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

Abstract

We study the full angular distribution of semileptonic rare charm baryon decays in which the secondary baryon undergoes weak decay with sizable polarization parameter,analyzing decay chains allow for seven additional observables compared to three-body decays such as Λ c → p + − , with different sensitivities to the |∆c| = |∆u| = 1 weak couplings. Opportunities to test the standard model in c → u transitions with standard model null testsand other angular observables are worked out. We show that a joint model-independent analysis of the leptonic A FB , hadronic A H FB , and combined forward-backward asymmetry A H FB 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 H FB is also accessible with dineutrino c → uν ν modes and probes right-handed currents.

Null test BSM searches with rare charm baryon decays

“…We discuss further opportunities in rare charm four-body decay modes based on recent results in Ref. [4] and conclude in Sec. 5.…”

“…Recently, further null test opportunities were presented for (quasi-) four-body decay chains of charmed baryons, where the final state baryon further decays weakly with sizable polarization parameter 𝛼 [4]. These self analyzing four-body final states offer a rich angular distribution with complementary sensitivities to NP couplings.…”

“…We refer to Ref. [4] for further details, but exemplary discuss for the decay chain Ξ + 𝑐 → Σ + (→ 𝑝𝜋 0 )𝜇 + 𝜇 − the forward-backward asymmetry of the final state hadron system 𝐴 H FB , which can be defined in close analogy to 𝐴 FB in Eq. ( 4).…”

“…The upper plot is taken from Ref. [4] and shows several BSM scenarios (see legend) and the SM. The lower row plots further illustrate the sensitivity to 𝐶 7 and 𝐶 9, (10) via decreasing benchmark values.…”

“…Null test observables, already part of the ongoing precision programs of 𝑏 → 𝑠ℓ + ℓ − transitions, vanish in the SM and hence any signal indicates BSM physics, which makes null tests inevitable in New Physics (NP) searches in |Δ𝑐| = |Δ𝑢| = 1 processes. In particular, the spin structure in rare charm baryon decays offers a rich angular distribution, including several clean null tests [3,4]. Recent experimental and theoretical progress of rare charm decays is compiled in Ref.…”