CP violation in the hyperon decays $\Sigma \to N\pi$

Abstract

The study of $CP$ violation in hyperon transitions has a long history. In the early 2000s the HyperCP experiment made a major effort to seek $CP$-odd signals in the decay sequence ${\Xi }^{-}\to \Lambda {\pi }^{-}$ and $\Lambda \to p{\pi }^{-}$, which motivated more searches. Most recently the BESIII and LHCb Collaborations have acquired or improved the upper bounds on $CP$ violation in a variety of hyperon nonleptonic processes, including ${\Sigma }^{+}\to n{\pi }^{+}$ and ${\Sigma }^{+}\to p{\pi }^0$. These measurements have not reached the standard-model level yet, but have stimulated a renewed interest in $CP$-violating new physics in strange-quark decay beyond what is constrained by the parameters $\epsilon$ and ${\epsilon }^{\prime }$ from the kaon sector. In this paper, after updating the standard-model expectations for $CP$-odd observables in the modes ${\Sigma }^{\pm }\to N\pi$, we revisit new-physics scenarios that could enhance the corresponding quantities in $\Lambda \to N\pi$ and $\Xi \to \Lambda \pi$ and apply them to the ${\Sigma }^{\pm }$ modes. We find that the $CP$ asymmetries in the latter can be significantly increased over the standard-model expectations, at levels which may be tested in the ongoing BESIII experiment and in future endeavors such as PANDA and the Super Tau Charm Facility.

arXiv comment24 pages, 5 figures, slightly revised, matches publication

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