Transverse electron polarization in the neutron decay - Direct search for scalar and tensor couplings in weak interaction

摘要

The Standard Model (SM) predictions of T-violation for weak decays of systems built up of u and d quarks are by 7 to 10 orders of magnitude lower than the experimental accuracies attainable at present. It is a general presumption that time reversal phenomena are caused by a tiny admixture of exotic interaction terms. Therefore, weak decays provide a favorable testing ground in a search for such feeble forces. Physics with very slow, polarized neutrons has a great potential in this respect. An experiment seeking for small deviations from the SM in two observables, N and R, that are for the first time addressed experimentally in free neutron decay and that are exclusively sensitive to real and imaginary parts of the same linear combination of the scalar and tensor interaction coupling constants has been completed at the Paul Scherrer Institute, Villigen, Switzerland. The analysis of the experimental data has been completed recently leading to, among others, the best direct constraint for the imaginary part of the R-parity violating MSSM contribution. The success of the applied technique results in a new project devoted to the simultaneous measurement of seven correlation coefficients: H, L, N, R, S, U and V. Five of them (H, L, S, U and V) have never before been measured in weak decays. Such a systematic exploration of the transverse electron polarization will generate from the neutron decay alone a complete set of constraints for the real and imaginary parts of the weak scalar and tensor interactions on the level of 5 × 10~(?4) or better.