A new method for suppressing excited-state contaminations on the nucleon form factors

One of the most challenging tasks in lattice calculations of baryon form factors is the analysis and control of excited-state contaminations. Taking the isovector axial form factors of the nucleon as an example, both a dispersive representation and a calculation in chiral effective field theory show that the excited-state contributions become dominant at fixed source-sink separation when the axial current is spatially distant from the nucleon source location. We address this effect with a new method in which the axial current is localized by a Gaussian wave-packet and apply it on a CLS ensemble with $N_f=2+1$ flavors of O($a$) improved Wilson fermions with a pion mass of $m_\pi=200\,$MeV.