Publications

2026

  1. Hit-rate capability of a silicon strip detector module for decay positron detection in the J-PARC muon g-2/EDM experiment
    Ryuto Azuma , Katsunori Awa , Shunsuke Doi
    Journal of Instrumentation , 21 (07) , P07039 (2026)
    Abstract

    In the J-PARC muon g-2/EDM experiment, a silicon strip detector will be used to detect positrons from muon decays. The detector consists of planes of detector modules arranged radially. The expected maximum hit rate reaches 1.4 MHz per sensor strip, and achieving high detection efficiency even under such hit-rate conditions is a key performance requirement. We have developed the smallest unit of the detector module, and its performance was evaluated using a muon beam at the J-PARC MLF H-line. The specifications of the detector module and the evaluated hit-rate capability are described in this article.

  2. Depth-Resolved μSR Using Ultra-Slow Muons at the J-PARC MUSE Facility
    Sohtaro Kanda , Yu Oishi , Yutaka Ikedo
    Journal of Physics: Conference Series , 3222 (1) , 012016 (2026)
    Abstract

    At the U-line in J-PARC MLF MUSE, ultra-slow muons (USM) are generated by laser ionization of thermal muonium (Mu) in vacuum. Mu drifts in vacuum with a Maxwellian velocity distribution reflecting the production target temperature; consequently, the USM obtained from Mu ionization also possess correspondingly low energies. At the U-line, a high-temperature tungsten foil (2000 K, corresponding to 0.2 eV) and a room-temperature silica aerogel disk (300 K, 25 meV) are used. These USM are focused and accelerated by electrostatic lenses and transported to the experimental areas. In the U1A experimental area, a muon spin spectrometer is installed for USM-μSR measurements. The implantation energy of muons into the sample can be controlled in the range of sub-keV to 30 keV by adjusting the voltage of a high-voltage platform on which the entire spectrometer is mounted. Whereas surface muons with an energy of 4 MeV, commonly used in materials science research, are suitable probes for bulk samples, USM are well-suited for measurements on thin film samples or interfaces within materials. Recently, we successfully demonstrated the implantation of muons selectively into a platinum thin layer sandwiched by silica layers. In this study, depth-resolved measurements were performed by scanning the beam implantation energy. This contribution presents demonstration results of USM-μSR measurements on multilayer thin film samples.

  3. Muon Cooling for Muonium Spectroscopy and Interferometry
    Sohtaro Kanda
    Journal of Physics: Conference Series , 3222 (1) , 012011 (2026)
    Abstract

    Precision measurements of muonium, a purely leptonic atom, provide a unique platform for stringent tests of the Standard Model and searches for new physics beyond it. The sensitivity of these tests, however, is often limited by the precision of the muon mass. To overcome this limitation, we propose a Ramsey-Bordé atom interferometer with a muonium beam to determine the muon mass with unprecedented precision. A critical requirement for such an experiment is the availability of a bright, low-energy muonium beam. This paper reports on the development of a multi-stage muon cooling system designed to produce such a beam. The system combines a solid rare-gas moderator for producing epithermal muons with a subsequent laser ionization stage for generating an ultra-slow muon beam. We present the conceptual design of the cooling system and discuss the status of simulation studies for optimizing the generation and transport of slow muons.

  4. Simulations of a Muonium Atom Interferometer with Light Pulses
    Sohtaro Kanda
    JPS Conference Proceedings , 45 , 011017 (2026)
    Abstract

    We present a simulation study of a Ramsey-Bordé interferometer for muonium atoms using light pulses, aimed at a precise determination of the muon mass. Precision measurements involving muons serve as a powerful probe for exploring physics beyond the Standard Model. However, their potential is limited by the precision of muon mass, which has been obtained through muonium spectroscopy. To overcome this limitation, we have proposed a muonium atom interferometer for muon mass determination utilizing the photon recoil shift. Since low-energy muons and a slow muonium beam are necessary for interferometry, a generation scheme for them has been designed. Here, we discuss the overview of the planned experiment and the development status of a Monte Carlo simulation framework for numerically computing the signals observed in the interferometer.

