Collisional deexcitation of exotic hydrogen atoms in highly excited states

The deexcitation of exotic hydrogen atoms in highly excited states in collisions with hydrogen molecules has been studied using the classical-trajectory Monte Carlo method. The Coulomb transitions with large change of principal quantum number n have been found to be the dominant collisional deexcitation mechanism at high n. The molecular structure of the hydrogen target is shown to be essential for the dominance of transitions with large Δn. The external Auger effect has been studied in the eikonal approximation. The resulting partial wave cross-sections are consistent with unitarity and provide a more reliable input for cascade calculations than the previously used Born approximation. Received 28 May 2002 Published online 15 October 2002 RID="a" ID="a"e-mail: thomas@physik.unizh.ch     

Scattering of light exotic atoms in excited states

The differential and total cross-sections for the scattering of muonic, pionic, kaonic and antiprotonic hydrogen in excited states from atomic hydrogen have been calculated for the purpose of atomic cascade calculations. The scattering problem is treated in a fully quantum mechanical framework which takes the energy shifts and, in the case of the hadronic atoms, the widths of the ns states into account. The validity of semiclassical approximations is critically examined. Received 4 December 2001 and Received in final form 4 February 2002     

X-ray transitions from antiprotonic noble gases

The onset of antiprotonic X-ray transitions at high principal quantum numbers and the occurrence of electronic X-rays in antiprotonic argon, krypton, and xenon has been analyzed with the help of Multiconfiguration Dirac-Fock calculations. The shell-by-shell ionisation by Auger electron emission, characterised by appearance and disappearance of X-ray lines, is followed through the antiprotonic cascade by considering transition and binding energies of both the antiproton and the remaining electrons. Electronic lines could be attributed partly to specific states of the antiprotonic atom de-excitation.     

Kinetics of muon catalyzed fusion processes in solid H/D mixture

This paper presents the final results of an experimental study of the kinetics of the muon catalysed fusion (MCF) in solid hydrogen-deuterium mixtures (H/D) at a temperature of 3 K. The experiment E742 was carried out on a TRIUMF meson facility in Canada. Four exposures were performed at different deuterium concentrations in the H/D mixture: c_d = 0.0005, 0.02, 0.15 and 0.75. A simultaneous analysis of the measured time distributions of the 5.5 MeV γ-quanta and the 5.3 MeV conversion muons obtained from nuclear fusion in the pdμ molecule allowed to extract the values of MCF chain parameters in the H/D mixture: the fusion partial rates for different nuclear spin states of the pdμ molecule, and the pdμ molecule formation rate. The experimental data fitting procedure was conducted in two ways: using solely the analytical formulae describing the kinetics of the MCF processes in the H/D mixture, and the detailed Monte Carlo simulation of the entire experiment. The results obtained by these two methods are consistent with each other and confirm the existence of the Wolfenstein-Gerstein effect.     

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     

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     

From solar proton burning to pionic deuterium through the Nambu-Jona-Lasinio model of light nuclei

Within the Nuclear Nambu-Jona-Lasinio model of light nuclei (the NNJL model), describing strong low-energy nuclear interactions, we compute the width of the energy level of the ground state of pionic deuterium. The theoretical value fits well the experimental data. Using the cross-sections for the reactions _e + d p + p + e^- and _e + d p + n + _e, computed in the NNJL model, and the experimental values of the events of these reactions, detected by the SNO Collaboration, we compute the boron neutrino fluxes. The theoretical values agree well with the experimental data and the theoretical predictions within the Standard Solar Model by Bahcall. We argue the applicability of the constraints on the astrophysical factor for the solar proton burning, imposed by helioseismology, to the width of the energy level of the ground state of pionic deuterium. We show that the experimental data on the width satisfy these constraints. This testifies an indirect measurement of the recommended value of the astrophysical factor for the solar proton burning in terrestrial laboratories in terms of the width of the energy level of the ground state of pionic deuterium.     

Electron — positron quantum droplets

A new physical object, electron-positron quantum droplet, is suggested. Structure, stability and dynamics of such objects are discussed. The analysis is based on the non-relativistic self-consistent local-density approximation. An essential role of many-body effects in the formation of the droplets is demonstrated. Their properties are compared with the known physical objects such as metal clusters and clusters of excitons in a solid.     

