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，通过激光共振电离方法产生超慢μ子。在RIKEN-RAL μ子设施3号端口的慢离子光学装置的建造于2001年夏天完成。然后，我们有机会在Port 3获得5天的μ子束时间，其中约5 x 105表面μ子/s束，动量为27 MeV/c。质子加速器的重复频率为50 Hz，因此激光系统的工作频率与μ子脉冲同步（25 Hz），只有在引入激光时才能观察到清晰的峰值，而在不引入激光时则观察不到。此外，在预期的飞行时间和预期的质量/Q对应的慢μ子观察到这个峰值。我们还测量了慢μ子产额的依赖关系作为不同波长的函数。其峰值为820.4nm。这些证据表明Mu是通过1 s-2 p跃迁电离的。另一方面，Mu的莱曼-α光 关于我们 通过这种测量进行了实验校准。这就是为什么我们声称我们成功地用激光共振电离方法从表面μ子束产生了慢μ子。在测量过程中，慢μ子的速率为0.03μ+/s。有几个原因被认为是如此之小的比率。第一个原因是表面μ子束的很大一部分被具有小孔径的准直器阻挡。我们必须重新设计光束导管没有准直器在通往慢离子光学系统的路上。第二个原因是我们没有时间调整表面μ子的动量，使表面μ子停留在钨靶的后表面上，我们可能不得不更换50和25μm的钽箔，因为表面μ子的动量可以被几个束窗减小。第三，我们需要改进真空紫外（Vacuum Ultra Violet，VUV）的产生，它比KEK激光系统低一到两个数量级，通过改进这些实验条件，我们期望慢μ子的产额至少提高100到1000倍，这将适用于μ+SR的研究。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