核子电磁形状因子的味分解
Flavor decomposition of the nucleon electromagnetic form factors
摘要：
背景：质子和中子中电荷和磁化强度的空间分布被编码在核子电磁形状因子中。形状因子都近似于一个简单的偶极函数，归一化的电荷或磁矩的核子。质子和中子形状因子之间的差异以及GEn与零的偏差对上夸克和下夸克对形状因子的贡献之间的差异敏感。研究方法：我们将最近对中子形状因子的测量与质子形状因子的最新提取结合起来，考虑到双光子交换修正，并包括对所有形状因子的不确定性的估计，以获得一组完整的测量结果，最高可达Q ^2约为4（GeV/c）^2。我们用它来提取上夸克和下夸克的贡献，我们比较最近的拟合和计算。结果如下：我们发现上夸克和下夸克对G_E和G_M的贡献有很大的差异，这意味着电荷和磁化强度分布有明显的味依赖性。比值GEp/GMp的快速下降并不出现在单个夸克形状因子中，而是由上夸克和下夸克贡献之间的抵消引起的。我们发现，下夸克对狄拉克和泡利形状因子的贡献偏离了先前分析所建议的1/Q^4标度行为。最后，虽然最近的模型提供了一个一般良好的定性描述的数据，下夸克的贡献G_E/G_M和F_2/F_1没有重现的任何模型。最后，我们注意到，虽然包含来自CLAS的最新$\gmn$数据稍微修改了高- $Q^2$，但这些数据与之前较低$Q^2$的测量值之间的紧张关系具有更显着的影响，这表明需要该区域的额外数据。
英文摘要：
Background: The spatial distribution of charge and magnetization in the proton and neutron are encoded in the nucleon electromagnetic form factors. The form factors are all approximated by a simple dipole function, normalized to the charge or magnetic moment of the nucleon. The differences between the proton and neutron form factors and the deviation of GEn from zero are sensitive to the difference between up- and down-quark contributions to the form factors. Methods: We combine recent measurements of the neutron form factors with updated extractions of the proton form factors, accounting for two-photon exchange corrections and including an estimate of the uncertainties for all of the form factors to obtain a complete set of measurements up to Q^2 approximately 4 (GeV/c)^2. We use this to extract the up- and down-quark contributions which we compare to recent fits and calculations. Results: We find a large differences between the up- and down-quark contributions to G_E and G_M, implying significant flavor dependence in the charge and magnetization distributions. The rapid falloff of the ratio GEp/GMp does not appear in the individual quark form factors, but arises from a cancellation between the up- and down-quark contributions. We see indications that the down-quark contributions to the Dirac and Pauli form factors deviate from the suggested 1/Q^4 scaling behavior suggested by a previous analysis. Finally, while recent models provide a generally good qualitative description of the data, the down-quark contribution to G_E/G_M and F_2/F_1 are not reproduced by any of the models. Finally, we note that while the inclusion of recent $\gmn$ data from CLAS modifies the high-$Q^2$ slightly, the tension between these data and previous measurements at lower $Q^2$ has a more significant impact, suggesting the need for additional data in this region.
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