1,648 research outputs found
The Influence of High Multiplicities at RHIC on the Gamov Factor
The corrections for two-pion correlations due to electromagnetic final-state
interactions at high secondary multiplicities are investigated. The analysis is
performed by solving the Schr\"odinger equation with a potential which is
dictated by the multi-particle environment. Two different post-freeze-out
scenarios are examined. First, for a uniformly spread environment of secondary
particles, a screened Coulomb potential is exploited. It is shown that the
presence of a static and uniform post-freeze-out medium results in a noticeable
deviation from the standard Gamov factor. However, after going to a more
realistic model of an expanding pion system, this conclusion changes
drastically. We argue that the density of the secondary pions n_\pi(t,R), where
R is a distance from the fireball, is bounded from above by n_\pi(t,R)\le
const/R^2 for all times t. Then, a two-particle scalar potential which is found
as a solution of the Maxwell equation for non-uniform medium replaces the
screened one. Even this upper limit does not result in an essential deviation
from the Gamov correction.Comment: 11 pages, 7 figures, minor text corrections are mad
Photoproduction and the Gluon Structure of the Nucleon
Using short distance QCD methods based on the operator product expansion, we
calculate the photoproduction cross section in terms of the gluon
distribution function of the nucleon. Comparing the result with data, we show
that experimental behaviour of the cross section correctly reflects the
-dependence of the gluon distribution obtained from deep inelastic
scattering.Comment: 8 pages, latex, 4 figure
New Signals of Quark-Gluon-Hadron Mixed Phase Formation
Here we present several remarkable irregularities at chemical freeze-out
which are found using an advanced version of the hadron resonance gas model.
The most prominent of them are the sharp peak of the trace anomaly existing at
chemical freeze-out at the center of mass energy 4.9 GeV and two sets of highly
correlated quasi-plateaus in the collision energy dependence of the entropy per
baryon, total pion number per baryon, and thermal pion number per baryon which
we found at the center of mass energies 3.8-4.9 GeV and 7.6-10 GeV. The low
energy set of quasi-plateaus was predicted a long time ago. On the basis of the
generalized shock-adiabat model we demonstrate that the low energy correlated
quasi-plateaus give evidence for the anomalous thermodynamic properties inside
the quark-gluon-hadron mixed phase. It is also shown that the trace anomaly
sharp peak at chemical freeze-out corresponds to the trace anomaly peak at the
boundary between the mixed phase and quark gluon plasma. We argue that the high
energy correlated quasi-plateaus may correspond to a second phase transition
and discuss its possible origin and location. Besides we suggest two new
observables which may serve as clear signals of these phase transformations.Comment: 14 pages, 4 figures, new signals of QGP formation are suggeste
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