149 research outputs found
pi-/pi+ ratio in heavy ions collisions: Coulomb effect or chemical equilibration?
We calculate the pi-/pi+ ratio for Pb+Pb at CERN/SPS energies and for Au+Au
at BNL/AGS energies using a (3+1) dimensional hydrodynamical model. Without
consideration of Coulomb effect an enhancement of this ratio at low mt is found
compatible with that observed in these experiments. Our calculations are based
on previous (3+1) dimensional hydrodynamical simulations (HYLANDER), which
described many other aspects of experimental data. In this model the observed
enhancement is a consequence of baryon and strangeness conservation and of
chemical equilibration of the system and is caused by the decay of produced
hyperons, which leads to a difference in the total number of positive and
negative pions as well. Based on the same approach, we also present results for
the pi-/pi+ ratio for S+S (CERN/SPS) collisions, where we find a similar
effect. The absence of the enhancement of the pi-/pi+ ratio in the S+S data
presented by the NA44 Collaboration, if confirmed, could indicate that chemical
equilibration has not yet been estabilished in this reaction.Comment: 8 pages and 2 figures, submmited to Phys. Lett. B. This reviewed
version (Nov.29,1996) contains more details about the model simulated
efficiency considering the experimental detection conditions. Other small
modifications were mad
Higher Order Bose-Einstein Correlations test the Gaussian Density Matrix Approach
A multiparticle system produced by a large number of independent sources is
described by a gaussian density matrix W. All theoretical approach to
Bose-Einstein Correlatios Cn in high energy physics use this form for W. One of
the most salient consequences of this form is the fact that all higher order
(n>2) moments of the current distribution can be expressed in terms of the
first two. We test this property by comparing the data on C2(Q^2), C3(Q^2) and
C4(Q^2) from pion-p and K-p reactions at 250 GeV/c with the predictions of a
general quantum statistical space-time approach. Even a simplified version of
such approach can account for the data. Previous attempts along these lines,
which did not use the space-time approach, met with difficulties.Comment: 17 pages (including one Table) and 2 figures. To appear in Physics
Letters B (PLB 13397
Thermal photon production in heavy ion collisions
Using a three-dimensional hydrodynamic simulation of the collision and an
equation of state containing a first order phase transition to the quark-gluon
plasma, we study thermal photon production for collisions at
AGeV and for collisions at AGeV. We obtain
surprisingly high rates of thermal photons even at the lower energy, suggesting
that, contrary to what was expected so far, photon production may be an
interesting topic for experimental search also at the Alternating Gradient
Synchrotron. When applied to the reaction at AGeV, our model can
reproduce preliminary data obtained by the WA80 Collaboration without having to
postulate the existence of an extremely long-lived mixed phase as was recently
proposed.Comment: 9 pages, figures are uudecoded compressed and tare
Soft Photons from Off-shell Particles in a Hot Plasma
Considering the propagation of off-shell particles in the framework of
thermal field theory, we present the general formalism for the calculation of
the production rate of soft photons and dileptons from a hot plasma. This
approach is illustrated with an electrodynamic plasma. The photon production
rate from strongly interacting quarks in the quark-gluon plasma, which might be
formed in ultrarelativistic heavy ion collisions, is calculated in the
previously unaccessible regime of photon energies of the order of the plasma
temperature within an effective field theory incorporating dynamical chiral
symmetry breaking.Comment: 8 pages in RevTeX format, 3 figures uuencoded postscript added. Also
available by anonymous ftp at ftp://tpri6c.gsi.de/pub/phenning/qh95ga
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