N to Delta electromagnetic transition form factors from Lattice QCD

TL;DR

This paper computes the electromagnetic transition form factors for the gamma N to Delta process using lattice QCD, providing insights into the transition amplitudes and their ratios at various momentum transfers.

Contribution

It presents the first lattice QCD calculations of the gamma N to Delta transition form factors including electric quadrupole and Coulomb quadrupole amplitudes.

Findings

The magnetic dipole form factor is accurately determined.

The electric quadrupole amplitude is non-zero and negative.

The ratio R_EM is negative at studied momentum transfers.

Abstract

The magnetic dipole, the electric quadrupole and the Coulomb quadrupole amplitudes for the transition $\gamma N\to \Delta$ are evaluated both in quenched lattice QCD at $\beta=6.0$ and using two dynamical Wilson fermions simulated at $\beta=5.6$. The dipole transition form factor is accurately determined at several values of momentum transfer. On the lattices studied in this work, the electric quadrupole amplitude is found to be non-zero yielding a negative value for the ratio, $ R_{EM}$, of electric quadrupole to magnetic dipole amplitudes at three values of momentum transfer.