Antiprotonic Helium Atoms

Abstract

At CERN's antiproton decelerator (AD), the ASACUSA (atomic spectroscopy and collisions using slow antiprotons) collaboration, a Japan–Austria–Hungary–Italy–Denmark–Germany group led by the author, has been working on the precision laser spectroscopy of antiprotonic helium atoms since 2000 [1]. By comparing the measured laser transition frequencies with three-body quantum electrodynamics (QED) calculations [2–4], we have determined the antiproton-to-electron mass ratio m p /me to the level of 2 × 10−9 [5]. Together with the atomic transition frequencies in hydrogen and deuterium, our results (assuming CPT symmetry, i.e., the equality of particle-antiparticle masses) yield information on the Rydberg constant, the proton and deuteron charge radii, and the relative atomic mass of the electron, in the CODATA recommended values of the fundamental physical constants 2006 [6].