Development and application of ultra slow muon generation by laser resonant ionization method

我们一直在与RIKEN-RAL μ子科学小组合作，研究激光共振电离法产生超慢μ子的方法。在RIKEN-RAL介子设施3号港口的慢离子光学的建设于2001年夏天完成。然后我们有机会在Port3进行5天的介子束时间测试，在那里我们可以获得5 × 105个表面介子/秒，动量为27 MeV/c。质子加速器以50Hz的重复频率运行，因此激光系统与每秒25Hz的μ子脉冲同步运行。只有在引入激光的情况下，我们才能观察到一个清晰的峰值，而在没有引入激光的情况下则没有。在期望的TOF和对应于慢介子的期望质量/Q中也观察到这个峰值。我们还测量了慢μ子产率作为不同波长的函数的依赖性。其峰值为820.4 nm。这个证据表明Mu是通过1s-2p跃迁电离的。另一方面，用该测量对Mu…More的莱曼α光进行了实验校准。这就是为什么我们声称我们成功地用激光共振电离法从表面介子束产生慢介子。在测量过程中，慢μ子的速率为0.03μ+/s。有几个原因可以解释为什么这个比率如此之小。第一个原因是表面介子束的很大一部分被具有小孔径的准直器阻挡。我们必须重新设计没有准直器的光束导管在使用慢离子光学的过程中。二是我们没有时间调整表面介子的动量，使表面介子停在钨靶的后表面。我们可能需要交换50 μm和25μm的tangs箔，因为表面μ子的动量会被几个光束窗口所减少。三是提高真空紫外（VUV）的产生，与KEK激光系统相比，VUV的产生要低一两个数量级。通过改善这些实验条件，我们期望慢μ子的产率至少提高100到1000倍，这将适用于μ+SR研究。少

We have been collaborating with the RIKEN-RAL muon science group on the ultra slow muon generation by the laser resonant ionization method. Construction of the slow ion optics at Port 3 at RIKEN-RAL muon facility was completed on the summer of 2001. Then we had a chance of muon beam time for 5 days at Port3 where about 5 x 105 surface muons/s beam with a momentum of 27 MeV/c is available. The proton accelerator operates at 50Hz repetition rate, therefore the laser system was operated synchronized with the every second muon pulse(25Hz).We could observe a clear peak only when laser lights were introduced, but not when laser lights were not introduced. Also this peak was observed in the expected TOF and in the expected MASS/Q corresponding to the slow muon.We also measured dependence of the slow muon yield as a function of the difference wavelength. It peaked at 820.4 nm. This evidence is showing that Mu is ionized through the 1s-2p transition. On the other hand, the Lyman-α light for Mu … More was experimentally calibrated by this measurement. This is why we claimed we succeeded in the slow muon generation by the laser resonant ionization method originated from the surface muon beam. During this measurement, the rate of the slow muon was 0.03μ+/s. There are considered several reasons why the rate was so small. The first reason is that a lot of fraction of the surface muon beam is blocked by a collimator with a small aperture. We have to redesign the beam duct without the collimator on the way to the slow ion optics. The second is that we had no time to adjust the momentum of the surface muon so that surface muon stops on the rear surface of the tungsten target.We may have to exchange tangsten foils of 50 and 25μm, since momentum of the surface muon can be reduced by the several beam windows. The third is that we need to improve the VUV (Vacuum Ultra Violet) generation which is lower than one or two order of magnitude compared with the KEK laser system.By improving those experimental conditions, we expect at least 100 to 1000 times larger yield of the slow muons which will be suitable for the μ+SR studies. Less