315 research outputs found
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
Multiple electromagnetic electron positron pair production in relativistic heavy ion collisions
We calculate the cross sections for the production of one and more
electron-positron pairs due to the strong electromagnetic fields in
relativistic heavy ion collisions. Using the generating functional of fermions
in an external field we derive the N-pair amplitude. Neglecting the
antisymmetrisation in the final state we find that the total probability to
produce N pairs is a Poisson distribution. We calculate total cross sections
for the production of one pair in lowest order and also include higher-order
corrections from the Poisson distribution up to third order. Furthermore we
calculate cross sections for the production of up to five pairs including
corrections from the Poisson distribution.Comment: 13 pages REVTeX, 4 Postscript figures, This and related papers may
also be obtained from http://www.phys.washington.edu/~hencken
Structure of the Coulomb and unitarity corrections to the cross section of pair production in ultra-relativistic nuclear collisions
We analyze the structure of the Coulomb and unitarity corrections to the
single pair production as well as the cross section for the multiple pair
production. In the external field approximation we consider the probability of
pair production at fixed impact parameter between colliding
ultra-relativistic heavy nuclei. We obtain the analytical result for this
probability at large as compared to the electron Compton wavelength. We
estimate also the unitary corrections to the total cross section of the
process.Comment: 10 pages, 2 figures, RevTeX, references correcte
Photon-Photon and Photon-Hadron Interactions at Relativistic Heavy Ion Colliders
In central collisions at relativistic heavy ion colliders like the
Relativistic Heavy Ion Collider RHIC/Brookhaven and the Large Hadron Collider
LHC (in its heavy ion mode) at CERN/Geneva, one aims at detecting a new form of
hadronic matter --- the Quark Gluon Plasma. We discuss here a complementary
aspect of these collisions, the very peripheral ones. Due to coherence, there
are strong electromagnetic fields of short duration in such 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. Then photon-photon physics at various gamma-gamma-invariant mass
scales is discussed. The region of several GeV, relevant for RHIC is dominated
by QCD phenomena (meson and vector meson pair production). Invariant masses of
up to about 100 GeV can be reached at LHC, and the potential for new physics is
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.Comment: 10 pages, Proceedings of the Erice Summer School on Heavy Ion Physics
199
Semiclassical theory of spin-orbit interactions using spin coherent states
We formulate a semiclassical theory for systems with spin-orbit interactions.
Using spin coherent states, we start from the path integral in an extended
phase space, formulate the classical dynamics of the coupled orbital and spin
degrees of freedom, and calculate the ingredients of Gutzwiller's trace formula
for the density of states. For a two-dimensional quantum dot with a spin-orbit
interaction of Rashba type, we obtain satisfactory agreement with fully
quantum-mechanical calculations. The mode-conversion problem, which arose in an
earlier semiclassical approach, has hereby been overcome.Comment: LaTeX (RevTeX), 4 pages, 2 figures, accepted for Physical Review
Letters; final version (v2) for publication with minor editorial change
Semiclassical dynamics of a spin-1/2 in an arbitrary magnetic field
The spin coherent state path integral describing the dynamics of a
spin-1/2-system in a magnetic field of arbitrary time-dependence is considered.
Defining the path integral as the limit of a Wiener regularized expression, the
semiclassical approximation leads to a continuous minimal action path with
jumps at the endpoints. The resulting semiclassical propagator is shown to
coincide with the exact quantum mechanical propagator. A non-linear
transformation of the angle variables allows for a determination of the
semiclassical path and the jumps without solving a boundary-value problem. The
semiclassical spin dynamics is thus readily amenable to numerical methods.Comment: 16 pages, submitted to Journal of Physics
Bound-free pair production in ultra-relativistic ion collisions at the LHC collider: Analytic approach to the total and differential cross sections
A theoretical investigation of the bound-free electron-positron pair
production in relativistic heavy ion collisions is presented. Special attention
is paid to the positrons emitted under large angles with respect to the beam
direction. The measurement of these positrons in coincidence with the
down--charged ions is in principle feasible by LHC experiments. In order to
provide reliable estimates for such measurements, we employ the equivalent
photon approximation together with the Sauter approach and derive simple
analytic expressions for the differential pair--production cross section, which
compare favorably to the results of available numerical calculations. Based on
the analytic expressions, detailed calculations are performed for collisions of
bare Pb ions, taking typical experimental conditions of the LHC
experiments into account. We find that the expected count rate strongly depends
on the experimental parameters and may be significantly enhanced by increasing
the positron-detector acceptance cone.Comment: 10 pages, 4 figure
Semiclassical theory of spin-orbit interaction in the extended phase space
We consider the semiclassical theory in a joint phase space of spin and
orbital degrees of freedom. The method is developed from the path integrals
using the spin-coherent-state representation, and yields the trace formula for
the density of states. We discuss special cases, such as weak and strong
spin-orbit coupling, and relate the present theory to the earlier approaches.Comment: 36 pages, 8 figures. Version 2: revised Sec. 4.4 and Appendix B;
minor corrections elsewher
Strong suppression of Coulomb corrections to the cross section of e+e- pair production in ultrarelativistic nuclear collisions
The Coulomb corrections to the cross section of pair production in
ultrarelativistic nuclear collisions are calculated in the next-to-leading
approximation with respect to the parameter
( are the Lorentz factors of colliding nuclei). We found
considerable reduction of the Coulomb corrections even for large
due to the suppression of the production of pair
with the total energy of the order of a few electron masses in the rest frame
of one of the nuclei. Our result explains why the deviation from the Born
result were not observed in the experiment at SPS.Comment: 4 pages, RevTe
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