High-precision spectroscopy of cold trapped HD+: towards metrology of particle masses

Abstract. Molecular hydrogen ions (H_2^+, HD^+, ...) are the simplest molecules, and their simplicity makes them interesting systems for fundamental physics studies and for methodological investigations in the novel field of cold molecules.The energies of molecular hydrogen ions, in particular the rotational and vibrational energies (in atomic units) are functions of the particle masses (electron, proton, deuteron), the Coulomb interaction, and to a lesser extent the magnetic properties of these particles. Significant theoretical advances now permit to calculate these energies ab-initio with an inacccuracy below 1 part in 10^9. This includes important contributions from relativistic and QED corrections.The dependence of transition energies on the electron-to-proton mass ratio makes these molecules also candidates for a laboratory search for a possible time-dependence of this fundamental constant. In this talk I will describe the status of the Düsseldorf experiment on precision laser spectroscopy of sympathetically cooled HD+, including the most recent developments towards enhanced precision.