$^7$Li($p,e^+e^-$)$^8$Be过程与X17玻色子的从头算研究
Ab initio investigation of the $^7$Li($p,e^+e^-$)$^8$Be process and the X17 boson
AI总结：
针对ATOMKI合作组观测到的轻核衰变电子-正电子角关联异常，本研究用带连续态的无核壳模型从头算$^7$Li质子俘获相关过程，分析散射态影响并计算X17玻色子相关截面，为异常解读提供理论支撑。
摘要：
ATOMKI合作组近期报告了在$^4$He、$^8$Be和$^{12}$C的高能衰变中观测到电子-正电子角关联异常的结果。这些异常可通过一种质量约为17 MeV的新玻色子的产生及后续衰变来解释。对于这些实验中用到的质子俘获反应里的对产生过程的理论理解，对异常现象的解读至关重要。我们将带连续态的无核壳模型（No-Core Shell Model with Continuum, NCSMC）应用于$^7$Li上的质子俘获过程。NCSMC以手征两核子与三核子相互作用为唯一输入，统一描述轻核中的束缚态与非束缚态。我们研究了$^8$Be的结构、$p+^7$Li弹性散射、$^7$Li($p,γ$)$^8$Be截面以及内对产生过程$^7$Li($p,e^+ e^-$)$^8$Be。我们讨论了初始散射态的恰当处理对电子-正电子角关联谱的影响，并将结果与已有的ATOMKI数据集进行了对比。最后，我们针对假设的X17粒子的若干 proposed 模型，计算了$^7$Li($p,X$)$^8$Be的截面。
英文摘要：
Observations of anomalies in the electron-positron angular correlations in high-energy decays in $^4$He, $^8$Be, and $^{12}$C have been reported recently by the ATOMKI collaboration. These could be explained by the creation and subsequent decay of a new boson with a mass of ${\sim}17$ MeV. Theoretical understanding of pair creation in the proton capture reactions used in these experiments is important for the interpretation of the anomalies. We apply the ab initio No-Core Shell Model with Continuum (NCSMC) to the proton capture on $^7$Li. The NCSMC describes both bound and unbound states in light nuclei in a unified way with chiral two- and three-nucleon interactions as the only input. We investigate the structure of $^8$Be, the $p+^7$Li elastic scattering, the $^7$Li($p,γ$)$^8$Be cross section and the internal pair creation $^7$Li($p,e^+ e^-$)$^8$Be. We discuss the impact of a proper treatment of the initial scattering state on the electron-positron angular correlation spectrum and compare our results to available ATOMKI data sets. Finally, we calculate $^7$Li($p,X$)$^8$Be cross sections for several proposed models of the hypothetical X17 particle.
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