BRAND – exploring transverse polarization of electrons emitted in neutron decay

Neutron and nuclear beta decay correlation coefficients are sensitive to the exotic scalar and tensor interactions that are not included in the Standard Model (SM). The proposed experiment BRAND will measure simultaneously seven neutron correlation coefficients: H , L , N , R , S , U and V that depend on the transverse electron polarization – a quantity which vanishes in the SM. Five of these correlations: H , L , S , U and V were never attempted experimentally before. The expected impact of the proposed experiment is comparable to that of frequently measured “traditional” correlation coefficients ( a , b , A , B , D ) but offers completely different systematics and additional sensitivity to imaginary parts of the scalar and tensor couplings. In order to demonstrate the feasibility of the challenging techniques such as the event-by-event decay kinematics reconstruction together with the electron polarimetry a test setup was installed at the cold neutron beam line PF1B at the Laue-Langevin Institute, Grenoble, France. In this contribution, the results of the first run as well as plans for the run in Autumn 2021 will be discussed.