Meson Science Research with Intense Muon Beam

1988年，东京大学介子科学实验室（UTMSL）和加拿大温哥华三大学介子研究中心（TRIUMF）在蒙补所介子科学特别项目研究资助基金的帮助下，共同完成了一条新的慢速和直流负介子通道。现在，这个位于TRIUMF介子区域的通道为日本和国际研究人员提供了一个使用世界上最强负介子束的机会。在目前的“KOKUSAI-GAKUJTYUTSU-KENKYU”的支持下，利用这种新的负介子通道进行了许多重要的介子实验。氧在高温超导材料中的重要性已被许多理论家和许多实验家所强调，并存在一些合适的探针。在氧核捕获的负介子是一种最有效的能探测氧位局部电场和磁场的显微探针。utmsl - rikenyamanashi大学的联合…More小组使用非常纯的LaSrCuO单晶发现了对应于不同氧位的两种不同的负μ子信号。研究了不同掺杂浓度下的顺磁位移和弛豫速率。得到了温度依赖性和晶体轴依赖性。该实验的部分内容已在第五届muSR国际会议（牛津，1990）和国际高Tc会议（金泽，1991）上报道。对另一组高Tc材料YBzCuO也进行了负介子研究。结果表明，超导样品的mu^-SR信号幅值较小，而反铁磁有序样品的mu^-SR信号幅值较大。为了全面了解磁性氧化物中的负介子行为，对各种三维金属氧化物进行了系统的研究。另一方面，正介子已被确立为一种独特而合适的显微探针，用于检测反铁磁有序或弱磁场局域，这是用其他方法很难观察到的。因此，mu^+SR被广泛应用于高温超导体的研究。进一步研究了新型高Tc超导材料Bi_2Sr_2YCuO_y、Bi_2(Sr_<1-x>、La_x)_2Cuo_y、YBa(Cu_<1-x>、Cu_x)O、PrCuO、gdccuo等。另一项成就是成功测量了位于0.6Gp高压研究厚壁腔内的高Tc材料的mu^+SR。利用在碳上捕获的负介子形成取代的类硼杂质，对一维聚合物聚乙炔进行了佩尔斯不稳定性转变的研究。通过检测二次电子数的分布，研究了慢介子与薄膜的相互作用。从发射电子的平均数目分布来看，得到了电荷不对称效应。在5 Mev/c - 12 Mev/c的动量区，得到了电荷对称效应[n(mu^+)-n(mu^-)]/[n(mu^+)+n(mu^-)]，称为巴卡斯效应（停止功率的不对称效应）。在TRIUMF， CERN， GSI和Saclay进行了新的介子产生探索性实验。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灭。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