  5. Feasibility Studies for Stopping Power Measurements Using Ultra-Slow Muons
    Ayato Miura , Kazuhiko Ninomiya , Makoto Inagaki
    JPS Conference Proceedings , 45 , 011013 (2026)
    Abstract

    Data on the fundamental interactions of charged particles with materials, such as stopping power and cross section, provide important information for various research fields. Our research group plans to measure the muon stopping power in the low-energy region of several tens of kiloelectronvolts. In this study, to conduct a stopping power measurement experiment, we measured the precise energy of muons provided by the U-line in the J-PARC MLF, investigated the muon intensity, and evaluated the detector performance. In addition, we estimated the beam profile expected in this experimental setup using Monte Carlo calculations and evaluated the measurement conditions.

  6. Demonstration of energy-resolved muon spin spectroscopy using a Cherenkov calorimeter
    Yue Ma , Sohtaro Kanda , Shiro Matoba
    Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment , 1092 , 171842 (2026)
    Abstract

    We report the first energy-resolved μSR spectrometer, exploiting the energy–angle correlation of Michel-decay positrons to enhance the figure of merit (FoM) without increasing muon flux. Two SF6W lead-glass calorimeters, placed symmetrically about the sample at the J-PARC Materials and Life Science Experimental Facility (MLF) S1 beamline, measure each decay positron’s energy event-by-event, and an offline amplitude threshold scan selects high-energy positrons to maximize the FoM. At B=100G transverse, the optimized threshold raises the fitted asymmetry from 0.262±0.001 to 0.416±0.001, a 26% FoM gain over the conventional configuration. The technique is robust across transverse fields of 20–100 G and applies directly as an upgrade to existing μSR spectrometers worldwide.

  7. Direct observation of muonic molecules in resonance states critical to muon catalyzed fusion
    Y. Toyama , T. Azuma , D. A. Bennett
    Science Advances , 12 (16) , eaed3321 (2026)
    Abstract

    Muon catalyzed fusion (μCF) is a plasma-free process in which the formation of muonic hydrogen molecules precedes and enables fusion between their constituent nuclei. Despite decades of study, the reaction dynamics of μCF remain elusive. Recent theories predict that resonance states of the muonic molecules play a key role and that these states can be probed using x-ray techniques. Using an array of transition-edge sensor microcalorimeters with 10-fold improved energy resolution compared to conventional silicon detectors, we observed x-rays from resonance states of muonic deuterium molecules despite an intense background. The spectrum is well explained by high-precision calculations incorporating the vibrational states. This work identifies the long-overlooked resonance state pathway as crucial in μCF and provides the direct evidence of the efficient muonic molecular formation. High-resolution x-ray spectroscopy with a cryogenic detector reveals long-ignored resonance states driving muon catalyzed fusion.

  8. Muon Spin Spectrometer at MLF MUSE U1A: Commissioning Results and Upgrade Plans
    Sohtaro Kanda , Yutaka Ikedo , Yu Oishi
    JPS Conference Proceedings , 45 , 011044 (2026)
    Abstract

    Muons serve as a highly sensitive local magnetic probe in materials science. While traditional μSR relies on 4 MeV surface muons, investigations of thin films and interfacial phenomena demand precisely controlled low-energy muon beams. At J-PARC MLF MUSE, the U1 beamline delivers ultra-slow muons (USM) via laser ionization of thermal muonium. In the U1A experimental area, a muon spin spectrometer has been installed for USM-μSR measurements. The spectrometer is mounted on a high-voltage platform for implantation energy control from nearly zero to 30 keV. Comprehensive beam characterization has demonstrated a spatial beam profile of 4 mm FWHM and a temporal width of 2 ns at the spectrometer’s sample position. Commissioning of the spectrometer has demonstrated stable beam alignment and high time resolution in positron detection. In this work, we report these commissioning results and discuss potential upgrades for expanding the instrument’s capabilities for future user programs.

