2023/03/13 by Lu, H., Holderer, O., Ioffe, A. +6
#Atomic Physics (physics.atom-ph) #FOS: Physical sciences #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.2303.07031
We report the first results from a new approach for measuring the 3He neutron incoherent scattering length bi. bi is directly proportional to the difference Δb=b+-b- in the two low-energy s-wave neutron-nucleus scattering amplitudes b+ and b-, corresponding to the singlet J=0 and triplet J=1 states of the neutron-3He interaction, respectively. An accurate measurement of bi can help distinguish among different models of three-nucleon interactions by comparison to \it ab initio nuclear theory calculations. The neutron birefringence caused by Δb results in neutron spin rotation around the nuclear polarization. We measured Δb using polarized neutron spin rotation and the transmission of neutrons through a 3He gas target polarized in situ by spin-exchange optical pumping. This brief test measurement, conducted at the FZ-Jülich neutron spin echo spectrometer at the Heinz Maier Leibnitz Zentrum (MLZ), yielded Δb = [-5.27 ± 0.05 (stat.) - 0.05 (syst.)] fm. We argue that this method can be improved in precision to resolve the discrepancies between two prior measurements of bi which are dependent on the polarized absorption cross section σp. Further with absolute 3He polarization via NMR (in a properly-shaped cell) concurrent with accurate neutron transmission measurements, σp can be measured to obtain independent values of b+ and b-.