Latest news from PS205 High-precision laser spectroscopy of antiprotonic helium atoms

Abstract

We have performed laser spectroscpy of metastable antiprotonic helium atoms (or “atomcules”) ( p He + ) and have observed a density dependence of the resonance vacuum wavelengths for the known transitions ( n, l) = (39,35) → (38,34) and (37,34) → (36,33). They showed linear red-shifts of 0.61 ± 0.01 GHz and 0.22 ± 0.02 GHz per 1 g/ℓ, respectively. With the shift parameters above, the transition vacuum wavelengths were extrapolated to zero-density limits, yielding λ 0 = 597.2570 ± 0.0003 nm and λ 0 = 470.7220 ± 0.0006 nm, respectively. These values were compared with the result of recent theoretical calculations on the energy of the Coulombic three-body system. including relativistic corrections and the Lamb shift. The agreements between our experimental values and the calculations have become as good as 2 × 10 −6. This sets a severe constraint on the antiproton charge (−Q p ) and mass (M p ) that |Q p−Q p |/e < 5 × 10 −7 |M p−M p /M p × 5 × 10 −7 , under a more precisely known constraint on the charge-to-mass ratio. Thus we have opened a new possibility of measuring fundamental constants of the antiproton.