Improved Measurements of Muonic Helium Ground-State Hyperfine Structure at a Near-Zero Magnetic Field
P Strasser1,2,3, S Fukumura4, R Iwai1
1Muon Science Laboratory, Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan.
Physical Review Letters
|January 5, 2024
Summary
New measurements of muonic helium atom hyperfine structure (HFS) provide a more precise value for fundamental constants. This research advances our understanding of atomic physics and tests theories of quantum electrodynamics.
Area of Science:
- Atomic Physics
- Quantum Electrodynamics
- Fundamental Constants
Background:
- Muonic helium atom hyperfine structure (HFS) measurements are crucial for testing three-body atomic systems and bound-state quantum electrodynamics.
- These measurements also determine fundamental constants, including the negative muon's magnetic moment and mass.
- Comparing positive and negative muons tests CPT invariance.
Purpose of the Study:
- To perform new ground-state HFS measurements of muonic helium-4 atoms at near-zero magnetic field.
- To improve the precision of previous measurements and test CPT invariance.
- To investigate the isotopic effect on frequency shifts in muonium and muonic helium.
Main Methods:
- Utilized the world's most intense pulsed negative muon beam at the Muon Science Facility (MuSAIF) of Japan Proton Accelerator Research Complex (J-PARC).
- Employed a small admixture of CH4 as an electron donor to efficiently form neutral muonic helium atoms.
- Conducted measurements at near-zero magnetic field and under conditions to study density-dependent frequency shifts.
Main Results:
- Achieved a new, more precise measurement of the ground-state HFS of muonic helium-4: Δν=4464.980(20) MHz (4.5 ppm).
- This result surpasses the precision of all previous measurements conducted at both weak and high magnetic fields.
- No isotopic effect was observed between muonium and muonic helium within the current experimental precision.
Conclusions:
- The new HFS measurement of muonic helium-4 significantly improves precision, aiding tests of quantum electrodynamics and fundamental constant determination.
- The study demonstrates the capability of the J-PARC MuSAIF facility for advanced atomic physics research.
- The absence of an observed isotopic effect provides valuable data for understanding muonic atoms and their interactions.
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