Theoretical analysis of the $\gamma\gamma \to \pi^0 \eta$ process

TL;DR

This paper provides a theoretical analysis of the gamma-gamma to pi-eta process, focusing on resonance states, and estimates the two-photon decay width of the a0(980) resonance using dispersive formalism.

Contribution

It introduces a dispersive formalism with coupled-channel Omnès representation for the s-wave resonance and models the d-wave as a Breit-Wigner, offering a novel approach to analyze this process.

Findings

Estimated the a0(980) two-photon decay width as 0.27(4) keV.

Analyzed the gamma-gamma to pi-eta process up to 1.4 GeV.

Provided a theoretical framework for resonance analysis.

Abstract

We present a theoretical study of the $\gamma\gamma \to \pi\eta$ process from the threshold up to 1.4 GeV in the $\pi\eta$ invariant mass. For the s-wave $a_0(980)$ resonance state we adopt a dispersive formalism using a coupled-channel Omn\`es representation, while the d-wave $a_2(1320)$ state is described as a Breit-Wigner resonance. An analytic continuation to the $a_0(980)$ pole position allows us to extract its two-photon decay width as $\Gamma_{a_0\to\gamma\gamma}=0.27(4)$ keV.