Search

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 present form of the Standard Model (SM) describes weak process in terms of vector and axial-vector type interaction, with fully left handed massless neutrinos. Any experimental deviation from the SM predictions will in special cases reveal the need for extensions to the SM. The longitudinal polarization of the positron emitted from polarized muon present a simple and sensitive case. We present hereafter the status of a longitudinal polarization measurement of these positrons. [ABSTRACT FROM AUTHOR]

A new facility for particle physics with polarized cold neutrons has been taken into operation at the spallation source SINQ at PSI. After extraction of the first beam, its intensity and polarization have been measured as a function of the neutron wavelength. The beam characteristics are among the best in the world for studies of neutron decay. An experimental area was constructed with infrastructure support for convenient experimentation. The physics program will focus on detailed investigations of the free neutron decay process, in particular fundamental symmetries of the weak interaction. The first approved experiment is a novel search for time reversal violation. [ABSTRACT FROM AUTHOR]

A new facility for particle physics has been installed at the spallation source SINQ. An experimental area has been constructed for a series of experiments fed by a high intensity, polarized cold neutron beam. The physics program for this new facility will focus on free neutron decay studies addressing mainly the questions of fundamental symmetries (time reversal and parity) in the weak interactions. [ABSTRACT FROM AUTHOR]