417 research outputs found
Exclusive and inclusive muon pair production in collisions of relativistic nuclei
The exclusive production of one pair in collisions of two
ultra-relativistic nuclei is considered. We present a simple method for the
calculation of the Born cross section for this process based on an improved
equivalent photon approximation. We find that the Coulomb corrections to this
cross section (corresponding to multi-photon exchange of the produced
with the nuclei) are small while the unitarity corrections
(corresponding to the exchange of light-by-light blocks between nuclei) are
large. This is in sharp contrast to the exclusive pair production
where the Coulomb corrections to the Born cross section are large while the
unitarity corrections are small. We calculate also the cross section for the
production of one pair and several pairs in the leading
logarithmic approximation. Using this cross section we find that the inclusive
production of pair coincides in this approximation with its Born
value.Comment: 16 pages, 4 figure
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.Comment: 6 pages, to be published in the proceedings of the Photon'99
conferenc
Nuclear Breakup of Borromean Nuclei
We study the eikonal model for the nuclear-induced breakup of Borromean
nuclei, using Li11 and He6 as examples. The full eikonal model is difficult to
realize because of six-dimensional integrals, but a number of simplifying
approximations are found to be accurate. The integrated diffractive and
one-nucleon stripping cross sections are rather insensitive to the
neutron-neutron correlation, but the two-nucleon stripping does show some
dependence on the correlation. The distribution of excitation energy in the
neutron-core final state in one-neutron stripping reactions is quite sensitive
to the shell structure of the halo wave function. Experimental data favor
models with comparable amounts of s- and p-wave in the Li11 halo.Comment: 34 pages REVTeX, 14 postscript figures. Small changes in comparison
with experimen
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
Production of Low Mass Electron Pairs Due to the Photon-Photon Mechanism in Central Collisions
We calculate the probability for dilepton production in central relativistic
heavy ion collisions due to the gamma-gamma mechanism. This is a potential
background to more interesting mechanisms. We find that this mechanism is
negligible in the CERES experiments. Generally, the contribution due to this
mechanism is small in the central region, while it can be large for small
invariant masses and forward or backward rapidities. A simple formula based on
the equivalent photon approximation and applications to a possible scenario at
RHIC are also given.Comment: 10 pages REVTeX, 5 Figures, for related work see
http://quasar.physik.unibas.ch/~hencken
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