Impact of $N^*$ and $Λ^*$ resonances on $CP$ violation in $Λ_b^0$ decays

Abstract

The four-body decay $Λ_b^0\to pK^-π^+π^-$ has led to the first observation of baryonic $CP$ violation. However, the underlying subprocesses $Λ_b^0\to N^* M$ and $Λ_b^0\to Λ^* M$, as well as the roles of excited nucleon ($N^*$) and hyperon ($Λ^*$) resonances, remain largely unexplored. Within the constituent quark model, we identify the relevant resonant states contributing to these underlying two-body transitions, including $N(1535)$, $N(1520)$, $Λ(1670)$, $Λ(1690)$, together with the remaining $1P$-wave baryon states. We obtain the resonant branching fraction ${\cal B}(Λ_b^0\to pK^-π^+π^-) =(30.0^{+2.8+4.0}_{-1.3-3.4}\pm1.8)\times10^{-6}$, while the resulting ${\cal A}_{CP}(Λ_b^0\to pK^-π^+π^-)=(3.18\pm0.11\pm0.13\pm0.11)\%$ provides a natural interpretation of the first observed baryonic $CP$ asymmetry. Our analysis establishes the first comprehensive framework for quantifying the impact of excited baryon resonances in multi-body beauty-baryon decays, with the associated mechanism generally applicable to baryonic $CP$ asymmetries.