High-Energy Neutron-LiquidHe4-Scattering and theHe4Condensate Density

A simple theory of high-energy neutron scattering from liquid ${\mathrm{He}}^4$ is developed. The inelastic scattering cross section for this process is related, for sufficiently high momentum transfer, to two parameters characterizing the ${\mathrm{He}}^4$ momentum distribution. These two parameters are the average kinetic energy per particle and the fraction of particles in the zero-momentum condensate. Comparison of the theory with recent experimental data indicates that the condensate fraction $\frac{{\rho }_0}{\rho }$ is approximately 0.06 at $T=1.27\mathrm{}°$K.