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

We have performed laser spectroscopy of metastable antiprotonic helium atoms (or 'atomcules') (pbarHe+) 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 λ0 597.2570 ± 0.0003 nm and λ0 = 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 2x10-6. This sets a severe constraint on the antiproton charge (-Qpbar) and mass (Mpbar) that vertical bar Qp - Qpbar vertical bar/e<5x10-7 and vertical bar Mp - Mpbar vertical bar /Mp<5x10-7, 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