CP violation in two-body hadronic Λb decays in the PQCD approach

Abstract

We systematically investigate the CP-averaged branching ratios and CP violations (CPVs) for the two-body hadronic decays Λb→ph, where h runs through the mesons π−, ρ−, a1−(1260), K−, K*−, K1−(1270), and K1−(1400), in the perturbative QCD approach to order αs2 in the strong coupling. Various topological amplitudes are obtained by incorporating subleading-twist hadron distribution amplitudes, which exhibit reasonable hierarchical patterns, sizable strong phases, and non-negligible higher-power corrections. The predicted direct CPVs in Λb→pπ−,pK−, different from those in similar B meson decays, are as small as the current data. The low CPV in Λb→pπ− results from the cancelation between the S- and P-wave CPVs, while the one in Λb→pK− is determined by the tiny S-wave CPV. However, individual partial-wave CPVs can exceed 10%, consistent with direct CPVs in B meson decays. The CPVs in the Λb→pK1−(1270),pK1−(1400) channels are relatively larger. In particular, CPVs above 20% appear in the up-down asymmetries associated with the final-state angular distributions of Λb→pK1−(1270),pK1−(1400), followed by the secondary K1→Kππ decays. These observables offer promising prospects for firmly establishing baryon CPVs. The decay asymmetry parameters of Λb→ph are also predicted for future experimental confrontations.