  9. Time-of-Flight Measurement of Ultra-Slow Muons at J-PARC MUSE
    Yuga Nakazawa , Taihei Adachi , Jun-ichi Ohnishi
    JPS Conference Proceedings , 45 , 011018 (2026)
    Abstract

    We performed time-of-flight (TOF) measurements of ultra-slow muon (USM) beam for transmission muon microscope and USM-μSR measurements at J-PARC Muon Science Establishment (MUSE). USMs are produced by laser ionization of thermal muonium emitted from a heated tungsten target. The generated USMs are electrostatically extracted and transported to the experimental areas. The TOF distributions and energy of the USM were evaluated by acquiring the time spectrum using a micro-channel plate with delay line anode (MCP-DLD) installed in the transport beamline. This paper reports the results of the TOF measurements of the USM beam.

2025

  1. Application of Hard X-Ray and Gamma-Ray TES Microcalorimeter at Accelerator Facility
    Takeshi Y. Saito , Shinji Okada , Yuichi Toyama
    IEEE Transactions on Applied Superconductivity , 35 (5) , 1-5 (2025)
    Abstract

    The X-ray spectroscopy of the muonic atom has attracted atomic, nuclear, and particle physicists since its discovery. The properties of a muonic atom, such as its binding energy or atomic radius, are different from an ordinary atom because of the difference in the mass between the muon and electron. Our collaboration has employed superconductor transition-edge sensor (TES) microcalorimeters for the x-ray spectroscopy of the muonic atom. Thanks to the recent detector development, the 44-keV lines from muonic Ar, which is important for the precision test of bound-state quantum electrodynamics, and the 76-keV lines from muonic Si, which is of interest from the viewpoint of the measurement of nuclear radii, have been reached by the dynamic range of the state-of-art TES microcalorimeters. An accelerator facility that can produce a high-intensity muon beam is necessary for such spectroscopic experiments. We performed a commissioning experiment of the hard x-ray and gamma-ray TES microcalorimeter at the J-PARC MLF MUSE muon beam line. The energy resolution, gain stability, and performance of timing selection of the pulses were evaluated in the environment of a large-scale accelerator facility.

  2. Precision measurements of muonium and muonic helium hyperfine structure at J-PARC
    Patrick Strasser , Mitsushi Abe , Kanta Asai
    The European Physical Journal D , 79 (3) , 20 (2025)
    Abstract

    At the J-PARC Muon Science Facility (MUSE), the MuSEUM collaboration is now performing new precision measurements of the ground state hyperfine structure (HFS) of both muonium and muonic helium atoms. High-precision measurements of the muonium ground-state HFS are recognized as one of the most sensitive tools for testing bound-state quantum electrodynamics theory to precisely probe the standard model and determine fundamental constants of the positive muon magnetic moment and mass. The same technique can also be employed to measure muonic helium HFS, obtain the negative muon magnetic moment and mass, and test and improve the theory of the three-body atomic system. Measurements at zero magnetic field have already yielded more accurate results than previous experiments for both muonium and muonic helium atoms. High-field measurements are now ready to start collecting data using the world’s most intense pulsed muon beam at the MUSE H-line. We aim to improve the precision of previous measurements ten times for muonium and a hundred times or more for muonic helium. We review all the key developments for these new measurements, focusing on the high-field experiment, and report the latest results and prospects.

2024

  1. Hexapole state selector for focusing and polarizing muonium
    Sohtaro Kanda
    Interactions , 245 (1) , 78 (2024)
    Abstract

    Muonium, a hydrogen-like atom composed of a positive muon and an electron, is pivotal for precision tests of the Standard Model and searches for new physics through exotic atom spectroscopy. Aiming to achieve a breakthrough in precision measurements involving muons and muonium, the development of a high-brightness muonium beam is under study. Such a beam would facilitate atom interferometry using muonium, leading to a high-precision measurement of the muon mass. For this purpose, the potential of a hexapole magnet as a focusing device to improve the muonium beam’s brightness was considered. Monte Carlo simulations of muonium trajectories within a magnetic field indicate promising prospects for enhancing the beam’s brightness.

