Timeline of heavy-baryon semileptonic-decay results

A timeline of experimental and lattice-QCD results for Λ_b, Λ_c, and Ξ_c semileptonic decays, 2011-present.

2025

High-precision lattice-QCD calculation of the Ξ_c→Ξ form factors using domain-wall fermions. The resulting Standard-Model prediction for the Ξ_c⁰→Ξ^-e⁺ν branching fraction is a factor 1.5 higher than the previous prediction by Zhang et al., and a factor of 3.4 higher than the experimental value reported by the Particle Data Group, but consistent with approximate SU(3) flavor-symmetry relations to Λ_c decay branching fractions.

C. Farrell and S. Meinel, https://arxiv.org/abs/2504.07302

2024

First observation of the decay Λ_c→n e⁺ν by BESIII. The measured branching fraction is consistent with my 2017 SM prediction using lattice-QCD and using |V_cd| from unitarity. The BESIII measurement and lattice calculation together yield the first determination of |V_cd| from a baryon decay.

BESIII Collaboration, https://arxiv.org/abs/2410.13515 (Nature Communications)

2024

Higher-sensitivity search for the rare decay Λ_c→pμ⁺μ^- by LHCb.

LHCb Collaboration, https://arxiv.org/abs/2407.11474 (Phys. Rev. D)

2023

First measurement of the Λ_b→Λ^*(1520)μ⁺μ^- differential branching fraction by LHCb. At high q², the results are consistent with our 2021 SM prediction using lattice QCD.

LHCb Collaboration, https://arxiv.org/abs/2302.082627 (Phys. Rev. Lett.)

2022/2023

High-precision measurements of the Λ_c→Λe⁺ν and Λ_c→Λμ⁺ν branching fractions and angular distributions by BESIII, and updated determination of the CKM matrix element |V_cs|. Form-factor shapes fitted to the data are in some tension with my 2016 lattice-QCD predictions.

BESIII Collaboration, https://arxiv.org/abs/2207.14149 (Phys. Rev. Lett.) and https://arxiv.org/abs/2306.02624 (Phys. Rev. D)

2022

First measurement of the Λ_c→Λ^*(1520)e⁺ν branching fraction by BESIII. The result is consistent with our 2021 lattice-QCD prediction.

BESIII Collaboration, https://arxiv.org/abs/2207.11483 (Phys. Rev. D)

2022

First observation of the decay Λ_b→Λ_c τ^- ν and first measurement of the lepton-flavor-universality ratio R(Λ_c) by LHCb. The central value of the measured R(Λ_c) is lower than the SM prediction using our 2015 form factors from lattice QCD, in contrast to the excesses seen in mesonic decays.

LHCb Collaboration, https://arxiv.org/abs/2201.03497 (Phys. Rev. Lett.)

2021

First lattice-QCD calculation of the Λ_c→Λ^*(1520) form factors.

S. Meinel, G. Rendon,
https://arxiv.org/abs/2107.13084 and https://arxiv.org/abs/2107.13140
(Phys. Rev. D)

2021

First lattice-QCD calculation of the Λ_b→Λ_c^*(2595) and Λ_b→Λ_c^*(2625) form factors.

S. Meinel, G. Rendon, https://arxiv.org/abs/2103.08775 (Phys. Rev. D)

(updated in https://arxiv.org/abs/2107.13140)

2020

First lattice-QCD calculation of the Λ_b→Λ^*(1520) form factors.

S. Meinel, G. Rendon, https://arxiv.org/abs/2009.09313 (Phys. Rev. D)

(updated in https://arxiv.org/abs/2107.13140)

2021

ALICE measurement of the ratio of Ξ_c⁰→Ξ^-e⁺ν and Ξ_c⁰→Ξ^-π⁺ branching fractions. The semileptonic branching fraction obtained by multiplying the ratio with a Belle measurement of the Ξ_c⁰→Ξ^-π⁺ branching fraction from 2018 is consistent with the Standard-Model prediction using lattice QCD by Zhang et al..

ALICE Collaboration, https://arxiv.org/abs/2105.05187 (Phys. Rev. Lett.)

2021

First lattice-QCD calculation of the Ξ_c→Ξ form factors. The resulting Standard-Model prediction for the Ξ_c⁰→Ξ^-e⁺ν branching fraction is a factor 1.8 higher than the experimental value from Belle, but is still lower than expected from approximate SU(3) flavor-symmetry relations to Λ_c decay branching fractions.

