arXiv subjects

G. Baur

Publications and source records attributed to G. Baur.

31 records · Page 2Linked to original sources

arXiv2001

Higher order effects in electromagnetic dissociation of neutron halo nuclei

We investigate higher order effects in electromagnetic dissociation of neutron halo nuclei using a simple and realistic zero range model for the neutron-core interaction. In the sudden (or Glauber) approximation all orders in the target-core interaction are taken into account. Small deviations from the sudden approximation are readily calculated. We obtain very simple analytical results for the next-to-leading order effects, which have a simple physical interpretation. For intermediate energy electromagnetic dissociation, higher order effects are generally small. We apply our model to Coulomb dissociation of $^{19}$C at 67 A MeV. The analytical results are compared to numerical results from the integration of the time-dependent Schroedinger equation. Good agreement is obtained. We conclude that higher order electromagnetic effects are well under control.

nucl-th↗

arXiv2000

The Past and Future of Coulomb Dissociation in Hadron- and Astrophysics

Breakup reactions are generally quite complicated, they involve nuclear and electromagnetic forces including interference effects. Coulomb dissociation is an especially simple and important mechanism since the perturbation due to the electric field of the nucleus is exactly known. Therefore firm conclusions can be drawn from such measurements. Electromagnetic matrixelements, radiative capture cross-sections and astrophysical S-factors can be extracted from experiments. We describe the basic theory, give analytical results for higher order effects in the dissociation of neutron halo nuclei and briefly review the experimental results obtained up to now. Some new applications of Coulomb dissociation for nuclear astrophysics and nuclear structure physics are discussed.

nucl-th↗

arXiv2000

Coherent and incoherent atomic scattering: Formalism and application to pionium interacting with matter

The experimental determination of the lifetime of pionium provides a very important test on chiral perturbation theory. This quantity is determined in the DIRAC experiment at CERN. In the analysis of this experiment, the breakup probabilities of of pionium in matter are needed to high accuracy as a theoretical input. We study in detail the influence of the target electrons. They contribute through screening and incoherent effects. We use Dirac-Hartree- Fock-Slater wavefunctions in order to determine the corresponding form factors. We find that the inner-shell electrons contribute less than the weakly bound outer electrons. Furthermore, we establish a more rigorous estimate for the magnitude of the contributions form the transverse current (magnetic terms thus far neglected in the calculations).

physics.atom-ph↗

arXiv2000

Mechanisms for Direct Breakup Reactions

We review some simple mechanisms of breakup in nuclear reactions. We mention the spectator breakup, which is described in the post-form DWBA. The relation to other formulations is also indicated. An especially important mechanism is Coulomb dissociation. It is a distinct advantage that the perturbation due to the electric field of the nucleus is exactly known. Therefore firm conclusions can be drawn from such measurements. Some new applications of Coulomb dissociation for nuclear astrophysics are discussed.

nucl-th↗

arXiv1999

Coherent Interactions with heavy ions at CMS

Due to coherence, there are strong electromagnetic fields of short duration in very peripheral collisions. They give rise to photon-photon and photon-nucleus collisions with high flux up to an invariant mass region hitherto unexplored experimentally. After a general survey photon-photon luminosities in relativistic heavy ion collisions are discussed. Special care is taken to include the effects of strong interactions and nuclear size. Then photon-photon physics at various invariant mass scales is discussed. Invariant masses of up to about 100 GeV can be reached at LHC, and in addition the potential for new physics is available. Photonuclear reactions and other important background effects, especially diffractive processes are also discussed. Lepton-pair production, especially electron-positron pair production is copious. Due to the strong fields there will be new phenomena, especially multiple e+e- pair production.

