5,415 research outputs found
Asymptotic properties of the solutions of a differential equation appearing in QCD
We establish the asymptotic behaviour of the ratio for
, where is a solution, vanishing at infinity,
of the differential equation
on the domain and . Some results are valid for more general 's.Comment: 6 pages, late
Partonic Energy Loss and the Drell-Yan Process
We examine the current status of the extraction of the rate of partonic
energy loss in nuclei from A dependent data. The advantages and difficulties of
using the Drell-Yan process to measure the energy loss of a parton traversing a
cold nuclear medium are discussed. The prospects of using relatively low energy
proton beams for a definitive measurement of partonic energy loss are
presented.Comment: 12 pages, 2 figure
Prompt Photon and Inclusive Production at RHIC and LHC
We present results for prompt photon and inclusive production in p-p
and A-A collisions at RHIC and LHC energies. We include the full
next-to-leading order radiative corrections and nuclear effects, such as
nuclear shadowing and parton energy loss. We find the next-to-leading order
corrections to be large and dependent. We show how measurements of
production at RHIC and LHC, at large , can provide valuable
information about the nature of parton energy loss.
We calculate the ratio of prompt photons to neutral pions and show that at
RHIC energies this ratio increases with approaching one at
GeV, due to the large suppression of production. We show that at the
LHC, this ratio has steep dependence and approaches 10% effect at GeV.Comment: Talk presented by I. Sarcevic, to appear in the Proceedings of Quark
Matter 2002; 4 pages including 4 color figure
Uniaxial pressure dependencies of the phase transitions in GdMnO
GdMnO shows an incommensurate antiferromagnetic order below
K, transforms into a canted A-type antiferromagnet below K, and for
finite magnetic fields along the b axis ferroelectric order occurs below
K. From high-resolution thermal expansion measurements along all
three principal axes, we determine the uniaxial pressure dependencies of the
various transition temperatures and discuss their correlation to changes of the
magnetic exchange couplings in MnO ().Comment: 2 pages, 3 figures, submitted to JMMM (Proceedings of ICM'06, Kyoto
On p_T-broadening of high energy partons associated with the LPM effect in a finite-volume QCD medium
We study the contributions from radiation to -broadening of a high
energy parton traversing a QCD medium with a finite length . The interaction
between the parton and the medium is described by decorrelated static multiple
scattering. Amplitudes of medium-induced gluon emission and parton self-energy
diagrams are evaluated in the soft gluon limit in the BDMPS formalism. We find
both the double-logarithmic correction from incoherent scattering, which is
parametrically the same as that in single scattering, and the logarithmic
correction from the LPM effect. Therefore, we expect a parametrically large
correction from radiation to the medium-induced -broadening in
perturbative QCD.Comment: 19 pages, focusing only on calculations about the medium-induced
diagrams, origin for double-log reinterpreted, final version to appear in
JHE
Kinetic equilibration in heavy ion collisions: the role of elastic processes
We discuss the question of thermalization during the very early stages of a
high energy heavy ion collision. We review a recent study where we explicitely
showed that, contrarily to a widely used assumption, elastic collisions between
the produced partons are not sufficient to rapidly drive the system toward
local kinetic equilibrium. We then briefly discuss recent developments
concerning the description of kinetic equilibration and comment on some open
issues related to phenomenology.Comment: Talk given at "Quark Matter 2002", July 17-24, Nantes, Franc
Medium-induced gluon radiation and jet quenching in heavy ion collisions
In this brief review, I summarize the new developments on the description of
gluon radiation by energetic quarks traversing a medium as well as the
observable consequences in high-energy heavy ion collisions. Information about
the initial state is essential for a reliable interpretation of the
experimental results and will also be reviewed. Comparison with experimental
data from RHIC and expectation for the future LHC will be given.Comment: 16 pages, 9 postscript figures. Invited brief review for Modern
Physics Letters
Experimental investigations of synchrotron radiation at the onset of the quantum regime
The classical description of synchrotron radiation fails at large Lorentz
factors, , for relativistic electrons crossing strong transverse
magnetic fields . In the rest frame of the electron this field is comparable
to the so-called critical field T. For quantum corrections are essential for the description of
synchrotron radiation to conserve energy. With electrons of energies 10-150 GeV
penetrating a germanium single crystal along the axis, we have
experimentally investigated the transition from the regime where classical
synchrotron radiation is an adequate description, to the regime where the
emission drastically changes character; not only in magnitude, but also in
spectral shape. The spectrum can only be described by quantum synchrotron
radiation formulas. Apart from being a test of strong-field quantum
electrodynamics, the experimental results are also relevant for the design of
future linear colliders where beamstrahlung - a closely related process - may
limit the achievable luminosity.Comment: 11 pages, 18 figures, submitted to PR
Chemical Equilibration in Hadronic Collisions
We study chemical equilibration in out-of-equilibrium Quark-Gluon Plasma
using the first principles method of QCD effective kinetic theory, accurate at
weak coupling. In longitudinally expanding systems--relevant for relativistic
nuclear collisions--we find that for realistic couplings chemical equilibration
takes place after hydrodynamization, but well before local thermalization. We
estimate that hadronic collisions with final state multiplicities
live long enough to reach approximate
chemical equilibrium, which is consistent with the saturation of strangeness
enhancement observed in proton-proton, proton-nucleus and nucleus-nucleus
collisions.Comment: 7 pages, 3 figures, see also our companion paper arXiv:1811.03068, v2
small changes, published versio
Angular intricacies in hot gauge field theories
It is argued that in hot gauge field theories, "Hard Thermal Loops" leading
order calculations call for a definite sequence of angular averages and
discontinuity (or Imaginary part prescription) operations, and run otherwise
into incorrect results. The ten years old collinear singularity problem of hot
, provides a striking illustration of that fate.Comment: 14 pages, 1 figur
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