Neutron Polarimetry Using a Polarized 3He Cell for the aCORN Experiment

Abstract

The neutron polarization of the NG-C beamline at the NIST Center for Neutron Research was measured as part of the aCORN neutron beta decay experiment. Neutron transmission through a polarized 3 He spin filter cell was recorded while adiabatic fast passage (AFP) nuclear magnetic resonance (NMR) reversed the polarization direction of the 3 He in an eight-step sequence to account for drifts. The dependence of the neutron transmission on the spin filter direction was used to calculate the neutron polarization. The time dependent transmission was fit to a model which included the neutron spectrum, and 3 He polarization losses from spin relaxation and AFP-NMR. The polarization of the NG-C beamline was found to be |P n | ≤ 4 × 10 −4 with 90 % confidence.

Measurement of the neutron decay electron-antineutrino angular correlation by the aCORN experiment

“…), an upper limit that confirmed the null polarization. The direct neutron polarization measurement on NG-C is described in detail in another publication [36]. We combine the B up and B down results for the aCORN NG-C run a = −0.10758 ± 0.00136(stat) ± 0.00148(sys) (NG-C combined).…”