Hyperfine Interactions 106 (1997) 237–244 237 Ultra slow muons generated by laser resonant ionization of thermal muonium produced by 500-MeV protons with hot tungsten Y. Miyake a , K. Shimomura a , A.P. Mills a,b and K. Nagamine a,c a Meson Science Laboratory, University of Tokyo (UT-MSL), Hongo, Bunkyo-ku, Tokyo 113, Japan b Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, USA c Muon Science Laboratory, Institute of Physics and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan We report recent progress to date on the UT-MSL/KEK “Ultra Slow Muon” project, in which thermal muonium (Mu) atoms are generated from the surface of a hot tungsten target placed at the primary 500 MeV proton beam line and resonantly ionized by intense u.v. lasers synchronized with the emission of the Mu. The positive muon ionization fragments are collected by electrostatic beam optics to form a beam of slow positive muons. 1. Introduction At UT-MSL/KEK we have been pursuing the “Ultra Slow Muon Project”, in which thermal muonium (designated as Mu; consisting of a μ + and an e - ) atoms are gen- erated from the surface of a hot tungsten foil [1], placed at the primary 500 MeV proton beam line and ionized by intense lasers synchronized with the emission of Mu. This project was started in 1991 in order to develop a tool to explore new fields of muon sciences such as surface/boundary physics (chemistry) and precise atomic physics (QED) etc. Recently, by developing a Ti-Sapphire (TiS) laser system to gen- erate Lyman-α photons and employing a 6N-tungsten target, we have succeeded in the generation of ultra slow muons by the laser resonant ionization method [2]. On the other hand, the moderation method in rare gas solids is under development at PSI [3]. In this report, recent developments of the ultra slow muon project at UTMSL are reported.  J.C. Baltzer AG, Science Publishers