High-Momentum-Transfer Neutron-Liquid-Helium Scattering bose Condensation

Neutron inelastic scattering with high momentum transfers was used to probe the single-particle motions in liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at temperatures ranging from 4.2 to 1.27°K. The observed scattered neutron distributions below $T_{\lambda }$ are consistent with a two-component model of liquid helium involving condensation into a zero-momentum ground state. A fractional condensate density of (7.4±1.5)% and an average kinetic energy per particle of 14.1±0.6°K for helium at 1.27°K is deduced from a comparison of the experimental results with a theory for high-energy neutron-liquid-He scattering.