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A comprehensive study of $Λ_c^- \to Λ(\to p π) μ^- \bar ν_μ$ incorporating SMEFT implications and right-handed neutrino

Priyanka Boora, Siddhartha Karmakar, Dinesh Kumar, Kavita Lalwani

TL;DR

This work investigates the semileptonic charm baryon decay Λ_c^- → Λ( → pπ) μ^- ν_μ within a model-independent EFT framework that includes both left-handed and right-handed neutrinos. By constructing the low-energy LEFT Hamiltonian for c → s μ ν and identifying the SMEFT operators that map onto it, the authors perform both direct LEFT fits and SMEFT-informed global analyses to obtain tight indirect bounds on the Wilson coefficients at Λ = 1 TeV. Using these bounds, they compute differential decay rates, forward-backward asymmetries, baryon and lepton polarizations, and the full four-body angular coefficients, for both the three-body Λ_c^- → Λ μ^- ν_μ and the four-body Λ_c^- → Λ( → pπ) μ^- ν_μ decays, revealing enhanced sensitivity to vector operators with right-handed quark currents, especially in polarization observables and certain angular coefficients such as M1, M5, M6, and M7. The results identify clean NP probes, notably the observable ${ m M}_7$ in the four-body channel and the longitudinal Λ polarization ${ m P}_L^ ext{Λ}$, which can discriminate among LH and RH neutrino scenarios and potential UV completions, with concrete predictions testable at BESIII, Belle II, and LHCb.

Abstract

Charm baryon decays provide a complementary probe of new physics beyond the Standard Model. We study the decay $Λ_c^- \to Λ(p π) μ^- \bar ν_μ$ in a model-independent effective field theory framework. This study covers both the left-handed and right-handed neutrino interactions in the $c \to s μν_μ$ transition. For the left-handed neutrino operators, we incorporate the implications of the Standard Model effective field theory and do a global fit considering several observables sensitive to these operators. Based on the allowed parameter space of the new-physics operators, we analyze the differential rates, forward-backward asymmetries, polarization asymmetries of the final-state hadron and lepton in $Λ_c^- \to Λμ^- \bar ν_μ$, and the angular coefficients in 4-body angular distribution of $Λ_c^- \to Λ(\to p π) μ^- \bar ν_μ$. Our results highlight distinctive signatures of certain operators involving right-handed quark currents and provide predictions that can be tested at BESIII, Belle II, and LHCb.

A comprehensive study of $Λ_c^- \to Λ(\to p π) μ^- \bar ν_μ$ incorporating SMEFT implications and right-handed neutrino

TL;DR

This work investigates the semileptonic charm baryon decay Λ_c^- → Λ( → pπ) μ^- ν_μ within a model-independent EFT framework that includes both left-handed and right-handed neutrinos. By constructing the low-energy LEFT Hamiltonian for c → s μ ν and identifying the SMEFT operators that map onto it, the authors perform both direct LEFT fits and SMEFT-informed global analyses to obtain tight indirect bounds on the Wilson coefficients at Λ = 1 TeV. Using these bounds, they compute differential decay rates, forward-backward asymmetries, baryon and lepton polarizations, and the full four-body angular coefficients, for both the three-body Λ_c^- → Λ μ^- ν_μ and the four-body Λ_c^- → Λ( → pπ) μ^- ν_μ decays, revealing enhanced sensitivity to vector operators with right-handed quark currents, especially in polarization observables and certain angular coefficients such as M1, M5, M6, and M7. The results identify clean NP probes, notably the observable in the four-body channel and the longitudinal Λ polarization , which can discriminate among LH and RH neutrino scenarios and potential UV completions, with concrete predictions testable at BESIII, Belle II, and LHCb.

Abstract

Charm baryon decays provide a complementary probe of new physics beyond the Standard Model. We study the decay in a model-independent effective field theory framework. This study covers both the left-handed and right-handed neutrino interactions in the transition. For the left-handed neutrino operators, we incorporate the implications of the Standard Model effective field theory and do a global fit considering several observables sensitive to these operators. Based on the allowed parameter space of the new-physics operators, we analyze the differential rates, forward-backward asymmetries, polarization asymmetries of the final-state hadron and lepton in , and the angular coefficients in 4-body angular distribution of . Our results highlight distinctive signatures of certain operators involving right-handed quark currents and provide predictions that can be tested at BESIII, Belle II, and LHCb.

Paper Structure

This paper contains 29 sections, 47 equations, 8 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Theoretical Framework
  3. Form Factors
  4. Helicity Amplitudes
  5. Constraining the NP Wilson coefficients
  6. Angular Distributions of the Decay
  7. $\Lambda_c^- \to \Lambda \mu^- \nu_{\mu}$ Decay
  8. $\Lambda_c^- \to \Lambda (p \pi) \mu^- \nu_{\mu}$ Decay
  9. Results
  10. Predictions of observables for Left-Handed Neutrinos
  11. $\Lambda_c^- \to \Lambda \mu^- \nu_{\mu}$ Decay
  12. $\Lambda_c^- \to \Lambda \,(p \pi)\, \mu^- \nu_{\mu}$ Decay
  13. Predictions on observables for Right-Handed Neutrinos
  14. $\Lambda_c^- \to \Lambda \mu^- \nu_{\mu}$ Decay
  15. $\Lambda_c^- \to \Lambda \,(p \pi)\, \mu^- \nu_{\mu}$ Decay
  16. ...and 14 more sections

Figures (8)

  • Figure 1: Constraints on the LEFT WCs incovling LHNs. The cyan regions denote that constraining observables are mediated directly via $c\to s\mu \nu_\nu$ transition. Orange regions denote SMEFT implied constraints.
  • Figure 2: Constraints on the LEFT WCs incovling RHNs. The constraining observables are mediated directly via $c\to s\mu \nu_\nu$ transition.
  • Figure 3: LHN: $q^2$ spectra for the differential branching fraction (top left), forward-backward asymmetry (top right), $\Lambda$ polarization asymmetry (bottom left), and muon polarization asymmetry (bottom right) for three-body decay.
  • Figure 4: LHN: $q^2$ spectra for the $\mathcal{M}_0^{\nu_L}$ (top left), $\mathcal{M}_1^{\nu_L}$ (top right), $\mathcal{M}_2^{\nu_L}$ (bottom left), and $\mathcal{M}_3^{\nu_L}$ (bottom right) for four-body decay.
  • Figure 5: LHN: $q^2$ spectra for the $\mathcal{M}_4^{\nu_L}$ (top left), $\mathcal{M}_5^{\nu_L}$ (top right), $\mathcal{M}_6^{\nu_L}$ (middle left), $\mathcal{M}_7^{\nu_L}$ (middle right) and $\mathcal{M}_8^{\nu_L}$ (bottom) for four-body decay.
  • ...and 3 more figures