Q.-A. Zhang et al., https://arxiv.org/abs/2103.07064 (Chin. Phys. C)

2021

Belle measurement of the ratios of Ξ_c⁰→Ξ^-l⁺ν (l=e,μ) and Ξ_c⁰→Ξ^-π⁺ branching fractions. The semileptonic branching fractions obtained by multiplying these ratios with a Belle measurement of the Ξ_c⁰→Ξ^-π⁺ branching fraction from 2018 are much lower than expected from approximate SU(3) flavor-symmetry relations to Λ_c decay branching fractions.

Belle Collaboration, https://arxiv.org/abs/2103.06496 (Phys. Rev. Lett.)

2018

Measurement of the Λ_b→Λμ⁺μ^- angular moments by LHCb. The SM predictions shown use our 2016 lattice-QCD results for the form factors.

LHCb Collaboration, https://arxiv.org/abs/1808.00264 (JHEP)

2017

Search for the rare decay Λ_c→pμ⁺μ^- by LHCb.

LHCb Collaboration, https://arxiv.org/abs/1712.07938 (Phys. Rev. D)

2017

First lattice-QCD calculation of the Λ_c→N (N=p,n) form factors.

S. Meinel, https://arxiv.org/abs/1712.05783 (Phys. Rev. D)

2017

Measurement of the shape of the Λ_b→Λ_cμ^-ν differential decay rate, confirming our 2015 lattice-QCD prediction.

LHCb Collaboration, https://arxiv.org/abs/1709.01920 (Phys. Rev. D)

2016

First lattice-QCD calculation of the Λ_c→Λ form factors and first precise determination of the CKM matrix element |V_cs| from baryon decays.

S. Meinel, https://arxiv.org/abs/1611.09696 (Phys. Rev. Lett.)

2016

First absolute measurement of the Λ_c→Λμ⁺ν branching fraction by BESIII.

BESIII Collaboration, https://arxiv.org/abs/1611.04382 (Phys. Lett. B)

2016

First lattice-QCD calculation of the Λ_b→Λ form factors with physical-mass b quarks.

W. Detmold, S. Meinel, https://arxiv.org/abs/1602.01399 (Phys. Rev. D)

2015

First absolute measurement of the Λ_c→Λe⁺ν branching fraction by BESIII.

BESIII Collaboration, https://arxiv.org/abs/1510.02610 (Phys. Rev. Lett.)

2015

Determination of the ratio of CKM matrix elements |V_ub/V_cb| from Λ_b→pμ^-ν and Λ_b→Λ_cμ^-ν decays by LHCb, using our lattice-QCD calculation of the form factors. This is the first determination of |V_ub/V_cb| from baryon decays and the first at a hadron collider. The result disfavors right-handed couplings beyond the SM as an explanation of the exclusive-inclusive discrepancy in mesonic determinations of |V_ub|.

LHCb Collaboration, https://arxiv.org/abs/1504.01568 (Nature Physics)

2015

Measurement of the Λ_b→Λμ⁺μ^- differential branching fraction and angular distribution by LHCb. The SM prediction shown uses our 2012 lattice-QCD results for the form factors.

LHCb Collaboration, https://arxiv.org/abs/1503.07138 (JHEP)

2015

First lattice-QCD calculation of the Λ_b→p and Λ_b→Λ_c form factors with physical-mass b quarks, and Standard-Model prediction for the lepton-flavor-universality ratio R(Λ_c).

W. Detmold, C. Lehner, S. Meinel, https://arxiv.org/abs/1503.01421 (Phys. Rev. D)

2013

First lattice-QCD calculation of the Λ_b→p form factors with static b quarks.

W. Detmold, C.-J. D. Lin, S. Meinel, M. Wingate, https://arxiv.org/abs/1306.0446 (Phys. Rev. D)

2012

First lattice-QCD calculation of the Λ_b→Λ form factors with static b quarks.

W. Detmold, C.-J. D. Lin, S. Meinel, M. Wingate, https://arxiv.org/abs/1212.4827 (Phys. Rev. D)

2011

First observation of the rare decay Λ_b→Λμ⁺μ^- by CDF.

CDF Collaboration, https://arxiv.org/abs/1107.3753 (Phys. Rev. Lett.)