| dc.description |
High-energy resolution inelastic neutron scattering data on excitations in superfluid and normal <sup>4</sup>He at SVP at wave vectors Q beyond the roton, 2.0 ≤ Q ≤ 4.0 Å<sup>−1</sup>, are presented. The narrow energy resolution of these measurements reveals that the energy of the elementary excitation comes up to twice the roton energy, 2Δ, at Q = 2.8<sup>−1</sup> and the energy remains constant at 2Δ between Q ≃ 3.0<sup>−1</sup> and the end point of the dispersion curve at Q = 3.6<sup>−1</sup>. The width of the peak is also unobservably small from Q = 2.8<sup>−1</sup> out to the end point, W = 2Γ < 20 μeV. |
