246 research outputs found
Forward-Backward Multiplicity Correlations in Au+Au Collisions at = 200 Gev
The study of correlations among particles produced in different rapidity
regions may provide understanding of the mechanisms of particle production.
Correlations that extend over a longer range are observed in hadron-hadron
interactions only at higher energies. Results for short and long-range
multiplicity correlations (Forward-Backward) are presented for Au+Au collisions
at = 200 GeV. The growth of long range correlations are
observed as a function of the pseudorapidity gap in central Au+Au collisions.
The Dual Parton model and Color Glass Condensate phenomenology have been
explored to understand the origin of long range correlations.Comment: 8 pages, 4 figures, IWCF06, Hangzhou, China, Nov. 21-24, 200
Single - particle correlations in events with the total disintegration of nuclei
New experimental data on the behaviour of the single-particle two-dimensional
correlation functions R versus Q (Q is the number of nucleons emitted from nuc-
lei) and Ap (Ap is the mass of projectile nuclei) are presented in this paper.
The interactions of protons, d, 4He and 12C nuclei with carbon nuclei (at a
momentum of 4.2 A GeV/c) are considered.The values of R are obtained separately
for pi minus mesons and protons.In so doing,the values of R are normalized so
that -1=<R=<1.The value of R=0 corresponds to the case of the absence of corre-
lations.It has been found that the Q- and Ap-dependence of R takes place only
for weak correlations (R< 0.3).In the main (90 %),these correlations are con-
nected with the variable pt and have a nonlinear character, that is the regi-
ons with different characters of the Q-dependence of R are separated: there is
a change of regimes in the Q-dependences of R.The correlations weaken with
increasing Ap, and the variable R gets the least values of all the considered
ones in 12CC interactions.Simultaneously with weakening the correlations in the
region of large Q, the character of the Q-dependence of R changes.Comment: 17 pages, submitted to Phys. Rew.
Transverse Energy per Charged Particle and Freeze-Out Criteria in Heavy-Ion Collisions
In relativistic nucleus-nucleus collisions the transverse energy per charged
particle, E_T/N_ch, increases rapidly with beam energy and remains
approximately constant at about 800 MeV for beam energies from SPS to RHIC. It
is shown that the hadron resonance gas model describes the energy dependence,
as well as the lack of centrality dependence, qualitatively. The values of
E_T/N_ch are related to the chemical freeze-out criterium E/N about 1 GeV valid
for primordial hadrons.Comment: 8 pages, 5 figure
The strange-quark chemical potential as an experimentally accessible "order parameter" of the deconfinement phase transition for finite baryon-density
We consider the change of the strange-quark chemical potential in the phase
diagram of nuclear matter, employing the Wilson loop and scalar quark
condensate order parameters, mass-scaled partition functions and enforcing
flavor conservation. Assuming the region beyond the hadronic phase to be
described by massive, correlated and interacting quarks, in the spirit of
lattice and effective QCD calculations, we find the strange-quark chemical
potential to change sign: from positive in the hadronic phase - to zero upon
deconfinement - to negative in the partonic domain. We propose this change in
the sign of the strange-quark chemical potential to be an experimentally
accessible order parameter and a unique, concise and well-defined indication of
the quark-deconfinement phase transition in nuclear matter.Comment: 22 pages, 14 figures within text, 2 figures(6,B3) as separate files.
To be published in J.Phys.G: Nucl.&Part.Phys. G28 (2002
Multiplicity Distributions and Rapidity Gaps
I examine the phenomenology of particle multiplicity distributions, with
special emphasis on the low multiplicities that are a background in the study
of rapidity gaps. In particular, I analyze the multiplicity distribution in a
rapidity interval between two jets, using the HERWIG QCD simulation with some
necessary modifications. The distribution is not of the negative binomial form,
and displays an anomalous enhancement at zero multiplicity. Some useful
mathematical tools for working with multiplicity distributions are presented.
