Negative muon beam status at the D-line of MUSE, J-PARC

At the Muon Science Establishment (MUSE) in the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC), the D-line is a unique beamline capable of providing both positive and negative decay muons. To utilize these muon beams more efficiently and effectively, we upgraded the electrostatic separator, adjusted the kicker timing, conducted beam momentum measurements, and minimized the background for negative muon spin relaxation (µ-SR) measurements. These upgrades and commissioning efforts have resulted in a reduction in the amount of contaminating electrons and background noise, thereby yielding a cleaner signal. We also determined the optimal conditions for the kicker in a single bunching operation. The standard deviation of the muon beam momentum distribution, as measured in the D1 area, was estimated to be approximately 3%. These enhancements have enabled us to utilize a beam of higher quality than was previously possible.