  2. Dual-mode rectangular microwave cavity for precision spectroscopy of hyperfine structure in muonium
    R. Iwai , S. Fukumura , M. Fushihara
    Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment , 1064 , 169434 (2024)
    Abstract

    Precision microwave spectroscopy of the ground-state hyperfine structure in muonium provides a stringent test of the Standard Model in particle physics. The MuSEUM collaboration is preparing for such a measurement, aiming for precision down to ≈1 ppb, utilizing the world’s most intense pulsed muon beam at J-PARC. The measurement of the Zeeman-split structure with an external magnetic field of 1.7T also precisely determines the muon’s magnetic moment (≈10 ppb). In the future, improved precision of the magnetic moment can be potentially obtained by measurements with different magnetic field strengths, however, it entails upgrading current cylindrical microwave cavities to rectangular ones. As the first step for the upgrade, we have developed a dual-mode rectangular cavity for the measurement with 2.9T field. The electromagnetic design and production have been established, and frequency sweeping with two desired modes has been successfully demonstrated. Moreover, the overall performance of the measurement at 2.9T field was evaluated with Monte Carlo simulations. These studies pave the way for a further extension of the MuSEUM experiment at various strengths of the magnetic fields.

2023

  1. Improved Measurements of Muonic Helium Ground-State Hyperfine Structure at a Near-Zero Magnetic Field
    P. Strasser , S. Fukumura , R. Iwai
    Phys. Rev. Lett. , 131 , 253003 (2023)
  2. Proof-of-Principle Experiment for Testing Strong-Field Quantum Electrodynamics with Exotic Atoms: High Precision X-Ray Spectroscopy of Muonic Neon
    T. Okumura , T. Azuma , D. A. Bennett
    Phys. Rev. Lett. , 130 , 173001 (2023)
  3. The Ultra-Slow Muon beamline at J-PARC: present status and future prospects
    S Kanda , N Teshima , T Adachi
    Journal of Physics: Conference Series , 2462 (1) , 012030 (2023)
    Abstract

    At J-PARC MLF, MUSE provides the world-highest flux of pulsed muon beams. U-Line, one of the four beamlines in the facility, features an intense surface muon beam from Super-Omega and Ultra-slow muon generated by laser ionization of thermal muonium in vacuo. The Ultra-slow muon beam is characterized by variable energy from sub-keV to tens of keV and a time resolution of several tens of times better than that of ordinary pulsed beams. These features enable the study of interesting phenomena localized at surfaces and near interfaces and fast dynamics that cannot be observed with ordinary pulsed beams. Commissioning of the beamline and instruments is underway in preparation for the start of user programs. This paper presents an overview of the facility, its current status, and its prospects.

  4. In-flight muon spin resonance and muonium interferometry
    Sohtaro Kanda
    Journal of Physics: Conference Series , 2462 (1) , 012029 (2023)
    Abstract

    The muon and muonium play a unique role in materials science as a tiny magnetometer and an emulator of hydrogen in matter. However, there are few examples of their application as matter waves. This is because the surface muon and its simple slowing-down in a degrader cannot keep sufficient coherence. Low-energy muons from laser ionization of muonium can be used to obtain slow muonium with small temporal and spatial spread. Like an ordinary atomic interferometer, a muonium interferometer has a variety of potential applications. For example, muonium spectroscopy using interference effects, studies of quantum interference effects such as a measurement of the Berry phase, and precise measurements of fundamental constants will be possible using muonium interferometry. In this contribution, we discuss the in-flight spectroscopy of muonium and the potential of muonium interferometry.

