Role of resonances in rho^0 -> pi^+ pi^- gamma

TL;DR

This paper investigates how sigma(600) and a_1(1260) resonances influence the rho^0 -> pi^+ pi^- gamma decay, highlighting the importance of interference effects and resonance parameters in matching experimental data.

Contribution

It introduces a gauge-invariant method to enhance resonant effects in decay distributions and analyzes the impact of specific resonances on decay rates.

Findings

Resonance parameters significantly affect decay branching ratios.

Interference between resonances and bremsstrahlung can alter decay distributions.

Proper sign choice of a_1(1260) enhances agreement with experimental data.

Abstract

We study the effect of the sigma(600) and a_1(1260) resonances in the rho^0 -> pi^+ pi^- gamma decay, within the meson dominance model. Major effects are driven by the mass and width parameters of the sigma(600), and the usually neglected contribution of the a_1(1260), although small by itself, may become sizable through its interference with pion bremsstrahlung, and the proper relative sign can favor the central value of the experimental branching ratio. We present a procedure, using the gauge invariant structure of the resonant amplitudes, to kinematically enhance the resonant effects in the angular and energy distribution of the photon. We also elaborate on the coupling constants involved.