Excitations in superfluid 4He beyond the roton

PACS. 67.40Db { Quantum statistical theory; ground state, elementary excitations. PACS. 61.12−q { Neutron diraction and scattering. Abstract. { High-energy resolution inelastic neutron scattering data on excitations in super-fluid and normal 4He at SVP at wave vectors Q beyond the roton, 2:0 Q 4:0 A −1, are presented. The narrow energy resolution of these measurements reveals that the energy of the elementary excitation comes up to twice the roton energy, 2, at Q = 2:8 A −1 and the energy remains constant at 2 between Q ’ 3:0 A −1 and the end point of the dispersion curve at Q = 3:6 A −1. The width of the peak is also unobservably small from Q = 2:8 A −1 out to the end point, W = 2Γ < 20 eV. The energy and lifetime of the elementary phonon-roton excitations (EE) in superfluid 4He are accurately known at low wave vector up to the roton wave vector, Q 1:92