The N to Delta electromagnetic transition form factors from Lattice QCD

TL;DR

This paper uses lattice QCD to calculate electromagnetic transition form factors between nucleons and Delta particles, providing new insights into their deformation and confirming experimental observations.

Contribution

It introduces a novel method combining optimal interpolating fields and overconstrained analysis to accurately compute transition form factors in lattice QCD.

Findings

R_EM and R_SM are non-zero and negative, indicating deformation.

First lattice QCD evidence for non-zero quadrupole ratios.

Results agree qualitatively with experimental data.

Abstract

The magnetic dipole, the electric quadrupole and the Coulomb quadrupole amplitudes for the transition \gamma N\to \Delta are calculated in quenched lattice QCD at \beta=6.0 with Wilson fermions. Using a new method combining an optimal combination of interpolating fields for the $\Delta$ and an overconstrained analysis, we obtain statistically accurate results for the dipole form factor and for the ratios of the electric and Coulomb quadrupole amplitudes to the magnetic dipole amplitude, R_{EM} and R_{SM}, up to momentum transfer squared 1.5 GeV^2. We show for the first time using lattice QCD that both R_{EM} and R_{SM} are non-zero and negative, in qualitative agreement with experiment and indicating the presence of deformation in the N- Delta system.