Probing for new physics with rare charm baryon (Λc, Ξc, Ωc) decays

We analyze rare charm baryon decays within the standard model and beyond. We identify all null test observables in unpolarized Lambda(c)-> pl(+)l(-), l = e, mu decays, and study the new physics sensitivities. We find that the longitudinal dilepton polarization fraction F-L is sensitive to electromagnetic dipole couplings C-7((i))} , and to the right-handed 4-fermion vector coupling C-9'. The forward-backward asymmetry, A(FB), due to the GIM-suppression a standard model null test already, probes the left-handed axialvector 4-fermion coupling C-10; its CP-asymmetry, A(FB)(CP) probes CP-violating phases in C-10. Physics beyond the standard model can induce branching ratios of dineutrino modes Lambda(c)-> p nu nu over bar up to a few times 10(-5), and one order of magnitude smaller if lepton flavor universality is assumed, while standard model rates are negligible. Charged lepton flavor violation allows for striking signals into e(+/-)mu(-/+) final states, up to 10(-6) branching ratios model-independently, and up to order 10(-8) in leptoquark models. Related three-body baryon decays Xi(c)-> Sigma ll, Xi(c)-> Lambda ll and Omega(c)-> Xi ll offer similar opportunities to test the standard model with vertical bar Delta c vertical bar = vertical bar Delta u vertical bar = 1 transitions.

Automated summary

The study highlights the sensitivity of observables such as the longitudinal dilepton polarization fraction and forward-backward asymmetry to new physics, detecting electromagnetic dipole couplings and 4-fermion vector couplings. Physics beyond the standard model can induce very high branching ratios, while standard model rates are negligible. Lepton flavor violation can also lead to striking signals.