The N to Delta electromagnetic transition form factors from Lattice QCD

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.