Abstract
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 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 $a_{\mu}$ 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 $1.5\times 10^{-21}~e\cdot\mbox{cm}$.
We review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon. This is performed in a perturbative expansion in the fine-structure constant α and is ...broken down into pure QED, electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluated up to and including O(α5) with negligible numerical uncertainty. The electroweak contribution is suppressed by (mμ∕MW)2 and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops and is known to better than one percent. Hadronic contributions are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. The leading hadronic contribution appears at O(α2) and is due to hadronic vacuum polarization, whereas at O(α3) the hadronic light-by-light scattering contribution appears. Given the low characteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, in particular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to a detailed account of recent efforts to improve the calculation of these two contributions with either a data-driven, dispersive approach, or a first-principle, lattice-QCD approach. The final result reads aμSM=116591810(43)×10−11 and is smaller than the Brookhaven measurement by 3.7σ. The experimental uncertainty will soon be reduced by up to a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. This and the prospects to further reduce the theoretical uncertainty in the near future – which are also discussed here – make this quantity one of the most promising places to look for evidence of new physics.
A strategy to design of a dedicated beam transport line for J-PARC Muon g-2/EDM experiment is described. To accomplish three-dimensional beam injection into the MRI-type compact storage ling, ...transverse beam phase spaces (X and Y components) should be coupled appropriately. We introduce a X-Y coupling, extended Twiss-parameters, and transfer-matrix of the entire transport line. We also discuss about detailed parameters of rotating quadruple magnets along the transport line.
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.
The J-PARC Muon <inline-formula><tex-math notation="LaTeX">g-2</tex-math></inline-formula>/EDM Experiment uses a superconducting solenoid magnet to store positive muons, which generates a magnetic ...field of 3T. A highly uniform magnetic field is required, which is less than <inline-formula><tex-math notation="LaTeX">0.2\, \rm{ppm}_\rm{p-p}</tex-math></inline-formula> (peak-to-peak) in a muon storage region of <inline-formula><tex-math notation="LaTeX">(333\pm 15) \rm{mm}</tex-math></inline-formula> in radius and <inline-formula><tex-math notation="LaTeX">\pm 50 \rm{mm}</tex-math></inline-formula> in height around the magnet center. The magnetic field error due to manufacturing tolerance was evaluated with a Monte Carlo simulation. This paper introduces the evaluation of magnetic field error due to manufacturing tolerance with a Monte Carlo simulation implemented in C++17. Assuming tolerance to be within <inline-formula><tex-math notation="LaTeX">0.1\, \rm{mm}</tex-math></inline-formula> or <inline-formula><tex-math notation="LaTeX">0.1\, \rm{mrad}</tex-math></inline-formula>, the uniformity was calculated to be <inline-formula><tex-math notation="LaTeX">179\, \rm{ppm}_\rm{p-p}</tex-math></inline-formula> at the worst case. We performed shimming simulation by using truncated singular value decomposition regularization. As a result, it was confirmed that the worst field error could be compensated to the uniformity of <inline-formula><tex-math notation="LaTeX">0.17\, \rm{ppm}_\rm{p-p}</tex-math></inline-formula> with a present shimming system. Furthermore, we performed the shimming simulation for wider range of the manufacturing tolerances to investigate the shimming system limit. We concluded that the magnet had to be manufactured with an accuracy less than at least <inline-formula><tex-math notation="LaTeX">0.5\, \rm{mm}</tex-math></inline-formula> or <inline-formula><tex-math notation="LaTeX">0.5\, \rm{mrad}</tex-math></inline-formula>.
COMET Phase-I technical design report Abramishvili, R; Adamov, G; Allin, A ...
