Asymmetry observables in e+ e- --> pi+ pi- gamma in the phi region within a chiral unitary approach

TL;DR

This paper investigates charge and forward-backward pion asymmetries in e+ e- --> pi+ pi- gamma reactions near the phi resonance, using a chiral unitary approach to incorporate various decay mechanisms and final state interactions.

Contribution

It introduces a comprehensive chiral unitary model to evaluate phi decay contributions and final state interactions, improving the understanding of asymmetries in the reaction.

Findings

Good agreement with KLOE data for forward-backward asymmetry.

Predictions show charge asymmetry is highly sensitive to chiral loop effects.

Model successfully reproduces asymmetries both at and off the phi peak.

Abstract

We make a theoretical study of the charge and forward-backward pion asymmetries in the e+e- --> pi+ pi- gamma process on and off the phi resonance energy. These observables are rather sensitive to the inner details of the theoretical models to describe the reaction. In addition to the standard implementation of the initial state radiation (ISR) and the Bremsstrahlung contribution to the final state radiation (FSR), we use the techniques of the chiral unitary approach to evaluate the contribution from the mechanisms of phi decay into pi+pi-gamma. This contribution involves the implementation of final state interaction from direct chiral loops, the exchange of vector and axial-vector resonances and the final state interaction through the consideration of the meson-meson unitarized amplitudes, which where found important in a previous work describing the phi --> pi pi gamma. We find a good reproduction of the experimental data from KLOE for the forward-backward asymmetry, both at the phi peak and away from it. We also make predictions for the angular distributions of the charge asymmetry and show that this observable is very sensitive to the chiral loops involved in phi radiative decay.