QCD saturation and $\gamma^{*}$-$\gamma^{*}$ scattering

Two photon collisions at high energy have an important theoretical advantage: the simplicity of the initial state, which gives us a unique opportunity to calculate these processes for large virtualities of both photons in the perturbative QCD approach. In this paper we study QCD saturation in two photon collisions in the framework of the Glauber-Mueller approach. The Glauber-Mueller formula is derived emphasising the impact parameter dependence (b_t) of the dipole-dipole amplitude. It is shown that non-perturbative QCD contributions are needed to describe the large b _t behaviour, and the way how to deal with them is suggested. Our approach can be viewed as the model for the saturation in which the entire impact parameter dependence is determined by the initial conditions. The unitarity bound for the total cross section, its energy dependence as well as predictions for future experiments are discussed. It is argued that the total cross section increases faster than any power of in a wide range of energy or x, namely -, where reflects the x dependence of the gluon density and is the pion mass. Received: 22 November 2002 / Revised version: 27 January 2003 / Published online: 5 May 2003 RID="a" ID="a" e-mail: kozlov@post.tau.ac.il RID="b" ID="b" e-mail: leving@post.tau.ac.il and levin@mail.desy.de     

Study of thermally excited nuclei through <Emphasis Type="Italic">E</Emphasis>1 and <Emphasis Type="Italic">E</Emphasis>2 decay from collective modes

The nuclear system at the limit of excitation energy and angular momentum is here studied in the case of the superdeformed nucleus ¹⁴³Eu using -spectroscopy techniques. The data are based on a EUROBALL experiment using the reaction ³⁷Cl + ¹¹⁰Pd Eu + 4n. The influence of thermal energy on superdeformed configurations is investigated through the analysis of the quasi-continuum spectra formed by E2 transitions among states of excited rotational bands with energy extending up to 4-5 MeV above the yrast line. In particular, the effective lifetimes of the discrete rotational bands forming ridge structures in - coincidence matrices is measured by a Doppler Shift Attenuation Method. The deduced quadrupole deformation of 10 eb indicates that the nucleus maintains its collectivity with increasing excitation energy, supporting the superdeformed character of the excited nuclear rotation. The obtained number of superdeformed discrete bands forming the ridge structures is found in good agreement with microscopic cranked shell model calculations including the decay-out process into the lower deformation minimum. In addition, the nuclear properties at higher excitation energies are investigated through the E1 -decay of the giant dipole resonance (GDR). It is found that the intensity of the superdeformed yrast and excited bands increases by a factor of approximately 1.6 when a coincidence with a high-energy -ray is required, showing the importance of the E1 cooling in the feeding mechanism of the superdeformed states.Received: 2 December 2002, Published online: 2 March 2004PACS: 21.10.Tg Lifetimes - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.60. + j      

Perturbation foundation of <Emphasis Type="Italic">q</Emphasis>-deformed dynamics

In the q-deformed theory the perturbation approach can be expressed in terms of two pairs of undeformed position and momentum operators. There are two configuration spaces. Correspondingly there are two q-perturbation Hamiltonians; one originates from the perturbation expansion of the potential in one configuration space, the other one originates from the perturbation expansion of the kinetic energy in another configuration space. In order to establish a general foundation of the q-perturbation theory, two perturbation equivalence theorems are proved. The first is Equivalence Theorem I: Perturbation expressions of the q-deformed uncertainty relations calculated by two pairs of undeformed operators are the same, and the two q-deformed uncertainty relations undercut Heisenberg's minimal one in the same style. The general Equivalence Theorem II is: for any potential (regular or singular) the expectation values of two q-perturbation Hamiltonians in the eigenstates of the undeformed Hamiltonian are equivalent to all orders of the perturbation expansion. As an example of singular potentials the perturbation energy spectra of the q-deformed Coulomb potential are studied. Received: 6 September 2002 / Revised version: 21 October 2002 / Published online: 14 April 2003 RID="a" ID="a" e-mail: jzzhang@physik.uni-kl.de, jzzhang@ecust.edu.cn     

