2019 Spring Physics Colloquium
강연일자: 2019. 04. 23. 화. 오후 5시
장소: 아산이학관 433호
강연자: 최선호 (서울대학교)
강연주제: Peeking Beyond the Standard Model via Magnetic Moment of Muon
At J-PARC of Japan, a new, very different approach
is in progress to measure the magnetic moment anomaly g-2 and the electric
dipole moment of the muon. Currently, there is a larger than 3 sigma
discrepancy between the Standard Model prediction and the experimental value
for g-2. New experiments for muon g-2 aims to reduce experimental errors by at
least factor 3 from the previous 0.46 ppm. The new method at J-PARC involves
muons orbiting in pure magnetic field without any focusing electric field. This
requires a muon beam of low emittance which can be achieved by stopping the
secondary muon beams and re-accelerating them. This releases the constraint on
the so-called magic momentum and makes it possible for a compact muon storage.
The surface muons from pion decay are collected and stopped inside the silica aerogel
target, where they form neutral muonium, which diffuses out to vacuum with only
thermal motion. An external laser then ionizes the neutral muonium to have
muons back at low emittance for re-acceleration to 300 MeV/c. The accelerated
muons are injected into storage magnet for observation of the spin precession.
The direction of the muon spin can be determined by decay positrons with
relatively high energy. The decay positrons will be detected and their
trajectories are reconstructed by silicon detectors in the shape of vanes
inside the muon storage area. The magnetic moment anomaly g-2 can be measured
by the additional spin precession with respect to the momentum of the muon,
while up-down asymmetry of the high energy positrons is sensitive to the
electric dipole moment. The stopping and re-accelerating muon beams
necessitates considerable amount of R&D and progresses are made at various
components of the experiment. The uniformity and stability of the storage
magnetic field necessary for the pursued precision also requires some new idea.
The presentation will be focused on the overview, current status and future
prospects for J-PARC muon g-2/edm experiment.