Amplitude- and truncated partial-wave analyses combined: A single-channel method for extracting photoproduction multipoles directly from measured data

Amplitude- and truncated partial-wave analyses are combined into a single-channel method for extracting multipoles directly from measured data. In practice, we have created a two-step procedure which is fit to the same database: in the first step we perform an energy-independent amplitude analysis where continuity is achieved by constraining the amplitude phase, and the result of this first step is then taken as a constraint for the second step where a constrained, energy-independent, truncated partial-wave analysis is done. The method is tested on the world collection of data for eta photoproduction, and the obtained fit results are very good. The sensitivity to different possible choices of amplitude phase is investigated and it is demonstrated that the present database is insensitive to notable phase changes due to an incomplete database. New measurements are recommended to remedy the problem.