Exclusive \eta production in pp reactions

Angular distributions for the exclusive reaction observed via the decay channel have been measured at GeV, 2.50 GeV and 2.85 GeV (excess energies Q = 324 MeV, 412 MeV and 554 MeV). The polar angle of the shows an anisotropy with respect to the beam direction for the lowest energy, which vanishes for the higher energies. The anisotropy of the pp polar angle increases slightly with the beam energy.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 14.40.Aq , K, and mesons - 25.40.Ve Other reactions above meson production thresholds (energies > 400 MeV)Y. Bedfer: Present address: DAPNIA/SPhN, CEA Saclay, France.A. Brenschede: Present address: Syngenio AG, StuttgartF. Brochard: Present address: LPHNHE, Ecole Polytechnique 91128 Palaiseau, France.Seonho Choi: Present address: Temple University, Philadelphia, PA, USA.R. Dressler: Present address: Paul Scherrer Institut, Villigen, CH-5232.J. Foryciarz: Present address: Motorola Polska Software Center, Kraków, Poland.H.-W. Pfaff: Present address: d-fine GmbH, Eschborn.     

Parity non-conservation in proton-proton elastic scattering

The parity-non-conserving longitudinal asymmetry in proton-proton (p p) elastic scattering is calculated in the lab energy range 0-350 MeV using contemporary, realistic strong-interaction potentials combined with a weak-interaction potential comprised of - and -meson exchanges as exemplified by the DDH model. Values for the - and -meson coupling constants, and , are determined from comparison with the measured asymmetries at 13.6 MeV, 45 MeV, and 221 MeV.Received: 30 September 2002, Published online: 22 October 2003PACS: 21.30.-x Nuclear forces - 24.80. + y Nuclear tests of fundamental interactions and symmetries - 25.40.Cm Elastic proton scattering     

Quark mass dependence of the nuclear forces

We investigate the behavior of the nuclear force as a function of the light-quark masses m _q in the framework of chiral effective field theory at next-to-leading order. The unknown m _q -dependent short-range contribution is estimated by means of dimensional analysis. We calculate various observables for different values of m _q . We found no new bound states and a larger deuteron binding energy, MeV, in the chiral limit.Received: 30 September 2002, Published online: 22 October 2003PACS: 11.30.Rd Chiral symmetries - 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 21.30.Cb Nuclear forces in vacuum - 21.30.Fe Forces in hadronic systems and effective interactions     

High-spin states in the <Superscript>97</Superscript>Tc nucleus

High-spin states in the ⁹⁷Tc nucleus have been studied by in-beam γ-ray spectroscopy with the reaction ⁸²Se(¹⁹F,4nγ) at 68 MeV incident energy. Excited states have been observed up to about 8 MeV excitation and spin 43/2. The observed level scheme is compared with results of shell model calculations. Received: 22 November 2002 / Accepted: 23 December 2002 / Published online: 18 March 2003 RID="a" ID="a"e-mail: bucurescu@tandem.nipne.ro RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="c" ID="c"Present address: Università di Padova, Padova, Italy. Communicated by C. Signorini     

Experiments on the search for the NN-decoupled NN\pi-resonance d’

The status on the search for NN-decoupled -resonances is reviewed with regard to recent experimental searches in the pionic double-charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.Received: 30 September 2002, Published online: 22 October 2003PACS: 14.20.Gk Baryon resonances with S = 0 - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 25.40.Ve Other reactions above meson production thresholds (energies 400 MeV)     

Some phenomenological consequences of the time-ordered perturbation theory of QED on non-commutative spacetime

A framework was recently proposed for doing perturbation theory on non-commutative (NC) spacetime. It preserves the unitarity of the S matrix and differs from the naive, popular approach already at the lowest order in perturbation when time does not commute with space. In this work, we investigate its phenomenological implications at linear colliders, especially the TESLA at DESY, through the processes of . We find that some NC effects computed previously are now modified and that there are new processes which now exhibit NC effects. Indeed, the first two processes get corrected at tree level as opposed to the null result in the naive approach, while the third one coincides with the naive result only in the low energy limit. The impact of the earth's rotation is incorporated. The NC signals are generally significant when the NC scale is comparable to the collider energy. If this is not the case, the non-trivial azimuthal angle distribution and day-night asymmetry of events due to Lorentz violation and the earth's rotation will be useful in identifying signals. We also comment briefly on the high energy behavior of the cross section that grows linearly in the center of mass energy squared and argue that it does not necessarily contradict some statements, e.g., the Froissart-Martin bound, achieved in ordinary theory. Received: 29 November 2002 / Revised version: 11 March 2003 / Published online: 5 May 2003 RID="a" ID="a" e-mail: liaoy@itp.uni-leipzig.de RID="b" ID="b" e-mail: dehne@itp.uni-leipzig.de     

