Measurements of anisotropic mass of magnons confined in a harmonic trap in superfluid ${}^3$He-B

We can pump magnons to a nearly harmonic magneto-textural trap in superfluid ${}^3$He-B. Using the NMR spectroscopy of levels in the trap we have measured the anisotropic magnon mass and related values of the spin-wave velocities. Based on our measurements we provide values of the Fermi-liquid parameter $F_1^a$.