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

Publisher Website

19 January 2005

journal article
research article
Published by American Physical Society (APS) in Physical Review Letters

Vol. 94 (2) , 021802
https://doi.org/10.1103/physrevlett.94.021802

Abstract

The two transverse polarization components

P_{T_{1}}

and

P_{T_{2}}

of the

e^{+}

from the decay of polarized

μ^{+}

have been measured as a function of the

e^{+}

energy. Their energy averaged values are

⟨ P_{T_{1}} ⟩ = (6.3 \pm 7.7 \pm 3.4) \times 10^{- 3}

and

⟨ P_{T_{2}} ⟩ = (- 3.7 \pm 7.7 \pm 3.4) \times 10^{- 3}

. From the energy dependence of

P_{T_{1}}

and

P_{T_{2}}

the decay parameters

η, η^{''}

and

α^{'} / A, β^{'} / A

are derived, respectively. Assuming only one additional coupling besides the dominant

V - A

interaction one gets improved limits on

η

,

β^{'} / A

, and the scalar coupling constant

g_{R R}^{S} : η = (- 2.1 \pm 7.0 \pm 1.0) \times 10^{- 3}

,

β^{'} / A = (- 1.3 \pm 3.5 \pm 0.6) \times 10^{- 3}

,

R e {g_{R R}^{S}} = (- 4.2 \pm 14.0 \pm 2.0) \times 10^{- 3}

, and

I m {g_{R R}^{S}} = (5.2 \pm 14.0 \pm 2.4) \times 10^{- 3}

.

Keywords

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