Relativistic gravitation

Classical dynamics, often called 'molecular dynamics' when applied to atoms and molecules, is much easier than solving the many-body Schrodinger equation for a number of reasons. In particular, correlation and rearrangement are simple in classical dynamics. Fermion molecular dynamics (FMD) is a quasi-classical method for treating quantum-mechanical systems using classical equations of motion with momentum-dependent model potentials added to the usual Hamiltonian. These model potentials constrain the motion to satisfy the Heisenberg uncertainty and the Pauli exclusion principles. We discuss the foundations of the FMD model and its applications to atomic and molecular structure, ion-atom collisions, stopping powers, formation of antiprotonic atoms, and multiple ionization of atoms in strong laser fields.     

The \overline{\mbox{\sf P}}{\sf ANDA} detector at FAIR

Selected problems of collisional processes in exotic atoms are discussed. The emphasis is on the collisional effects in antiprotonic helium including formation of antiprotonic atoms, collisional quenching of hot and thermalized metastable antiprotonic helium, shift and broadening of E1 and M1 spectral lines.     

Radial compression of an antiproton cloud for production of intense antiproton beams

We report here the radial compression of a large number of antiprotons ( approximately 5 x 10(5)) in a strong magnetic field under ultrahigh vacuum conditions by applying a rotating electric field. Compression without any resonant structures was demonstrated for a range of frequencies from the sideband frequency of 200 kHz to more than 1000 kHz. The radial compression achieved is a key technique for synthesizing and manipulating antihydrogen atoms and antiprotonic atoms.     

Mass and magnetic moment of the antiproton by the exotic atom method

Precision determinations of the mass and magnetic moment of the antiproton were made by the exotic atom method. Antiprotons were stopped in lead or uranium targets. De-excitation X-rays from the antiprotonic atoms were viewed by a high resolution Ge (Li) detector. Six principal transitions of the p?Pb spectrum (16 → 15 to 11 → 10) were analyzed to deduce a value of the antiproton mass. The fine structure splittings of the 11 → 10 and 12 → 11 transitions of p?Pb and p?U were used to determine a value of the antiproton magnetic moment. Our computed values of the energy eigenvalues of the (n, l, j) levels included corrections due to vacuum polarization and higher order radiative terms, electron screening, nuclear finite size and nuclear polarization. In the case of the p?U data, an additional shift due to the dynamic E2 mixing of nuclear rotational levels with antiprotonic orbital levels was included. Noncircular transitions were included in the analysis of the data. The values obtained for the antiproton mass and magnetic moment, 938.179±0.058 MeV and ? 2.791±0.021 nuclear magnetons, respectively, are compared with the corresponding quantities pertaining to the proton, 938.2796 ± 0.0027 MeV and +2.793 nuclear magnetons, respectively (error 1.1 × 10^?6 nuclear magnetons).     

Scattering of low energy pions by 12C, 40Ca, 58,60,64Ni and the anomaly in pionic atoms

Several cases of anomalously small level shifts and widths are known in pionic atoms. These lead to pion-nucleus potentials which are different from those describing all other “normal” pionic atoms. Data on the elastic scattering of 19.5 MeV π^± by ¹²C and ⁴⁰Ca and 30 MeV π^± by ^58,60,64Ni is in very good agreement with predictions made with normal potentials and clearly rule-out potentials obtained from the “anomalous” cases.     

Control of Non-Neutral Plasmas and Generation of Ultra-Slow Antiproton Beam

The Antiproton Decelerator (AD) devoted primarily to atomic physics experiments has been stably operated since 2000. Until now, three proposals have been approved, two of which are on the production and spectroscopy of antihydrogen, and the third one is on atomic collisions and precision spectroscopy of antiprotonic atoms, ASACUSA collaboration. One of the unique features of the ASACUSA collaboration is to develop intense slow and ultra slow antiproton beams of high quality, which will open a new multidisciplinary field involving atomic physics, nuclear physics and elementary particle physics. The ultra slow antiprotons will be prepared by combining the AD (down to 5.3 MeV), the RFQD (Radio Frequency Quadrupole Decelerator) (down to several tens keV), and an electron cooling device which will be called “MUSASHI” (Monoenergetic Ultra Slow Antiproton Source for High-precision Investigations) (down to several eV). MUSASHI produces the eV antiproton beam through an electron cooling of trapped antiprotons and a radial compression followed by an extraction through a transport beam line. The transport beam line is specially designed so that the pressure at the trap region can be maintained more than six orders of magnitude better than the collision region and at the same time the transport efficiency is kept at almost 100%. The ultra slow antiproton beam allows for the first time to study collision dynamics such as antiprotonic atom formation and ionization processes under single collision conditions, and also to study spectroscopic nature of various metastable antiprotonic atoms such as p, He⁺, He⁺⁺, etc. Metastable p are particularly interesting because they allow to make high precision spectroscopy of two body exotic atoms. Production and spectroscopy of antiprotonic atoms consisting of unstable exotic nuclei will also be discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of different ion stopping models on calculated parameters of the radiation damage of materials