hep-ph↗

arXiv1999

Photon-Photon and Photon-Hadron Physics at Relativistic Heavy Ion Colliders

Due to the coherence of all the protons in a nucleus, there are very strong electromagnetic fields of short duration in relativistic heavy ion collisions. They give rise to quasireal photon-photon and photon-nucleus collisions with a large flux. RHIC will begin its experimental program this year and such types of collisions will be studied experimentally at the STAR detector. RHIC will have the highest flux of (quasireal) photons up to now in the GeV region. At the LHC the invariant mass range available in gamma-gamma-interactions will be of the order of 100 GeV, i.e., in the range currently available at LEP2, but with a higher gamma-gamma-luminosity. Therefore one has there also the potential to study new physics. (Quasireal) photon-hadron (i.e., photon-nucleus) interactions can be studied as well, similar to HERA, at higher invariant masses. Vector mesons can be produced coherently through photon-Pomeron and photon-meson interactions in exclusive reactions such as A+A -> A+A+V, where A is the heavy ion and V=rho,omega,phi or J/Psi.

hep-ph↗

arXiv1999

Influence of damping on the excitation of the double giant resonance

We study the effect of the spreading widths on the excitation probabilities of the double giant dipole resonance. We solve the coupled-channels equations for the excitation of the giant dipole resonance and the double giant dipole resonance. Taking Pb+Pb collisions as example, we study the resulting effect on the excitation amplitudes, and cross sections as a function of the width of the states and of the bombarding energy.

nucl-th↗

arXiv1997

Antihydrogen production and accuracy of the equivalent photon approximation

The production of antihydrogen in flight in antiproton-nucleus collisions is calculated theoretically in the Plane Wave Born Approximation (which is equivalent to the straight line semiclassical approximation). Antihydrogen has been produced in this way at LEAR/CERN and is presently studied at FERMILAB at various antiproton energies. Dirac wave functions for the leptons are used, taking first order (Z.alpha) corrections into account. Analytical results are obtained for differential cross-sections. Total cross sections are obtained by numerical integration. The dependence on the transverse momentum transfer is studied and the accuracy of the equivalent photon approximation and a recent variant by Munger, Brodsky,and Schmidt is discussed as a function of beam energy.

hep-ph↗

arXiv1997

Quasireal photons in nucleus-nucleus collisions at intermediate and high energies, applications to nuclear structure, nuclear astrophysics and particle physics

Introduction Theory of electromagnetic excitation and dissociation (Inelastic scattering at high energies: one-photon exchange, semiclassical approach and Glauber theory; Higher order electromagnetic effects, small xi-approximation) Discussion of experimental results for nuclear structure Coulomb dissociation as a tool to measure radiative capture processes relevant to nuclear astrophysics Antihydrogen production and electromagnetic processes at relativistic heavy ion colliders Conclusions

nucl-th↗

arXiv1997

Bremsstrahlung Pair Production In Relativistic Heavy Ion Collision

We calculate production of electron- and muon-pairs by the bremsstrahlung process in hadron collisions and compare it with the dominant two-photon process. Results for the total cross section are given for proton-proton and heavy-ion collisions at energies of the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC).

nucl-th↗

arXiv1996

Comment on "A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy Ion Physics"

We critically discuss the recently developed quantum-mechanical equivalent photon spectrum by Benesh et al. We point out that the key point, the strong absorption in heavy ion collisions, is not treated adequately. Conclusions drawn from such a spectrum are invalid. Equivalent photon spectra appropriate for heavy ions, have been given before in quantal as well as semiclassical versions and were found to be very satisfactory.

nucl-th↗

arXiv1996

Effects of Strong Interaction on the Electromagnetic Dissociation

We investigate effects of strong interactions on the electromagnetic dissociation of nuclei in heavy ion collisions. We start from the eikonal approach to the equivalent photon method to describe the electromagnetic contributions to the cross section of peripheral collisions. We summarize some results of this approach and characterize recent experiments in "universal plots". In the second part of this work, we give a straight forward method to include transitions induced by the strong interactions between the ions. We introduce different methods to obtain the nuclear transition potential, and study the behavior of the resulting nuclear contributions.

nucl-th↗

arXiv1995

Multiple Electromagnetic Excitation in Fast Peripheral Heavy Ions Collisions

We study the corrections of first order electromagnetic excitation due to higher order electromagnetic interactions. An effective operator is introduced which takes these effects into account in the sudden approximation. Evaluating the matrix-elements of this operator between the relevant states corrections to the first order result are obtained in a simple way. As an example we discuss the excitation of the first excited state in 11Be. It tends to improve the agreement between experiment and theory.

nucl-th↗