Precision spectroscopy of antiprotonic helium atoms and ions-weighing the antiproton

Abstract

A radiofrequency quadrupole antiproton decelerator, a femtosecond optical frequency comb and continuous-wave pulse-amplified laser were used to measure 12 transition frequencies of antiprotonic helium (metastable three-body neutral atom consisting of an electron, an antiproton and a helium nucleus) to fractional precisions of (9-16)× 10-9. Comparisons with three-body QED calculations yielded an antiproton-to-electron mass ratio of mp/me =1836.152674(5). The physics of antiprotonic helium atom spectroscopy and the method of mp/me determination are presented, and future prospects are discussed. © 2008 Springer-Verlag Berlin Heidelberg.