[en] We compare our analysis of neutron decay observables with a recently reported tritium half-life measurement to investigate the insight they may provide into the admixture of a 17 keV c^-2 neutrino in the electron flavour. (author)

[en] We have developed a positron-polarimeter, based on the time-resolved spectroscopy of positronium hyperfine states, in which the uncontrolled systematic errors in the comparison of two beta-decays have been reduced to the 10^-4 level. A comparison of Fermi (¹⁴O) and Gamow-Teller (¹⁰C) transitions yielded, within errors, identical polarizations. The combination of this result with that of Wichers et al yields the world-average of R = 1.001 ± 0.003. This result constrains the product of the mixing angle ζ and mass-squared ratio δ of the left- and right-handed W bosons in left-right symmetric models to: -0.52 < ζ δ (10⁺³) < 0.75

No abstract available

[en] Published in summary form only

[en] Published in summary form only

[en] We report the relative polarization of the P_F/P_GT=0.9996±0.0037 for the positrons emitted by the pure Fermi ¹⁴O and the pure Gamow-Teller ¹⁰C decays, using a technique based on the observation of the positronium-decay time spectrum. The radioisotopes to be compared are part of the same source, eliminating some of the potential systematic errors which may vitiate relative polarization measurements of high precision. Combining our result with a similar ²⁶Al^m/³⁰P decay positron comparison obtained by Bhabha polarimetry, we deduce the following constraint on the product of the mixing angle ζ and mass-squared ratio δ of the chiral W bosons assumed in left-right symmetric models: -0.0004<ζδ<0.0007 (90% C.L.). Our result also constrains possible scalar and tensor admixtures to the dominant vector and axial-vector currents: C_S+C'_S/C_V-C_T+C'_T/C_A =0.003±0.018 (90% C.L.)

[en] The relative polarization of positrons emitted in pure Fermi (¹⁴O) and Gamow-Teller (¹⁰C) decays has been measured using a new technique based on time-resolved positronium decay. The result P_GT/P_F=0.9996±0.0037 provides constraints on possible right-handed and scalar-tensor current admixtures to the weak interaction of -4<ζδx10⁴<7 and |(C_S/C_V)-(C_T/C_A)|=(1±9)x10^-3 (90% C.L.), respectively

[en] The polarization of positrons in the decay of ¹⁴O (pure Fermi) has been measured relative to that of ¹⁰C (pure Gamow-Teller) using a new technique based on the time-resolved spectroscopy of hyperfine positronium decay. Combined with the absolute experimental value for Gamow-Teller decay polarization, the result is P(¹⁴O) = (1.02±0.056). This constitutes the first use of this technique in an online configuration, and demonstrates its ability for reaching eventual precisions of 0.1% in relative polarization measurements. (orig.)

[en] We examine recent claims that experiments on neutron-decay are at variance with the standard V-A helicity structure of the standard model. The analysis presented here combines the neutron data with other recent experimental results and theoretical elaborations in the field of nuclear beta decay. If interpreted in the framework of left-right symmetric models, the data favour the existence of a right-handed weak gauge boson with mass between 207 and 369 GeV c² at 95% CL. The fit using the standard V-A helicity structure has a χ² of 8.52 for four degrees of freedom and excludes the V-A solution at 2.53 standard deviations. This exclusion is due mainly to the new neutron asymmetry data and is in disagreement with the conclusions drawn from muon decay and from the K_L-K_S mass difference in the framework of manifest left-right symmetric models. (Author)

[en] Published in summary form only