Improved Measurements of Muonic Helium Ground-State Hyperfine Structure at a Near-Zero Magnetic Field

Abstract

Muonic helium atom hyperfine structure (HFS) measurements are a sensitive tool to test the three-body atomic system and bound-state quantum electrodynamics theory, and determine fundamental constants of the negative muon magnetic moment and mass. The world's most intense pulsed negative muon beam at the Muon Science Facility of the Japan Proton Accelerator Research Complex allows improvement of previous measurements and testing further $CPT$ invariance by comparing the magnetic moments and masses of positive and negative muons (second-generation leptons). We report new ground-state HFS measurements of muonic helium-4 atoms at a near-zero magnetic field, performed for the first time using a small admixture of CH${}_4$ as an electron donor to form neutral muonic helium atoms efficiently. Our analysis gives $\Delta \nu$ = 4464.980(20) MHz (4.5 ppm), which is more precise than both previous measurements at weak and high fields. The muonium ground-state HFS was also measured under the same conditions to investigate the isotopic effect on the frequency shift due to the gas density dependence in He with CH${}_4$ admixture and compared with previous studies. Muonium and muonic helium can be regarded as light and heavy hydrogen isotopes with an isotopic mass ratio of 36. No isotopic effect was observed within the current experimental precision.

arXiv comment7 pages, 4 figures, 2 tables

References in corpus (10)

• Final Report of the Muon E821 Anomalous Magnetic Moment Measurement at BNL
• Measurement of the Negative Muon Anomalous Magnetic Moment to 0.7 ppm
• The Mu-MASS (MuoniuM lAser SpectroScopy) experiment
• New precise spectroscopy of the hyperfine structure in muonium with a high-intensity pulsed muon beam
• Hyperfine Splitting in Muonium: Accuracy of the Theoretical Prediction
• Rabi-Oscillation Spectroscopy of the Hyperfine Structure of Muonium Atoms
• Ground State Hyperfine Structure of Muonic Helium Atom
• Penning-Trap Mass Measurement of Helium-4
• The hyperfine structure of the ground states in the helium muonic atoms
• Higher-order QED corrections to the hyperfine splitting in ${}^3$He

Cited by in corpus (1)

• Precision measurements of muonium and muonic helium hyperfine structure at J-PARC