Laser spectroscopy of the antiprotonic helium atom–molecule {\bar pHe}^+

The metastable antiprotonic helium atom–molecule (in short, atomcule), , which was discovered in 1991 as being the cause of the anomalous longevity of antiprotons with an overall lifetime of about 3 μs, now provides an exotic playground for laser spectroscopy, helped by the existence of numerous long lived states with 1–2 μs lifetimes. This three body system is characterized by a large angular momentum l ∼ 38 of coupled with the electron in the 1s ground orbital, and looks like an exotic hydrogen isotope with many different “nuclear states” as well as an exotic molecule with two centers (He²⁺ and ). So far, a number of laser resonance transitions have been identified. The present talk will cover the following topics: (1) high precision spectroscopy in comparison with three body theories involving the relativistic effect and QED, and (2) hyperfine structure of ;laser-microwave triple resonance. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

High precision X-ray spectroscopy in hydrogen-like fermionic and bosonic atomic systems

Some time after its formation an exotic atom may be considered a hydrogen-like system consisting of a nucleus and an exotic particle in a bound state. In this situation it is an ideal tool to study cascade properties, while for the innermost orbits it can be used to probe the interaction with the nucleus. From an extended series of experiments using high resolution X-ray spectroscopy for both aspects typical examples are reported and preliminary results are given: 1. To determine the complex scattering length in H the hyperfine transitions have been measured. 2. To determine the pion mass the 5 4 transitions in N have been studied. In all cases a major contribution to the uncertainty originates from the calibration. Therefore a new method is proposed that will establish a universal set of high precision calibration lines for pionic, muonic and electronic systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

The nature of the {\bar p} metastability in helium

A new interpretation of the nature of the metastable states of antiprotons in helium is proposed. The first step is the formation of an ion ( ), which shall be called “ioncule”. After its decay a neutral “atomcule” ( ) is formed which was observed in the experiments on metastable antiprotonic helium. This model explains the experiments in a natural way, in particular the quenching by atomic and molecular admixtures and the pressure dependence of quenching in pure helium. At high helium densities the ioncule creates a vacuum bubble in helium. It is shown that the annihilation of slowed-down can be suppressed at helium pressures of ∼ 10 000 bar. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Theoretical analysis of collisional shift and broadening of antiprotonic helium spectral lines

Effect of medium density on shift and broadening of ( ) spectral lines is considered in the framework of binary-collision approximation with an effective ( )–He potential including the long-range attraction and short-range repulsion. Quantum calculations of the scattering phase shifts at reasonable values of the potential parameters allow to explain the main features of the observed density effect on the shape of ( ) spectral lines in low-temperature helium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Auger decay rates of antiprotonic helium

Auger decay rates of the metastable antiprotonic helium ^3,4He e are calculated. The variational method and solution of coupled differential equations are combined to determine the initial metastable state wave function. Besides metastable states, the calculation reveals specific short-lived states of the antiprotonic helium with an essentially different structure of the wave function. An effect of mixture of the wave functions is taken into account to calculate the decay rate for a few metastable states, which are close in energy to the short-lived ones. This revised version was published online in August 2006 with corrections to the Cover Date.     

NMR dynamics in disordered magnets

The excitation dynamics of site diluted magnets can be described at low energies (long length scales) by magnons, and above a crossover frequency, ω_c, (short length scales) by fractons. The density of fracton states is given by , where is the fracton dimensionality. Dilution gives rise to a characteristic length ξ∝(p−p _c)^ν, wherep _c is the critical concentration for (magnetic) percolation. The crossover frequency ω_c is proportional to ξ^-1[1+(θ/2)], where θ is the rate at which the diffusion constant decays with distance for diffusion on an equivalent network. A fractal dimensionD describes the density of magnetic sites on the infinite network, and . For percolating networks, for all dimensions ≥2. Neutron scattering structure factor measurements by Uemura and Birgeneau compare well with calculations using fracton concepts. Magnons are extended at low energies, while the fracton states are geometrically localized, with a wave function envelope proportional to exp . Here, is the fracton length scale at frequency ω. The exponentd _ϕ lies between 1 andd _min, the chemical length index (of the order of 1.6 in three dimensions). The localization of the magnetic excitations causes a spread in the NMR relaxation rates. A given nuclear moment will experience only a limited set of fracton excitations, resulting in an overall non-exponential decay of the NMR relaxation signal. When strong cross-relaxation is present, the relaxation will be exponential, but the temperature dependence will be strongly altered from the concentrated result.     

Nuclear moments of neutron deficient iridium isotopes from laser spectroscopy

Laser spectroscopy measurements have been performed on neutron deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d⁷6s^{2 4}F_9/2 → 5d⁷6s6p ⁶F_11/2 at 351.5 nm have been studied for the ^182–189Ir, and ^191,193Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the HFS measurements and the changes of the mean square charge radii from the IS measurements. A large mean square charge radius change between ¹⁸⁷Ir and ¹⁸⁶Ir and between and has been observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Antiproton–hydrogen and antihydrogen–hydrogen annihilation at sub‐Kelvin temperatures

The main properties of the interaction of ultra low‐energy antiprotons (E⩽10^-6 a.u.) and antihydrogen with atomic hydrogen are established. Elastic and inelastic cross‐sections and Protonium formation spectrum are calculated within quantum mechanical coupled channels approach. The results of calculations differ strongly from predictions made by extrapolation of semiclassical models to the energy domain of interest. It is shown that the main feature of the observables behaviour is determined by existence of a family of H, H near‐threshold metastable states. This revised version was published online in July 2006 with corrections to the Cover Date.     

