Neutron-deuteron analyzing power data atEn=22.5MeV

Abstract

We present measurements of $n$-$d$ analyzing power, ${A}_{y}(\ensuremath{\theta})$, at ${E}_{n}=22.5$ MeV. The experiment uses a shielded neutron source which produced polarized neutrons via the ${}^{2}$H($\stackrel{P\vec}{d}$,$\stackrel{P\vec}{n}$)${}^{3}$He reaction. It also uses a deuterated liquid-scintillator center detector and six pairs of liquid-scintillator neutron side detectors. Elastic neutron scattering events are identified by using time-of-flight techniques and by setting a window in the center detector pulse-height spectrum. The beam polarization is monitored by using a high-pressure helium gas cell and an additional pair of liquid-scintillator side detectors. The $n$-$d$ ${A}_{y}(\ensuremath{\theta})$ data were corrected for finite-geometry and multiple-scattering effects using a Monte Carlo simulation of the experiment. The 22.5-MeV data demonstrate that the three-nucleon analyzing power puzzle also exists at this energy. They show a significant discrepancy with predictions of high-precision nucleon-nucleon potentials alone or combined with Tucscon-Melbourne or Urbana IX three-nucleon forces, as well as currently available effective-field theory based potentials of next-to-next-to-next-to-leading order.