b-baryon decays of $Ξ_b^- \to Ξ^- D$ 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 $\barρ$ and $\barη$ the CKM elements with the decay rate ratios of $R_i= Γ(Ξ_b^- \to Ξ^-D_{i} ) / Γ( Ξ_b^- \to Ξ^-D^0 )$ without the charge conjugate states. As a complementary, we also examine the decay distributions of $Λ_b \to Λ(\to p π^- ) D$. There are in total 32 decay observables, which can be parameterized by 9 real parameters, allowing the experiments to extract the angle $γ\equiv \arg(-V_{ud}V_{ub}^*/V_{cd}V_{cb}^*)$ in the CKM unitarity triangle. In addition, the feasibilities of the experimental measurements are discussed. We find that $\barρ$ and $\barη$ can be extracted at LHCb Run3 from $Ξ_b^- \to Ξ^- D$, and a full analysis of $Λ_b \to Λ(\to p π^-)D$ is available at LHCb Run4.