Masashi Otani

Status of the Muon g-2/EDM Experiment at J-PARC (E34)

Though Standard Model (SM) for elementary particle physics was complete by the Higgs observation at LHC, many problems such as dark matter and the baryon-antibaryon asymmetry of the Universe still remain unsolved. These questions indicate that new physics (NP) will emerge at higher energy scale. One of the indications for NP up to now is in the muon anomalous magnetic moment (g-2); there is 3.3σ discrepancy between the SM prediction and measurement by the E821 experiment [1] with an accuracy of 0.54 ppm. One of the other windows to NP is the muon electric dipole moment (EDM); having the CPT symmetry, the EDM violates CP, which is necessary for the baryon-antibaryon asymmetry while strongly suppressed in SM. The J-PARC muon g-2/EDM experiment (E34) [2] aims to measure the muon g-2 and EDM with an accuracy of 0.1 ppm and a sensitivity of 10 e ・ cm, respectively, to cast light on NP. Fig.1 shows our experimental setup. To achieve the world best accuracy, high intensity beam at J-PARC MUSE and novel technique of the ultra-cold muon beam are used. The ultra-cold beam enables muons to be stored and detected in the magnetic field with no electric focusing, resulting in no need to choose the magic momentum of 3.094 GeV/c used for decades and minimizing dimensions of the stored magnetic field and its systematics. We are intensively developing the muon beamline, the ultra-cold muon source, detector etc. to start the experiment in the late 2010s. Current status of the experiment is reported in this presentation.

Beam dynamics design of the muon linac high-beta section

A muon linac development for a new muon g-2 experiment is now going on at J-PARC. Muons from the muon beam line (H line) at the J-PARC muon science facility are once stopped in a silica-aerogel target, and room temperature muoniums are evaporated from the aerogel. They are dissociated with lasers, then accelerated up to 212 MeV using a linear accelerator. For the accelerating structure from 40 MeV, disk-loaded traveling-wave structure is applicable because the particle beta is more than 0.7. The structure itself is similar to that for electron linacs, however, the cell length should be harmonic to the increase of the particle velocity. In this paper, the beam dynamics design of this muon linac using the disk-loaded structure (DLS) is described.

The low energy muon beam profile monitor for the muon g−2/EDM experiment at J-PARC

The muon g−2/EDM experiment at J-PARC aims to measure the muon anomalous magnetic moment and electric dipole moment with high precision by utilising an ultracold muon beam. The current muon g−2 discrepancy between the Standard Model prediction and the experimental value is about 3.5 standard deviations. This experiment requires a development of the muon LINAC to accelerate thermal muons to the 300 MeV/c momentum. Detectors for beam diagnostics play a key role in such an experiment. The beam profile monitoring system has been designed to measure the profile of the low energy muon beam. It was tested during two beam tests in 2016 at the MLF D2 line at J-PARC. The detector was used with positive muons, Mu-(μ+ e− e−), p and H-, e− and UV light. The system overview and preliminary results are given. Special attention is paid to the spatial resolution of the beam profile monitor and online monitor software used during data taking.

H line; a beam line for fundamental physics study

The muon facility, J-PARC (Muon Science Establishment; MUSE), has been operating since the first beam in 2008. Starting with a 200 kW proton beam, a beam intensity of 3 × 106 muons/s was reached in 2009 which was the most intense pulsed muon beam in the world. From the 2 cm thick graphite target, four secondary muon beam lines are designed to be extracted. Three beam lines currently exist, the first being operational and the other two undergoing commissioning. The fourth and the last beam line, the H line, is planned to be constructed. This new beam line is designed to have a large acceptance, provides the ability to tune the momentum, and use a kicker magnet and/or a Wien filter. The H line is designed to provide an intense beam of 108 surface muons/s for fundamental physics studies to observe new physics beyond the standard model. Such studies require high statistics and they need to occupy the experimental areas for a relatively long period.

Development of a Muon Linac for the G-2/EDM Experiment at J-PARC

We are developing a linac dedicated to the muon acceleration for muon g-2/EDM experiment at J-PARC. The muon linac consists of a radio-frequency-quadrupole (RFQ), an inter-digital H-mode (IH) drift tube linac (DTL), a diskand-washer (DAW) -type coupled cell linac (CCL), and a disk-loaded structure. This paper describes the design of each structure and current progress towards muon acceleration with the RFQ, which is expected to be the first practical realization of muon acceleration in the world.