EXPLORATORY STUDIES OF ANOMALOUSLY LONG-LIVED HADRONIC ATOMS

(1)利用欧洲核子研究中心（CERN）的LEAR反质子束流，在氦介质中开展了长寿命反质子的扩展实验计划。不仅在液相中，而且在气相和固相中，观察到3%的停止反质子的寿命约为3-4微秒。其次，激光共振光谱技术的发展，以澄清这种反常的寿命的机制。提出的方法是利用强脉冲激光诱导亚稳态和短寿命态之间的受激跃迁，并在延迟湮没时间谱中检测到作为尖峰的跃迁。许多共振跃迁的成功观测已经出现。观察到的共振波长与理论预期一致，这表明亚稳性来自大角动量的长寿命状态。包括超精细结构观测在内的精密光谱学为粒子-反粒子对称性和少体理论提供了重要的数据。用激光光谱研究了氦原子和外界原子分子对亚稳原子的各种影响。(2)利用600 MeV的~（208）Pb（d，3 He）反应，在GSI上发现了~（207）Pb的深束缚π介子态。

(1) Extensitive experimental programs on long-lived antiprotons in helium media have been carried out by using the antiproton beam from LEAR at CERN.First, delayd annihilation time spectra of antiprotons were measured precisely. Not only in liquid phase but also in gas and solid phase 3% of stopped antiprotons were observed to have lifetimes about 3-4 microseconds. Secondly, laser resonance spectroscopy was developed to clarify the mechanism of this anomalous longevity. The method proposed was to induce stimulated transitions between a metastable state and a short-lived state using an intense pulsed laser and to detect the transition as a sharp spike in delayd annihilation time spectra. Successful observations of many resonance transitions came out. The resonance wavelengths observed agree with theoretical expectations, which established that the metastability arises from long-lived states of large angular momenta. The precise spectroscopy including the observation of hyperfine structure has provided important data on the particle-antiparticle symmetry and few-body theories. Various effects of surrounding helium and foregn atoms and molecules on the metastable atoms have also been found and studied by laser spectroscopy.(2) Deeply-bound pionic states in 207Pb have been discocovered at GSI using the 208Pb (d, 3He) reaction at 600 MeV.