Time-evolution of cascade processes of muonic atoms in hydrogen-helium mixtures

The time-dependence of the population of muonic hydrogen states in hydrogen-helium mixtures is calculated for principal quantum number n. The number of muons transferred to helium nuclei is also determined. The dependence of the population of the ground state of muonic hydrogen on time and target density and the helium concentration is also considered. The results are in agreement with recent experimental data. The comparison of the calculated yield of K lines of X-ray in pure hydrogen and deuterium with experimental data indicates the essential role of the Coulomb deexcitation process. Possible Stark mixing is also analysed. Received 17 February 1999 and Received in final form 9 June 1999     

Antiproton-deuteron annihilation at low energies

Recent experimental data obtained by the OBELIX collaboration on ˉpD and ˉp⁴ He total annihilation cross sections are analyzed. The combined analysis of these data with existing antiprotonic atom data allows, for the first time, the imaginary parts of the S-wave scattering lengths for the two nuclei to be extracted. The obtained values are: Im a^sc ₀= [−0.62 ± 0.02 stat) ± 0.04 (sys)] fm for ˉpD and Im a^sc ₀= [−0.36 ± 0.03 (stat)^+0.19 _−0.11 (sys)] fm for ˉp ⁴He. This analysis indicates an unexpected behaviour of the imaginary part of the ˉp-nucleus S-wave scattering length as a function of the atomic weight A: |Im a^sc ₀| (macr;pp) > |Im a^sc ₀| (ˉpD) > |Im a^sc ₀ (ˉp⁴ He). Received: 3 November 1999 / Revised version: 15 December 1999     

On kaonic hydrogen. Phenomenological quantum field theoretic model revisited

We argue that due to isospin and U-spin invariance of strong low-energy interactions the S-wave scattering lengths a ⁰ ₀ and a ¹ ₀ of ˉN scattering with isospin I = 0 and I = 1 satisfy the low-energy theorem a ⁰ ₀ +3a ¹ ₀ = 0 valid to leading order in chiral expansion. In the model of strong low-energy ˉN interactions at threshold (Eur. Phys. J. A 21, 11 (2004)) we revisit the contribution of the Σ(1750) resonance, which does not saturate the low-energy theorem a ⁰ ₀ +3a ¹ ₀ = 0, and replace it by the baryon background with properties of an SU(3) octet. We calculate the S-wave scattering amplitudes of K^-N and K^-d scattering at threshold. We calculate the energy level displacements of the ground states of kaonic hydrogen and deuterium. The result obtained for kaonic hydrogen agrees well with recent experimental data by the DEAR Collaboration. We analyse the cross-sections for elastic and inelastic K^-p scattering for laboratory momenta 70MeV/c < p _K < 150MeV/c of the incident K^--meson. The theoretical results agree with the available experimental data within two standard deviations.     

On kaonic deuterium. Quantum field-theoretic and relativistic covariant approach

We study kaonic deuterium, the bound K^-d state A_{K d}. Within a quantum field-theoretic and relativistic covariant approach we derive the energy level displacement of the ground state of kaonic deuterium in terms of the amplitude of K^-d scattering for arbitrary relative momenta. Near threshold our formula reduces to the well-known DGBT formula. The S-wave amplitude of K^-d scattering near threshold is defined by the resonances (1405), (1750) and a smooth elastic background, and the inelastic channels K^-d NY and K^-d NY, where Y = ^±,^{0} and ^{0}, where the final-state interactions play an important role. The Ericson-Weise formula for the S-wave scattering length of K^-d scattering is derived. The total width of the energy level of the ground state of kaonic deuterium is estimated using the theoretical predictions of the partial widths of the two-body decays A_Kd NY and experimental data on the rates of the NY pair production in the reactions K^-d NY. We obtain _{1s} = (630±100)eV. For the shift of the energy level of the ground state of kaonic deuterium we predict _{1s} = (325±60)eV.     

Precision measurements of kaonic atoms at DA ΦNE and future perspectives

The DAΦNE electron-positron collider at the Frascati National Laboratories has made available a unique “beam" of negative kaons providing unprecedented conditions for the study of the low-energy kaon-nucleon interaction, a field still largely unexplored. The DEAR (DAΦNE Exotic Atom Research) experiment at DAΦNE and its successor SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) aim at a precision measurement of the strong-interaction shift and width of the fundamental 1s level, via the measurement of the X-ray transitions to this level, for kaonic hydrogen and kaonic deuterium. The aim is to extract the isospin-dependent antikaon-nucleon scattering lengths and to contribute to the understanding of aspects of chiral symmetry breaking in the strangeness sector.     

