Search

Recent measurements of fine-structure splitting in $$\bar p$$ atoms ofYb are analysed. Effects of nuclear deformation are calculated. The strength of nuclear spin-orbit coupling is determined and its implications on the N $$\bar N$$ potential are discussed. [ABSTRACT FROM AUTHOR]

The first results are presented of electron cooling experiments in the Low-Energy Antiproton Ring (LEAR) at CERN, performed with a proton beam of about 50 and 21 MeV. The number of stored protons ranged from 10 to 3 × 10. Cooling times of the order 1 s and proton drag rates of up to 0.7 MeV/s were obtained. The capture of cooling electrons by protons producing hydrogen atoms was used to derive an effective electron temperature (0.25 eV). From the angular profile of the neutral hydrogen beam an upper limit of 3π mm.mrad could be deduced for the horizontal equilibrium proton-beam emittance. The lowest equilibrium momentum spread was 2 × 10 (FWHM), as derived from the analysis of the longitudinal Schottky signal. This Schottky signal exhibited an unusual behaviour with beam intensity and under certain conditions showed a doublepeak structure which was associated with collective beam noise. For very cold beams transverse instabilities were observed, which resulted in a rapid spill-off of protons and a stabilization at lower intensities. The threshold of these instabilities was raised by heating the proton or the electron beam. The cooling of a bunched proton beam was investigated. The reduction of the proton momentum spread led to bunch lengths of about 2 m, containing 3 × 10 protons. [ABSTRACT FROM AUTHOR]

The strong ¯ p-nucleus spin-orbit interaction was investigated in a measurement of the strong-interaction effects of the 9→8 transition in ¯ pYb 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 Δ E=2408±26 eV consists of the electromagnetic fine-structure splitting Δ E=2350 eV and an additional splitting Δɛ=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 ¯ pBa, 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 forYb may be attributed to a spin-orbit (LS) term in the complex strong-interaction potential. [ABSTRACT FROM AUTHOR]

It is shown that electron pick-up from a cooling electron beam can be used to extract an ion beam from a storage ring. The technique is described and extraction times are estimated. A few applications for medium-energy ion storage rings are given. [ABSTRACT FROM AUTHOR]

The yields of the atomic 4→3 transitions in antiprotonicN,O,F, andNa were measured at the CERN antiproton facility, LEAR. From these, the widths Γ of the 4 f levels were determined to be 136±19meV (N); 603±22 meV (O); 731±35 meV (O); 795±23 meV (O); 2.79±0.16 eV (F); and 23.8±7.4 eV (Na). [ABSTRACT FROM AUTHOR]

The X-ray spectrum emerging from a liquid-hydrogen target when stopping antiprotons was measured with high resolution in order to determine the strong interaction shift and width of the atomic 1 s level. Owing to strong Stark quenching only weak structures could be observed. The upper limit of the yield of any one of the K-series transitions is 3.5×10 (95% C.L.) per stopped antiproton, assuming no broadening of the 1 s level. Possible identifications of the weak lines with the K-series transitions are discussed. [ABSTRACT FROM AUTHOR]

The X-ray spectrum associated with K stopping in liquid hydrogen was measured with high resolution Si(Li) detectors. The total K X-ray yield is not larger than 8×10 per stopped K assuming no line broadening. A weak line pattern was found, which was tentatively ascribed to the K H K-series X-rays. The shift and width of the 1 s level, deduced from this pattern, are ε=+270±80 eV and Γ=560±260 eV, respectively. [ABSTRACT FROM AUTHOR]

The absorption of stopped π inTa andBi has been investigated by studying prompt and delayed γ-ray spectra. Absolute cross-sections for the yield of isotopes per captured π in ( π, xn) reactions, as well as the relative probability of populating nuclear states of different spins have been measured for the hafnium and lead isotopes, respectively. A spin as high as 20 has been observed in the production ofPb. The ground-state rotational bands of the hafnium isotopes are excited to spin values up to 16. Neutron multiplicities as large as 15 have been observed for both targets. A neutron multiplicity of ≃8 is most probable for both tantalum and bismuth targets. The strong interaction monopole energy shift ɛ and width Γ for the 4 f level are found to be ε(Ta)=540±100eV; ɛ(Bi)=1790±150 eV; Γ(Ta)=225±57 eV; Γ(Bi) =1166±70 eV. The quadrupole moments, determined from the hyperfine splitting of the 4 f pionic atom level, are Q=3.30±0.06 b and Q=}-0.50±0.08 b forTa andBi, respectively. [ABSTRACT FROM AUTHOR]

Energies and widths of pionic 3 d-2 p transitions ofZn,Ge, andAs have been measured with a Ge detector. The values of the 2 p shifts obtained from the measurement ε(Zn)=7.0±1.4keV, ε(Ge)=5.5±0.9keV, and ε(As)=4.6±0.9keV show a decreasing behaviour for large Z, which is caused by an increasing s-wave contribution as predicted by theory. [ABSTRACT FROM AUTHOR]

Antiprotonic x ray spectra ofNd andNd have been measured with Ge detectors. Different attenuations of the two fine structure components of the antiprotonic x ray group (n=9 → n=8) due to the E2 nuclear resonance effect were observed inNd. Experiment and present theory disagree. We propose to supplement the ¯p-nucleus potential by a spin-orbit term. [ABSTRACT FROM AUTHOR]