Laboratory Constraints on a 33.9 MeV/c^2 Isosinglet Neutrino: Status and Perspectives

An anomaly in the time behaviour of the signals observed by the KARMEN Collaboration may be interpreted as the possible decay signature of a 33.9 MeV/c$^2$ mainly sterile neutrino. This note discusses the parameter space still open for the mixing of this hypothetical particle with the neutrinos of known leptonic flavour, considering the experimental results which became available recently, as well as those to be expected from forthcoming measurements. It is concluded that if no positive signature is observed, the envisaged laboratory experiments are not expected to close enterily the parameter space of mixing amplitudes. However, a proper reassessment of the ALEPH upper bound on the $\nu_\tau$ neutrino mass including the possibility of $\tau$ flavour mixing, would certainly help in reducing the parameter space left open.Comment: LaTeX file, 11 pages, one figure available on reques

Constraints on the left-right symmetric models from the unitarity of the Kobayashi-Maskawa matrix

The author surveys the experimental information which, combined with the unitarity-requirement of the Kobayashi-Maskawa matrix, provides further constraints on the parameters of the manifest left-right symmetric model. The author finds that these considerations, independently of any other input, constrain the left-right mixing angle of the two /b W/-bosons of the model to a few milliradians.Anglai

Corrélation Béta-Gamma polarise circulaire dans Au198 et Sb122.

Docteur en Sciences -- UC

Scalar interaction limits from the beta-ne correlation of trapped radioactive atoms

We have set limits on contributions of scalar interactions to nuclear beta decay. A magneto-optical trap (MOT) provides a localized source of atoms suspended in space, so the low-energy recoiling nuclei can freely escape and be detected in coincidence with the beta. This allows reconstruction of the neutrino momentum, and the measurement of the beta-neutrino correlation, in a more direct fashion than previously possible. The beta-neutrino correlation parameter of the 0+ to 0+ pure Fermi decay of 38mK is $\tilde{a}$=0.9981+-0.0030+-0.0037, consistent with the standard model prediction a=1. Comment: 4 pages, 3 figures, accepted by Phys. Rev. Lett., centroid change