A new phenomenological τ–α interaction Original Research Article

We present a potential model, with distinctive features, reproducing angular distributions and analyzing power data for τ–α scattering from 20 to 30 MeV τ energy with regular variation of the parameters. The distinctive features are: (1) a spin–orbit term which incorporates the influence of central depression in the α nucleus, and, (2) central terms which are strongly parity dependent. The parity dependence of the real central term is such that the odd-parity component has both a greater rms radius and greater volume integral than the even-parity component. These parity dependence characteristics had been predicted by the inversion of the RGM S-matrix. Our result supports a considerable contribution from three-nucleon exchange processes. The predicted 1/2− level of 7Be is shifted 3 MeV relative to a previous one-level R-matrix formula fit, and depends strongly on the geometry of the spin–orbit potential.