Strange Electromagnetic Form Factors of the Nucleon with N_{f}=2+1 O(a)-Improved Wilson Fermions.

D Djukanovic,J Wilhelm,H Wittig,K Ottnad

doi:10.1103/physrevlett.123.212001

D Djukanovic, J Wilhelm + Show 2 more

Open Access

https://doi.org/10.1103/physrevlett.123.212001

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Abstract

We present results for the strange contribution to the electromagnetic form factors of the nucleon computed on the coordinated lattice simulation ensembles with N_{f}=2+1 flavors of O(a)-improved Wilson fermions and an O(a)-improved vector current. Several source-sink separations are investigated in order to estimate the excited-state contamination. We calculate the form factors on six ensembles with lattice spacings in the range of a=0.049-0.086 fm and pion masses in the range of m_{π}=200-360 MeV, which allows for a controlled chiral and continuum extrapolation. In the computation of the quark-disconnected contributions, we employ hierarchical probing as a variance-reduction technique.

Highlights

The contributions of strange sea quarks to the nucleon electromagnetic form factors, which characterize the charge and current distribution in the nucleon, have been of high interest in the last decades
We present results for the strange contribution to the electromagnetic form factors of the nucleon computed on the coordinated lattice simulation ensembles with Nf 1⁄4 2 þ 1 flavors of OðaÞ-improved Wilson fermions and an OðaÞ-improved vector current
Strange electromagnetic form factors can be measured through the parityviolating asymmetry, arising from the interference of the electromagnetic and neutral weak interactions, in the elastic scattering of polarized electrons on unpolarized protons

Summary

Published by the American Physical Society

The disconnected three-point function factorizes into separate traces for the strange quark loop and the nucleon two-point function. Cs3;Vμ ðq; z0; p0; y0; x; ΓνÞ 1⁄4 he−iqxLsVμ ðq; z0Þ · C2ðp0; y0; x; ΓνÞiG; ð1Þ where Ls and C2 denote the strange loop, given in Eq (4), and the nucleon two-point function, respectively. Traces over the strange quark loops can be stochastically estimated using four-dimensional noise vectors η. We find that the statistical error of the strange quark loop is reduced by a factor of 5 when using 512 Hadamard vectors, compared to the estimate based on 512 U(1) noise vectors, for nearly the same cost. To extract the strange contribution to the electromagnetic form factors of the nucleon, we consider the ratios (see [20,21,22]). Performing the spectral decomposition and only taking the ground state into account, these ratios read

RsV μ

Vs μ

GsE GsM