The role of angle dependent phase rotations of reaction amplitudes in $\eta$ photoproduction on protons

TL;DR

This paper demonstrates that accounting for angle-dependent phase rotations in reaction amplitudes aligns different partial wave analyses in eta photoproduction, improving consistency and highlighting the need for new measurements.

Contribution

It introduces the importance of phase rotations in PWA and shows that considering them makes different analyses nearly identical, enhancing understanding of eta photoproduction.

Findings

Aligns ED and SE PWA results for E0+ multipole

Shows improved agreement among multipoles after phase correction

Highlights the need for new measurements of unmeasured observables

Abstract

It has recently been proven that the invariance of observables with respect to angle dependent phase rotations of reaction amplitudes mixes multipoles changing also their relative strength [1]. All contemporary partial wave analyses (PWA) in $\eta$ photoproduction on protons, either energy dependent (ED) [2-5] or single energy (SE) [6] do not take this effect into consideration. It is commonly accepted that there exist quite some similarity in the $E0+$ multipole for all PWA, but notable differences in this, but also in remaining partial waves still remain. In this paper we demonstrate that once this phase rotations are properly taken into account, all contemporary ED and SE partial wave analysis become almost identical for the dominant $E0+$ multipole, and the agreement among all other multipoles becomes much better. We also show that the the measured observables are almost equally well reproduced for all PWA, and the remaining differences among multipoles can be attributed solely to the difference of predictions for unmeasured observables. So, new measurements are needed.