A Realistic Solvable Model for the Coulomb Dissociation of Neutron Halo Nuclei

As a model of a neutron halo nucleus we consider a neutron bound to an inert core by a zero range force. We study the breakup of this simple nucleus in the Coulomb field of a target nucleus. In the post-form DWBA (or, in our simple model CWBA (``Coulomb Wave Born Approximation'')) an analytic solution for the T-matrix is known. We study limiting cases of this T-matrix. As it should be, we recover the Born approximation for weak Coulomb fields (i.e., for the relevant Coulomb parameters much smaller than 1). For strong Coulomb fields, high beam energies, and scattering to the forward region we find a result which is very similar to the Born result. It is only modified by a relative phase (close to 0) between the two terms and a prefactor (close to 1). A similar situation exists for bremsstrahlung emission. This formula can be related to the first order semiclassical treatment of the electromagnetic dissociation. Since our CWBA model contains the electromagnetic interaction between the core and the target nucleus to all orders, this means that higher order effects (including postacceleration effects) are small in the case of high beam energies and forward scattering. Our model also predicts a scaling behavior of the differential cross section, that is, different systems (with different binding energies, beam energies and scattering angles) show the same dependence on two variables x and y.Comment: to appear in the Proceedings of ENAM2001, 3rd Internation Conference on Exotic Nuclei and Atomic Masse

Transverse momentum distribution of vector mesons produced in ultraperipheral relativistic heavy ion collisions

We study the transverse momentum distribution of vector mesons produced in ultraperipheral relativistic heavy ion collisions (UPCs). In UPCs there is no strong interaction between the nuclei and the vector mesons are produced in photon-nucleus collisions where the (quasireal) photon is emitted from the other nucleus. Exchanging the role of both ions leads to interference effects. A detailed study of the transverse momentum distribution which is determined by the transverse momentum of the emitted photon, the production process on the target and the interference effect is done. We study the total unrestricted cross section and those, where an additional electromagnetic excitation of one or both of the ions takes place in addition to the vector meson production, in the latter case small impact parameters are emphasized.Comment: 12 pages, REVTeX manuscrip

Ultraperipheral Collisions

Ultraperipheral collisions at heavy ion colliders use the strong Coulomb fields surrounding the ions to study photon-photon and photon-hadron processes at high energy. A number of processes of interest are discussed here.Comment: 12 pages, Talk presented at "Physics at LHC", Vienna, Austria, July 13-17, 2004. To be published in Czechoslovak Journal of Physic

Study of Postacceleration Effects in the Coulomb Dissociation of Neutron Halo Nuclei

We investgate the breakup of one-neutron halo nuclei in the Coulomb field of a target nucleus. In the post-form distorted wave Born approximation theory of this reaction, with only Coulomb distortions in the entrance and the outgoing channels, an analytic solution for the breakup $T$-matrix is known. We study this $T$-matrix and the corresponding cross-sections numerically. This formula can be related to the first order semiclassical treatment of the electromagnetic dissociation. This theory contains the electromagnetic interaction between the core and the target nucleus to all orders. We show that higher order effects (including postacceleration) are small in the case of higher beam energies and forward scattering. We investigate the beam energy dependence of the postacceleration effects. They are found to be quite important for smaller beam energies (slow collisions), but almost negligible at larger ones.Comment: 13 pages, 4 figure

Radial fall of a test particle onto an evaporating black hole

A test particle falling into a classical black hole crosses the event horizon and ends up in the singularity within finite eigentime. In the `more realistic' case of a `classical' evaporating black hole, an observer falling onto a black hole observes a sudden evaporation of the hole. This illustrates the fact that the discussion of the classical process commonly found in the literature may become obsolete when the black hole has a finite lifetime. The situation is basically the same for more complex cases, e.g. where a particle collides with two merging black holes. It should be pointed out that the model used in this paper is mainly of academic interest, since the description of the physics near a black hole horizon still presents a difficult problem which is not yet fully understood, but our model provides a valuable possibility for students to enter the interesting field of black hole physics and to perform numerical calculations of their own which are not very involved from the computational point of view.Comment: 6 pages, 3 figures, LATE

Bound-Free Electron-Positron Pair Production in Relativistic Heavy Ion Collisions

We study the bound-free electron-positron pair production in relativistic heavy ion collisions to different bound states in a full Plane Wave Born Approximation (PWBA) calculation. Exact Dirac wave functions are used for both the bound electron and the free positron in the final states. Results for the Relativistic Heavy Ion Collider RHIC as well as the forthcoming Large Hadron Collider (LHC) are given. This process is one of the dominant beam loss processes and can become critical for the operation with heavy ions. A simple parameterization is given as well. We compare our results with calculations of other groups.Comment: 15 pages, 1 figure, improved discussion, one table adde