Study of deeply-bound pionic atoms

这项研究的目的是从理论和实验上研究深度束缚的介子原子态，特别是IS和2P态，并获得关于原子核中有效介子质量的信息。我们还发展了一种新的方法来研究ETA和omega介子的介质质量。两年来取得的主要成果如下：1.为了探索质子原子的束缚态，我们用~(？)lt；~(206)&gt；~(？)受重核束缚的重子的波函数与核有很大的重叠，因此适合于研究原子核中的介子行为。然而，还没有在实验中观察到这样的状态。理论研究表明，如果选择Pb2O6作为靶，就有可能将2p态和IS态识别为激发能谱中的清晰峰。因此，我们进行了实验，并成功地观测到了2p和is峰。当详细的分析工作完成后，我们期望能高精度地确定π介子的有效质量。介子原子实验的成功促使我们研究利用无反冲(d，^3He)反应研究其他介子，如ETA和欧米伽的行为的可行性。我们首先估算了介子-核光学势，并通过求解Klein-Gordon方程确定了介子的结合能和宽度。在这两种情况下，势都具有很强的吸引力，并预言了束缚态的存在。然后，我们使用格林函数方法和Eikonal近似来估计反应截面。我们发现，即使在考虑了各种背景过程之后，也可以观察到束缚态峰。基于这项研究的实验方案被提交给GSI，并被批准为S214。

The purpose of the research is to study theoretically as well as experimentally the deeply-bound pionic atom states, in particular is and 2p states, and to obtain information on the effective pion mass in nuclei. We also developed a new method to study the in-medium masses of eta and omega mesons. The major achievements during the two years are as follows :1. In order to search for the is bound state of pionic atom, we carried out an experiment using the ^<206>Pb(d, ^3He) reaction. The wavefunction of the pionic is state bound to a heavy nucleus has a large overlap with the nucleus, hence suitable to study the behavior of pions in nuclei. However, no such states have been experimentally observed. Theoretical studies have suggested that it is possible to identify 2p as well as is states as clear peaks in the excitation-energy spectrum, if Pb2O6 is chosen as the target. We therefore carried out the expriment, and successfully observed the 2p and is peaks. When the detailed analysis, being carried out, is completed, we expect to determine the pion effective mass with a high precision.2. The success of the pionic atom experiment motivated us to study the feasibility of studying the behavior of other mesons, such as eta and omega, by using the recoilless (d, ^3He) reaction. We first estimated the meson-nucleus optical potential, and determined the binding energies and widths of mesons by solving the Klein-Gordon equation. In both cases, the potentials were strongly attractive, and the existence of bound states are predicted. We then used the Green function method and the Eikonal approximation to estimate the reaction cross sections. We found that the bound-state peaks can be observed, even after taking account of various background processes. An experimental proposal based on this study was submitted to GSI, and was approved as S214.