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Abstract This paper introduces a new approach to measure the muon magnetic moment anomaly $a_{\\mu} = (g-2)/2$ and the muon electric dipole moment (EDM) $d_{\\mu}$ at the J-PARC muon facility. The goal of our experiment is to measure $a_{\\mu}$ and $d_{\\mu}$ using an independent method with a factor of 10 lower muon momentum, and a factor of 20 smaller diameter storage-ring solenoid compared with previous and ongoing muon $g-2$ experiments with unprecedented quality of the storage magnetic field. Additional significant differences from the present experimental method include a factor of 1000 smaller transverse emittance of the muon beam (reaccelerated thermal muon beam), its efficient vertical injection into the solenoid, and tracking each decay positron from muon decay to obtain its momentum vector. The precision goal for $a_{\\mu}$ is a statistical uncertainty of 450 parts per billion (ppb), similar to the present experimental uncertainty, and a systematic uncertainty less than 70 ppb. The goal for EDM is a sensitivity of $1.5\\times 10^{-21}~e\\cdot\\mbox{cm}$.

Oil bodies are intracellular structures present in the seed and leaf cells of many land plants. Seed oil bodies are known to function as storage compartments for lipids. However, the physiological function of leaf oil bodies is unknown. Here, we show that leaf oil bodies function as subcellular factories for the production of a stable phytoalexin in response to fungal infection and senescence. Proteomic analysis of oil bodies prepared from Arabidopsis (Ambidopsis thaliana) leaves identified caleosin (CLO3) and a-dioxygenase (α-DOX1). Both CLO3 and α-DOX1 were localized on the surface of oil bodies. Infection with the pathogenic fungus Colletotrichum higginsianum promoted the formation of CLO3-and α-DOX1-positive oil bodies in perilesional areas surrounding the site of infection. α-DOX1 catalyzes the reaction from α-linolenic acid (a major fatty acid component of oil bodies) to an unstable compound, 2-hydroperoxyoctadecatrienoic acid (2-HPOT). Intriguingly, a combination of α-DOX1 and CLO3 produced a stable compound, 2-hydroxyoctadecatrienoic acid (2-HOT), from α-linolenic acid. This suggests that the colocalization of α-DOX1 and CLO3 on oil bodies might prevent the degradation of unstable 2-HPOT by efficiently converting 2-HPOT into the stable compound 2-HOT. We found that 2-HOT had antifungal activity against members of the genus Colletotrichum and that infection with C. higginsianum induced 2-HOT production. These results defined 2-HOT as an Arabidopsis phytoalexin. This study provides, to our knowledge, the first evidence that leaf oil bodies produce a phytoalexin under a pathological condition, which suggests a new mechanism of plant defense.

High precision measurements of the ground state hyperfine structure (HFS) of muonium is a stringent tool for testing bound-state quantum electrodynamics (QED) theory, determining fundamental constants of the muon magnetic moment and mass, and searches for new physics. Muonium is the most suitable system to test QED because both theoretical and experimental values can be precisely determined. Previous measurements were performed decades ago at LAMPF with uncertainties mostly dominated by statistical errors. At the J-PARC Muon Science Facility (MUSE), the MuSEUM collaboration is planning complementary measurements of muonium HFS both at zero and high magnetic field. The new high-intensity muon beam that will soon be available at H-Line will provide an opportunity to improve the precision of these measurements by one order of magnitude. An overview of the different aspects of these new muonium HFS measurements, the current status of the preparation for high-field measurements, and the latest results at zero field are presented.

The South Pacific region is characterized by a broadly elevated seafloor known as the South Pacific superswell. This region has a concentration of midplate volcanoes that experienced massive eruptions in the mid‐Cretaceous period (90–120 Ma). These characteristics suggest the presence of a large‐scale mantle plume beneath the South Pacific, called the South Pacific superplume. The geometry, origin depth, temperature, and composition of the superplume remain controversial, however, mainly due to the lack of seismological data that documents the mantle structure beneath the South Pacific. Seismic stations are sparse in the area due to its remote ocean environment. To obtain a better seismic image of the superplume, we deployed temporary broadband seismographs on oceanic islands and the seafloor in the South Pacific, which made possible the highest spatial resolution that has ever been achieved for the mantle structure beneath the region. The seismic image obtained from this new seismic data indicates that large‐scale low‐velocity anomalies (on the order of 1000 km in diameter), indicative of the superplume, are located from the bottom of the mantle to a depth of 1000 km, and small‐scale low‐velocity anomalies (on the order of 100 km in diameter) are present above it. A comparison of the seismic image with recent mantle convection studies based upon laboratory and numerical experiments suggests that the superplume may be a hot and chemically distinct mantle dome, and that the small‐scale anomalies may be narrow plumes generated from the top of the dome. This model may explain various characteristics of hot spots in the South Pacific, such as the seafloor swell, short‐lived hot spot chains, and the periodicity of massive eruptions.

