Low-Energy D-Wave Effects in Neutral Pion Photoproduction

TL;DR

This paper investigates the impact of D waves on neutral pion photoproduction near threshold, showing their importance for accurate data analysis and low-energy constant extraction within Chiral Perturbation Theory.

Contribution

It introduces a method to include D waves in photoproduction analysis using Born terms and vector mesons, improving the reliability of multipole extraction.

Findings

D waves are essential for accurate $E_{0+}$ multipole extraction.

F-wave contributions are negligible near threshold.

Including D waves refines the assessment of low-energy constants.

Abstract

The contribution of D waves to physical observables for neutral pion photoproduction in the near threshold region is studied. Heavy Baryon Chiral Perturbation Theory to one loop, and up to ${\cal O}(q^4)$, is used to account for the S and P waves, while D waves are added in an almost model-independent way using standard Born terms and vector mesons. It is found that the inclusion of D waves is necessary to extract the $E_{0+}$ multipole reliably from present and forthcoming data and to assess the low-energy constants of Chiral Perturbation Theory. Arguments are presented demonstrating that F-wave contributions are negligible in the near-threshold region.