The nucleon to Delta electromagnetic transition form factors in lattice QCD

TL;DR

This paper computes nucleon to Delta electromagnetic transition form factors using lattice QCD with different fermion formulations, revealing non-zero quadrupole form factors and emphasizing the role of pion cloud effects in aligning theory with experiment.

Contribution

It presents the first accurate lattice QCD calculations of the subdominant quadrupole form factors, demonstrating their non-zero values and the significance of dynamical sea quarks.

Findings

Quadrupole form factors are non-zero, indicating deformation.

Unquenched results align better with experimental data.

Pion cloud contributions are crucial for accurate modeling.

Abstract

The electromagnetic nucleon to Delta transition form factors are evaluated using two degenerate flavors of dynamical Wilson fermions and using dynamical sea staggered fermions with domain wall valence quarks. The two subdominant quadrupole form factors are evaluated for the first time in full QCD to sufficient accuracy to exclude a zero value, which is taken as a signal for deformation in the nucleon-Delta system. For the Coulomb quadrupole form factor the unquenched results show deviations from the quenched results at low q^2 bringing dynamical lattice results closer to experiment, thereby confirming the importance of pion cloud contributions on this quantity.