NMRON studies of MnBr2 \cdot 4H2O in applied magnetic fields

NMRON studies for the ⁵⁴Mn transitions in antiferromagnetic MnBr₂ 4H₂O, in the millikelvin regime, are presented and discussed. New values are given for (i) the sum of the effective molecular exchange and magnetic anisotropy fields acting on the Mn²⁺ ions, =2.23(2) T, and (ii) the magnetic dipole hyperfine splitting, A=-201.99(1) MHz, electric quadrupole hyperfine splitting P=0.049(8) MHz and pseudoquadrupole splitting =1.63(2) MHz for the ⁵⁴Mn nuclei.     

Low Temperature Hydrogen Antihydrogen Interactions

In view of current interest in the trapping of antihydrogen ( ) atoms at low temperatures [1–3], we have carried out a full four-body variational calculation to determine s-wave elastic phase shifts for hydrogen antihydrogen scattering, using the Kohn Variational Principle. Terms outside the Born–Oppenheimer approximation have been taken into account using the formalism of Kołos and Wolniewicz [4]. As far as we are aware, this is the first time that these terms have been included in an H scattering calculation. This is a continuation of earlier work on H– interactions [5–7]. Preliminary results differ substantially from those calculated using the Born–Oppenheimer approximation [8–10]. A method is outlined for reducing this discrepancy and taking the rearrangement channel into account. This revised version was published online in August 2006 with corrections to the Cover Date.     

Energy dependence of the charge exchange reaction from muonic hydrogen to oxygen

The charge exchange reaction of negative muons from the atom to oxygen has been measured in gaseous mixtures of H₂ + O₂. The measurements were performed at three different relative oxygen concentrations ranging from 0.2% to 0.8% and total pressures 3.5–15 bar. A mean transfer rate of , describing the transfer from the ground state of thermalized atoms to oxygen, was determined. In order to investigate the energy dependence of the transfer rate, Monte Carlo simulations of the thermalization and the muon transfer were carried out. The comparison of measured and simulated time spectra yielded an epithermal transfer rate =3.9 10¹¹ s^-1 in the energy interval 0.12–0.22 eV. The analysis with the model of Two components shows that all measured time spectra can be reproduced with the same set of parameters.     

Preferred Invariant Symplectic Connections on Compact Coadjoint Orbits

Let be the Haag--Kastler net generated by the (2) chiral current algebra at level 1. We classify the SL(2, )-covariant subsystems by showing that they are all fixed points nets ^H for some subgroup H of the gauge automorphisms group SO(3) of . Then, using the fact that the net ₁ generated by the (1) chiral current can be regarded as a subsystem of , we classify the subsystems of ₁. In this case, there are two distinct proper subsystems: the one generated by the energy-momentum tensor and the gauge invariant subsystem .     

Relaxation effects in the Mössbauer spectra of iron complexes with fatty acids

Six new oxo trinuclear iron(III) complexes of the type [Fe₃O(R–COO)₆(H₂O)₃] X, where X= or Cl^– and R=C₅, C₇, C₈, C₉ were synthesized and investigated by Infra Red, Mössbauer Spectroscopy and magnetic measurements. The data pointed to a high spin state (S=5/2) for iron and for antiferromagnetic interactions. The asymmetrical shape of the Mössbauer doublet and its temperature dependence was treated using the Blume relaxation model. The relaxation process is influenced by both X and R components.     

The COMPLIS experiment on neutron deficient Au, Pt and Ir isotopes

The COMPLIS (COllaboration for spectroscopic Measurements using a Pulsed Laser Ion Source) experiment is carried out at the ISOLDE Booster facility at CERN. The aim is to measure the hyperfine structure and the isotope shift of a series of radioactive laser desorbed atoms by multiple step laser ionization. This technique is especially suitable for refractory elements not directly available as beams from the isotope separator. By collecting a primary radioactive beam, it is possible to delay the laser desorption as long as necessary to obtain the particular daughter of interest. Laser spectroscopy measurements have been carried out on very neutron deficient gold, platinum and iridium isotopes. Magnetic moments μ_I, spectroscopic quadrupole moments and changes of the nuclear mean square charge radius along each isotopes series have been extracted. From some results, a detailed comparison with the predictions of the models is presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preliminary Results for Capture of Negative Muons and Antiprotons by Noble-Gas Atoms

Cross sections for capture of negative muons (μ⁻) and antiprotons ( ) by helium, neon, argon, krypton, and xenon atoms (incomplete for the two heaviest noble-gas atoms) are calculated using the fermion molecular dynamics (FMD) method. These cross sections are used to estimate the capture ratios in mixtures, but these ratios are not precise since the total energy-loss cross sections have not yet been determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

A study of the nuclear-medium influence on neutral-strange-particle production in deep-inelastic neutrino scattering

The influence of nuclear effects on the production of neutral strange particles (V ⁰) is investigated using the data obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam (with E _v =3−30 GeV) at the Serpukhov accelerator. The mean multiplicity of V ⁰ particles in nuclear interactions, , is found to exceed significantly that in “quasideuteron” interactions, . The ratio of is larger than that for π⁻ mesons, . It is shown that the multiplicity gain of V ⁰ particles can be explained by intranuclear interactions of produced pions. The text was submitted by the authors in English.     

Contribution of Sea Quarks and Gluons to the Proton Spin

Contributions of sea quark and gluon spins to the proton spin in Drell-Jahn processes and direct production of photons in proton-proton and proton-antiproton collisions are studied in the present work. Analytical expressions for two-spin asymmetries and are derived. In both processes, these asymmetries are studied and analyzed as functions of the kinematic variables , x _T, and x _F. Measurements of two-spin asymmetries and make it possible to determine the individual contributions of sea quark and gluon spins to the proton spin.