{
  "abstract": "Tau spin correlations at the $Z$ pole probe CP violation with a sensitivity that depends strongly on the spin projection. For a fixed $Z$ sample, transverse moments avoid the chirality suppression of longitudinal and triple-product observables, enhancing the response by a factor $m_Z/2m_τ=26$. Two transverse moments also select the axial tau charge, gaining $|a_τ/v_τ|=13.5$; the sign-weighted normal moment has a response $521$ times that of the triple product. These two transverse moments give single-parameter uncertainties no more than $14\\%$ above our calculated Cramer-Rao bound for independent single-pion measurements, approaching the best precision within this analysis. A five-moment fit with $5\\%$ off-peak luminosity yields statistical uncertainties of $4.5 (5.5)\\times10^{-7}$ and $2.7 (3.2)\\times10^{-6}$ on $\\operatorname{Re}\\widetilde{d}_τ^W$ and $\\operatorname{Im}\\widetilde{d}_τ^W$, respectively, at FCC-ee (CEPC), improving on ALEPH by three orders of magnitude. The electromagnetic-dipole uncertainty is $9.6 (12)\\times10^{-6}$ on $\\operatorname{Re}\\widetilde{d}_τ^γ$, two orders beyond Belle. These projections assume ideal angular reconstruction and constant form factors across the scan.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.18892",
  "author_total": 4,
  "authors": [
    {
      "name": "Xin-Yu Du"
    },
    {
      "name": "Zi-Yue Zou"
    },
    {
      "name": "Xiao-Gang He"
    },
    {
      "name": "Keping Xie"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/4fsmfk0da4z2h.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.18892",
  "fulltext_url": null,
  "id": "4fsmfk0da4z2h",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.18892",
  "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-ex"
    ],
    [
      "arxiv",
      "hep-ph"
    ],
    [
      "openalex",
      "3106|Particle physics theoretical and experimental studies"
    ]
  ],
  "openalex": "W7213506380",
  "pdf_url": "https://arxiv.org/pdf/2609.18892",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-16",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/4fsmfk0da4z2h.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:22:01Z",
      "native_id": "2609.18892",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.18892"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:hep-ex",
      "subfield": "high-energy"
    }
  ],
  "title": "Transverse Tau Spin Correlations and the Weak Electric Dipole Moment at Future $Z$ Factories",
  "title_text": "Transverse Tau Spin Correlations and the Weak Electric Dipole Moment at Future Z Factories",
  "type": "preprint",
  "updated_at": "2026-10-30T12:22:01Z",
  "url": "https://research.draconitic.com/paper/4fsmfk0da4z2h",
  "venue": "arXiv",
  "versions": []
}