Search

We study the full angular distribution of semileptonic rare charm baryon decays in which the secondary baryon undergoes weak decay with sizable polarization parameter, Ξ c + → Σ + (→ p π 0) ℓ + ℓ - , Ξ c 0 → Λ 0 (→ p π -) ℓ + ℓ - and Ω c 0 → Ξ 0 (→ Λ 0 π 0) ℓ + ℓ - . Such self-analyzing decay chains allow for seven additional observables compared to three-body decays such as Λ c → p ℓ + ℓ - , with different sensitivities to the | Δ c | = | Δ u | = 1 weak couplings. Opportunities to test the standard model in c → u transitions with standard model null tests and other angular observables are worked out. We show that a joint model-independent analysis of the leptonic A FB ℓ , hadronic A FB H , and combined forward–backward asymmetry A FB ℓ H together with the fraction of longitudinally produced leptons, F L , is able to pin down the dipole couplings C 7 , C 7 ′ and the semileptonic (axial-) vector ones C 10 , C 9 ′ , C 10 ′ . A FB H is also accessible with dineutrino c → u ν ν ¯ modes and probes right-handed currents. [ABSTRACT FROM AUTHOR]

We analyze rare charm baryon decays within the standard model and beyond. We identify all null test observables in unpolarized Λc→ pℓ+ℓ−, ℓ = e, μ decays, and study the new physics sensitivities. We find that the longitudinal dilepton polarization fraction FL is sensitive to electromagnetic dipole couplings C 7 ′ , and to the right-handed 4-fermion vector coupling C 9 ′ . The forward-backward asymmetry, AFB, due to the GIM-suppression a standard model null test already, probes the left-handed axialvector 4-fermion coupling C10; its CP–asymmetry, A FB CP probes CP-violating phases in C10. Physics beyond the standard model can induce branching ratios of dineutrino modes Λc→ pν ν ¯ 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±μ∓ final states, up to 10−6 branching ratios model-independently, and up to order 10−8 in leptoquark models. Related three-body baryon decays Ξc→ Σℓℓ, Ξc→ Λℓℓ and Ωc→ Ξℓℓ offer similar opportunities to test the standard model with |∆c| = |∆u| = 1 transitions. [ABSTRACT FROM AUTHOR]