2022

  1. A search for atomic parity violation in muonic atoms using a high-intensity pulsed muon beam at J-PARC
    Kanda, Sohtaro
    EPJ Web Conf. , 262 , 01010 (2022)
  2. Toward a high-precision measurement of the muon lifetime with an intense pulsed muon beam at J-PARC
    Sohtaro Kanda
    PoS , NuFact2021 , 215 (2022)

2021

  1. Rabi-oscillation spectroscopy of the hyperfine structure of muonium atoms
    S. Nishimura , H. A. Torii , Y. Fukao
    Phys. Rev. A , 104 , L020801 (2021)
  2. Dynamical Response of Transition-Edge Sensor Microcalorimeters to a Pulsed Charged-Particle Beam
    Takuma Okumura , Toshiyuki Azuma , Douglas A. Bennett
    IEEE Transactions on Applied Superconductivity , 31 (5) , 1-4 (2021)
    Abstract

    A superconducting transition-edge sensor (TES) microcalorimeter is an ideal X-ray detector for experiments at accelerator facilities because of good energy resolution and high efficiency. To study the performance of the TES detector with a high-intensity pulsed charged-particle beam, we measured X-ray spectra with a pulsed muon beam at the Japan Proton Accelerator Research Complex (J-PARC) in Japan. We found substantial temporal shifts of the X-ray energy correlated with the arrival time of the pulsed muon beam, which was reasonably explained by pulse pileup due to the incidence of energetic particles from the initial pulsed beam.

  3. Deexcitation Dynamics of Muonic Atoms Revealed by High-Precision Spectroscopy of Electronic K X Rays
    T. Okumura , T. Azuma , D. A. Bennett
    Phys. Rev. Lett. , 127 , 053001 (2021)
  4. Development of microwave cavities for measurement of muonium hyperfine structure at J-PARC
    K S Tanaka , M Iwasaki , O Kamigaito
    Progress of Theoretical and Experimental Physics , 2021 (5) , 053C01 (2021)
    Abstract

    The MuSEUM collaboration is planning measurements of the ground-state hyperfine structure (HFS) of muonium at the Japan Proton Accelerator Research Complex (J-PARC), Materials and Life Science Experimental Facility. The high-intensity beam that will soon be available, the H-line, allows for more precise measurements by one order of magnitude. We plan to conduct two staged measurements. First, we will measure the Mu-HFS in a near-zero magnetic field, and thereafter we will measure it in a strong magnetic field. We have developed two microwave cavities for this purpose. Furthermore, we evaluated the systematic uncertainties from such a fluctuation of microwave fields and confirmed the requirements for the microwave system; we use a microwave field distribution calculated with the finite element method.

  5. New precise spectroscopy of the hyperfine structure in muonium with a high-intensity pulsed muon beam
    S. Kanda , Y. Fukao , Y. Ikedo
    Physics Letters B , 815 , 136154 (2021)
    Abstract

    A hydrogen-like atom consisting of a positive muon and an electron is known as muonium. It is a near-ideal two-body system for a precision test of bound-state theory and fundamental symmetries. The MuSEUM collaboration performed a new precision measurement of the muonium ground-state hyperfine structure at J-PARC using a high-intensity pulsed muon beam and a high-rate capable positron counter. The resonance of hyperfine transition was successfully observed at a near-zero magnetic field, and the muonium hyperfine structure interval of νHFS=4.463302(4)GHz was obtained with a relative precision of 0.9 ppm. The result was consistent with the previous ones obtained at Los Alamos National Laboratory and the current theoretical calculation. We present a demonstration of the microwave spectroscopy of muonium for future experiments to achieve the highest precision.

