States Of Antiprotonic Helium Atom Research Articles

Hyperfine structure of metastable states inHe+3p¯atom

For the metastable states of antiprotonic helium atoms, {sup 3}He{sup +}p, the fine and hyperfine splittings of energy levels are calculated within the framework of the Breit-Pauli Hamiltonian. The latter represents the {alpha}{sup 2} order relativistic corrections to the nonrelativistic energy. Results include as well the leading {alpha}{sup 3} order contribution due to the anomalous magnetic moment of electron. The final relative accuracy of the hyperfine intervals is estimated to be about 5x10{sup -5}.

Capture of slow antiprotons by helium atoms

A consistent quantum mechanical calculation of partial cross-sections leading to different final states of antiprotonic helium atom was performed. For the four-body scattering wave function, corresponding to the initial state, as well as for the antiprotonic helium wave function, appearing in the final state, adiabatic approximations were used. Further, symmetric and non-symmetric effective charge (SEC, NEC) approximations were introduced for the two-electron wave functions in the field of the two fixed charges of the He nucleus and the antiproton. Calculations were carried out for a wide range of antiprotonic helium states and incident energies of the antiproton below the first ionization threshold of the He atom. The origin of the rich low-energy structure of certain cross-sections is discussed in detail.

HIGH-PRECISION COULOMB THREE-BODY CALCULATION OF ANTIPROTONIC HELIUM ATOMS

Using the non-adiabatic coupled rearrangement channel method, energy levels of metastable states of antiprotonic helium atoms are precisely calculated. A dual character of the atom is effectively described with atomic and molecular type coordinate systems. By introducing three rearrangement channels, correlation effects in the three-body system has been sufficiently incorporated. The complex coordinate rotation method is employed to take a resonant boundary condition of metastable states into account. The relativistic and QED corrections are considered with the first order perturbation theory. Calculated transition frequencies are in excellent agreement with observed values. This agreement gives best limit of the antiproton mass with 54 ppb uncertainty. This uncertainty is estimated by calculated transition frequencies with the antiproton mass slightly shifted from the proton mass.

Quenching of metastable states of antiprotonic helium atoms by collisions with H2 molecules

Laser resonance transitions between normally metastable states of antiprotonic helium atoms were induced making use of state dependent quenching effects caused by trace admixtures of H2 to the target helium gas. With this method of “H2-assisted inverse resonances” the decay rates of the states (n,l)=(39,l),l=36,37,38, and (38,l),l=35,36,37 of p̄He+ were determined as a function of the H2 admixture. The quenching cross sections at 30 K deduced therefrom for the states with n=39 were found to be of the order of the geometrical cross section for p̄He+–H2 collisons (2⋅10−15 cm2), with a moderate decrease with increasing l. Within a given cascade with constant v=n−l−1, the quenching cross sections for states with n=38 are smaller by a factor of 4–6 than those for states with n=39.

Energies and Relativistic Corrections for the Metastable States of Antiprotonic Helium Atoms

We present accurate results for the energy levels of antiprotonic helium atoms with the relativistic and QED corrections of order {alpha}{sup 4}mc{sup 2} taken into account. These results reduce the discrepancy between theory and experiment to about 5{endash}10ppm and rigorously confirm Condo{close_quote}s model of metastability for the long-lived fraction of antiprotonic helium. The present level of precision enables the unambiguous ascription of quantum numbers to all of the transition lines observed so far. {copyright} {ital 1997} {ital The American Physical Society}

Hydrogen-Assisted Laser-Induced Resonant Transitions between Metastable States of Antiprotonic Helium Atoms

Laser resonance transitions between normally metastable states of antiprotonic helium atoms were observed making use of state dependent quenching effects caused by small admixtures of ${\mathrm{H}}_{2}$ molecules. By selectively shortening the lifetimes of states with higher principal quantum number $n$ as compared to those of lower $n$, this method for the first time provides access to all initially populated metastable states of $\overline{p}{\mathrm{He}}^{+}$ atoms. This was demonstrated by observing the transitions $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(38,l)\ensuremath{\rightarrow}(39,l+1)$, $l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}35,36,37$ and $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(37,l)\ensuremath{\rightarrow}(38,l+1)$, $l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}34,35,36$.

A possible way to promote antihydrogen formation via metastable antiprotonic helium atoms

A new way to promote antihydrogen formation via the recently discovered long-lived metastable states of antiprotonic helium atoms is discussed. Recombination processes such ase−¯pHe++ +e+e− →e+¯p + He0 are possible in this respect.