核子形状因子多极模型中的对数修正和软光子现象
Logarithmic corrections and soft photon phenomenology in the multipole model of the nucleon form factors
摘要：
在基于色散关系的多极模型下，分析了现有的核子电磁形状因子的实验数据。一个很好的拟合的数据是通过考虑系数的多极展开作为对数函数的动量传递平方。超收敛关系，应用到这个系数，使模型同意酉约束和pQCD渐近的Dirac和泡利形状因子。软光子发射提出的Rosenbluth，偏振和光束-目标-不对称数据之间的差异负责的机制。结果表明，实验测得的截面不仅依赖于狄拉克和泡利形状因子，但也对发射的光子的平均数。对于质子，这个数字被证明是不同的不同类型的实验测量，然后估计唯象。对于中子，同样的机制预言，来自不同类型实验的数据必须以高精度相吻合。所有实验数据的联合拟合以$χ^2/dof=0.86$的精度再现$Q^2-$依赖性。该模型的预测，即1）质子形状因子$G_E/G_M$的比率对于Rosenbluth，极化和束-靶-不对称实验是不同的，以及2）类似的比率对于中子是几乎相同的，可以用于该模型的实验验证。
英文摘要：
We analyzed the presently available experimental data on nucleon electromagnetic form factors within a multipole model based on dispersion relations. A good fit of the data is achieved by considering the coefficients of the multipole expansions as logarithmic functions of the momentum transfer squared. The superconvergence relations, applied to this coefficients, makes the model agree with unitary constraints and pQCD asymptotics for the Dirac and Pauli form factors. The soft photon emission is proposed as a mechanism responsible for the difference between the Rosenbluth, polarization and beam--target--asymmetry data. It is shown, that the experimentally measured cross sections depend not only on the Dirac and Pauli form factors, but also on the average number of the photons emitted. For proton this number is shown to be different for different types of experimental measurements and then estimated phenomenologically. For neutron the same mechanism predicts, that the data form different types of experiments must coincide with high accuracy. A joint fit of all the experimental data reproduce the $Q^2-$dependence with the accuracy $χ^2/dof=0.86$. Predictions of the model, that 1) the ratios of the proton form factors $G_E/G_M$ are different for Rosenbluth, polarization and beam--target--asymmetry experiments and 2) similar ratios are nearly the same for neutron, can be used for experimental verification of the model.
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