Studies Secondary Electron Emission in Slow Antiproton-Matter

在原子和固体物理学中，带负电荷的“重”粒子，如反质子、负μ子等，可以作为研究电荷不对称效应的绝佳探针。其中，来自欧洲核子研究中心LEAR的反质子束因其高质量和高强度而成为最好的。目前的研究是先前项目“反质子箔碰撞中的二次电子发射研究”（#0104403:1989-1990）的延伸。我们的第一步是通过测量反质子箔碰撞中向前发射的二次电子的能谱来研究“尾流”电子。我们已经进行了几个实验，将5.9MeV的反质子束（到目前为止可能的最低能量）降解为几百个KeV的降解膜，在那里人们只能得到宽能量和角分布的光束。我们的主要观测结果是：(1)v_p-v_e周围的光谱，其中upsilone是电子速度，与简单的预测相反，相当平滑，有非常弱的反隆起迹象；(2)在正确的能量位置观察到一个小的凸起，强度合理，这与理论评估一致。作为参考实验，我们还测量了He气体靶中正向发射的电离电子的强度与向同一方向散射的初级电子的强度一致，其中明显观察到反尖，这与反质子实验有很好的对比。RFQ加速器技术的最新发展使我们能够获得低至-200KeV的“减速”单能反质子束。我们正在用这种高质量的超慢光束扩展我们的实验，这将提供，例如，关于尾流电子存在的明确答案，以及进一步通过晶体引导慢重粒子的可能性，等等。

In atomic and solid state physics, "heavy" particles with negative charge like antiprotons, negative muons etc., can be fantastic probes to investigate Charge asymmetry effects. Among others, antiproton beams from LEAR at CERN are the best because of its high quality and high intensity.The present research is an extension of the previous project, "Studies on Secondary electron emission in antiproton-foil collisions (#0104403 : 1989-1990). Our first step had been devoted to the investigation on "wake-riding" electrons through measurements of energy spectra of secondary electrons emitted in the forward direction in antiproton-foil collisions. We have performed a couple of experiments degrading 5.9MeV antiproton beams (the lowes possible energy upto now)to several hundred KeV degrader foils, where one can only get a beam of wide energy and angular distribution. Our principal observations have been, (1)the spectra around v_p-v_e, where upsilone is the electron velocity, are rather smooth with very weak indication of an anticusp as opposed to simple-minded predictions, and (2) a small bump is observed at the right energy position with reasonable intensity, which is consistent with theoretical evaluations.As a reference experiment, we have also measured the intensity of ionized electrons emitted in the forward direction in coincidence with primary electrons scattered in the same direction for He gas target, where an anticusp is clearly observed which is in good contrast with antiproton experiment.Recent development of RFQ accelelator technique enables us to get "deccelelated"monoenergetic antiproton beam as low as -200KeV. We are on the way to extend our experiment with this high quality ultra slow beams, which will provide, e.g., the definite answer on the existence of the wake riding electrons, and further the possibility of channeling of slow heavy particles through crystals, etc.