Anisotropic attenuation of zero sound in superfluid 3He-A

The anisotropic attenuation of zero sound in superfluid 3He-A at 29.3 bar pressure has been measured at 24.4, 34.2, 44.2, 54.0, 63.9, 73.7, 83.5, and 93.4 MHz. The clapping mode resonance has been observed at all frequencies, and the reentrant normal flapping resonance has been measured for the first time. Analysis of these results leads to an f-wave pairing parameter, x-13 = -0.1±0.05, and a determination of strong coupling corrections to the energy gap far from Tc. The clapping mode data is consistent with a nontrivial, strong coupling correction to the mode frequency, reducing it by 6%