Blackbody source and detector of ballistic quasiparticles in 3He-B: Emission angle from a wire moving at supercritical velocity.
Using a new quasiparticle detector and source consisting of a blackbody radiator, we have made the first measurements of the divergence of a beam of quasiparticles produced by a vibrating-wire resonator moving at supercritical velocities in superfluid $^{3}\mathit{B}$ at the zero-temperature limit. At velocities just above the critical velocity of \ensuremath{\Delta}/3${\mathit{p}}_{\mathit{F}}$ we see a very narrow beam directed along the direction of motion of the wire. As the maximum wire velocity increases the beam spreads to saturate at a half-angle divergence of approximately 55\ifmmode^\circ\else\textdegree\fi{} at a maximum velocity of order \ensuremath{\Delta}/${\mathit{p}}_{\mathit{F}}$.