[PRad] Proton Radius LQCD Calculations

[gasparan at jlab.org]

  Thank you Patrick for this interesting new publication. I do not think
 that it was announced before in our collaboration.
 Very interesting work with important results. The first is that it
 confirms the PRad result on the proton radius. I remember that our results
 on Rp tended to be smaller than our 0.83 averaged value. Second result
 is more interesting on the form factor. Their results suggest correctness
of the
 PRad form factor's tendency.
 Hope we will be able to perform the PRad-II experiment with a better
 accuracy than the PRad was.

 Ashot


> Dear all,
> I am not sure if it has been discussed before in this group. The latest
> lattice QCD calculations of the e.m. FFs have achieved uncertainties
> comparable to ep scattering data uncertainties. You can have a look at the
> below referenced PRL and its companion paper in PRD.
>
> Best regards,
> Patrick
>
> https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.211901
>
>
> https://journals.aps.org/prd/abstract/10.1103/PhysRevD.109.094510
> Electromagnetic form factors of the nucleon from ${N}_{f}=2+1$ lattice
> QCD<https://journals.aps.org/prd/abstract/10.1103/PhysRevD.109.094510>
> There is a long-standing discrepancy between different measurements of the
> electric and magnetic radii of the proton. Lattice QCD calculations are a
> well-suited tool for theoretical investigations of the structure of the
> nucleon from first principles. However, all previous lattice studies of
> the proton's electromagnetic radii have either neglected
> quark-disconnected contributions or were not extrapolated to the continuum
> and infinite-volume limit. Here, we present results for the
> electromagnetic form factors of the proton and neutron computed on the
> ($2+1$)-flavor coordinated lattice simulations (CLS) ensembles including
> both quark-connected and -disconnected contributions. From simultaneous
> fits to the ${Q}^{2}$-, pion-mass, lattice-spacing, and finite-volume
> dependence of the form factors, we determine the electric and magnetic
> radii and the magnetic moments of the proton and neutron. For the proton,
> we obtain as our final values
> $⟨{r}_{E}^{2}{⟩}^{p}=(0.672\\ifmmode\\pm\\else\\textpm\\fi{}0.014(\\mathrm
> journals.aps.org
>
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