It is demonstrated that ignoring particles with pt<0.2 has theoretical
advantages, in addition to being convenient experimentally.Comment: 24 pages, LaTeX, MSUHEP/94071
Overpopulation of in pp collisions: a way to distinguish statistical hadronization from string dynamics
The ratio originating from string decays is predicted
to be larger than unity in proton proton interactions at SPS energies (=160 GeV). The anti-omega dominance increases with decreasing beam energy.
This surprising behavior is caused by the combinatorics of quark-antiquark
production in small and low-mass strings. Since this behavior is not found in a
statistical description of hadron production in proton proton collisions, it
may serve as a key observable to probe the hadronization mechanism in such
collisions.Comment: 4 pages, 4 figure
Hadron Production and Phase Changes in Relativistic Heavy Ion Collisions
We study soft hadron production in relativistic heavy ion collisions in a
wide range of reaction energy, 4.8 GeV <sqrt{s_ NN}<200 GeV, and make
predictions about yields of particles using the statistical hadronization
model. In fits to experimental data, we obtain both statistical parameters as
well as physical properties of the hadron source. We identify the properties of
the fireball at the critical energy threshold, 6.26 GeV < sqrt{s_NN}^cr} <7.61
GeV, delineating for higher energies hadronization of an entropy rich phase. In
terms of the chemical composition, one sees a phase which at low energy is
chemically under-saturated, and which turns into a chemically over-saturated
state persisting up to the maximum accessible energy. Assuming that there is no
change in physical mechanisms in the energy range 15>sqrt{s_NN} \ge 200 GeV, we
use continuity of particle yields and statistical parameters to predict the
hadron production at sqrt{s_NN}=62.4 GeV, and obtain total yields of hadrons at
sqrt{s_NN}=130 GeV. We consider, in depth, the pattern we uncover within the
hadronization condition, and discuss possible mechanisms associated with the
identified rapid change in system properties at sqrt{s_NN ^cr}. We propose that
the chemically over-saturated 2+1 flavor hadron matter system undergoes a 1st
order phase transition.Comment: 23 pages; a) we correct an entropy yield error which the early SHARE
release contained; this changes tables and figures comprising physical
properties involving entropy, the data fits are unaffected. b) we
incorporated the latest strange hadron yields of NA49 and c) this version is
in press in EPJ
Thermal fluctuations in the interacting pion gas
We derive the two-particle fluctuation correlator in a thermal gas of
pi-mesons to the lowest order in an interaction due to a resonance exchange. A
diagrammatic technique is used. We discuss how this result can be applied to
event-by-event fluctuations in heavy-ion collisions, in particular, to search
for the critical point of QCD. As a practical example, we determine the shape
of the rapidity correlator.Comment: 12 pages, 4 figures, RevTe
Charged Particle Production in Proton-, Deuteron-, Oxygen- and Sulphur-Nucleus Collisions at 200 GeV per Nucleon
The transverse momentum and rapidity distributions of net protons and
negatively charged hadrons have been measured for minimum bias proton-nucleus
and deuteron-gold interactions, as well as central oxygen-gold and
sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net
protons at midrapidity in central nucleus-nucleus collisions increases both
with target mass for sulphur projectiles and with the projectile mass for a
gold target. The shape of the rapidity distributions of net protons forward of
midrapidity for d+Au and central S+Au collisions is similar. The average
rapidity loss is larger than 2 units of rapidity for reactions with the gold
target. The transverse momentum spectra of net protons for all reactions can be
described by a thermal distribution with `temperatures' between 145 +- 11 MeV
(p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The
multiplicity of negatively charged hadrons increases with the mass of the
colliding system. The shape of the transverse momentum spectra of negatively
charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and
central nucleus-nucleus collisions. The mean transverse momentum is almost
constant in the vicinity of midrapidity and shows little variation with the
target and projectile masses. The average number of produced negatively charged
hadrons per participant baryon increases slightly from p+p, p+A to central
S+S,Ag collisions.Comment: 47 pages, submitted to Z. Phys.
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