BRAND – search for BSM physics at TeV scale by exploring transverse polarization of electrons emitted in neutron decay

Neutron and nuclear beta decay correlation coefficients are linearly sensitive to the exotic scalar and tensor interactions that are not included in the Standard Model (SM). The proposed experiment will measure simultaneously 11 neutron correlation coefficients (a, a, B, D, H, L, N, R, S, U, V) where 7 of them (H, L, N, R, S, U, V) depend on the transverse electron polarization – a quantity that vanishes for the SM weak interaction. The neutron decay correlation coefficients H, L, S, U, V were never attempted experimentally before. The expected ultimate sensitivity of the proposed experiment that currently takes off on the cold neutron beamline PF1B at the Institut Laue-Langevin, Grenoble, France, is comparable to that of the planned electron spectrum shape measurements in neutron and nuclear β decays but offers completely different systematics and additional sensitivity to imaginary parts of the scalar and tensor couplings

Search for BSM physics with neutron beta decay in the BRAND project

Neutron and nuclear beta decay correlation coefficients are sensitive to the exotic scalar and tensor interactions hypotheses that are beyond the Standard Model (BSM). The BRAND project aims at a test of the Lorentz structure of weak interaction in neutron decay by precision measurements of yet unexplored transverse polarization of electrons in correlation with the neutron spin and electron and recoil proton momenta. The experiment will simultaneously measure eleven neutron correlation coefficients (a, A, B, D, H, L, N, R, S, U, V), where seven of them (H, L, N, R, S, U and V) depend on the transverse electron polarization. Five of these correlations: H, L, S, U and V were never attempted experimentally before. The expected ultimate sensitivity of the proposed experiment with respect to BSM couplings will be comparable to that of the ongoing and planned correlation measurements in neutron and nuclear beta decays but offers completely different systematics and additional sensitivity to imaginary parts of the scalar and tensor couplings. An overview of the project, physical motivation and applied experimental techniques were reported. The results of the first pilot run of the experiment performed recently using the cold neutron beam line PF1B at the Laue-Langevin Institute, Grenoble, France were presented, with an emphasis on the challenges of the proposed proton detection technique

BRAND – exploring transverse polarization of electrons emitted in neutron decay : feasibility demonstration experiment

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

Mott polarimeter for electrons from neutron decay in BRAND experiment

The BRAND experiment aims at the search of Beyond Standard Model (BSM) physics via measurement of exotic components of week interaction. For this purpose the eleven correlation coefficients of the neutron β decay will be measured simultaneously. Seven of them: H, L, N, R, S, U and V, are sensitive to the transverse polarization of electrons from free neutron decay. The correlation coefficients will be derived using Mott polarimetry and completely determined kinematics of products from the polarized neutron β decay. For this aim the beam of cold polarized neutrons available at the PF1B facility of the ILL, Grenoble will be utilized. The electron detection system features both the tracking and energy measurement capability as well as the Mott polarimetry for determination of the electron spin orientation. The 3D tracking is performed with the use of low density, helium based drift chamber with hexagonal cell structure which is optimised for β-particles. The Mott polarimeter is an integral part of the tacker. It consists of a thin Pb foil installed inside the drift chamber and two plastic scitillators, providing trigger and scattered electron energy measurement. The results of the first pilot run of the BRAND experiment performed in September'20 are reported with the emphasis on the description and the performance of the electron detection system and the Mott polarimeter