Two-photon laser spectroscopy of antiprotonic helium atoms, and the antiproton-to-electron mass ratio

摘要

Some two-photon transitions in antiprotonic helium atoms at the deep UV wavelengths λ = 139.8-197.0 nm were recently studied by laser spectroscopy. The thermal Doppler broadening of the observed antiprotonic resonances were reduced by exciting the atoms with two counterpropagating laser beams of wavelengths λ = 265-417 nm. The resulting narrow spectral lines allowed the measurement of three transition frequencies in antiprotonic helium-3 and helium-4 isotopes with fractional precisions of 2.3-5 parts in 10~9. By comparing the results with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). We briefly review these experimental results that were presented in Ref. [1].