Optische Messung der Elektronenstoß-Anregung von Helium,Neon und Krypton im Schwellenbereich mit hoher Energieauflösung

The optical electron-impact excitation functions ofp-levels of He, Ne and Kr show a sharp increase at threshold which is limited by the resolution of the apparatus (appr. 50 meV). Some ten meV above threshold most of them have a first resonance which is followed by several further ones. In Neon there are two strong “W”-profile double resonances the parent states of which could be the 2p ⁵ np (n=4, 5) states of the Ne-atom.     

On parity violation in α-decay

The Fermi liquid model of α-decay and the shell-model wave functions of Zuker, Buck and McGrory are used to calculate the “regular” and “irregular” (parity non-conserving) α-widths to some J^πT = 2±0 low-lying levels of ¹⁶O. The Pauli corrections in the α-channel wave functions are taken into account.     

Systematic trends in the beta minus strength functions of neutron-rich rubidium isotopes

Experimental β^?-strength functions (S_β) are presented for the odd-mass Rb isotope sequence A=89to97. As expected from general nuclear structure considerations, but in contrast to present purely statistical concepts, these strength functions exhibit well separated “pygmy” resonances and a systematic behaviour as a function of mass number and β-decay energy.     

Color-conductivity in nuclei and the EMC-effect

We advocate that gluons and quarks of sufficiently short wavelengths are delocalized in nuclei. This hypothesis leads us to structure functions measured in μ-nucleus scattering, which depend at fixedx only on the ratio of the resolving power 1/Q and the radius of the nucleusR _A, whereA denotes the mass number of the nucleus. Thus we suggest that the structure functionF ₂(x, Q ²,A) per nucleon of an isoscalar nucleusA scales essentially as \(F_2 (x,Q^2 ,A) = \tilde F_2 (x,R_A^2 \cdot Q^2 )\) with a universal function \(\tilde F_2\) . The ratio of the so obtained structure functions of iron to deuterium agrees rather well with the one measured recently by the European Muon Collaboration. This observation implies that nuclei are “color-insulators” at lowQ ², but “color conductors” at largeQ ².     

The electron energy loss spectrum of EuO(100)

Energy losses of 200 eV to 2 keV electrons reflected from a disordered EuO(100) crystal show a bulk plasmon loss consistent with just less than six “quasi free” electrons per EuO unit, and 5p → nd resonance losses above the 5p threshold. The ratio of intensity of the 4d¹⁰ 4fⁿ⁰ → 4d⁹ 4fⁿ⁺¹ “giant resonance” loss at 142 eV to the corresponding direct recombination feature varies with energy, while the direct recombination and related Auger channels show similar energy dependence.     

Relaxation in a Duffing potential

The solution of the equation of motion for a particle in a Duffing potential, V(x) = α₁x²/2 + α₂x⁴/4 (α₁, α₂ > 0) for arbitrary anharmonicity strength is characterized by the presence of odd frequencies which implies that velocity and position autocorrelation functions of such an oscillator in a microcanonical ensemble are also characterized by odd frequencies. It is, however, non-trivial to determine whether such “discrete” frequencies also characterize the autocorrelation functions in a canonical ensemble as discussed recently by Fronzoni et al. (J. Stat. Phys. 41 (1985) 553). We recover and extend upon the results of Fronzoni et al. to show analytically, via Mori-Lee theory, that “essentially discrete” (i.e. well-defined peaks with finite but “small” width) temperature-dependent frequencies characterize the autocorrelation functions in a canonical ensemble.     

Threshold singularities of theS-matrix and convergence of Haag-Ruelle approximations

We establish a one-to-one correspondence between the continuity properties of theS-matrix at the 2-particle threshold and the rate of convergence of the Haag-Ruelle approximations ψ(t) for asymptotic 2-particle states ψ with smooth wavefunctions. It turns out that the norm distance ∥ψ?ψ(t)∥ approaches 0 liktt ^?5/4 if theS-matrix has the normal threshold singularities and liket ^?3/4 in the exceptional case where the threshold has “absorbed” a bound state. These connections are valid both in relativistic quantum field theory and in non-relativistic models with short range interaction.     

