N to Delta electromagnetic transition form factors from Lattice QCD

Alexandrou, C.; de Forcrand, Ph.; Lippert, Th.; Neff, H.; Negele, J. W.; Schilling, K.; Schroers, W.; Tsapalis, A.

N to Delta electromagnetic transition form factors from Lattice QCD

Authors

Description

The magnetic dipole, the electric quadrupole and the Coulomb quadrupole amplitudes for the transition $γN\to Δ$ are evaluated both in quenched lattice QCD at $β=6.0$ and using two dynamical Wilson fermions simulated at $β=5.6$. 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.
Discussion of systematic errors and chiral extrapolation extended; Typos corrected; Version to appear in Phys. Rev. D.; 19 pages including 21 figures