Analysis of experimental data on neutron scattering from superfluid helium at large momentum transfers

In previous work an expression was developed which partially incorporates the effect of final-state interactions on thermal-neutron scattering from a many-body system. This expression is evaluated for a liquid ${\mathrm{He}}^4$ target at momentum transfers of 14.3 and 28.6 ${\mathrm{\AA }}^{-1\mathrm{}}$. The experimental results of Mook, Scherm, and Wilkinson for the scattering of neutrons from liquid helium are analyzed in terms of (a) a modified impulse approximation which includes final-state corrections only in the condensate contribution to the scattering and (b) an approximation which includes final-state effects on both condendate and noncondensate contributions to the scattering. These calculations substantiate a previous empirical assessment of the condensate portion of the scattering [(2.4 ± 1)%] and suggest that certain barely discernible features of the experimental scattering are real structures in the condensate contribution attributable to the structure of the liquid and the interaction potential of the helium atoms. Other helium properties deduced from the data at 1.2 and 4.2 $\stackrel{\mathrm{̊}}{\mathrm{K}}$ are single-particle momentum distribution, one-particle density matrix, and mean kinetic energy of the helium atoms. These quantities are compared with predictions from existing Monte Carlo numerical studies of the ground state of ${\mathrm{He}}^4$.