Higher order corrections to the processe^ + e^ - \to v\bar vy

A calculation of the neutrino counting reaction \(e^ + e^ - \to v\bar vy\) is presented and implemented in a Monte Carlo generator of unweighted events. The non-photonic corrections are included following the star-scheme. The photonic corrections have been exponentiated following the “inductive” and the “structure functions” approach. For a realistic experimental set-up, the total corrections around theZ ⁰ pole amount to ～5% with respect to the one-loop result. The final precision achieved is better than 1%.     

Amorphous GaP produced by ion implantation

Two types of non-crystalline states (“disordered” and “amorphous”) of GaP were produced by using ion implantation and post annealing. A structural-phase-transition-like annealing behaviour from the “disordered” state to the “amorphous” state was observed.The ion dose dependence and the annealing behaviour of the atomic structure of GaP implanted with 200 keV ? N⁺ ions were studied by using electron diffraction, backscattering and volume change measurements. The electronic structure was also investigated by measuring optical absorption and electrical conductivity.The implanted layer gradually loses the crystalline order with the increase of the nitrogen dose.The optical absorption coefficient α and electric conductivity σ of GaP crystals implanted with 200 keV?N⁺ ions of 1 × 10¹⁶ cm^?2 were expressed as αhν = C(hν ? E₀)ⁿ and log $\text{σ = A ? BT}{}^{\mathrm{<mtext>-</mtext><mtext>1</mtext><mtext>4</mtext>}}$, respectively. Moreover, the volume of the implanted layer increased about three percent and the electron diffraction pattern was diffused halo whose intensity monotonically decreases along the radial direction. These results indicate that the as-implanted layer has neither a long range order nor a short range order (“disordered state”).In the sample implanted at 1 × 10¹⁶ cm^?2, a structural phase-transition-like annealing stage was observed at around 400°C. That is, the optical absorption coefficient α abruptly fell off from 6 × 10⁴ to 7 × 10³ cm^?1 and the volume of the implanted layer decreased about 2% within an increase of less than 10 degrees in the anneal temperature. Moreover, the short range order of the lattice structure appeared in the electron diffraction pattern. According to the backscattering experiment, the heavily implanted GaP was still in the non-crystalline state even after annealing.These facts lead us to believe that heavily implanted GaP, followed by annealing at around 400°C, is in the “amorphous” state, although as-implanted Gap is not in the “amorphous” state but in the “disordered” state.     

QCD at lowQ 2—A correspondence relation for moments of structure functions

The precocious validity of QCD predictions in deep inelastic lepton nucleon scattering ande ⁺ e ^? annihilation is interpreted as a signal for an underlying “correspondence principle” relating perturbative and nonperturbative physics on theQ ² average. Correspondence relations for nonsinglet moments of deep inelastic structure functions are formulated, discussed and successfully tested against experiment. The relations provide an independent determination of the QCD ?-parameter from lowQ ² data in perfect agreement with results from largeQ ² analyses.     

Is the glass transition in some super-cooled polyphenyls preceded by molecular cluster formation?

A recently reported anomalous behaviour of the positronium annihilation rate with temperature in certain super-cooled organic liquids is explained in terms of a simple free-volume model modified in the presence of molecular cluster formation. This model apart from showing the entropic origin of the phenomenon accounts for the existence of the transition temperature “T_r” much above the glass-transition temperature T_g. It also predicts for the threshold temperature “T_r” fo clusters to commence formation a value of 310_-7.0^+8.0 K as against the experimental value of 304 K for ortho-terphenyl.     

The linked dipole chain model for DIS

The Linked Dipole Chain Model provides an interpolation between the regions of high Q² (DGLAP) and low x moderate Q² (BFKL) in DIS. It is a reformulation and a generalization of the results obtained by Ciafaloni, Catani, Fiorani and Marchesini, and it gives a unified treatment of “normal DIS”, boson-gluon fusion events and hard subcollisions in resolved photon-proton scattering. Thus the formalism provides a complete picture which incorporates all hard or semihard hadronic interactions in a simple way, which is suitable for a Monte Carlo treatment of both structure functions and final state properties. We also discuss non-leading effects which significantly reduce the increase of the structure function for very small x-values.     

