N to Delta electromagnetic transition form factors from Lattice QCD

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.

Comments: Discussion of systematic errors and chiral extrapolation extended; Typos corrected; Version to appear in Phys. Rev. D.; 19 pages including 21 figures