Experimental data for pion photoproduction including differential cross sections and various polarization observables from four reaction channels, $\gamma p\to {\pi }^{0}p, \gamma p\to {\pi }^{+}n, \gamma n\to {\pi }^{-}p$, and $\gamma n\to {\pi }^{0}n$, from threshold up to $W=2.2$ GeV were used in order to perform a single-energy partial-wave analysis with minimal model dependence by imposing constraints from unitarity and fixed-$t$ analyticity in an iterative procedure. Reaction models were only used as a starting point in the very first iteration. We demonstrate that with this procedure partial-wave amplitudes can be obtained which show only a minimal dependence on the initial model assumptions. The analysis was obtained in full isospin, and the Watson theorem is enforced for energies below $W=1.3$ GeV but is even fulfilled up to $W\approx 1.6$ GeV in many partial waves. Electromagnetic multipoles $E_{\ell \pm }$ and $M_{\ell \pm }$ are presented and discussed for $S,P,D$, and $F$ waves.

• Received 15 July 2021
• Accepted 20 August 2021

DOI:https://doi.org/10.1103/PhysRevC.104.034605