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.
We analyze rare charm baryon decays within the standard model and beyond. We identify all null test observables in unpolarized Λ c → p + − , = e, µ 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 , 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 CP FB , probes CP-violating phases in C 10 . Physics beyond the standard model can induce branching ratios of dineutrino modes Λ c → 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 Ξ c → Σ , Ξ c → Λ and Ω c → Ξ offer similar opportunities to test the standard model with |∆c| = |∆u| = 1 transitions.
We study the full angular distribution of semileptonic rare charm baryon decays in which the secondary baryon undergoes weak decay with sizable polarization parameter, $$\Xi _c^+\rightarrow \Sigma ^+\,(\rightarrow p\pi ^0)\ell ^+\ell ^-$$ Ξ c + → Σ + ( → p π 0 ) ℓ + ℓ - , $$\Xi _c^0\rightarrow \Lambda ^0\,(\rightarrow p \pi ^-)\ell ^+\ell ^-$$ Ξ c 0 → Λ 0 ( → p π - ) ℓ + ℓ - and $$\Omega _c^0\rightarrow \Xi ^0\,(\rightarrow \Lambda ^{0} \pi ^0)\ell ^+\ell ^-$$ 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 $$\Lambda _c \rightarrow p \ell ^+ \ell ^-$$ Λ c → p ℓ + ℓ - , with different sensitivities to the $$|\Delta c|=|\Delta u|=1$$ | Δ c | = | Δ u | = 1 weak couplings. Opportunities to test the standard model in $$c \rightarrow u$$ 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 $$A_{\text {FB}}^\ell $$ A FB ℓ , hadronic $$A_{\text {FB}}^{\text {H}}$$ A FB H , and combined forward–backward asymmetry $$A_{\text {FB}}^{\ell \text {H}}$$ A FB ℓ H together with the fraction of longitudinally produced leptons, $$F_L$$ F L , is able to pin down the dipole couplings $$C_{7},C^\prime _{7}$$ C 7 , C 7 ′ and the semileptonic (axial-) vector ones $$C_{10},C^\prime _{9},C^\prime _{10}$$ C 10 , C 9 ′ , C 10 ′ . $$A_{\text {FB}}^{\text {H}}$$ A FB H is also accessible with dineutrino $$c \rightarrow u \nu {\bar{\nu }}$$ c → u ν ν ¯ modes and probes right-handed currents.
Rare |Δ𝑐| = |Δ𝑢| = 1 processes uniquely probe flavor in the Standard Model and beyond from the up-type quark sector. Opportunities to search for BSM physics in charm arise from the severe GIM suppression which kills SM contributions to leptonic axial-vector contributions and suppresses CP violation. Semileptonic decays of charmed hadrons offer a variety of clean null test observables, featuring new physics effects which are even enhanced by resonance contributions. In particular angular observables in three-and self-analyzing four-body baryon decays, such as7 and (axial-)vector 4-fermion ones 𝐶 ( ) 9 (10) . There is sensitivity to BSM couplings as small as ∼ 0.01.
Rare |Δ𝑐| = |Δ𝑢| = 1 processes uniquely probe flavor in the Standard Model and beyond from the up-type quark sector. Opportunities to search for BSM physics in charm arise from the severe GIM suppression which kills SM contributions to leptonic axial-vector contributions and suppresses CP violation. Semileptonic decays of charmed hadrons offer a variety of clean null test observables, featuring new physics effects which are even enhanced by resonance contributions. In particular, angular observables in three-and self-analyzing four-body baryon decays, such as7 and (axial-)vector 4-fermion ones 𝐶 ( ) 9 (10) . There is sensitivity to BSM couplings as small as ∼ 0.01.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.