Torii, H A

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High-precision laser spectroscopy of antiprotonic helium atomculesand eects of collisions at high-density conditionsH.A. ToriiUniversity of Tokyo, Physics Institute, Komaba, 3-8-1, Meguro, Tokyo 153-0041, JAPANThe surprising metastability and the unique features of the neutral antiprotonic helium\atomcule" (pHe+) has been studied extensively by the PS205 collaboration at CERN-LEAR. We have so far found 13 resonant transitions among high-n, high-l metastablestates of the pHe+atomcule by the method of laser-induced annihilation spectroscopy.The observed transition energies showed excellent agreement with theoretical calculations,and thus established the level structures of this exotic atomcule.In the course of the experiment, we observed that the central frequency of the reso-nances shifted and broadened with density, and systematically studied this phenomenon.High-resolution laser spectroscopy was performed in helium media of 0.2{8.0 bar at 5.8{6.3 k and 15.2 k, for two of the discovered transitions (n; l) = (39; 35) ) (38; 34) and(37; 34) ) (36; 33). We have measured the density dependence and observed linear redshifts of 0:61 0:01 GHz and 0:22 0:02 GHz per 1 g/`, for the respective transitions at597 nm and 470 nm. These results are qualitatively explained by a theoretical calcula-tion based on the impact approximation with a van der Waals type collisional interactionbetween the atomcule and a helium atom, but certainly more elaborate theoretical workis needed for quantitative discussion.With the shift parameters above, the transition vacuum wavelengths were extrapolatedto zero-density limit, and these values were compared with recent theoretical calculationson the energy of the Coulombic three-body system, including relativistic corrections andthe Lamb shift. The observed transition energies were determined to a 510 7precision,and the agreements between our experimental values and the calculations are now as goodas 2{3  10 6. This already surpasses the currently known precision (5 10 5) of the pRydberg constant, and thus we have opened a new possibility of measuring fundamentalconstants of the antiproton.0204060801000.250.30.350 50 100 150l+597 nmShift (GHz)Density (g/l)+470 nm0.720.740.760.78597 nm470 nmFig.1 The central vacuum wavelength isplotted against the density of the target he-lium for the (n,l)=(39,35))(38,34): 597 nmand (37,34))(36,33): 470 nm resonancelines.Relativistic correctionKorobovKino et al.Elander et al.Non-relativistic  calculationsExperimental   value(39,35) fi (38,34)597.220 .240 .260Vacuum wavelength [nm]Lamb shiftFig.2 The experimental value of the(39,35))(38,34) wavelength is com-pared with recent theoretical valueswhich agree within precisions of afew ppm.

High-precision laser spectroscopy of antiprotonic helium atomcules and effects of collisions at high-density conditions

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