Meson Science Research with Intense Muon Beam

1988年，东京大学介子科学实验室(UTM)和加拿大凡康弗三大介子实验室(TRIUMF)在蒙彪霍介子科学专项研究补助金的帮助下，完成了一个新的慢直流负介子通道。现在，这个位于TRIUMF介子区的通道为日本和国际上的研究人员提供了使用世界上最强的负µ子束的机会。在目前“KOKUSAI-GAKUJTYUTSU-KENKYU”的支持下，利用这个新的负Muon通道已经进行了许多重要的Muon实验。氧在高T_c超导材料中的重要性已经被许多理论家和许多实验者所强调，但对于这些问题，已经有了一些合适的探索。在氧核捕获的负缪子是最有效的微观探测器之一，它可以探测氧位的局部电场和磁场。联合…UTM L-RIKEN-Yamanashi大学的更多小组利用非常纯的LaSrCuO单晶，发现了对应于不同氧位的两个不同的负Muon信号。研究了不同掺杂浓度下的顺磁漂移和弛豫速率。得到了它们与温度和晶轴的关系。这个实验的部分内容已经在第5届国际MUSR会议(牛津，1990)和国际高T_c会议(金泽，1991)上得到了报道。对另一组高T_c材料YBzCuO，也进行了负M介子研究。其中，超导样品的mU-SR信号幅度较小，而反铁磁有序样品的mU-SR信号较大。为了对磁性氧化物中的负Muon行为有一个全面的了解，我们对各种3D金属氧化物进行了系统的研究，另一方面，正Muon已经被建立为一种独特而合适的微观探针，用于探测反铁磁有序或弱磁局域场，这是用另一种方法很难观察到的。因此，Mu^+SR在高温超导体的研究中得到了广泛的应用。将研究扩展到新的高温超导材料Bi2Sr2YCuOy，Bi2(Sr&lt；1-x&gt；，Lax)2CuOy，YBA(Cu1-x&gt；另一项成果是成功地对厚壁室内的高T_c材料进行了Mu^+SR测量，用于高达0.6 Gg的高压研究。利用在碳上捕获的形成替代类硼杂质的负µ子，研究了一维聚合物聚乙炔的Peierls不稳定性转变。通过检测二次电子数的分布，研究了慢Muon与薄箔的相互作用。从发射电子的平均数分布可以得到电荷不对称效应。在动量为5 Mev/c-12 Mev/c的动量区，获得了电荷对称效应[n(mu^+)-n(mu^-)]/[n(mu^+)+n(mu^-)]，称为巴卡斯效应(停止功率不对称效应)。最令人兴奋的结果也是在氦介质中观察到的延迟反质子湮没。较少

In 1988 a new slow and D. C. negative muon channel was completed by the cooperative work between UTMSL (The University of Tokyo, Meson Science Laboratory) and TRIUMF (Tri-University Meson Facility, Vanconver, Canada) with the help of the Grant-in-Aid for special Project Research on Meson Science from Mombusho. Now, this channel located in the meson area of TRIUMF gives an opportunity for Japanese and international researchers to use the world strongest negative muon beam.With support of the present "KOKUSAI-GAKUJTYUTSU-KENKYU", many important muon experiments have been carried out by using this new negative muon channel.The importance of the oxygen in the high Tc superconducting materials have been emphasized by many theoreticians and also by many experimentalists, for which there exist a few proper probes. The negative muon captured at the oxygen nucleus is one of the most efficient microscopic probe which can detect the local electric and magnetic fields at the oxygen site.The joint … More group of UTMSL-RIKEN-Yamanashi University has found two different negative muon signals corresponding to different oxygen sites, using the very pure single srystal of LaSrCuO. The paramagnetic shift and the relaxation rate are studied for the various concentrations of the doped impurities. There temperature dependence as well as crystal axes dependences are obtained. The parts of this experiment have been reported at the 5th International Conference of muSR (Oxford, 1990) and International Conference on High Tc (Kanazawa, 1991).Also to the other group of high Tc materials YBzCuO, negative muon study was applied. There, rather small amplitude of mu^-SR signal was found for the sample which shows superconductivity but a fairly large signal was obtained for the sample which shows antiferromagnetic ordering. In order to obtain the general understanding of the negative muon behavior in the magnetic oxides a systematic study are carried out on the various 3d-metal oxides.On the other hands, the positive muon has been established as a unique and proper microscopic probes to detect antiferromagnetic ordering or weak magnetic local field, which is very difficult to be observed with another method. With this reason mu^+SR has intensively been applied on studiesof high Tc superconductors. The study was extended to new high Tc superconducting materials Bi_2Sr_2YCuO_y, Bi_2(Sr_<1-x>, La_x)_2Cuo_y, YBa(Cu_<1-x>, Cu_x)O, PrCuO, GdCeCuO etc. Another achievement is the success of mu^+SR measurement for the the high Tc material located inside the thick walled chamber for high pressure studies up to 0.6Gp.The study of Peierls instability transition has been performed for one dimensional polymers polyacetylene, using a negative muon captured at carbon forming a substitutional boron-like impurity.The interaction of slow muon and the thin foils was studied by detecting the distribution of secondary electron numbers. From the average number distribution of emitted electrons, charge asymmetric effect was obtained. The charge symmetric effect [n(mu^+)-n(mu^-)]/[n(mu^+)+n(mu^-)] called the Barkas effect (asymmetric effect in stopping power) was obtained for the momentum region 5 Mev/c - 12 Mev/c.New exploratory experiments on meson production have been carried out at TRIUMF, CERN, GSI and Saclay. The most exciting result is also the observation of delayed antiproton annihilation in helium medium. Less