Binding energy calculations for metal aggregates

Within the framework of the local density functional formalism the binding energies of atoms in metallic aggregates are computed. The calculations are based on the following approach: The total charge density is approximated by the superposition of the charge densities of the respective free atoms. The kinetic energy is obtained by a modified Thomas-Fermi-Weizsäcker expression, and the exchange/correlation energy is determined by theX -approximation. As a first example of application we have calculated the adsorption energies of Cu and Pd on tungsten and the formation energy of a vacancy in pure copper and in copper with Ge impurities. The results are in fair agreement with the respective experimental data.     

Associated strangeness production at threshold

The associated strangeness dissociation at threshold has been studied at the COSY-11 facility measuring the hyperon and the K ⁺ K ^- meson pair production. Measurements of the near-threshold and production via the reaction (S. Sewerinet al., Phys. Rev. Lett. 83, 682 (1999)) at COSY-11 have shown that the cross-section ratio exceeds the value at high excess energies ( MeV (A. Baldiniet al., Total Cross-Sections for Reactions of High-Energy Particles, Landolt-Börnstein, New Series, Vol. I/12 (Springer, Berlin, 1988))) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy. The near-threshold production of the charged kaon-antikaon pair is related to the discussion about the nature of the scalar states in the 1 GeV/c ² mass range, i.e. the f ₀(980) and a ₀(980) (O. Krehl, R. Rapp, J. Speth, Phys. Lett. B 390, 23 (1997)). The interpretation as a molecule is strongly dependent on the K- interaction which can be studied via the production channel. A first total cross-section value on the reaction at an excess energy of 17 MeV (C. Quentmeieret al., Phys. Lett. B 515, 276 (2001)), i.e. below the production threshold, was measured.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 14.20.Jn Hyperons - 14.40.Aq , K, and mesons - 25.40.Ep Inelastic proton scattering     

Aging and energy landscapes: application to liquids and glasses

The equation of state for a liquid in equilibrium, written in the potential energy landscape formalism, is generalized to describe out-of-equilibrium conditions. The hypothesis that during aging the system explores basins associated to equilibrium configurations is the key ingredient in the derivation. Theoretical predictions are successfully compared with data from molecular dynamics simulations of different aging processes, such as temperature and pressure jumps. Received 7 August 2002 / Received in final form 8 October 2002 Published online 19 December 2002 RID="a" ID="a"Present address: Laboratoire de Physique Théorique des Liquides, Université Pierre et Marie Curie, 4 place Jussieu, Paris 75005, France e-mail: mossa@lptl.jussieu.fr     

S = -1 meson-baryon scattering in coupled-channel unitarized Chiral Perturbation Theory

The s-wave meson-baryon scattering amplitude is analyzed for the strangeness S = -1 and isospin I = 0 sector in a Bethe-Salpeter coupled-channel formalism incorporating Chiral Symmetry. Four two-body channels have been considered: , , , . The needed two-particle irreducible matrix amplitude is taken from lowest-order Chiral Perturbation Theory in a relativistic formalism. Off-shell behaviour is parameterized in terms of low-energy constants, which outnumber those assumed in previous works and provide a better fit to the data. The position of the complex poles in the second Riemann sheet of the scattering amplitude determines masses and widths of the and resonances which compare well with accepted numbers.Received: 30 September 2002, Published online: 22 October 2003PACS: 11.10.St Bound and unstable states; Bethe-Salpeter equations - 11.30.Rd Chiral symmetries - 11.80.Et Partial-wave analysis - 13.75.Lb Meson-meson interactionsE. Ruiz Arriola: Spokesperson     

The low-energy limit of validity of the intranuclear cascade model

The intranuclear cascade model is generally considered to be valid when the incident particle has a sufficiently small de Broglie wavelength to interact with individual nucleons. On this basis, a lower limit of 200 MeV is usually quoted for the incident energy in nucleon-induced reactions. Here this statement is questioned. A pragmatic approach is used, which compares the predictions of the Liège intranuclear cascade model with available data at incident energy between 40 and 250 MeV. It is found that this model gives surprisingly good results at energies well below the limit mentioned above. Results are also compared with the predictions of other models commonly used in this energy range. Received: 2 September 2002 / Accepted: 22 October 2002 / Published online: 6 March 2003 RID="a" ID="a"e-mail: cugnon@plasma.theo.phys.ulg.ac.be RID="b" ID="b"e-mail: P.Henrotte@ulg.ac.be Communicated by G. Orlandini     

