arXiv subjects

J. Murata

Publications and source records attributed to J. Murata.

8 recordsLinked to original sources

arXiv2025

Lifetime measurement of the muonic atoms of enriched Si isotopes

Background: A muonic atom, composed of a negative muon and an atomic nucleus, undergoes two primary decay processes: muon-electron decay and muon nuclear capture. The branching ratio between these two processes can be determined from the measured lifetime of the muonic atom. While past researches have examined the general trend of muon capture rates across different nuclei, experimental and theoretical investigations into the isotope dependence of the lifetime remain limited. Purpose: The present study aims to measure the lifetimes of the muonic atom of isotopically enriched silicon isotopes. Methods: The experiment was conducted at the muon facility in the Material and Life Science Facility (MLF), J-PARC. A muon beam was stopped in various target materials, including isotopically enriched $^{28,29,30}$Si. The lifetimes of the muonic atoms were measured by detecting decay electrons using a $\mu$SR spectrometer. The decay spectra were analyzed by fitting with multi-exponential functions to account for contributions from the target nucleus and surrounding materials. Results: For the first time, the lifetimes of the muonic atom of isotopically enriched $^{28,29,30}$Si were measured. Additionally, seven other targets were studied to validate the experimental method and analysis procedure. The results were compared with theoretical models such as Primakoff, Goulard-Primakoff, and the recently-developed microscopic and evaporation model (MEM). Conclusions: The Primakoff and Goulard-Primakoff formulas, while reproducing certain aspects of the isotope dependence, require further refinement. The comparison with MEM calculations constrains the axial vector ($g_A$) and induced pseudoscalar ($g_P$) coupling constants. The present experiment establishes a method for measuring the lifetimes of the muonic atom and will contribute to future systematic investigations.

nucl-ex↗

arXiv2024

Development of Two-Dimensional Neutron Imager with a Sandwich Configuration

We have developed a two-dimensional neutron imager based on a semiconductor pixelated sensor, especially designed for experiments measuring of a spatial and a temporal behavior of quantum bound states of ultra-cold neutrons. Through these measurements, we expect to measure the ratio between the inertial and gravitational masses of neutrons and to test the equivalence principle in the quantum regime. As one of the principal neutron imagers, we fabricated a sensor with a sandwich configuration, named 10B-INTPIX4-sw, and tested its response to ultra-cold neutrons at the Los Alamos Neutron Science Center (LANSCE). We observed simultaneous events on both sandwiching sensors without significant loss of detection efficiency. The efficiency was evaluated to be about 16%, relative to the 10B/ZnS reference detector. The coincidence condition reduces its efficiency by a factor of about 3.

physics.ins-det↗

arXiv2017

Short-range test of the universality of gravitational constant $G$ at the millimeter scale using a digital image sensor

The composition dependence of gravitational constant $G$ is measured at the millimeter scale to test the weak equivalence principle, which may be violated at short range through new Yukawa interactions such as the dilaton exchange force. A torsion balance on a turning table with two identical tungsten targets surrounded by two different attractor materials (copper and aluminum) is used to measure gravitational torque by means of digital measurements of a position sensor. Values of the ratios $\tilde{G}_{Al-W}/\tilde{G}_{Cu-W} -1$ and $\tilde{G}_{Cu-W}/G_{N} -1$ were $(0.9 \pm 1.1_{\mathrm{sta}} \pm 4.8_{\mathrm{sys}}) \times 10^{-2}$ and $ (0.2 \pm 0.9_{\mathrm{sta}} \pm 2.1_{\mathrm{sys}}) \times 10^{-2}$ , respectively; these were obtained at a center to center separation of 1.7 cm and surface to surface separation of 4.5 mm between target and attractor, which is consistent with the universality of $G$. A weak equivalence principle (WEP) violation parameter of $η_{Al-Cu}(r\sim 1\: \mathrm{cm})=(0.9 \pm 1.1_{\mathrm{sta}} \pm 4.9_{\mathrm{sys}}) \times 10^{-2} $ at the shortest range of around 1 cm was also obtained.

gr-qc↗

arXiv2017

A new measurement of electron transverse polarization in polarized nuclear beta decay

The Mott polarimetry for T -Violation (MTV) experiment tests time-reversal symmetry in polarized nuclear beta decay by measuring an electron's transverse polarization as a form of angular asymmetry in Mott scattering using a thin metal foil. A Mott scattering analyzer system developed using a tracking detector to measure scattering angles offers better event selectivity than conventional counter experiments. In this paper, we describe a pilot experiment conducted at KEK-TRIAC using a prototype system with a polarized 8Li beam. The experiment confirmed the sound performance of our Mott analyzer system to measure T-violating triple correlation (R correlation), and therefore recommends its use in higher-precision experiments at the TRIUMF-ISAC.

nucl-ex↗

arXiv2014

Beam energy dependence of charged pion ratio in $^{28}$Si + In reactions

The double differential cross sections for $^{nat}$In($^{28}$Si, $π^{\pm}$) reactions are measured at 400, 600, and 800 MeV/nucleon. Both $π^+$ and $π^-$ are found to be emitted isotropically from a single moving source. The $π^- / π^+$ yield ratio is determined as a function of the charged pion energy between 25 and 100 MeV. The experimental results significantly differ from the prediction of the standard transport model calculation using the code PHITS. This discrepancy suggests that more theoretical works are required to deduce firm information on the nuclear symmetry energy from the $π^- / π^+$ yield ratio.

nucl-ex↗

arXiv2014

Development of a novel scintillation-trigger detector for the MTV experiment using aluminum-metallized film tapes

A new type of a trigger-scintillation counter array designed for the MTV experiment at TRIUMF-ISAC has been developed, which uses aluminum-metallized film tape for wrapping to achieve the required assembling precision of $\pm$0.5 mm. The MTV experiment uses a cylindrical drift chamber (CDC) as the main electron-tracking detector. The barrel-type trigger counter is placed inside the CDC to generate a trigger signal using 1 mm thick, 300 mm long thin plastic scintillation counters. Detection efficiency and light attenuation compared with conventional wrapping materials are studied.

physics.ins-det↗

arXiv2008

Ground-state electric quadrupole moment of 31Al

Ground-state electric quadrupole moment of 31Al (I =5/2+, T_1/2 = 644(25) ms) has been measured by means of the beta-NMR spectroscopy using a spin-polarized 31Al beam produced in the projectile fragmentation reaction. The obtained Q moment, |Q_exp(31Al)| = 112(32)emb, are in agreement with conventional shell model calculations within the sd valence space. Previous result on the magnetic moment also supports the validity of the sd model in this isotope, and thus it is concluded that 31Al is located outside of the island of inversion.

nucl-ex↗

arXiv2002

Optical Alignment System for the PHENIX Muon Tracking Chambers

A micron-precision optical alignment system (OASys) for the PHENIX muon tracking chambers is developed. To ensure the required mass resolution of vector meson detection, the relative alignment between three tracking station chambers must be monitored with a precision of 25$μ$m. The OASys is a straightness monitoring system comprised of a light source, lens and CCD camera, used for determining the initial placement as well as for monitoring the time dependent movement of the chambers on a micron scale.

nucl-ex↗