Determination of the antiproton-to-electron mass ratio by precision laser spectroscopy of pHe+

A femtosecond optical frequency comb and continuous-wave pulse-amplified laser were used to measure 12 transition frequencies of antiprotonic helium to fractional precisions of (9-16)x10(-9). One of these is between two states having microsecond-scale lifetimes hitherto unaccessible to our precision laser spectroscopy method. Comparisons with three-body QED calculations yielded an antiproton-to-electron mass ratio of Mp/me=1836.152674(5).     

Lipoide

Ohne Zusammenfassung     

Observation of cold, long-lived antiprotonic helium ions

Cold, two-body antiprotonic helium ions p 4He2+ and p 3He2+ with 100-ns-scale lifetimes, occupying circular states with the quantum numbers ni=28-32 and li=ni-1 have been observed. They were produced by cooling three-body antiprotonic helium atoms in an ultra-low-density helium target at temperature T approximately 10 K by atomic collisions, and then removing their electrons by inducing a laser transition to an autoionizing state. The lifetimes of p 3He2+ against annihilation induced by collisions were shorter than those of p 4He2+, and decreased for larger-ni states.     

Collisional quenching of metastable states of antiprotonic helium by hydrogen and deuterium molecules

The quenching of metastable states of antiprotonic helium by collisions with hydrogen and deuterium molecules was studied. A systematic investigation of the delayed annihilation time spectra at various H₂ and D₂ admixture ratios at the ppm level revealed characteristic changes of their shape, which indicated a strong principal and orbital quantum number dependent quenching of levels in both cases. Applying a laser spectroscopy technique to measure the lifetimes of individual states and cascades we deduced H₂ and D₂ quenching cross-sections for the states (n, l )= (39, 35) and (37, 34). These cross-sections establish for D₂ molecules the strong increase of the quenching efficiency with increasing principal quantum number n of the state under investigation previously reported for the case of H₂ admixtures. Our experiments indicate that the low-n state (37, 34) is somewhat less affected by D₂ than by H₂, while the high-n state (39, 35) is equally quenched by both isotopes. Received 2 October 2000     

The effect of a polymeric additive on the evaporation of organic aerocolloidal droplets

 The evaporation of single triethyl phosphate (TEP) micro-droplets containing a high molecular weight polymer, poly(methyl methacrylate) (PMAA), was inves-tigated using an electrodynamic trap and light scattering measurements to explore the suppression of evaporation by the additive. Pure-component evaporation rates were measured to determine the vapor pressure over a range of temperatures, and the polymer was found to significantly decrease the evaporation rate. A numerical solution of the problem of simultaneous solvent evaporation and polymer diffusion within the droplet indicated a rapid build-up of PMMA at the surface of the drop, but vapor/liquid thermodynamic considerations alone do not account for the observed reduction in the evaporation rate for the droplets containing PMMA. After significant evaporation of TEP occurred, the ultra-low evaporation rate was measured using changes in the Raman spectra associated with morphology-dependent resonances. The evaporation in this regime appears to be controlled by the rate of solvent molecules diffusing through the polymer matrix. Received: 17 June 1997 Accepted: 24 October 1997     

μ− SR in semiconductorsSR in semiconductors

μ⁻ SR experiments have been performed on Si between room temperature and 6 K. The amplitude of the muon spin precession signal in an applied magnetic field of 0.04 T decreased below 30 K. A zero-field measurement at 6 K revealed a μ⁻ spin precession frequency of 650 MHz. The muonic atom represents an aluminium acceptor in the silicon matrix, its electronic state is responsible for the μSR signal. A possible influence of the γ recoil produced by the X-ray cascade is discussed.     

Quenching of metastable antiprotonic helium atoms in collisions with deuterium molecules

Quenching of metastable antiprotonic helium atoms in collisions with deuterium molecules has been studied using laser spectroscopy at CERN's new Antiproton Decelerator facility. The quenching cross-sections of the states (n, l )= (39, 36), (39, 37), and (39, 38) were determined from the decay rates of the states which were observed using the “deuterium-assisted inverse resonance” (DAIR) method. The results revealed a similar (n, l )-dependence of the quenching cross-sections as in the case of hydrogen but the values were smaller by a factor of ∼1.5. Received 6 July 2001