## Abstract

We have performed laser spectroscopy of metastable antiprotonic helium atoms [Formula Presented] formed in helium media of 0.2–8.0 bars at 5.8–6.3 K and have observed a density dependence of the resonance vacuum wavelengths for the known transitions [Formula Presented] and [Formula Presented] They showed linear redshifts of [Formula Presented] GHz and [Formula Presented] GHz per 1 g/l, respectively. With the shift parameters above, the transition vacuum wavelengths were extrapolated to zero-density limits, yielding [Formula Presented] nm and [Formula Presented] nm, respectively. These values, with a 0.5-ppm precision, 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 agreement between our experimental values and the calculations has become as good as [Formula Presented] This excellent agreement in turn provides a precise value of the antiproton Rydberg constant that surpasses the currently known precision and sets a severe constraint on the antiproton charge [Formula Presented] and the mass [Formula Presented] that both [Formula Presented] and [Formula Presented] be less than [Formula Presented] when a more precisely known constraint on the charge-to-mass ratio is combined. Thus we have opened a possibility of determining fundamental constants of the antiproton.

Original language | English |
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Pages (from-to) | 223-229 |

Number of pages | 7 |

Journal | Physical Review A |

Volume | 59 |

Issue number | 1 |

DOIs | |

State | Published - 1999 |