有限原子核中核子电磁形状因子比值的局域核密度依赖计算
Local-nuclear-density dependent calculation of nucleon electromagnetic form factor ratios in finite nuclei
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中文总结 AI 辅助
该研究在协变量子蒙特卡罗框架内纳入原子核空间密度分布，计算有限原子核内核子电磁形状因子比值，预测了碳-12、氧-16、钙-40的质子与中子电磁双比值，为未来极化转移实验测量提供参考。
中文摘要 AI 辅助
我们计算束缚在有限原子核内的核子的电磁形状因子，并针对电形状因子（$G_E^*$）与磁形状因子（$G_M^*$）之比，按四动量转移平方$Q^2$给出预测。我们在协变量子蒙特卡罗（covariant spectator-QMC）框架内，扩展了先前的常密度计算，纳入有限原子核的空间核密度分布，量化了与先前应用中所用平均密度近似的偏差。通过对比$G_E^*/G_M^*$之比与自由空间中的$G_E/G_M$之比，可观测介质效应的影响，这一比值定义了与给定原子核相关的质子电磁双比值，该双比值有望消除部分系统不确定性。预计未来将在极化转移实验（$\boldsymbol{\text{e}} A, e'\boldsymbol{A}' \boldsymbol{p}$）中测量原子核内束缚质子对应的$G_E^*/G_M^*$比值。为应对该领域未来的测量，我们对双比值作出预测，以与原子核束缚质子能态的平均测量结果对比。我们研究的原子核为$^{12}$C、$^{16}$O和$^{40}$Ca。我们得出结论：采用核密度分布函数$\rho(r)$计算得到的形状因子，其抑制程度小于采用平均核密度计算的结果；结果表明，低密度表面区域的相对重要性随$Q^2$增大而提升，导致抑制程度弱于平均密度近似的预测；我们还对原子核内束缚中子对应的比值作出预测。
英文摘要
We calculate the electromagnetic form factors of nucleons bound in finite nuclei and make predictions to the ratio between the electric ($G_E^*$) and magnetic ($G_M^*$) form factors in terms of the square of the four-momentum transfer $Q^2$. We extend our previous constant-density calculations within the covariant spectator-QMC framework by incorporating the spatial nuclear density profiles of finite nuclei and quantify the deviations from the average-density approximation used in our previous applications. The impact of the medium effects can then be observed considering the ratio between $G_E^*/G_M^*$ and the ratio in free space $G_E/G_M$, that define the proton electromagnetic double ratio associated with a given nucleus. The double ratio is expected to remove some systematic uncertainties. There is the expectation that ratios $G_E^*/G_M^*$ associated with the bound protons inside the nucleus will be measured in the near future in polarization-transfer experiments $(\vec{e} A, e'\! A' \vec{p})$. Anticipating future measurements on the subject, we make predictions for the double ratios, to be compared with the average measurements on the energy states of protons bound to nuclei. We consider the nuclei $^{12}$C, $^{16}$O and $^{40}$Ca. We conclude that the form factors calculated using nuclear density profile function $ρ(r)$ are less suppressed than in the case of the results calculated using the average nuclear density. The results indicate that the relative importance of the low-density surface region increases with $Q^2$, leading to a weaker suppression than that predicted by the average-density approximation. We also make predictions for the ratios associated with neutrons bound to nuclei.
发表机构
- Soongsil University（崇实大学）
- Universidade Cidade de São Paulo（圣保罗城市大学）
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