  6. A LYSO calorimeter prototype for muonic X-ray detection
    Sohtaro Kanda , and K. Ishida
    RIKEN Accelerator Progress Report , 54 , 140 (2021)
  7. Measurement of muon spin rotation in muonic hydrogen atom
    Sohtaro Kanda , and K. Ishida
    RIKEN Accelerator Progress Report , 54 , 139 (2021)

2020

  1. X-ray Spectroscopy of Muonic Atoms Isolated in Vacuum with Transition Edge Sensors
    S. Okada , T. Azuma , D. A. Bennett
    Journal of Low Temperature Physics , 200 (5) , 445–451 (2020)
    Abstract

    High-resolution X-ray spectroscopy of the highly charged muonic atoms/ions isolated in vacuum is an ideal probe to explore quantum electrodynamics under extremely strong electric fields, which is one of the major topic in fundamental atomic physics. A feasibility test measurement with a low-density neon gas target was performed by observing X-rays emitted by muonic neon via the }}5 \backslashrightarrow 4}}transition, }}\backslashsim}} 6.3 keV, using a multi-pixel array of superconducting transition-edge-sensor (TES) microcalorimeters at the J-PARC muon facility. We successfully demonstrated the feasibility of muonic atom X-ray spectroscopy with a gas target at a pressure as low as 0.1 atom using TES array under an intense pulsed muon beam.

2019

  1. A new approach for measuring the muon anomalous magnetic moment and electric dipole moment
    M Abe , S Bae , G Beer
    Progress of Theoretical and Experimental Physics , 2019 (5) , 053C02 (2019)
    Abstract

    This paper introduces a new approach to measure the muon magnetic moment anomaly \a_{\μ} = (g-2)/2 and the muon electric dipole moment (EDM) \d_{\μ} at the J-PARC muon facility. The goal of our experiment is to measure \a_{\μ} and \d_{\μ} 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_{\μ} 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\⋅\\mbox{cm}\.

  2. Multiparticle azimuthal correlations for extracting event-by-event elliptic and triangular flow in Au + Au collisions at √sNN = 200 GeV
    A. Adare , C. Aidala , N. N. Ajitanand
    Phys. Rev. C , 99 , 024903 (2019)
  3. Precision spectroscopy of exotic atoms involving muons
    Sohtaro Kanda , Katsuhiko Ishida , and Koichiro Shimomura
    PoS , NuFACT2018 , 138 (2019)
  4. Negative muon spin rotation with low-density gas target under transverse magnetic field to solve the proton radius puzzle
    Sohtaro Kanda , K. Ishida , M. Iwasaki
    RIKEN Accelerator Progress Report , 52 , 180 (2019)

2018

  1. Production of π0 and η mesons in Cu+Au collisions at √sNN = 200 GeV
    C. Aidala , N. N. Ajitanand , Y. Akiba
    Phys. Rev. C , 98 , 054903 (2018)
  2. Pseudorapidity Dependence of Particle Production and Elliptic Flow in Asymmetric Nuclear Collisions of p+Al, p+Au, d+Au, and 3He+Au at √sNN = 200 GeV
    A. Adare , C. Aidala , N. N. Ajitanand
    Phys. Rev. Lett. , 121 , 222301 (2018)
  3. Measurement of the proton Zemach radius from the hyperfine splitting in muonic hydrogen atom
    Sohtaro Kanda , Katsuhiko Ishida , Masahiko Iwasaki
    Journal of Physics: Conference Series , 1138 (1) , 012009 (2018)
    Abstract

    Muonic hydrogen is a bound state of a proton and a negative muon. Its Bohr radius is 200 times smaller than that of an electronic hydrogen atom. Therefore, a spectroscopy of the muonic hydrogen is highly sensitive to the finite size effect of proton. Recent years, the proton charge radius was determined by the laser spectroscopy of the Lamb shifts in muonic hydrogen atom. The experiment determined the proton charge radius significantly smaller than the results of past measurements. This anomaly is called “proton radius puzzle” and it has been an important unsolved problem in subatomic physics. Towards solving the puzzle, a new measurement of the ground-state hyperfine splitting in muonic hydrogen was proposed. The hyperfine splitting of muonic hydrogen derives the proton Zemach radius, which is defined as a convolution of the charge distribution with the magnetic moment distribution. This experiment aims to determine the proton Zemach radius with 1% precision by a measurement of the decay electron angular asymmetry. In order to test the feasibility of the laser spectroscopy, a preliminary experiment to measure the hyperfine quenching rate was proposed.

