Deflection of Nonequilibrium Light Particles by the Nuclear Mean Field

Abstract

The sign of the average emission angle of nonequilibrium light particles was determined from the circular polarization of coincident $\ensuremath{\gamma}$ rays emitted from residual nuclei for $^{14}\mathrm{N}$-induced reactions on $^{154}\mathrm{Sm}$ at $\frac{E}{A}=20 \mathrm{and} 35$ MeV. Light particles ($p,d,t,\ensuremath{\alpha}$) are preferentially emitted to negative angles. This effect is consistent with deflection of the particles by the attractive nuclear mean field. Numerical solutions of the Boltzmann-Uehling-Uhlenbeck equation demonstrate that the experimental result is sensitive to the interplay between the nuclear mean field and nucleon-nucleon collisions.