Excitations in liquid4He beyond the roton

The dynamic structure factor S(Q,E) for liquid⁴He at saturated vapor pressure has been measured by inelastic neutron scattering for wave vectors Q between 1.9 and 2.8 Å^–1. The temperature dependence is studied for Q=2.3 Å^–1. The sharp phonon-roton peak gradually disappears with increasing temperature, while the scattering at higher energies is nearly temperature independent. The experimental results are compared with the density-quasiparticle interpretation introduced by Glyde and Griffin, and with a model describing the hybridization with the multiparticle excitations.