SPECAP · Precision laser spectroscopy of antiprotonic and pionic atoms

This proposal has two objectives. First, I propose to measure the antiproton mass relative to the electron mass with a fractional precision of 0.1 ppb by carrying out sub-Doppler two-photon laser spectroscopy of antiprotonic helium atoms. The antiproton mass would then be better known than the proton mass. The (anti)proton-to-electron mass ratio is regarded as a one of several fundamental physical constants which, like the fine structure constant α, is a dimensionless quantity of nature that can be measured to ppb-scale precision. The experiment would constitute the highest precision confirmation of CPT symmetry involving atoms containing antiprotons. A new buffer gas cooling technique will be used to cool down the atoms to temperature T<1.5 K, thereby reducing the residual Doppler width of the two-photon resonance signals caused by the thermal motion of the atom in the experimental target. A new quasi-cw laser with high peak power and narrow linewidth will be developed. In the later half of the project, high-quality antiproton beam from the new ELENA storage ring constructed at CERN will be used to reach higher precisions of 10^-11Second, I propose to measure the pion mass to a precision of <10^-8 by carrying out the first laser spectroscopy of pionic helium atoms, where the pion occupies a Rydberg state and the electron the 1s state. This corresponds to a >300-fold improvement in precision compared to the currently known mass, and approaches the fundamental limit imposed by the 26-ns lifetime of the pion. Past measurements of mπ show a bifurcation, i.e. two groups of experimental results near 139.570 and 139.568 MeV/c^2. The laser spectroscopy of pionic helium will provide an unambiguous value for the pion mass. This will improve the limit on the muon neutrino mass obtained from laboratory experiments, and reduce the uncertainty on the Fermi coupling constant. This will be the first time an atom containing a meson has been studied by laser spectroscopy.""