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 × 10 3 , respectively. The buncher cavity was successfully operated for longitudinal bunch size measurement of the muons accelerated by the RFQ.

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 (μ þ e − e −) accelerated with a radio-frequency quadrupole using the BWM. The bunch width was successfully measured to be σ ¼ 0.54 AE 0.11 ns, which is consistent with the simulation.

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.

The value of the muon anomalous magnetic moment (g − 2) exhibits a discrepancy of 3-4 σ between the standard model (SM) calculation and the experiment at the BNL. This may indicate physics beyond the SM. The J-PARC muon g−2/EDM experiment is a new approach for measuring the muon g−2 and electric dipole moment (EDM) with a reaccelerated thermal muon beam . This unique muon beam eliminates the systematic uncertainties related to the beam in the previous experiment at BNL. In contrast, new systematic uncertainties related to the detection efficiency are of concern. "Spin flip analysis" is effective in evaluating this effect. We can use this analysis method with a spin-flipped dataset. Our experiment uses a low-momentum muon beam, whose spin can be easily flipped. Data generated by a simplified Monte Carlo simulation with a time-dependent detection efficiency model motivated by the event pileup are analyzed with conventional and spin flip analyses for comparison. In conclusion, the spin flip analysis method is useful in studying the bias due to time-dependent inefficiency and then use more data for the g − 2 analysis. We developed a Wien-filter as a spin rotator for the reaccelerated thermal muon beam . The growth of the transverse emittance during spin rotation should not be substantial enough to satisfy the experimental requirements. The main cause of the emittance growth is the difference between the magnetic and electric forces along the beam path. Detailed designs of the magnetic yoke and electrodes are necessary. After a full model design, the emittance growth is evaluated as being +64% in the horizontal plane (x-x') and +56% in the vertical plane (y-y'). This is mainly caused by the additional electric fields. A detailed design will be conducted so that the additional electric fields can be minimized.

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