Ultracold neutrons were produced by transferring momentum from fast neutrons to these particles in a 2011 paper by Piegsa et al. Hydrodynamic transport of these particles can result in very high thermal conductivity due to wavelike heat transfer. These particles make up the linear portion of a dispersion relation that also includes maxons and rotons (15[1])in superfluid helium. Scattering between two of these particles can occur by a normal or an (*) Umklapp process. Depending on whether neighboring atoms are in or out of phase, these quasiparticles are classified as “optical” (10[1])or “acoustic.” In a crystal, these quasiparticles can be derived by considering each atom in its lattice site as a harmonic oscillator and then taking the normal modes. For 10 points, name these quasiparticles that are the quanta of sound. ■END■