# A position space method for the nucleon magnetic moment in lattice QCD

Research paper by **Constantia Alexandrou, Martha Constantinou, Giannis Koutsou, Konstantin Ottnad, Marcus Petschlies**

Indexed on: **24 May '16**Published on: **24 May '16**Published in: **High Energy Physics - Lattice**

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#### Abstract

The extraction of the magnetic form factor of the nucleon at zero momentum
transfer is usually performed by adopting a parametrization for its momentum
dependence and fitting the results obtained at finite momenta. We present a
position space method that allows to remove the momentum prefactor in the form
factor decomposition and hence compute the magnetic form factor directly at
zero momentum without the need to assume a functional form for its momentum
dependence. The method is explored on one ensemble using $N_f=2+1+1$ Wilson
twisted mass fermions with a light quark mass corresponding to
$M_\pi\approx373\mathrm{GeV}$ and a lattice spacing of
$a\approx0.082\mathrm{fm}$. For the isovector magnetic form factor we obtain
$G_M^\mathrm{isov}=4.45(17)_\mathrm{stat}(07)_\mathrm{sys}$ as our final
result, closer to the experimental value than the results obtained from a
standard dipole fit ansatz. In addition, we obtain estimates for the magnetic
moment of the proton and the neutron, leading to
$G_M^\mathrm{p}=2.73(9)_\mathrm{stat}(4)_\mathrm{sys}$ and
$G_M^\mathrm{n}=-1.72(6)_\mathrm{stat}(3)_\mathrm{sys}$, respectively.