{
  "abstract": "We investigate the polarization of the charged lepton in the semileptonic hyperon decay $Λ\\to p\\,\\ell^-\\barν_\\ell$ ($\\ell=e,μ$) within the Standard Model, using the form factors obtained from lattice QCD. We compute the longitudinal, transverse and normal polarization of the lepton, the forward-backward asymmetry of each lepton spin state, and the lepton flavor universality ratio $R_{μe}$. We show that the longitudinal polarization determines the ratio $g_1/f_1$ of the axial-vector to vector couplings, and that the forward-backward asymmetries of the electron and of negative-helicity muons determine the weak magnetism. The asymmetry of positive-helicity muons is fixed by kinematics up to a small dependence on the second-class form factors, whereas $R_{μe}$ is nearly independent of $g_1/f_1$ and the weak magnetism. For comparison, we also use the QCD sum-rule form factors, whose $g_1/f_1$ and weak magnetism are opposite in sign to experiment and lattice QCD, and find very different values for the observables that depend on them. Moreover, the $q^2$ dependence of $R_{μe}$ fixes the longitudinal polarization of the muon, which can thus be measured from the decay rates, without measuring the muon spin. The normal polarization is generated by the electromagnetic final-state interaction and provides the Standard Model reference for searches for time-reversal violation. The electron forward-backward asymmetry and $R_{μe}$ can be measured at BESIII and the proposed Super Tau-Charm Facility, and $R_{μe}$ also at LHCb. These measurements can test the Standard Model and the lattice-QCD form factors.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.35717",
  "author_total": 2,
  "authors": [
    {
      "name": "Qazi Maaz Us Salam"
    },
    {
      "name": "Ishtiaq Ahmed"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/d477xy9c1a3jh.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.35717",
  "fulltext_url": null,
  "id": "d477xy9c1a3jh",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.35717",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "hep-ph"
    ],
    [
      "openalex",
      "3106|Quantum Chromodynamics and Particle Interactions"
    ]
  ],
  "openalex": "W7223786354",
  "pdf_url": "https://arxiv.org/pdf/2610.35717",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-26",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/d477xy9c1a3jh.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:35:35Z",
      "native_id": "2610.35717",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.35717"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:hep-ph",
      "subfield": "high-energy"
    }
  ],
  "title": "Lepton polarization and sensitivity to the form factors in $Λ\\to p\\,\\ell^-\\barν_\\ell$ with lattice QCD",
  "title_text": "Lepton polarization and sensitivity to the form factors in Λ→ p ℓ^-ν̅_ℓ with lattice QCD",
  "type": "preprint",
  "updated_at": "2026-10-30T12:35:35Z",
  "url": "https://research.draconitic.com/paper/d477xy9c1a3jh",
  "venue": "arXiv",
  "versions": []
}