Attenuation of Zero Sound in LiquidHe3: A Probe of Superfluid Pairing

It is shown that the anomalous zero-sound attenuation at the transition "$A$" observed recently in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at about 2.7 mK can be understood by postulating pairing in a state of odd relative angular momentum. The attenuation is found to depend strongly on the angular variation and orientation of the gap parameter, providing information on the precise nature of the pairing. It is concluded that (1) Balian-Werthamer $p$-wave pairing can be ruled out, and (2) Anderson-Morel $p$-wave pairing is possible.