  4. Cross section and longitudinal single-spin asymmetry AL for forward W± → μ±ν production in polarized p+p collisions at √s = 510 GeV
    A. Adare , C. Aidala , N. N. Ajitanand
    Phys. Rev. D , 98 , 032007 (2018)
  5. Development of an intense mid-infrared coherent light source for muonic hydrogen spectroscopy
    Sohtaro Kanda , S. Aikawa , K. Ishida
    RIKEN Accelerator Progress Report , 51 , 214 (2018)
  6. Precision laser spectroscopy of the ground state hyperfine splitting in muonic hydrogen
    Sohtaro Kanda
    PoS , NuFact2017 , 122 (2018)

2017

  1. Cross section and transverse single-spin asymmetry of muons from open heavy-flavor decays in polarized p+p collisions at √s = 200 GeV
    C. Aidala , N. N. Ajitanand , Y. Akiba
    Phys. Rev. D , 95 , 112001 (2017)
  2. Direct measurement of muonium hyperfine splitting at J-PARC
    Sohtaro Kanda
    PoS , INPC2016 , 170 (2017)

2016

  1. Development of magnetic shield for the MuSEUM experiment
    Sohtaro Kanda
    RIKEN Accelerator Progress Report , 49 , 227 (2016)
  2. Development of a new positron counting system with SiPM readout for muon spin spectrometers
    Sohtaro Kanda
    PoS , PhotoDet2015 , 039 (2016)

2015

  1. Development of online muon beam profile monitor for the MuSEUM experiment
    Sohtaro Kanda
    RIKEN Accelerator Progress Report , 48 , 278 (2015)
  2. Precision Measurement of Muonium Hyperfine Splitting at J-PARC and Integrated Detector System for High-Intensity Pulsed Muon Beam Experiment
    S. Kanda , M. Aoki , Y. Fukao
    JPS Conference Proceedings , 8 , 025006 (2015)
    Abstract

    We, the MuSEUM Collaboration plan to perform the precision measurement of muonium’s ground state hyperfine splitting at J-PARC. It can be the best probe for the test of bound state QED and determination of muon mass. The key for the precision improvement is the high-intensity pulsed muon beam at J-PARC and high-rate capable positron detector. At the same time, understanding and suppression of the systematic uncertainties are essential to exceed the precision of the latest experimental result. Developments of an online muon beam monitor, a suitable target chamber, and a precise NMR probe are in progress for suppress the systematic uncertainties. In this paper, we discuss the experimental overview and development status of the integrated detector system for high-intensity pulsed muon beam. muonium hyperfine splitting, spectroscopy, detector development

  3. Laser Spectroscopy of Ground State Hyperfine Splitting Energy of Muonic Hydrogen
    M. Sato , K. Ishida , M. Iwasaki
    JPS Conference Proceedings , 8 , 025005 (2015)
    Abstract

    We propose a novel measurement of the hyperfine splitting energy in the ground-state muonic hydrogen at the J-PARC muon facility. A laser spectroscopy technique is combined with a measurement of decay asymmetry in spin polarization of muons. An intense tunable mid-infrared laser has been recently developed in RIKEN, which can induce a transition between the hyperfine sublevels with the energy difference of 0.183 eV corresponding to wavelength of 6.78 µm. The expected precision of the measurement is ∼2 ppm. The hyperfine splitting energy is directly connected to the proton Zemach radius, and provide crucial information on the proton internal structure and the proton radius puzzle.

