We will introduce three fundamental physics experiments at J-PARC MLF H-Line and the Hadron Hall South Experimental Building, as well as their interrelationships. Why muon is useful to approach new physics beyond the Standard Model, and how to explore the mysteries of the early universe by making full use of muon spin.
The muon science facility (MUSE), along with the neutron, hadron, and neutrino facilities, is one of the experimental areas of the J-PARC project, which was approved for construction in a period from 2001 to 2008. The MUSE facility is located in the Materials and Life Science Facility (MLF), which is a building integrated to include both neutron and muon science programs. After construction of the MLF building, the secondary muon lines were designed to extract efficiently either pions or muons from a muon production graphite target to the four muon beamline, the so-called D-Line, U-Line, S-Line and H-Line, enabling a variety of muon related experiments, at the ten experimental areas (D1, D2, U1A, U1B, S1, S2, S3, S4, H1 and H2) utilizing unique features of the pulsed muon beam. We have been working on the designing of the beamline components, utilizing various simulation codes.
One can produce light and heavy isotopes of hydrogen using positive or negative muons, which are called muonium (0.114 amu) and muonic helium (4.11 amu), respectively. These new hydrogen isotopes can open a new avenue of chemistry. In this article, we mainly describe our previous computational studies on muonium-containing molecules using quantum theory and emphasize their unique properties.
Abstract: Alkali metal clusters with an unpaired electron can be periodically arranged in a body-centered cubic structure in sodalite, a type of aluminosilicate zeolite, to form a Mott insulator accompanied with an antiferromagnetic ordering. This system does not contain any magnetic elements and is a novel magnetic system in which the magnetic order is realized by alkali metal s-electrons. In order to investigate the origin of the s-electron magnetism in detail, we present examples of studies using muon spin rotation/relaxation (μSR), synchrotron radiation Mössbauer spectroscopy, and neutron diffraction techniques. The spatial expansion of the s-electron wave functions of the nanoclusters with increasing alkali metal content has been directly observed by these experimental methods. This enhances the exchange interaction and increases the transition temperature (Néel temperature). A very simple model material of the Mott-Hubbard system is realized in s-electrons. We also point out that there are great expectations for the future contribution of computer science to this material system, especially to μSR experiments.
Muon is one of elementary particles, called lepton, with spin 1/2. Muon's spin interacts with magnetic and electric fields through its dipole moments. The anomalous magnetic (dipole) moment is calculated in the theory of particle physics, called the standard model, with a precision better than 0.5 parts-per-million. The past experiment indicated that the measured anomalous magnetic moment of muon is larger than the theoretical prediction. There has been a long-standing discussion that this anomaly might be a signature of new physics beyond the standard model. A new experiment with a novel technique of accelerating cold muon beam is under preparation in Japan. In this article, a concise review of anomalous magnetic moment of muon is given.
Muon is an elementary particle that has electric charge and spin. When muon with positive charge (μ+) is implanted in a substance, it stops as muon or it acquires an electron in the substance and becomes muonium (Mu). If the substance has an unsaturated bond, muonium attacks it to generate a radical (muoniated radical). By monitoring the change in direction of muon/muonium spins from the polarized state, we can monitor the fluctuation of the magnetic field near the muon/muonium stopping sites. In the case of biomolecules, fluctuations in the magnetic field result from fluctuations in electron spins or atomic nuclear spins near the muon/muonium stopping sites. Moreover, since positive muons as it were light protons, fluctuations of muon spin themselves have the possibility of giving us the monitoring tool for proton transfer. The research aiming to establish the application of the muon spin rotation, relaxation and resonance (μSR) technique for bioscience at J-PARC/MLF will be introduced together with the pioneering studies.
Muonium (Mu), which is a bound state of a positively charged muon and an electron, is very similar to the hydrogen atom and plays an interesting role in various studies using muons. In this article, I will briefly introduce the role of muonium in two very different fields of research: fundamental science, such as the precision test of the Standard Model and the search for new physics, and materials science applications, such as the elucidation of the origin of electrical conductivity in wide gap semiconductors.
A muon can make atomic orbit in the same way as an electron due to its negative charge and form a muonic atom. Because a muon has 207 times higher mass than that of an electron, the muon atomic orbit is very close to the nucleus. However, interestingly, it is known that the formation process of the muonic atom is influenced by the electron state of the muon capturing atom; the muon capture probability and the initial atomic level of the captured muon differ depending on the molecule even if the muon is captured on the same atom. Various studies on the electron state effects on the formation process of muonic atom have been done and recently the influence on initial state of the captured muon by the spatial distribution of electrons has been reported. In this paper, the chemical studies on the formation process of muonic atom are reviewed.
The on-the-fly ab initio density functional path integral molecular dynamics (PIMD) simulations, which can take account of both nuclear quantum and thermal effects, were performed, to quantitatively evaluate the structures of muoniated and hydrogenated acetone radicals, as well as some properties such as hyperfine coupling constant (HFCC). We found that the HFCC values are highly correlated with the molecular structure; especially, the large nuclear quantum effect of Mu extends the stretching motion of Mu-O bond and makes the expectation value of HFCC large.
We have applied an elemental analysis with muonic X-rays to an aluminum-laminated Li-ion battery. As a result, the metallic Li deposition on the graphite anode was successfully detected. We also demonstrated that the location of the deposition could be identified from the depth profile. This is expected to be useful in R & D for reuse and further safety of a Li-ion battery.
We investigated the electronic states of hydrogen in the transparent oxide semiconductor InGaZnO4 (IGZO) using elementary particle muons (Mu) as a light isotope of hydrogen. From the combination of the relaxation rate Δ in Kubo-Toyabe function observed by the muon spin rotation method and the simulation of hydrogen by the first-principles calculation, it was clarified that the muon in the crystalline IGZO and the amorphous thin film IGZO occupies Zn-O bind center position. By analogy with ZnO, it is suggested that the corresponding hydrogen acts as a donor. In contrast, Lorentz-type spectra observed in the hydrogenated thin film IGZO show that some muons exist as Mu−H− at oxygen vacancy positions.
The use of the muon for material sciences (μSR) was started about half a century ago. The μSR method was applied to many kinds of materials and the huge amount of scientific results were reported until now. One of the recent popular research fields to apply μSR is chemistry. Especially, new types of molecular magnets and superconducting systems are good targets for μSR to be applied. As applications of μSR are being expanded, requirements to achieve deeper information of electronic states of materials from μSR are being stronger year by year. In this report, we are going to introduce our recent research activities on the muon-site calculation by using a supercomputing system and how we can use computational efforts to discuss more electronic states of materials.