A dispersive analysis of low energy pion photo- and electroproduction

Full text:
pdf

Pre-published on:
February 07, 2024

Published on:
March 07, 2024

Abstract

A dispersive representation based on unitarity and analyticity is used to study the low energy $\gamma N \to \pi N\ \text{and}\ \gamma^* N \to \pi N$ partial wave amplitudes. Final state interactions of the $\pi N$ system are critical to this analysis. The left-hand cut contribution is estimated by invoking baryon chiral perturbation theory results, while the right-hand cut contribution responsible for final state interaction effects is taken into account via an Omn\`{e}s formalism with elastic phase shifts as input. It is found that a good numerical fit can be achieved with only one subtraction parameter, and the experimental data of the multipole amplitudes $E_{0+}, S_{0+}$ in the energy region below the $\Delta (1232)$ are well described when the photon virtuality $Q^2 \leq 0.1 \mathrm{GeV}^2$. Furthermore, we extend the partial wave amplitudes to the second Riemann sheet to extract the couplings of the subthreshold resonance $N^*(890)$. Its couplings extracted from the multipole amplitudes $E_{0+}, S_{0+}$ are comparable to those of the $N^* (1535)$ resonance.

DOI: https://doi.org/10.22323/1.413.0045

How to cite

Metadata are provided both in "article" format (very similar to INSPIRE) as this helps creating very compact bibliographies which can be beneficial to authors and readers, and in "proceeding" format which is more detailed and complete.

Open Access

Copyright owned by the author(s) under the term of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.