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Combined fit to ARGUS tau decay parameter measurements in ALBRECHT 1998, ALBRECHT 1995C, ALBRECHT 1993G, and ALBRECHT 1994E. ALBRECHT 1998 use tau pair events of the type ${{\mathit \tau}^{-}}$ ${{\mathit \tau}^{+}}$ $\rightarrow({{\mathit \ell}^{-}}{{\overline{\mathit \nu}}_{{{{{\mathit \ell}}}}}}{{\mathit \nu}_{{{\tau}}}})({{\mathit \pi}^{+}}{{\mathit \pi}^{0}}{{\overline{\mathit \nu}}_{{{\tau}}}}$), and their charged conjugates.

²	ABE 1997O assume $\eta $ = 0 in their fit. Letting $\eta $ vary in the fit gives a $\xi $ value of $1.02$ $\pm0.36$ $\pm0.05$.

Combined fit to ARGUS tau decay parameter measurements in ALBRECHT 1995C, ALBRECHT 1993G, and ALBRECHT 1994E. ALBRECHT 1995C uses events of the type ${{\mathit \tau}^{-}}$ ${{\mathit \tau}^{+}}$ $\rightarrow$ (${{\mathit \ell}^{-}}{{\overline{\mathit \nu}}_{{{{{\mathit \ell}}}}}}{{\mathit \nu}_{{{\tau}}}}$ ) (${{\mathit h}^{+}}{{\mathit h}^{-}}{{\mathit h}^{+}}{{\overline{\mathit \nu}}_{{{\tau}}}}$ ) and their charged conjugates.

⁴	ALBRECHT 1993G measurement determines $\vert \xi \vert $ for the case $\xi ({{\mathit e}}$) = $\xi ({{\mathit \mu}}$), but the authors point out that other LEP experiments determine the sign to be positive.

References

Except where otherwise noted, content of the 2025 Review of Particle Physics is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license. The publication of the Review of Particle Physics is supported by US DOE, MEXT (Japan), INFN (Italy) and CERN. Individual collaborators receive support for their PDG activities from their respective institutes or funding agencies. © 2025. See LBNL disclaimers.

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