We show how the position and residue of theS matrix pole can remain stable under changes in the form of the parametrization of theS matrix elements. We also derive a relation among the shifts in the Breit-Wigner resonance parameters under the same changes and verify the relation numerically for the case of Δ(1232). Despite its stability, the pole does not provide a unique definition of the resonance because of the existence of shadow poles.
Volume 95, 2021
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