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The transverse polarization components of the positrons from the decay of polarized muons have been measured at the Paul Scherrer Institute by annihilating in flight the decay positrons with polarized electrons. The use of a stroboscopic method greatly reduces systematic errors. The energy dependence of the transverse polarization component PT1, which lies in the plane spanned by muon spin and positron momentum, yields the low energy parameter η and thus an improved model-independent value of the Fermi coupling constant. A non-zero value of the transverse component PT2, which is perpendicular to the plane mentioned above, would be the first observation of time reversal violation in a purely leptonic decay. Part of the data (40 × 108 annihilation events) have been evaluated. Both PT1 and PT2, averaged over the positrons’ energy, are consistent with zero with a precision improved by a factor of three as compared with the previous measurement. The preliminary results are = (7 ± 8) × 10-3, = (-1 ± 8) × 10-3 in full agreement with the standard model. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The standard model of electroweak interactions predicts that the positrons from the decay of polarized positive muons are mainly longitudinally polarized. The measurement of the two transverse polarization components of the positron PT1 and PT2 is a sensitive tool to look for contributions from additional, exotic interactions and for the violation of time reversal invariance in this purely leptonic decay. The μPT - experiment at the Paul Scherrer Institute determines the three positron polarization components simultaneously with the same apparatus by making use of three different effects. By examining the temporal dependence of annihilation-in-flight of the decay positrons with polarized electrons a possible non-zero value of the transverse polarization is determined. The phase of this transverse polarization can be measured by making use of the decay asymmetry. Using the dependence of annihilation-in-flight on the angle between electron polarization and positron momentum leads to the determination of the longitudinal polarization which not only completes the measurement of the entire polarization vector but also serves as a sensitivity check. In order to deduce the polarization at the time and location of the muon decay a method based on Monte-Carlo simulations with full spin-dependence implemented is being developed. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

In the standard model (SM) of electroweak interactions the positron from the decay of polarized positive muons is mainly longitudinally polarized. The measurement of the two transverse polarization components, therefore, is a sensitive tool for contributions from additional, exotic, interactions. The energy dependence of the transverse polarization component P[sub T[sub 1]], which lies in the plane spanned by muon-spin and positron momentum, yields the low energy parameter η and thus an improved mode-independent value of the Fermi coupling constant. A non-zero value of the transverse component P[sub T[sub 2]], which is perpendicular to the above mentioned plane, would be the first observation of time reversal violation in a purely leptonic decay. The μ[sub P[sub T]] experiment at the Paul Scherrer Institute determines the three polarization components simultaneously with the same apparatus by making use of three different reactions (spatial and temporal dependence of annihilation-in-flight with polarized electrons as well as muon decay asymmetry). The use of a stroboscopic method greatly reduces systematic errors. The measurement of the longitudinal polarization serves mainly as a test of the sensitivity of the apparatus, while the measurement of the two transverse components will improve the current experimental limits. The preliminary results are P[sub T[sub 1]] = (7 ±13) x 10[sup -3], P[sub T[sub 2]] = (19±13) x 10[sup -3]. [ABSTRACT FROM AUTHOR]

n the standard model (SM) of electroweak interactions the positron from the decay of polarized positive muons is mainly longitudinally polarized. However the model also predicts a small transverse polarization component P[sub T[sub 1]], which lies in the plane spanned by muon-spin and positron momentum. Interference with additional, scalar couplings would result in substantial values for P[sub T[sub 1]] as well as in a non-zero value of the transverse component P[sub T[sub 2]] which is perpendicular to the above mentioned plane. A nonzero component P[sub T[sub 2]], proportional to the imaginary part of a possible scalar coupling, would be the first observation of time reversal violation in a purely leptonic decay. Measuring P[sub T[sub 1]], which is proportional to the real part, amounts to a model independent determination of the Fermi-coupling constant. The μ[sub P[sub T]] experiment [1] at the Paul Scherrer Institute will improve the current experimental limits P[sub T[sub 1]] = (16 ± 22) x 10[sup -3], P[sub T[sub 2]] = (7 ± 23) x 10[sup -3] by almost one order of magnitude. First preliminary results of the experiment are given. [ABSTRACT FROM AUTHOR]

The transverse polarization components of the positrons from the decay of polarized muons have been measured at the Paul Scherrer Institute by annihilating in flight the decay positrons with polarized electrons. The use of a stroboscopic method greatly reduces systematic errors. The energy dependence of the transverse polarization component PT1, which lies in the plane defined by muon spin and positron momentum, yields the low energy parameter η = (-2 ± 8) × 10 -3 and thus an improved model-independent value of the Fermi coupling constant. For the transverse polarization PT2, averaged over the positron energy, we obtain = (-4 ± 8) × 10-3. This improves the previous limit on the violation of time invariance in muon decay by a factor of three. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]