Pole positions and residues from pion photoproduction using the Laurent+Pietarinen expansion method

Understand

We have applied a new approach to determine the pole positions and residues from pion photoproduction multipoles.

• The method is based on a Laurent expansion of the partial wave T-matrices, with a Pietarinen series representing the regular part of energy-dependent and single-energy photoproduction solutions.
• The method has been applied to multipole fits generated by the MAID and GWU/SAID groups.
• We show that the number and properties of poles extracted from photoproduction data correspond very well to results from $\pi$N elastic data and values cited by Particle Data Group (PDG).