Analyzing Power of 3He(n, n)3He Between 1.60 and 5.54 MeV

We report the measurements of the analyzing power Ay(θ) of n-3He elastic scattering with unprecedented accuracy and angular coverage at five incident neutron energies between 1.60 and 5.54 MeV. To this end, we employed the polarization-transfer reactions 3H(p, n)3He and 2H(d, n)3He at 0° for neutron generation and a recently developed high-pressure 3He gas scintillator as an active target, enabling neutron-time-of-flight and 3He recoil-energy determinations. We obtained simultaneously the neutron polarization with a 4He-based polarimeter, capitalizing on the well-known n-4He Ay(θ). Our n-3He Ay(θ) data are compared to rigorous four-nucleon calculations using high-precision nucleon–nucleon potential models. The agreement between data and calculations is fair at the lower energies and becomes less satisfactory with increasing neutron energy. However, in comparison to the pure isotriplet p-3He system in the same energy region, the agreement between measured and calculated Ay is much better for the mixed (isotriplet and isosinglet) n-3He system, indicating large and somewhat counterintuitive isospin effects. We note that the incorporation of a Δ-mediated three-nucleon force in calculations of n-3He scattering was found to affect Ay(θ) negligibly, suggesting the need for the reconsideration of fundamental interactions in resolving the four-nucleon analyzing power puzzle first established about a decade ago in p-3He scattering.