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Register a new userLattice Calculation of the Strangeness Magnetic Moment of the Nucleon
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We report on a lattice QCD calculation of the strangeness magnetic moment of the nucleon. Our result is $G_M^s(0) = - 0.36 pm 0.20 $. The sea contributions from the u and d quarks are about 80% larger. However, they cancel to a large extent due to their electric charges, resulting in a smaller net sea contribution of $ - 0.097 pm 0.037 mu_N$ to the nucleon magnetic moment. As far as the neutron to proton magnetic moment ratio is concerned, this sea contribution tends to cancel out the cloud-quark effect from the Z-graphs and result in a ratio of $ -0.68 pm 0.04$ which is close to the SU(6) relation and the experiment. The strangeness Sachs electric mean-square radius $< r_s^2>_E$ is found to be small and negative and the total sea contributes substantially to the neutron electric form factor.
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We report a lattice QCD calculation of the strange quark contribution to the nucleons magnetic moment and charge radius. This analysis presents the first direct determination of strange electromagnetic form factors including at the physical pion mass. We perform a model-independent extraction of the strange magnetic moment and the strange charge radius from the electromagnetic form factors in the momentum transfer range of $0.051 ,text{GeV}^2 lesssim Q^2 lesssim 1.31 ,text{GeV}^2 $. The finite lattice spacing and finite volume corrections are included in a global fit with $24$ valence quark masses on four lattices with different lattice spacings, different volumes, and four sea quark masses including one at the physical pion mass. We obtain the strange magnetic moment $G^s_M(0) = - 0.064(14)(09), mu_N$. The four-sigma precision in statistics is achieved partly due to low-mode averaging of the quark loop and low-mode substitution to improve the statistics of the nucleon propagator. We also obtain the strange charge radius $langle r_s^2rangle_E = -0.0043 (16)(14),$ $text{fm}^2$.
We present the N_f=2+1 clover fermion lattice QCD calculation of the nucleon strangeness form factors. We evaluate disconnected insertions using the Z(4) stochastic method, along with unbiased subtractions from the hopping parameter expansion. We find that increasing the number of nucleon sources for each configuration improves the signal significantly. We obtain G_M^s(0) = -0.017(25)(07), where the first error is statistical, and the second is the uncertainties in Q^2 and chiral extrapolations. This is consistent with experimental values, and has an order of magnitude smaller error.
We report our (HPQCD) progress on the calculation of the Hadronic Vacuum Polarisation contribution to the anomalous magnetic moment of muon. In this article we discuss the calculations for the light (up/down) quark connected contribution using our method described in Phys.Rev. D89(2014) 11, 114501 and give an estimate for the disconnected contribution. Our calculation has been carried out on MILC Collaborations $n_f = 2+1+1$ HISQ ensembles at multiple values of the lattice spacing, multiple volumes and multiple light sea quark masses (including physical pion mass configurations).
We study the strangeness electromagnetic form factors of the nucleon from the N_f=2+1 clover fermion lattice QCD calculation. The disconnected insertions are evaluated using the Z(4) stochastic method, along with unbiased subtractions from the hopping parameter expansion. In addition to increasing the number of Z(4) noises, we find that increasing the number of nucleon sources for each configuration improves the signal significantly. We obtain G_M^s(0) = -0.017(25)(07), where the first error is statistical, and the second is the uncertainties in Q^2 and chiral extrapolations. This is consistent with experimental values, and has an order of magnitude smaller error. We also study the strangeness second moment of the partion distribution function of the nucleon, <x^2>_{s-bar{s}}.
The Goldberger-Treiman relation $M=2pi/sqrt{3}f^{rm cl}_pi$ where $M$ is the constituent quark mass in the chiral limit (cl) and $f^{rm cl}_pi$ the pion decay constant in the chiral limit predicts constituent quark masses of $m_u=328.8pm 1.1$ MeV and $m_d=332.3pm 1.1$ MeV for the up and down quark, respectively, when $f^{rm cl}_pi=89.8pm 0.3$ MeV is adopted. Treating the constituent quarks as bare Dirac particles the following zero order values $mu^{(0)}}_p=2.850pm 0.009$ and $mu^{(0)}}_n= -1.889pm 0.006$ are obtained for the proton and neutron magnetic moments, leading to deviations from the experimental data of 2.0% and 1.3%, respectively. These unavoidable deviations are discussed in terms of contributions to the magnetic moments proposed in previous work.
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