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 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 $1.5\times 10^{-21}~e\cdot\mbox{cm}$.
Highlights
The Standard Model (SM) [1,2] is an extremely successful theory of elementary particles
Our experiment introduced here is intended to measure aμ and dμ with a very different technique, using a 300 MeV/c reaccelerated thermal muon beam with 50% polarization, vertically injected into a magnetic resonance imaging (MRI)-type solenoid storage ring with 1 ppm local magnetic field uniformity for the muon storage region with an orbit diameter of 66 cm
A difference in the actual field distribution from the perfect case leads to a systematic uncertainty of 13 ppb, which is estimated from a precision spin-tracking simulation of muon beam storage
Summary
The Standard Model (SM) [1,2] is an extremely successful theory of elementary particles. Even when direct searches for new physics are limited in energy reach, indirect searches like precision measurements can become powerful probes of new physics It is reported [6,7,8,9,10] that there is at present a more than 3 σ discrepancy between the experimental value of the muon’s anomalous magnetic moment (aμ = (g − 2)/2, where g is the Landé g-factor of the muon) [11] and the PTEP 2019, 053C02 prediction for it. A focusing field index of n = 0.12–0.14 was used, which was necessary to contain the muons captured from pion decay In this proposed experiment, we greatly reduce the focusing requirement in the storage ring by using a reaccelerated thermal muon beam with a factor of 1000 smaller beam emittance. The average magnetic field seen by the muons in the storage ring is measured by the Larmor precession frequency of a free proton (ωp). According to a beam transport simulation [27], the beam will be focused on the focal point with standard deviations of 31 and 14 mm in the horizontal and vertical directions, respectively
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