Analyzing power in neutron-deuteron elastic scattering at Elabn=3 MeV.

Abstract

A measurement of the analyzing power ${\mathit{A}}_{\mathit{y}}$(\ensuremath{\theta}) in neutron-deuteron (n-d) elastic scattering below the deuteron breakup threshold is described, including a detailed discussion of the experimental apparatus and the treatment of systematic errors. The data provide a precise test of Faddeev calculations of the three-nucleon system and of the nucleon-nucleon interaction models used as inputs to these calculations. ${\mathit{A}}_{\mathit{y}}$ was measured at six angles from 44.5 \ifmmode^\circ\else\textdegree\fi{} c.m. to 145.7 \ifmmode^\circ\else\textdegree\fi{} c.m. to a precision of (7--13)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$. Polarized neutrons, produced by the $^{3}\mathrm{H}$(p\ensuremath{\rightarrow},n\ensuremath{\rightarrow}${)}^{3}$He reaction, were incident upon the target, a deuterated organic scintillator. Scattered neutrons were detected in fast coincidence with the recoil deuterons in the target. A computer simulation of the experiment was used to compensate for a number of systematic errors. Particularly important were corrections for neutron multiple scattering, accidental coincidences, and finite geometry effects. The ${\mathit{A}}_{\mathit{y}}$ data have a 2.2% scale factor uncertainty associated with uncertainty in the polarization of the incident neutron beam. The incident neutron polarization was measured in a separate experiment using n${\mathrm{\ensuremath{-}}}^{4}$He scattering from a liquid helium scintillator. The neutron polarization measurement also yielded an improved value for the polarization transfer coefficient [${\mathit{K}}_{\mathit{y}}^{\mathit{y}}$(${0}^{\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}$)=0.650\ifmmode\pm\else\textpm\fi{}0.019] in the $^{3}\mathrm{H}$(p\ensuremath{\rightarrow},n\ensuremath{\rightarrow}${)}^{3}$He reaction at ${\mathit{E}}_{\mathrm{lab}}^{\mathit{p}}$=3.80 MeV. A comparison of the ${\mathit{A}}_{\mathit{y}}$ data to Faddeev calculations shows that the discrepancy in ${\mathit{A}}_{\mathit{y}}$ observed previously at higher energies continues below the breakup threshold. A comparsion of the ${\mathit{A}}_{\mathit{y}}$ data to a recent phase shift analysis of proton-deuteron (p-d) scattering indicates that observed differences between n-d and p-d analyzing powers are only partially explained by Coulomb effects.