Abstract The hadron spectrum at finite density is an important observable for exploring the origin of hadron masses. In the KEK-PS E325 experiment, the di-electron decays of $\\phi$ mesons inside and outside nuclei were measured using $12 \\,\\mathrm{G}\\mathrm{e\\mathrm{V}}$ pA reactions. In the previous analysis, a significant excess was observed on the low-mass side of the $\\phi$ meson peak in the data for slow-moving $\\phi$ mesons ($\\beta \\gamma =p_{\\phi }/m_{\\phi }<1.25$) with the copper target, and in-medium vector meson spectral modification was verified. We used, for the first time, the PHSD transport approach to take into account the time evolution of the spatial density distribution of the target nuclei. Consistent with the previous analysis, a significant excess was observed in the present analysis as well. It was found that incorporating momentum dependence into the spectral modification leads to better agreement with the experimental results. For the slow-moving $\\phi$ mesons with the copper target, the newly obtained modification parameters are consistent with those from the previous analysis within the uncertainties.

A negative muonium ion (Mu−) source using an aluminum foil target (Al target) was developed as a low-energy muon source.Mu−ions are produced by irradiating the Al target with a 3-MeV positive muon (μ+) beam and observed using a microchannel plate. An experiment to produceMu−ions was conducted to evaluate the performance of thisMu−ion source. The measured event rate ofMu−ions was(1.7±0.3)×10−3Mu−/swhen the event rate of the incidentμ+beam was1.3×106/s. The experiment was conducted at the Muon Science Establishment, D-line in the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex. The formation probability, defined as the ratio of theMu−ions to the incident muons on the Al target, was(1.1±0.2(stat)+0.1−0.0(syst))×10−6. This Mu−ion source was first adopted in the commissioning of the muon accelerator at the D-line, and the event rate of the acceleratedMu−ions was consistent with the expectation. ThisMu−ion source boosted the development of the muon accelerator, and the practicality of this low-energy muon source obtained using a relatively simple apparatus was demonstrated.

We developed a new positron detector system called Kalliope, which is based on multi-pixel avalanch photo-diode (m-APD), application specific integrated circuit (ASIC), field programmable gated array (FPGA) and ethernet-based SiTCP data transfer technology. We have manufactured a general-purpose spectrometer for muon spin relaxation (μSR) measurements, employing 40 Kalliope units (1280 channels of scintillators) installed in a 0.4 T longitudinal-field magnet. The spectrometer has been placed at D1 experimental area of J- PARC Muon Science Establishment (MUSE). Since February of 2014, the spectrometer has been used for the user programs of MUSE after a short commissioning period of one week. The data accumulation rate of the new spectrometer is 180 million positron events per hour (after taking the coincidence of two scintillators of telescopes) from a 20×20 mm sample for double-pulsed incoming muons.

Muons have been accelerated by using a radio-frequency accelerator for the first time. Negative muonium atoms (Mu−), which are bound states of positive muons (μ+) and two electrons, are generated fromμ+’s through the electron capture process in an aluminum degrader. The generatedMu−’s are initially electrostatically accelerated and injected into a radio-frequency quadrupole linac (RFQ). In the RFQ, theMu−’s are accelerated to 89 keV. The acceleratedMu−’s are identified by momentum measurement and time of flight. This compact muon linac opens the door to various muon accelerator applications including particle physics measurements and the construction of a transmission muon microscope.

Negative muonium atom (μ+e-e-, Mu-) has unique features stimulating potential interesting for several scientific fields. Since its discovery in late 1980's in vacuum, it has been discussed that the production efficiency would be improved using a low-work function material. C12A7 was a well-known insulator as a constituent of alumina cement, but was recently confirmed to exhibit electric conductivity by electron doping. The C12A7 electride has relatively low-work function (2.9 eV). In this paper, the negative muonium production measurement with several materials including a C12A7 electride film will be presented.

Muon acceleration is an important technique in exploring the new frontier of physics. A new measurement of the muon dipole moments is planned in J-PARC using the muon linear accelerator. The low-energy (LE) muon source using the thin metal foil target and beam diagnostic system were developed for the world's first muon acceleration. Negative muonium ions from the thin metal foil target as the LE muon source was successfully observed. Also the beam profile of the LE positive muon was measured by the LE-dedicated beam profile monitor. The muon acceleration test using a Radio-Frequency Quadrupole linac (RFQ) is being prepared as the first step of the muon accelerator development. In this paper, the latest status of the first muon acceleration test is described.