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

TL;DR

This paper introduces a novel, nearly theory-independent method combining amplitude and partial-wave analyses to extract photoproduction multipoles directly from experimental data, demonstrated on eta photoproduction data.

Contribution

A new two-step, single-channel method for extracting multipoles from measured data, combining amplitude and partial-wave analyses with minimal theoretical assumptions.

Findings

Method successfully applied to eta photoproduction data

Results show high fit quality and robustness against phase variations

Data sensitivity issues highlight need for new measurements

Abstract

Amplitude- and truncated partial-wave analyses are combined into a single procedure and a novel, almost theory-independent single-channel method for extracting multipoles directly from measured data is developed. In practice, we have created a two-step procedure which is fitted to the same data base: 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 data base is insensitive to notable phase changes, due to an incomplete database. New measurements are recommended to remedy the problem.