84 research outputs found
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 -matrix is known. We study
this -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
Electromagnetic Dissociation as a Tool for Nuclear Structure and Astrophysics
Coulomb dissociation is an especially simple and important reaction
mechanism. Since the perturbation due to the electric field of the nucleus is
exactly known, firm conclusions can be drawn from such measurements.
Electromagnetic matrix elements and astrophysical S-factors for radiative
capture processes can be extracted from experiments. We describe the basic
theory, new results concerning 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.Comment: 10 pages, 1 figure, to appear in Proceedings of the International
School on Nuclear Physics; 22nd Course: ``Radioactive Beams for Nuclear and
Astro Physics'', Erice/Sicily/Italy, September 16 - 24, 200
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