Probing for New Physics with Rare Charm Baryon ($Λ_c$, $Ξ_c$, $Ω_c$) Decays

Abstract

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.

Null test searches for BSM physics with rare charm decays

“…Especially NP in dipole operators leads to a different shape of the distribution, which can be understood from helicity arguments, as discussed in Ref. [23]. Also see Ref.…”

“…Input on branching ratios, masses and decay widths is taken from the PDG [26]. One finds 𝑎 𝜔 = 0.065 ± 0.016 and 𝑎 𝜙 = 0.110 ± 0.008 for the Λ 𝑐 → 𝑝𝜇 + 𝜇 − case, however the same procedure can be applied to other rare charm baryon modes [23], 𝐷 → 𝑃ℓ + ℓ − modes [15] and…”

“…The full dependence on Wilson coefficients and form factors of the angular coefficients 𝐾 1𝑠𝑠 , 𝐾 1𝑐𝑐 , 𝐾 1𝑐 is given in Ref. [23]. Fig.…”

“…Next to the rate, it is also possible to study the CP-asymmetry in an angular observable. For instance, 𝐴 CP FB probes the imaginary part of 𝐶 10 , complementary to the CP conserving 𝐴 FB [23].…”

“…The experimental and theoretical status of rare charm decays is presented in Ref. [5] and increasing and ongoing research interest [1,2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] manifests the importance of progress in the field.…”