We present results for the isovector electromagnetic form factors of the nucleon computed on the coordinated lattice simulations ensembles with N f = 2 + 1 flavors of O ( a ) -improved Wilson fermions and an O ( a ) -improved vector current. The analysis includes ensembles with four lattice spacings and pion masses ranging from 130 up to 350?MeV and mainly targets the low- Q 2 region. In order to remove any bias from unsuppressed excited-state contributions, we investigate several source-sink separations between 1.0 and 1.5?fm and apply the summation method as well as explicit two-state fits. The chiral interpolation is performed by applying covariant chiral perturbation theory including vector mesons directly to our form factor data, thus avoiding an auxiliary parametrization of the Q 2 dependence. At the physical point, we obtain μ = 4.71 ( 11 ) stat ( 13 ) sys for the nucleon isovector magnetic moment, in good agreement with the experimental value and ? r M 2 ? = 0.661 ( 30 ) stat ( 11 ) sys ? ? fm 2 for the corresponding square radius, again in good agreement with the value inferred from the e p -scattering determination [Bernauer et?al. , Phys. Rev. Lett. 105 , 242001 (2010)] of the proton radius. Our estimate for the isovector electric charge radius, ? r E 2 ? = 0.800 ( 25 ) stat ( 22 ) sys ? ? fm 2 , however, is in slight tension with the larger value inferred from the aforementioned e p -scattering data, while being in agreement with the value derived from the 2018 CODATA average for the proton charge radius.
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机译:我们在协调晶格模拟中核心的核心的核心电磁形式因子的结果存在于与O(a)的n f = 2 + 1味道的N f = 2 + 1味道和O(a)为-improved载体电流的核心。该分析包括具有四个晶格间距的合奏,距离高达350孔的130级,主要针对低Q 2区域。为了从未抑制的兴奋状态贡献中删除任何偏差,我们调查了1.0和1.5的几个源区分离,并应用求和方法以及显式的双态适合。通过将包括载体渗透的协调性手性扰动理论直接应用于我们的形状因子数据来执行手性插值,从而避免了Q 2依赖性的辅助参数化。在物理点,我们获得核心isovector磁矩的μ= 4.71(11)统计(13)SYS,与实验价值吻合良好r m 2? = 0.661(30)统计(11)SYS?还FM 2对于相应的方形半径,再次与从E P-arcattering判定推断的值良好一致[Bernauer 等吗? ,物理。 rev. lett。 105,242001(2010)]质子半径。我们对Isovector电荷半径的估计,?呃2? = 0.800(25)stat(22)sys?还然而,FM 2具有轻微的张力,从上述E P-armattering数据推断出较大的值,同时与来自模块电荷半径的2018个Codata的值达成一致。
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