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Muon Decay: Measurement of the Transverse Polarization of the Decay Positrons and its Implications for the Fermi Coupling Constant and Time Reversal Invariance

2005; American Physical Society; Volume: 94; Issue: 2 Linguagem: Inglês

10.1103/physrevlett.94.021802

1092-0145

N. Danneberg, W. Fetscher, K. Köhler, J. Lang, Thomas Schweizer, A. von Allmen, K. Bodek, L. Jarczyk, St. Kistryn, J. Smyrski, A. Strzałkowski, J. Zejma, K. Kirch, A. Kozela, E. Stephan,

Neutrino Physics Research

The two transverse polarization components ${P}_{{\mathrm{T}}_{1}}$ and ${P}_{{\mathrm{T}}_{2}}$ of the ${e}^{+}$ from the decay of polarized ${\ensuremath{\mu}}^{+}$ have been measured as a function of the ${e}^{+}$ energy. Their energy averaged values are $⟨{P}_{{\mathrm{T}}_{1}}⟩=(6.3\ifmmode\pm\else\textpm\fi{}7.7\ifmmode\pm\else\textpm\fi{}3.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and $⟨{P}_{{\mathrm{T}}_{2}}⟩=(\ensuremath{-}3.7\ifmmode\pm\else\textpm\fi{}7.7\ifmmode\pm\else\textpm\fi{}3.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. From the energy dependence of ${P}_{{\mathrm{T}}_{1}}$ and ${P}_{{\mathrm{T}}_{2}}$ the decay parameters $\ensuremath{\eta},{\ensuremath{\eta}}^{\ensuremath{'}\ensuremath{'}}$ and ${\ensuremath{\alpha}}^{\ensuremath{'}}/A,{\ensuremath{\beta}}^{\ensuremath{'}}/A$ are derived, respectively. Assuming only one additional coupling besides the dominant $V\ensuremath{-}A$ interaction one gets improved limits on $\ensuremath{\eta}$, ${\ensuremath{\beta}}^{\ensuremath{'}}/A$, and the scalar coupling constant ${g}_{RR}^{S}:\text{ }\text{ }\ensuremath{\eta}=(\ensuremath{-}2.1\ifmmode\pm\else\textpm\fi{}7.0\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, ${\ensuremath{\beta}}^{\ensuremath{'}}/A=(\ensuremath{-}1.3\ifmmode\pm\else\textpm\fi{}3.5\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, $\mathrm{R}\mathrm{e}{{g}_{RR}^{S}}=(\ensuremath{-}4.2\ifmmode\pm\else\textpm\fi{}14.0\ifmmode\pm\else\textpm\fi{}2.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, and $\mathrm{I}\mathrm{m}{{g}_{RR}^{S}}=(5.2\ifmmode\pm\else\textpm\fi{}14.0\ifmmode\pm\else\textpm\fi{}2.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.