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

我们一直在与RIKEN-al Muon科学小组合作，通过激光共振电离方法产生超慢Muon。2001年夏天，在里肯-拉尔Muon设施的3号端口的慢离子光学装置的建造已经完成。然后我们有机会在PORT 3上获得5天的Muon束流时间，在那里可以获得动量为27 MeV/c的5×10~5表面Muons/S束流。质子加速器以50赫兹的重复频率工作，因此激光系统与每秒(25赫兹)的Muon脉冲同步工作。只有当引入激光时，我们才能观察到明显的峰值，而当没有引入激光时，我们观察不到明显的峰值。在预期TOF和对应于慢Muon的预期质量/q中也观察到了这一峰值。我们还测量了慢Muon产额与不同波长的关系。它在820.4 nm处达到峰值。这一证据表明，Mu是通过1s-2p跃迁电离的。另一方面，莱曼-α灯为Mu…更多的是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利用激光共振电离方法产生了慢缪子，这种方法源于表面µ子束。在这次测量中，慢µ子的速率为0.03μ/S。有几个原因可以解释为什么这个速率这么小。第一个原因是表面上的一大部分µ子束被一个小口径的准直器挡住了。在进入慢离子光学系统的过程中，我们必须重新设计不带准直器的束流管。二是我们没有时间调整表面介子的动量，使得表面介子停止在钨靶的背面，我们可能需要交换50和25μm的缠绕箔，因为表面介子的动量可以通过几个束窗来降低。三是我们需要改进真空紫外光的产生，使之比KEK激光系统低一个或两个数量级，通过改进这些实验条件，我们预计将产生至少100到1000倍的慢µ子，这将适合于μSR研究。较少

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