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arXiv 1702.08027nucl-th
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从弹性电子-质子散射截面数据中唯象提取双光子交换振幅

Phenomenological extraction of two-photon exchange amplitudes from elastic electron-proton scattering cross section data

I. A. Qattan

备注：
14 pages, 8 figures, submitted to Phys. Rev. C
发表信息：
Phys. Rev. C 95, 055205 (2017)
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摘要：

在这项工作中，我改进和扩展到低和高$Q^2$值的提取的$\varepsilon$依赖的实部的双光子交换（TPE）振幅相对于磁形状因子，以及比率$P_l/P_l^{Born} (\varepsilon,Q^2)$通过使用世界数据上的$σ_R(\varepsilon,Q^2)$与精确的新数据覆盖的低动量区域，这是敏感的大尺度结构的核子。我提供了简单的参数化的TPE振幅，以及估计的拟合不确定性。提取的TPE振幅与以前的唯象提取和TPE计算进行比较。通过使用TPE振幅的新参数化提取$P_l/P_l^{Born}$比，并与先前的提取、TPE计算和在$Q^2$ = 2.50（GeV/c）$^2$的直接测量进行比较。提取的TPE幅度在几个百分点的水平上，并且随着$Q^2$的增加而大致呈线性，其中它们在高$Q^2$时变为非线性。相反，$Y_M$，这是主要由弹性贡献的影响，我发现$Y_E$的非弹性贡献的影响，在大$Q^2$值。虽然$Y_E$和$Y_3$在幅度上不同，但它们具有相反的符号并且倾向于部分地彼此抵消。这表明TPE对$σ_R(\varepsilon,Q^2)$的修正主要是由$Y_M$驱动的，在较小程度上是由$Y_3$驱动的，与以前的唯象提取和强子TPE计算一致。

英文摘要：

In this work, I improve on and extend to low and high $Q^2$ values the extractions of the $\varepsilon$ dependence of the real parts of the two-photon exchange (TPE) amplitudes relative to the magnetic form factor, as well as the ratio $P_l/P_l^{Born} (\varepsilon,Q^2)$ by using world data on $σ_R(\varepsilon,Q^2)$ with an emphasis on precise new data covering the low-momentum region which is sensitive to the large-scale structure of the nucleon. I provide simple parametrizations of the TPE amplitudes, along with an estimate of the fit uncertainties. The extracted TPE amplitudes are compared with previous phenomenological extractions and TPE calculations. The $P_l/P_l^{Born}$ ratio is extracted by using the new parametrizations of the TPE amplitudes and compared to previous extractions, TPE calculations, and direct measurements at $Q^2$ = 2.50 (GeV/c)$^2$. The extracted TPE amplitudes are on the few-percentage-points level and behave roughly linearly with increasing $Q^2$ where they become nonlinear at high $Q^2$. Contrary to $Y_M$, which is influenced mainly by elastic contributions, I find $Y_E$ to be influenced by inelastic contributions at large $Q^2$ values. While $Y_E$ and $Y_3$ differ in magnitude, they have opposite sign and tend to partially cancel each other. This suggests that the TPE correction to $σ_R(\varepsilon,Q^2)$ is driven mainly by $Y_M$ and to a lesser extent by $Y_3$ in agreement with previous phenomenological extractions and hadronic TPE calculations.

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