Experimental study of Deeply-bound Pionic Atoms

这个项目的目的是用一种新的核反应方法来寻找深束缚的电子原子，如电子Pb的1s和2p态。由于介子在达到深束缚态之前就会被原子核吸收，因此用传统的介子x射线光谱学来研究这种状态是不可能的。我们在法国萨克莱用SPES IV光谱仪进行了Pb（d,2p）实验，在加拿大TRIUMF用MRS光谱仪进行了Pb（n,d）实验，在萨克莱用SPES I光谱仪进行了Pb（d,^3He）实验。相应的理论工作也已完成。（d,2p）反应如果形成截面和理论预测的一样大，实验达到了能找到离子原子峰的灵敏度。然而，没有观察到峰值。（n,d）和（d,^3He）理论（d,2p）实验中没有观察到峰的原因后来通过详细的理论工作被理解，（n,d）或（d,^3He）反应被发现更适合于产生深束缚的电子原子。（d,^3He）反应数据在实验室框架中3h / h下采集。理论指导我们选择更小的角度来增加截面，但由于实验上的困难，我们无法选择更小的角度。在光谱中没有发现峰，但作为副产物，首次测量了p(d,^3He)pi^0的介子产生截面。（n,d）反应在介子产生阈值附近，出现了一个能量和截面与理论预测一致的结构。然而，统计显著性太小，无法得出强有力的结论，而中子束的使用也难以大大提高统计精度。

The aim of this project is to search for deeply-bound pionic atoms, such as 1s and 2p states of pionic Pb, using a novel nuclear-reaction method. The study of such states using the conventional pionic X-ray spectroscopy is impossible, since pions will be absorbed by the nucleus before they can reach the deeply bound states.We carried out Pb(d,2p) experiments using the SPES IV spectrometer at Saclay (France), Pb(n,d) experiments using the MRS spectrometer at TRIUMF (Canada), and Pb(d,^3He) experiments using the SPES I spectrometer at Saclay. Corresponding theoretical works have been done also.1. (d,2p) reactionThe experiment reached the sensitivity with which we should be able to find the pionic-atom peak, if the formation cross section was as large as was theoretically predicted. However, no peak was observed.2. (n,d) and (d,^3He) theoryThe reason for the non-observation of peaks in the (d,2p) experiment was later understood through detailed theoretical works, and (n,d) or(d,^3He) reactions were found to be more suited for the production of deeply-bound pionic atoms.3. (d,^3He) reactionData were taken at 3ﾟ in the laboratory frame. Theory guides us to go to smaller angles to increase the cross section, but due to experimental difficulties, we were unable to go to much smaller angles. No peak was identified in the spectrum, but as a by product, the pion production cross section for p(d,^3He)pi^0 was measured for the fist time.4. (n,d) reactionNear the pion production threshold, a structure, whose energy and cross section were consistent with theoretical prediction, was seen. However, the statistical significance was too small to draw strong conclusions, and the use of neutron beam makes it difficult to much improve the statistical accuracy.