Helicity Amplitudes of the Lambda(1670) and two Lambda(1405) as dynamically generated resonances

TL;DR

This paper calculates the helicity amplitudes and radiative decay widths of Lambda(1670) and Lambda(1405) resonances, treating them as dynamically generated states within chiral dynamics, and explores their internal structure through decay ratios.

Contribution

It provides the first detailed calculation of helicity amplitudes and decay widths for Lambda(1670) and Lambda(1405) as dynamically generated resonances in chiral dynamics.

Findings

Lambda(1670) radiative decay width to gamma Lambda is 3 ± 2 keV.

Lambda(1670) radiative decay width to gamma Sigma^0 is 120 ± 50 keV.

The K Xi component influences the decay ratio and the resonance's structure.

Abstract

We determine the helicity amplitudes A_1/2 and radiative decay widths in the transition Lambda(1670) to gamma Y (Y=Lambda or Sigma^0). The Lambda(1670) is treated as a dynamically generated resonance in meson-baryon chiral dynamics. We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 3 \pm 2 keV and to gamma Sigma^0 as 120 \pm 50 keV. Also, the Q^2 dependence of the helicity amplitudes A_1/2 is calculated. We find that the K Xi component in the Lambda(1670) structure, mainly responsible for the dynamical generation of this resonance, is also responsible for the significant suppression of the decay ratio Gamma_{gamma Lambda}/Gamma_{gamma Sigma^0}. A measurement of the ratio would, thus, provide direct access to the nature of the Lambda(1670). To compare the result for the Lambda(1670), we calculate the helicity amplitudes A_1/2 for the two states of the Lambda(1405). Also, the analytic continuation of Feynman parameterized integrals of more complicated loop amplitudes to the complex plane is developed which allows for an internally consistent evaluation of A_1/2.