Direct numerical solution of the Boltzman transport equation for incident ions and knocked-off atoms of the target is applied for range and damage calculations. The influence of physical parameters in a model of ion stopping in matter on the obtained range and damage distribution is investigated in the range of ion energies from 1 KeV to 1 MeV. All the examined interatomic potentials give close values of mean depths and higher moments of range and damage distributions. The influence of differences in electronic stopping is also studied. The obtained results are compared with experimental data and the results of other calculations.     

Kaonic helium atoms

Recent progress on the x-ray spectroscopy of kaonic helium atoms as well as on the precision laser spectroscopy of antiprotonic helium atoms are presented. Some historical background connecting these two exotic helium atoms is also discussed.     

The {\bar p}-He atom – an antiproton trap

The experiments on metastable antiprotonic helium atoms are reviewed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Microwave spectroscopy measurements of the hyperfine structure in antiprotonic 3He

We shall present here the first experimental results for microwave spectroscopy of the hyperfine structure of antiprotonic He-3 and a comparison to numerical simulations of the measurement. Due to the helium nuclear spin, antiprotonic He-3 has a more complex hyperfine structure than antiprotonic He-4 which has already been studied before. Thus a comparison between theoretical calculations and the experimental results will provide a more stringent test of the three-body quantum electrodynamics (QED) theory. The comparison of measured data to simulations allows to investigate the collisional processes between the helium atoms of the target medium and the antiprotonic helium atomcules. The collision rates can not be calculated exactly, but estimated by comparison of numeric simulations with the experimental results. Two out of four super-super-hyperfine (SSHF) transition lines of the (n, L)?=?(36, 34) state were observed. The measured frequencies of the individual transitions are 11.12559(14)?GHz and 11.15839(18)?GHz, less than 1?MHz higher than the current theoretical values, but still within their estimated errors. The frequency difference between the two lines also agrees with theoretical calculations.     

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.     

Measurement of balmer and lyman X-rays in antiprotonic hydrogen isotopes at pressures below 300 hPa

X-Rays of Balmer and Lyman transitions in antiprotonic hydrogen and of Balmer transitions in antiprotonic deuterium were observed at pressures below 300 hPa using Si(Li) semiconductor detectors. The measurement was performed at the LEAR-facility at a beam momentum of 202 MeV/c. In order to stop antiprotons in a low pressure gaseous target with high efficiency, a novel technique, the cyclotron trap has been used. Absolute yields were determined and compared with cascade calculations. A distinct difference in the cascade of antiprotonic hydrogen and deuterium is found. The parameters of strong interaction in antiprotonic hydrogen are determined to be? _1s=?(620±100) eV,Γ _1s=(1130±170) eV andΓ _2p=(32±10) meV.     

Antiprotonic helium

Recent measurements of the 2p and 3d atomic levels and lifetimes in antiprotonic helium seem to indicate an inconsistency, when interpreted in terms of an optical potential based on parameters extracted from heavier antiprotonic atoms. Here it is shown that this inconsistency is removed, when the data is described in terms of a multiple scattering formalism that treats correctly the number of nucleons and their correlations in the rescattering terms.     

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.     

Optical-model analysis of exotic atom data: (II). Antiprotonic and sigma atoms

Data for antiprotonic and sigma atoms are fitted using a simple optical model with a potential proportional to the nuclear density. The potential strength can be related to the free hadron-nucleon scattering length using a model due to Deloff. A good overall representation of the data is also obtained with a black-sphere model.     

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.     

Atomic Spectroscopy and Collisions Using Slow Antiprotons – the ASACUSA Experiment at CERN-AD

Hyperfine Interactions - The scope of the ASACUSA experiment is the study of atomic physics with low-energy antiprotons, namely high-precision spectroscopy of antiprotonic atoms, the study of...     

Antiproton-proton annihilation at rest in H2 gas into π+ π− π0

Zeitschrift für Physik C Particles and Fields - Annihilation of antiprotonic hydrogen atoms into π+ π? π0 is studied by stopping antiprotons from LEAR in hydrogen gas. Two...     

Unified approach to nuclear densities from exotic atoms

Parameters of nuclear density distributions are derived from least-squares fits to strong interaction observables in exotic atoms. Global analyses of antiprotonic and pionic atoms show reasonably good agreement between the two types of probes regarding the average behaviour of root-mean-square radii of the neutron distributions. Apparent conflict regarding the shape of the neutron distribution is attributed to different radial sensitivities of these two probes.     

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.