The origin of doublet bands observed in $A \sim 130$ nuclei

The results obtained with the GASP array in the mass region are reviewed, emphasizing the study of excited highly deformed bands and their decay out, the discovery of chiral doublet bands in the odd-odd Pr nuclei and of stable triaxial bands in Nd nuclei close to the N = 82 shell closure. The very recent studies of nuclei near the proton drip line are described. A discussion of the origin of the various doublet bands observed in odd-odd nuclei of the mass region is presented.Received: 10 October 2002, Published online: 17 February 2004PACS: 23.20.Lv Gamma transitions and level energies - 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.Ev Collective models - 25.70.-z Low and intermediate energy heavy-ion reactions     

Electromagnetic form factors of the $\Delta(1232)$ excitation

In the resonance region we have precisely determined the electromagnetic properties of the -resonance, in particular the E2/M1 ratio . For pion electroproduction recent experimental data from Mainz, Bates, Bonn and JLab for Q² up to 4.0 (GeV/c)² have been analyzed with the isobar model MAID. The extracted E2/M1 ratio shows, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and becomes positive with increasing Q². This is a possible indication of a very slow approach toward the pQCD region. The C2/M1 ratio near the photon point is found as . At high Q², the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached. The electromagnetic-transition form factors of the excitation are parameterized and fitted to the electroproduction data. This also shows a zero-crossing of the electric form factor G_E^* at (GeV/c)².Received: 1 November 2002, Published online: 15 July 2003PACS:   13.40.Gp Electromagnetic form factors - 13.60.Le Meson production - 14.20.Gk Baryon resonances with S=0 - 25.20.Lj Photoproduction reactions     

Birth and long-time stabilization of out-of-equilibrium coherent structures

We study an analytically tractable model with long-range interactions for which an out-of-equilibrium very long-lived coherent structure spontaneously appears. The dynamics of this model is indeed very peculiar: a bicluster forms at low energy and is stable for very long time, contrary to statistical mechanics predictions. We first explain the onset of the structure, by approximating the short time dynamics with a forced Burgers equation. The emergence of the bicluster is the signature of the shock waves present in the associated hydrodynamical equations. The striking quantitative agreement with the dynamics of the particles fully confirms this procedure. We then show that a very fast timescale can be singled out from a slower motion. This enables us to use an adiabatic approximation to derive an effective Hamiltonian that describes very well the long time dynamics. We then get an explanation of the very long time stability of the bicluster: this out-of-equilibrium state corresponds to a statistical equilibrium of an effective mean-field dynamics. Received 28 February 2002 / Received in final form 24 July 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: Thierry.Dauxois@ens-lyon.fr RID="b" ID="b"UMR-CNRS 5672 RID="c" ID="c"UMR 5582     

Mott effect and J/\psi dissociation at the quark-hadron phase transition

We investigate the in-medium modification of pseudoscalar and vector mesons in a QCD-motivated chiral quark model by solving the Dyson-Schwinger equations for quarks and mesons at finite temperature for a wide mass range of meson masses, from light ( , ) to open-charm (D, D ^*) states. At the chiral/deconfinement phase transition, the quark-antiquark bound states enter the continuum of unbound states and become broad resonances (hadronic Mott effect). We calculate the in-medium cross-sections for charmonium dissociation due to collisions with light hadrons in a chiral Lagrangian approach, and show that the D- and D ^*-meson spectral broadening lowers the threshold for charmonium dissociation by - and -mesons. This leads to a step-like enhancement in the reaction rate. We suggest that this mechanism for enhanced charmonium dissociation may be the physical mechanism underlying the anomalous suppression observed by NA50.Received: 30 September 2002, Published online: 22 October 2003PACS: 05.20.Dd Kinetic theory - 12.38.Mh Quark-gluon plasma - 14.40.-n Mesons - 25.75.Nq Quark deconfinement, quark-gluon plasma production, and phase transitions