Studies Secondary Electron Emission in Slow Antiproton-Matter

在原子和固态物理中，具有负电荷的“重”粒子，如反质子、负µ子等，可以成为研究电荷不对称效应的奇妙探测器。其中，欧洲核子研究中心LEAR的反质子束流是最好的，因为它的质量和强度都很高。本研究是前一个项目《反质子-箔碰撞中的二次电子发射研究(#0104403：1989-1990年)》的延伸。我们的第一步致力于通过测量反质子-箔碰撞中正向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5.9 MeV的反质子束(到目前为止的Lowes可能能量)降级到几百keV的降解箔，在那里人们只能得到能量和角分布很宽的束流。我们的主要观测结果是：(1)V_p-V_e附近的光谱相当平滑，与头脑简单的预测相反，有很弱的反聚焦迹象；(2)在正确的能量位置上观察到一个小的凸起，强度合理，这与理论评估是一致的。作为参考实验，我们还测量了He气体靶正向发射的电离电子和同一方向散射的初级电子的强度。这与反质子实验形成了很好的对比。RFQ加速器技术的最新发展使我们能够获得低至-200keV的“解离”单能反质子束。我们正在用这种高质量的超慢光束来扩展我们的实验，它将提供，例如，关于尾流搭载电子的存在的明确答案，以及进一步证明慢重粒子通过晶体的可能性，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.