Measurement of branching fractions and decay asymmetry parameters for Λc+ → Λh+ and Λc+ → Σ0h+ (h=K,π), and search for CP violation in baryon decays

Science Bulletin. 2023.

Kinoshita K., Aihara H., Aushev T., Bodrov D., Pakhlova G., Uglov T.

We report a study of Λ+c→Λh+ and Λ+c→Σ0h+ (h=K,π) decays based on a data sample of 980~fb−1 collected with the Belle detector at the KEKB energy-asymmetric e+e− collider. The first results of direct CP asymmetry in two-body singly Cabibbo-suppressed (SCS) decays of charmed baryons are measured, AdirCP(Λ+c→ΛK+)=+0.021±0.026±0.001 and AdirCP(Λ+c→Σ0K+)=+0.025±0.054±0.004. We also make the most precise measurement of the decay asymmetry parameters (α) for the four modes of interest and search for CP violation via the α-induced CP asymmetry (AαCP). We measure AαCP(Λ+c→ΛK+)=−0.023±0.086±0.071 and AαCP(Λ+c→Σ0K+)=+0.08±0.35±0.14, which are the first AαCP results for SCS decays of charmed baryons. We search for Λ-hyperon CP violation in Λ+c→(Λ,Σ0)π+ and find AαCP(Λ→pπ−)=+0.013±0.007±0.011. This is the first time that hyperon CP violation has been measured via Cabibbo-favored charm decays. No evidence of baryon CP violation is found. We also obtain the most precise branching fractions for two SCS Λ+c decays, B(Λ+c→ΛK+)=(6.57±0.17±0.11±0.35)×10−4 and B(Λ+c→Σ0K+)=(3.58±0.19±0.06±0.19)×10−4. The first uncertainties are statistical and the second systematic, while the third uncertainties come from the uncertainties on the world average branching fractions of Λ+c→(Λ,Σ0)π+.

Keywords: CP violation, Belle detector, Branching fraction, Charmed baryons, Singly Cabibbo-suppressed decay, decay asymmetry parametry

Publication based on the results of: Development of new methods for searching for physics beyond the Standard Model in experiments at the Super Charm-Tau Factory and Belle at the KEKB B-Factory (2023)