Fitting elastic-scattering cross sections with coupled channels

A simple method is described for searching for the optical-model parameters that produce best fits to elastic-scattering cross sections in the case where the elastic channel is coupled to other reaction channels. The back-coupling amplitudes from the nonelastic channels are obtained from the coupled-channels calculations and supplied as input to a new optical-model search code CUPID, where they are added to each calculation of the optical-model amplitudes. Iteration of the procedure converges rapidly. An interface program SUMAMP is also described. This program can also combine several sets of amplitudes that result from coupled-channel calculations with one-way couplings and convert the sum to cross sections.