1,016 research outputs found
High Energy Nuclear Collisions
Highlights of the results from ultrarelativistic heavy ion collisions at
CERN-SPS are reviewed. In particular, I discuss how the experimental results
indicate that a collective strongly interacting system has been produced, and
what are the implications towards the Quark Gluon Plasma. The physical ideas
behind measuring certain observables are introduced. The future program of high
energy nuclear collisions at BNL-RHIC and CERN-LHC/ALICE is also briefly
discussed.Comment: Plenary talk at the International Europhysics Conference on High
Energy Physics, EPS-HEP99, Tampere, Finland, July 1999; 21 page
Minijets in ultrarelativistic heavy ion collisions at future colliders
The role of minijet production as initial conditions for QGP production at
in nuclear collisions at the LHC and RHIC energies is
discussed.Comment: 15 pages, including 2 figures, an invited article to Comments on
Nuclear and Particle Physic
Initial state of the QGP from perturbative QCD + saturation
The production of the initial state of the QGP in very high-energy
collisions is discussed within the framework of perturbative QCD and
saturation. The next-to-leading order computation of the transverse energy of
minijets is reviewed. Saturation of parton production, conjectured to occur at
a dynamically determinable perturbative scale, leads to estimates of the
initial densities. The final state multiplicities are predicted by assuming an
isentropic hydrodynamical further evolution. Comparison with RHIC data is
shown.Comment: 10 pages, 8 figures. Invited talk at the International Conference on
Statistical QCD, August 2001, Bielefel
Pre-thermalization dynamics: initial conditions for QGP at the LHC and RHIC from perturbative QCD
I discuss how the initial conditions for QGP-production in ultrarelativistic
heavy ion collisions at the LHC and RHIC can be computed from perturbative QCD.Comment: 11 pages, including 2 figures. A lecture at the International School
on the Physics of Quark Gluon Plasma, June 3-6, 1997, Hiroshim
Baryon-to-entropy ratio in very high energy nuclear collisions
We compute as a function of rapidity the baryon number carried by quarks
and antiquarks with 2 GeV produced in Pb+Pb collisions at
TeV energies. The computation is carried out in lowest order QCD perturbation
theory using structure functions compatible with HERA results. At GeV
the initial gluon density is both transversally saturated and thermalised in
the sense that the energy/gluon equals to that of an ideal gas with the same
energy density. Even at these high energies the initial net baryon number
density at at fm will be more than the normal nuclear matter
density but the baryon-to-entropy ratio is only .
Further evolution of the system is discussed and the final baryon-to-entropy
ratio is estimated.Comment: 19 pages, including 10 ps-figure
On the sensitivity of the dijet asymmetry to the physics of jet quenching
The appearance of monojets is among the most striking signature of jet
quenching in the context of ultrarelativistic heavy-ion collisions.
Experimentally, the disappearance of jets has been quantified by the ATLAS and
CMS collaborations in terms of the dijet asymmetry observable A_J. While the
experimental findings initially gave rise to claims that the measured A_J would
challenge the radiative energy loss paradigm, the results of a systematic
investigation of A_J in different models for the medium evolution and for the
shower-medium interaction presented here suggest that the observed properties
of A_J arise fairly generically and independent of specific model assumptions
for a large class of reasonable models. This would imply that rather than
posing a challenge to any particular model, the observable prompts the question
what model dynamics is not compatible with the data.Comment: 8 pages, 6 figures, added computations of jet R_AA and R=0.2 result
Testing collinear factorization and nuclear parton distributions with pA collisions at the LHC
Global perturbative QCD analyses, based on large data sets from
electron-proton and hadron collider experiments, provide tight constraints on
the parton distribution function (PDF) in the proton. The extension of these
analyses to nuclear parton distributions (nPDF) has attracted much interest in
recent years. nPDFs are needed as benchmarks for the characterization of hot
QCD matter in nucleus-nucleus collisions, and attract further interest since
they may show novel signatures of non- linear density-dependent QCD evolution.
However, it is not known from first principles whether the factorization of
long-range phenomena into process-independent parton distribution, which
underlies global PDF extractions for the proton, extends to nuclear effects. As
a consequence, assessing the reliability of nPDFs for benchmark calculations
goes beyond testing the numerical accuracy of their extraction and requires
phenomenological tests of the factorization assumption. Here we argue that a
proton-nucleus collision program at the LHC would provide a set of measurements
allowing for unprecedented tests of the factorization assumption underlying
global nPDF fits.Comment: 4 pages, 5 figure
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