2014

  1. Nuclear matter effects on J/ψ production in asymmetric Cu + Au collisions at √sNN = 200 GeV
    A. Adare , C. Aidala , N. N. Ajitanand
    Phys. Rev. C , 90 , 064908 (2014)
  2. New μSR spectrometer at J-PARC MUSE based on Kalliope detectors
    K M Kojima , T Murakami , Y Takahashi
    Journal of Physics: Conference Series , 551 (1) , 012063 (2014)
    Abstract

    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.

  3. Enhancement of muonium emission rate from silica aerogel with a laser-ablated surface
    G. A. Beer , Y. Fujiwara , S. Hirota
    Progress of Theoretical and Experimental Physics , 2014 (9) , 091C01 (2014)
    Abstract

    Emission of muonium (\\μ^+e^-\) atoms from a laser-processed aerogel surface into vacuum was studied for the first time. Laser ablation was used to create hole-like regions with diameter of about 270 \\μ\m in a triangular pattern with hole separation in the range of 300–500 \\μ\m. The emission probability for the laser-processed aerogel sample is at least eight times higher than for a uniform one.

  4. Precision measurement of muonium hyperfine splitting at J-PARC; development of high-rate positron detector
    Sohtaro Kanda
    RIKEN Accelerator Progress Report , 47 , 264 (2014)
  5. Development of High-Rate Positron Tracker for the Muonium Production Experiment at J-PARC
    S. Kanda , H. Fujimori , Y. Fukao
    JPS Conference Proceedings , 2 , 010404 (2014)
    Abstract

    Ultra slow muon is realized by laser ionization of muonium from the production target. The key issue for ultra slow muon is the yield and space-time distribution of muonium. In order to maximize the intensity of ultra slow muon beam, we are developing a muonium production target. There are two major candidates as a target; hot tungsten and silica aerogel. For the target development and its performance evaluation, we need highly rate-capable positron tracker for muonium detection. We have studied basic characteristics of the detector constructed from scintillation fiber and SiPM. As a result of prototype development and its performance evaluation, we finalized the detector design with adequate trackback resolution and high event rate capability for our experiment. The full scale detector was constructed and its laboratory test is ongoing. We have plans of beam experiment with the full scale detector at TRIUMF and J-PARC. The test at TRIUMF will be performed in October 2013 and we submitted an experimental proposal to J-PARC MLF for FY2013.

  6. Muonium production target for the muon g-2/EDM experiment at J-PARC
    Sohtaro Kanda
    Nuclear Physics B - Proceedings Supplements , 253-255 , 212-213 (2014)
    Abstract

    There is more than three standard-deviations discrepancy between measurement and theoretical prediction of the muon anomalous magnetic moment. We are going to measure the precision value of muon g−2 and search for physics beyond standard model. In addition, we can search for muon EDM which violates CP symmetry. CP violation in charged lepton sector is currently not found. We are developing the “Ultra Cold Muon Beam” instead of tertiary muon beam with electric focusing. Ultra cold muon is realized by laser ionization of muonium (bound state of a muon and an electron) from the production target. Increase of muonium yield is essential for our experimental goal; 0.1ppm statistical precision. Muonium production experiment at J-PARC MLF MUSE is planned in 2012 autumn. In this paper, we discuss the development of muonium production target and positron detector for the study.

2013

  1. Measurement of muonium emission from silica aerogel
    P. Bakule , G.A. Beer , D. Contreras
    Progress of Theoretical and Experimental Physics , 2013 (10) , 103C01 (2013)
    Abstract

    Emission of muonium (\\μ^{+}e^{-}\) atoms from silica aerogel into vacuum was observed. Characteristics of muonium emission were established from silica aerogel samples with densities in the range from 29 mg cm−3 to 178 mg cm−3. Spectra of muonium decay times correlated with distances from the aerogel surfaces, which are sensitive to the speed distributions, and follow general features expected from a diffusion process, while small deviations from a simple room-temperature thermal diffusion model are identified. The parameters of the diffusion process are deduced from the observed yields.