Progress of theoretical and experimental physics,
03/2020, Letnik:
2020, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
The Technical Design for the COMET Phase-I experiment is presented in this paper. COMET is an experiment at J-PARC, Japan, which will search for neutrinoless conversion of muons into ...electrons in the field of an aluminum nucleus ($\mu$–$e$ conversion, $\mu^{-}N \rightarrow e^{-}N$); a lepton flavor-violating process. The experimental sensitivity goal for this process in the Phase-I experiment is $3.1\times10^{-15}$, or 90% upper limit of a branching ratio of $7\times 10^{-15}$, which is a factor of 100 improvement over the existing limit. The expected number of background events is 0.032. To achieve the target sensitivity and background level, the 3.2 kW 8 GeV proton beam from J-PARC will be used. Two types of detectors, CyDet and StrECAL, will be used for detecting the $\mu$–$e$ conversion events, and for measuring the beam-related background events in view of the Phase-II experiment, respectively. Results from simulation on signal and background estimations are also described.
The development of a vertical kicker system is an important part of a three-dimensional spiral-injection scheme. The beam injected at a pitch angle of a few tens of degrees was controlled by applying ...a pulsed magnetic field using a vertical kicker system inside the storage magnet. The stored muon beam then followed a vertical betatron motion around the midplane of the storage magnet owing to the weak focusing magnetic field. Accurate control of the pulsed kick is crucial for minimizing the amplitude of the vertical betatron oscillation. The specifications of the pulsed magnetic field and detailed design of the kicker system at the test beam bench are discussed herein.
This study is about a design method for ASSMs (Active Shield Steering Magnets). ASSMs will be applied to a g-2/EDM precise measurements experiment which is under preparation in J-PARC. The experiment ...needs a very homogeneous 3.0 T magnetic field using a superconducting magnet with iron yoke. Muons are injected through spiral orbits in the fringe field and two ASSMs are planned for orbit fine tuning. ASSMs need to generate steering magnetic fields without additional error field. Then, they need active shields, and they are ASSMs. For such ASSMs, a design method has been developed and trial design have been done, using a technique of the MRI GC design method which can well determine 3D current pattern on surfaces.
The generation of thermal muons by laser ionization of muonium (μ+e−) confined in multi-layer silica aerogel structures is simulated. Thermal muonium generated inside the silica aerogel is emitted ...into the sandwiched vacuum regions between the aerogel layers separated by a few millimeters. The model for muonium emission is validated against emission measurements from single aerogel samples. The efficiency of thermal muon generation in this configuration is predicted to increase by several times compared with a single-layer design.
Magnetic field shimming using low saturation magnetization material was tested to realize spatial magnetic field homogeneity of less than 1 ppm. The magnetic moment per unit mass were measured for ...three candidates, that is, Nickel, magnetic fluid and magnetic putty, and it was verified that those have low magnetic moments suitable for precise shimming below 1 ppm. The magnetic shimming test was performed using MRI magnet for MuSEUM experiment at 1.2 T with iron plates, Ni thin plates and magnetic putty. The magnetic shimming with iron plates was conducted employing the two step shimming scheme, and the homogeneity could be reached to 0.29 ppm peak-to-peak (ppm<inline-formula><tex-math notation="LaTeX">_\text{pp}</tex-math></inline-formula>) after six shimming trials. Then, the precise shimming was carried out with Ni thin plates and magnetic putty, and the homogeneity could be reached to 0.16 ppm peak-to-peak with Nickel and 0.17 ppm<inline-formula><tex-math notation="LaTeX">_\text{pp}</tex-math></inline-formula> with magnetic putty. No deformation of putty in the magnetic field was observed even after two months. The magnetic field monitoring for two months showed that magnetic field strength and homogeneity largely depended on the temperature, and the temperature of the magnet room has to be controlled within <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 0.35 degC under the circumference condition of the shimming test in order to keep the magnetic field change and the homogeneity within <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 0.1 ppm. In addition, it is showed that the refilling of LHe in the MuSEUM magnet system should be performed once per 29 days The practical implementation method for magnetic putty was suggested for the existing magnet system by using plastic spacers with holes.
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