Structure functions and general final state properties in the linked dipole chain model

We have in an earlier paper, [1], presented a generalization, the Linked Dipole Chain Model LDC, of the model developed by Ciafaloni-Catani-Fiorani-Marchesini, [2], to decribe the structure functions and the states in Deep Inelastic Scattering events. In this paper we would like to present an investigation of a set of general features of the LDC Model, viz the behaviour of the structure functions (we will show how the result interpolates in a precise way in between the well-known DGLAP and BFKL approaches), the average bremsstrahlung emission in the states and finally a partitioning of the structure functions into three different channels: the “ordinary” parton-probe events, where all bremsstrahlung emissions are below the probeQ ², the boson-gluon fusion events where the last splitting of the parton chains contain transverse momentum aboveQ ², and the resolved Rutherford scattering events between the probe and the hadron (where the largest transverse momentum occur somewhere along the emission lines away from the ends).     

Distinctive signatures for new particles in e+ e− annihilation and z-decay

New particles and new interactions reveal themselves most clearly where standard model contributions are negligibly small. A prominent example with this advantage is the one-lepton inclusive longitudinal structure function (W_L) in e⁺ e^? annihilation and Z-decay. We discuss general features of this approach and present structure functions for two types of new particles (heavy charged fermion, e.g. new sequential lepton or top quark; and supersymmetric scalar lepton, i.e. slepton), along with the (small) standard model “background”. The x-dependence of W_L provides a distinct signature of the identity of the new particle. Extensions of this approach are discussed.     

Quadratic corrections to three‐point functions

Following the recent progress on the calculation of three‐point correlators with two “heavy” (with large quantum numbers) and one “light” states at strong coupling, we compute the logarithmic divergent terms of leading bosonic quantum corrections to correlation functions with “heavy” operators corresponding to simple string solutions in AdS₅ × S⁵. The “light” operator is chosen to be the dilaton. An important relation connecting the corrections to both the dimensions of “heavy” states, and the structure constants is recovered.     

Atomic collective excitations in liquid lead

The atomic dynamics of liquid lead at the temperature T = 600 K has been simulated on the basis of the embedded atom model potential (the “embedded” atom model making it possible to effectively take into account the many-particle interactions) in order to study the mechanisms of formation of the atomic collective excitations. Spectra of the dynamic structure factor S(k, ω) and the spectral densities of the time correlation functions of the longitudinal \(\tilde C_L\) (k, ω) and transverse \(\tilde C_T\) (k, ω) currents have been calculated for the wavenumber region 0.11 Å^?1 ≤ k ≤ 2.01 Å^?1. It has been established that the dynamics of density fluctuations is characterized by two dispersion “acoustic-like” branches of the longitudinal and transverse polarization.     

Inclusive production of neutral kaons inK − p interactions at 32 GeV/c

The inclusive production of neutral kaons inK ^? p interactions at 32 GeV/c is studied in final states with one, two and three strange particles (K ⁿ or Λ). Inclusive and topological cross sections are obtained and their energy dependence discussed by comparison with lower energy data. The invariant differential cross sections of neutral kaons are studied as a function of Feynmanx, the c.m. rapidity and the transverse momentum, and a comparison is made with data at 14.3 GeV/c. Invariantx-distributions are obtained separately for “indirect” neutral kaons from \(\bar K*(890)\) decays and for “prompt” kaons. We also discuss the possibility of connecting quark structure functions with hadron fragmentation spectra at this c.m. energy \(\sqrt s \simeq 8 GeV\) .     

The method of uniqueness,a new powerful technique for multiloop calculations

We present a new method for multiloop calculations that provides an “algebraic” procedure to evaluate the renormalization group functions up to five loops. As an example, a final analytical expression for the five-loop β-function in the ?⁴ theory is given.