Search

As a new method to determine the resonance frequency, Rabi-oscillation spectroscopy has been developed. In contrast to the conventional spectroscopy which draws the resonance curve, Rabi-oscillation spectroscopy fits the time evolution of the Rabi oscillation. By selecting the optimized frequency, it is shown that the precision is twice as good as the conventional spectroscopy with a frequency sweep. Furthermore, the data under different conditions can be treated in a unified manner, allowing more efficient measurements for systems consisting of a limited number of short-lived particles produced by accelerators such as muons. We have developed a fitting function that takes into account the spatial distribution of muonium and the spatial distribution of the microwave intensity to apply the new method to ground-state muonium hyperfine structure measurements at zero field. This was applied to the actual measurement data and the resonance frequencies were determined under various conditions. The result of our analysis gives $\nu_{\rm HFS}=4\ 463\ 301.61 \pm 0.71\ {\rm kHz}$, which is the world's highest precision under zero field conditions., Comment: 6 pages, 5 figures

A destructive monitor to measure the longitudinal bunch width of a low-energy and low-intensity muon beam was developed. This bunch-width monitor (BWM) employed microchannel plates to detect a single muon with high time resolution. In addition, constant-fraction discriminators were adopted to suppress the time-walk effect. The time resolution was measured to be 65 ps in rms using a picosecond-pulsed laser. This resolution satisfied the requirements of the muon linac of the J-PARC E34 experiment. We measured the bunch width of negative-muonium ions (${\ensuremath{\mu}}^{+}{e}^{\ensuremath{-}}{e}^{\ensuremath{-}}$) accelerated with a radio-frequency quadrupole using the BWM. The bunch width was successfully measured to be $\ensuremath{\sigma}=0.54\ifmmode\pm\else\textpm\fi{}0.11\text{ }\text{ }\mathrm{ns}$, which is consistent with the simulation.

Muonium is one of the best probes for the test of the bound-state QED, owing to the absence of the effect from the internal structure of nucleons. The recent establishment of intense pulsed muon beams at Japan Proton Accelerator Research Complex (J-PARC) paves the way to improved measurement of the muonium ground-state hyperfine structure (MuHFS). The measurement of MuHFS also determines the muon magnetic moment precisely, which is an important input parameter for the measurements of muon g-2, which is known for the 3-sigma discrepancy between the experiment and the theory. Muonium Spectroscopy Experiment Using Microwave (MuSEUM) collaboration aims to improve the precursor MuHFS experiment by a factor of ten. We present the status of the project and the prospect.

The muon anomalous magnetic moment $(g-2)_{\mu}$ and electric dipole moment (EDM) are sensitive to new physics beyond the Standard Model. We aim to measure $(g-2)_{\mu}$ with a precision of 0.1 parts per million and search for EDM with a sensitivity of $10^{-21}~e \cdot$cm at J-PARC. In this experiment, we use a silicon strip detector with high granularity and fast response to detect positrons from muon decay. We report on the development status of the silicon strip detector.

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 1,000 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 statistical uncertainty of 450 part 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 $1.5\times 10^{-21}~e\cdot\mbox{cm}$., Comment: 24 pages, 14 figures

A buncher cavity has been developed for the muons accelerated by a radio-frequency quadrupole linac (RFQ). The buncher cavity is designed for β = v ∕ c = 0 . 04 at an operational frequency of 324 MHz. It employs a double-gap structure operated in the TEM mode for the required effective voltage with compact dimensions, in order to account for the limited space of the experiment. The measured resonant frequency and unloaded quality factor are 323.95 MHz and 3 . 06 × 1 0 3 , respectively. The buncher cavity was successfully operated for longitudinal bunch size measurement of the muons accelerated by the RFQ.

An inter-digital H-mode drift-tube linac (IH-DTL) is developed in a muon linac at the J-PARC E34 experiment. IH-DTL will accelerate muons from 0.34 MeV to 4.5 MeV at a drive frequency of 324 MHz. Since IH-DTL adopts an APF method, with which the beam is focused in the transverse direction using the RF field only, the proper beam matching of the phase-space distribution is required before the injection into the IH-DTL. Thus, an IH-DTL prototype was fabricated to evaluate the performance of the cavity and beam transmission. As a preparation of the high-power test, a test coupler is designed and fabricated. In this paper, the development of the coupler and the result of the low-power measurement will be presented., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

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 positron tracking detector is developed for the J-PARC muon g − 2 /EDM (E34) experiment. It uses silicon strip sensors for positron detection and signals from sensors are transferred to the front-end readout system via flexible printed circuits (FPCs) glued on the sensors. The front-end readout system consists of application specific integrated circuits (ASICs) on FPCs and the field-programmable gate array (FPGA)-based readout board. Mass production of silicon strip sensors is ongoing. Designs of the FPC on the sensor and the front-end ASIC were fixed and their mass production has been started. Development of other detector components are also ongoing. The status of these developments and fabrications are presented.

The muon anomalous magnetic moment $(g -2)_{\mu}$ and electric dipole moment (EDM) are sensitive to new physics beyond the Standard Model. We aim to measure $( g -2 ) _{\mu}$ with a precision of 0.1 parts per million and search for EDM with a sensitivity of 10-21e. cm at J-PARC. In this experiment, we use a silicon strip detector with high granularity and fast response to detect positrons from muon decay. The readout ASIC is required to tolerate a high hit rate of 1.4 MHz per strip, to be stable to the change of hit rate by a factor of 1 /150, and to have deep memory for the period of $\sim 40 \mu \mathrm{s}$ with 5 ns resolution. The prototype readout ASIC "SliT128A" has been fabricated using the Silterra $0.18- \mu \mathrm{m}$ CMOS process. We also connected the SliT128A with a silicon strip sensor and tested it with a muon beam at J-PARC. In this paper, we report the performance of the prototype ASIC itself and the prototype detector module.