Determination of the antiproton-to-electron mass ratio by laser spectroscopy of

• Published in: Hyperfine interactions 2009, Vol.194 (1-3), p.1-6
• Main Authors: Barna, D., Dax, A., Eades, J., Gomikawa, K., Hayano, R. S., Hori, M., Horváth, D., Juhász, B., Ono, N., Pirkl, W., Widmann, E., Torii, H. A.
• Format: Article
• Language: English
• Subjects: Atomic; Condensed Matter Physics; Hadrons; Heavy Ions; Molecular; Nuclear Physics; Optical and Plasma Physics; Physics; Physics and Astronomy; Surfaces and Interfaces; Thin Films
• ISSN: 0304-3843; 1572-9540
• DOI: 10.1007/s10751-009-0022-9

Helium is unique in the sense that about 3% of low-energy antiprotons stopped in it survive with an average lifetime of a few microseconds, forming metastable states of the exotic antiprotonic helium atom ( -He  + +  -e   −). This lifetime is sufficient to carry out laser spectroscopy measurements of atomic transitions of this exotic atom. The antiproton-to-electron mass ratio can be deduced from comparisons with three-body QED calculations. A systematic study of the energy levels of this exotic atom started soon after its discovery, continuously aiming for higher precision (for a review see Yamazaki et al., Phys Rep 366:183, ( 2002 ) and references therein). Recently, at the Antiproton Decelerator of CERN, a femtosecond optical frequency comb and continuous-wave pulse-amplified laser were used to measure 12 transition frequencies to fractional precisions of (9 − 16)×10  − 9 , yielding an antiproton-to-electron mass ratio of 1836.152674(5).