Each single-energy, single-channel partial-wave analysis is inherently model-dependent

Svarc et al. [Phys. Rev. C 97, 054611 (2018)] have shown that without fixing the reaction-amplitude phase, different partial waves at neighboring energies in single-energy, single-channel partial wave analysis reproduce experimental data identically, but are discontinuous and disconnected. To obtain the continuous solution, the phase has to be fixed to some continuous value. In the same reference it has also been shown that the change of the angular part of the reaction-amplitude phase mixes partial waves, so the pole structure of any single-energy single-channel partial wave analysis depends on the chosen phase. As in any single-channel analysis the overall reaction-amplitude phase cannot be determined because of continuum ambiguity, it is in principle free and has to be taken from some coupled-channel model. Because of the difference in the angular part of the phase, choosing different phases results in the change of the pole content of the obtained solution. Therefore, single-energy single-channel partial wave analysis is inherently model dependent, and the number of poles it contains strongly depends on the choice of the phase. In that reference these facts have been illustrated on the pseudoscalar meson production toy model. This truth is now for the full set of measured observables demonstrated on the realistic model of eta photoproduction presented in Svarc, Wunderlich, and Tiator [Phys. Rev. C 102, 064609 (2020)].

Automated summary

The study demonstrates that fixing the reaction-amplitude phase is crucial in single-energy, single-channel partial wave analysis to obtain a continuous solution. Changing the angular part of the phase can mix partial waves and affect the pole content of the solution. Therefore, the single-energy single-channel partial wave analysis is model-dependent and the number of poles is strongly influenced by the choice of phase.