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

Abstract

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 $$ {C}_7^{\left(\prime \right)} $$ C 7 ′ , and to the right-handed 4-fermion vector coupling $$ {C}_9^{\left(\prime \right)} $$ 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, $$ {A}_{\mathrm{FB}}^{\mathrm{CP}} $$ A FB CP probes CP-violating phases in C10. Physics beyond the standard model can induce branching ratios of dineutrino modes Λc→ pν$$ \overline{\nu} $$ 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.

Endpoint relations for baryons

“…These relations have been verified explicitly, in the form factor basis (3.1) and (3.6), with resuling helicity amplitudes in (3.13) and (3.19) 11 The situation in charm changes drastically in the presence of new physics, which is much less constrained than in beauty. In fact FL tests the Standard Model [25]. A concrete BSM study for Λc → pµ + µ − reveals a possible relative deviation in the 20%-and 10%-bin of roughly 45% and 25%, respectively.…”

“…Rare baryonic decays are suitable for experimental study at high luminosity flavour facilities, such as LHCb [17], Belle II [18], BES III [19], and possible future machines [20]. Efforts exist for Hyperons [21] and in charm [22][23][24][25]. In beauty, the situation is more advanced, and first studies with angular distributions for b-baryon decays are available [26], as well as prospects for decays to spin 3/2 baryons, such as Λ b → Λ(1520) [27].…”

Pinning down $|Δc|=|Δu|=1$ couplings with rare charm baryon decays

“…The strong phases δ M are unknown and provide a significant amount of theoretical uncertainty. We neglect effects from intermediate η, η mesons as they are strongly localized and have a negligible effect on the (differential) branching ratio [12]. We further use isospin to relate the ρ and ω contributions [26], as no data on any of the B 0 → B 1 ρ branching ratios is available.…”

“…Rare semileptonic decays of charm baryons have been explored as a NP probe recently [9][10][11][12].…”

“…In [12] we analyzed the NP sensitivity of rare semileptonic decays of Λ c , Ξ c and Ω c -baryons, here collectively denoted by B 0 → B 1 + − with the initial (daughter) baryon denoted by B 0 (B 1 ), see and review some of the simpler observables already accessible with three-body decays. We work out the impact of the new null tests and other clean NP probes in Sec.…”