First direct observation of strong interaction spin-orbit effects in antiprotonic atoms

The strong ¯p-nucleus spin-orbit interaction was investigated in a measurement of the strong-interaction effects of the 9→8 transition in ¯p ¹⁷⁴Yb at the Low-Energy Antiproton Ring (LEAR) at CERN. This measurement was part of an experimental programme where, for the first time, the fine-structure components of the last observable X-ray transition in a ¯p atom, which carries information on the strong ¯p-nucleus interaction, were resolved and studied individually. The observed splitting ΔE _exp=2408±26 eV consists of the electromagnetic fine-structure splitting ΔE _FS=2350 eV and an additional splitting Δ?=58±26 eV. In addition, one finds a significant difference in the level widths of Δ=195±59 eV with the larger value_?=1216±41 eV for the lower fine-structure level. This experiment follows an earlier measurement on ¯p ¹³⁸Ba, where the transition 8→7 is influenced by the strong interaction. In this case, however, the fine-structure components could not be resolved. The results for¹⁷⁴Yb may be attributed to a spin-orbit (LS) term in the complex strong-interaction potential.     

First observation of two hyperfine transitions in antiprotonic He

A more general scale-setting procedure for General Relativity with Renormalization Group corrections is proposed. Theoretical aspects of the scale-setting procedure and the interpretation of the Renormalization Group running scale are discussed. The procedure is elaborated for several highly symmetric systems with matter in the form of an ideal fluid and for two models of running of the Newton coupling and the cosmological term. For a static spherically symmetric system with the matter obeying the polytropic equation of state the running scale-setting is performed analytically. The obtained result for the running scale matches the Ansatz introduced in a recent paper by Rodrigues, Letelier and Shapiro which provides an excellent explanation of rotation curves for a number of galaxies. A systematic explanation of the galaxy rotation curves using the scale-setting procedure introduced in this Letter is identified as an important future goal.     

Strong interaction effects in antiprotonic atoms

Yields of the last observable X-ray transitions in antiprotonic atoms have been measured for groups of neighbouring elements. In sulphur a natural line width and an energy shift could be observed. These data are compared with calculations describing the p?-nucleus interaction in terms of an optical potential using the free p?-N scattering lengths.     

Hadronic lamb shift in antiprotonic atoms

We estimate the difference between the anomalous magnetic moments of bound and free antiprotons and discuss its relevance in the magnetic fine structure of antiprotonic atoms.     

Metastable states of antiprotonic helium atoms

We discuss the latest theoretical achievements in calculations of energy transitions in the antiprotonic helium He⁺ p-0304; atoms. New variational calculations of the nonrelativistic energies with precision of ∼10^-10 a.u. and relativistic and QED corrections to the energy levels of mα ⁵ order are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

E2 nuclear resonance effect in pionic atoms

The quadrupole nuclear resonance effect in pionic atoms is considered, and the results of calculations for pionic atoms with distorted even-even nuclei are presented.     

High resolution X ray spectroscopy in light antiprotonic atoms

At the LEAR facility, CERN, antiprotonic Lα transitions in light elements have been investigated with a focussing crystal spectrometer. The high resolution of the experiment allowed for the first time to resolve in H the 2³P₀ state from the close lying states 2³P₂, 2¹P₁, and 2³P₁. In D the corresponding transitions were found to be more than an order of magnitude broader. To a large extent the results for H support the meson exchange model. This revised version was published online in August 2006 with corrections to the Cover Date.     

First observation of K X-rays from pp atoms

K and L series X-rays have been observed from p$\text{p}$ atoms formed in hydrogen gas at NTP in association with annihilations into neutral particles. The total K X-ray yield is (6.5 ± 3.2) × 10^?3 per stopped antiproton. A model-dependent fit of the K X-ray spectrum gives a K_α energy of 8.9±0.3 keV, corresponding to a strong interaction shift of (?0.5±0.3) keV.     

Study on antiprotonic atoms of light nuclei and isotopes

New data on strong interaction effects in light antiprotonic atoms (N, ¹⁶O, ¹⁸O, S) are presented. For the first time an isotope effect could be observed in p?-¹⁶O/¹⁸O which is used to gain new information about the p?-n interaction in nuclei. A comparison between all existing p?-atomic data and an optical model calculation is performed, yielding a set of fit parameters for the potential.     

High-accuracy calculation of meta-stable states of antiprotonic helium atoms

The variational calculation of energy levels for the antiprotonic helium atomcule ¯p^3,4He⁺ based on molecular expansion of the wave function is presented. We have taken into account the , and components of the molecular wave function that correspond to azimuthal magnetic momentam=0, 1, 2, respectively. It has been discovered that the contribution of the component to energy levels of the atomcule is about 5 × 10^–4 a.u. and the contribution of the component is about 10^–7 a.u. The test of convergence enables us to estimate the accuracy of the obtained results to about 10^–7 a.u. which is significantly better than all previous theoretical results.     

Energy levels of light antiprotonic atoms withl>0

The fine and hyperfine structure of light antiprotonic atoms in states of angular momentuml>0 is calculated. The fine (=l-dependent) structure is dominated by vacuum polarization up to a certainl-value (l=4 for¯pp), and by relativistic effects for largerl. Meson exchange is important only in the hyperfine (=spindependent) structure of theP-states. For¯pp and¯p ³He, the hadronic part of the hyperfine structure is dominated byπ ⁰-exchange.     

Measurement of the 4f strong interaction level width in light antiprotonic atoms

The yields of the atomic 4→3 transitions in antiprotonic¹⁴N,^16,17,18O,¹⁹F, and²³Na were measured at the CERN antiproton facility, LEAR. From these, the widths Γ_up of the 4f levels were determined to be 136±19meV (¹⁴N); 603±22 meV (¹⁶O); 731±35 meV (¹⁷O); 795±23 meV (¹⁸O); 2.79±0.16 eV (¹⁹F); and 23.8±7.4 eV (²³Na).     

Possible formation of antihydrogen atoms from metastable antiprotonic helium atoms and positrons/positroniums

The possible formation of antihydrogen atoms via the collision of metastable antiprotonic helium atoms with positrons and positroniums is discussed based on the known behavior of positrons in helium media.     

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     

Isotopic effect in the decay of antiprotonic helium

An important decay channel of recently discovered metastable antiprotonic helium atoms is the emission of an electron, i.e., the Auger transition. The rate of this process for a number of states of the ³He\barpe, ⁴He\barpe and ⁶He\barpe systems is calculated and a substantial isotopic effect is found. While the reduced mass of heavy particles increases slightly with increasing nucleus mass, the Auger transition rate decreases by about a factor of three. The explanation of this strong amplification is given and the role of this effect in experiments is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.