Remarks on strong phase shifts in weak nonleptonic baryon decays

TL;DR

This paper reviews strong phase shifts in weak baryon decays, highlighting their small sizes historically, recent large shifts observed, and proposes a unified parameterization to aid future $CP$ violation studies.

Contribution

It provides a comprehensive overview of strong phase conventions and introduces a unified parameterization for analyzing baryon decay phases.

Findings

Small phase shifts in hyperon decays below ten degrees.

Large phase shift observed in $ ext{Λ}_c^+ o ext{Ξ}^0 K^+$ decay.

Numerical results under the unified parameterization for future $CP$ violation research.

Abstract

A sizable strong-interaction phase shift in weak two-body nonleptonic baryon decay would enhance the possibility of discovering charge-conjugation parity ($CP$) violation in the baryon sector, which might help in the quest for understanding the matter-antimatter asymmetry in the universe. Over the past 60 years, empirical analyses involving different types of instruments, including fixed-target experiments and $e^+e^-$ colliders, have indicated that the phase shifts in nonleptonic hyperon decays are relatively small, below order ten degrees in size. A large phase shift, however, has been observed by BESIII in the decay of a charmed baryon into a hyperon and kaon, $\Lambda_c^+\to \Xi^0K^+$. In various experimental and theoretical studies on hyperon, charmed-baryon, and bottomed-baryon decays, different conventions have been adopted for defining the strong phases. It is important to be aware of this situation when obtaining global averages from different measurements and applying the results to future investigations on $CP$ violation among baryons. This paper gives an overview of the conventions employed in the literature for the strong phases and suggests a unified parameterization form applicable to the different alternatives. Numerical results under the unified parameterization form are also provided, which can serve as useful inputs to further pursuits of baryon $CP$ violation.