The Ultra-Slow Muon generation at J-PARC: the present status and future prospects

We will introduce the present status of Ultra-Slow Muon (USM) generation at J-PARC and prospects. One of the four beamlines at J-PARC MLF generates USM from intense surface muon beams (4 MeV). The surface muon is stopped in the muonium production target, and the USM (~0.2eV) are generated by resonant laser ionization of thermal muonium evaporating into the vacuum. The approaching 1000 USM per second has been achieved through the development of the intense Lyman-α laser system. Recently, this USM beam has been applied to material science with Muon Spin Rotation/Relaxation/Resonance method. It is known that the spin polarization of the generated USM is less than 50% due to the coupling between randomly polarized electrons and 100% polarized surface Muons in the Muonium production process. As one of the developments for the muon g-2 experiment to be carried out at J-PARC new USM beamline, we will introduce the prospect of spin re-polarization using circular polarized Lyman-α lasers.