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

At J-PARC MLF, MUSE provides the world-highest flux of pulsed muon beams. U-Line, one of the four beamlines in the facility, features an intense surface muon beam from Super-Omega and Ultra-slow muon generated by laser ionization of thermal muonium in vacuo. The Ultra-slow muon beam is characterized by variable energy from sub-keV to tens of keV and a time resolution of several tens of times better than that of ordinary pulsed beams. These features enable the study of interesting phenomena localized at surfaces and near interfaces and fast dynamics that cannot be observed with ordinary pulsed beams. Commissioning of the beamline and instruments is underway in preparation for the start of user programs. This paper presents an overview of the facility, its current status, and its prospects.