Acoustic nature of the boson peak in vitreous silica

New temperature-dependent inelastic X-ray scattering (IXS) and Raman scatte ring (RS) data are compared with each other and with existing inelastic neu tron scattering (INS) data in vitreous silica, in the 300-1775 K region. Th e IXS data show collective propagating excitations up to Q = 3.5 nm(-1). Th e temperature behaviour of the excitations at Q = 1.6 nm(-1) matches that o f the boson peak found in INS and RS. This supports the fact that the acous tic origin of the excess of vibrational states gives rise to the boson peak in this glass.