Twofold-broken rational tori and the uniform semiclassical approximation

We investigate broken rational tori consisting of a chain of four (rather than two) periodic orbits. The normal form that describes this configuration is identified and used to construct a uniform semiclassical approximation, which can be utilized to improve trace formulae. An accuracy gain can be achieved even for the situation when two of the four orbits are ghosts. This is illustrated for a model system, the kicked top. Received 3 August 1999     

Fermion gases in magnetic fields: a semiclassical treatment

The study of quantum degenerate gases has received much interest in these last years essentially thanks to the extremely important experimental results of the achievement of Bose-Einstein condensation of atoms and, very recently, of almost complete degeneracy of atomic fermion gases. Here we want to present the results of a semi-analytical method for the study of an interacting degenerate fermion gas based on semiclassical kinetic theory; special care has been devoted to the study of a rotating electron gas, in a cylindrically symmetrical configuration, radially confined by a uniform magnetic field. The model will lead to a particular Thomas-Fermi equation which is generalized to take into account finite temperature and average velocity of the gas, and which is further developed to consider the effects of external fields. Received 10 March 2000     

Propagation of light-pulses at a negative group-velocity

This paper deals with the apparent superluminal propagation of electromagnetic pulses in a linear dispersive medium. One specifically examines the possibility that the pulse leaving the medium may be nearly identical to the incident one (low distortion) and in significant advance of it (strongly negative group-delays). Favourable conditions are obtained in a dilute medium where the required anomalous dispersion originates in an ensemble of narrow absorption or gain lines. Analytical expressions of the advancement of the pulse centre-of-gravity and of the lowest order distortion are established from the transfer-function of the medium. The experiments already achieved with arrangements involving a single absorption-line or a gain-doublet are analysed in detail and compared. The considerable difficulties to overcome in order to attain advancements comparable to the pulse width without important distortion are pointed out. New and promising schemes involving a narrow dip in a gain profile or absorption-doublets are proposed. Received 4 July 2002 / Received in final form 8 November 2002 Published online 4 February 2003 RID="a" ID="a"e-mail: bruno.macke@univ-lille1.fr RID="b" ID="b"Unité Mixte de Recherche de l'Université et du CNRS (UMR 8523)     

Radiative transitions in highly ionised silicon-like ions

Transition energies, oscillator strengths and transition probability values for radiative transitions have been calculated for the highly ionised atoms of Si isoelectronic sequence from Mn¹¹⁺ to Kr²²⁺ for the singly excited states up to principal quantum number n = 7. Time-dependent coupled Hartree-Fock (TDCHF) theory has been used to estimate such transition properties. Most of the results for the oscillator strengths and transition probabilities are new. Transition energies agree reasonably well with available spectroscopic values. Received 25 January 2000 and Received in final form 24 October 2000     

Statistics of self-crossings and avoided crossings of periodic orbits in the Hadamard-Gutzwiller model

Employing symbolic dynamics for geodesic motion on the tesselated pseudosphere, the so-called Hadamard-Gutzwiller model, we construct extremely long periodic orbits without compromising accuracy. We establish criteria for such long orbits to behave ergodically and to yield reliable statistics for self-crossings and avoided crossings. Self-encounters of periodic orbits are reflected in certain patterns within symbol sequences, and these allow for analytic treatment of the crossing statistics. In particular, the distributions of crossing angles and avoided-crossing widths thus come out as related by analytic continuation. Moreover, the action difference for Sieber-Richter pairs of orbits (one orbit has a self-crossing which the other narrowly avoids and otherwise the orbits look very nearly the same) results to all orders in the crossing angle. These findings may be helpful for extending the work of Sieber and Richter towards a fuller understanding of the classical basis of quantum spectral fluctuations. Received 17 July 2002 Published online 29 November 2002     

Σ- atoms and the ΣN interaction

It is shown that among four models of the Nijmegen baryon-baryon interaction only model F --which leads to a repulsive potential felt by the Σ hyperon inside the nucleus-- is consistent both with the analysis of Σ^- atoms and of the (K ^-,π) reactions. The Nijmegen models are used to determine the strong complex single-particle (s.p.) potential of Σ^-, and to calculate the strong-interaction shifts and widths of the lowest observed levels of Σ^- atoms. The results obtained with model F are in best agreement with the experimental data. Received: 15 January 2002 / Accepted: 14 March 2002