79 research outputs found
Classical chromodynamics and heavy ion collisions
This paper is a slightly modified version of the introductory part of a
doctoral dissertation also containing the articles hep-ph/0303076,
hep-ph/0409328 and hep-ph/0409058. The paper focuses on the calculation of
particle production in a relativistic heavy ion collision using the
McLerran-Venugopalan model. The main part of the paper summarizes the
background of these numerical calculations. First we relate this calculation of
the initial stage af a heavy ion collision to our understanding of the whole
collision process. Then we discuss the saturation physics of the small x
wavefunction of a hadron or a nucleus. The classical field model of Kovner,
McLerran and Weigert is then introduced before moving to discuss the numerical
algorithms used to compute gluon and quark pair production in this model.
Finally we shortly review the results on gluon and quark-antiquark production
obtained in the three articles mentioned above.Comment: 55 pages, 11 figures, introductory part of a PhD thesi
Initial conditions in AA and pA collisions
A full understanding of the spacetime evolution of the QCD matter created in a heavy ion collision requires understanding the properties of the initial stages. In the weak coupling picture these are dominated by classical gluon fields, whose properties can also be studied via the scattering of dilute probes off a high energy hadron or nucleus. A particular challenge is understanding small systems, where LHC data is also showing signs of collective behavior. We discuss some recent results of on the initial matter production and thermalization in heavy ion collisions, in particular in the gluon saturation framework.Peer reviewe
High energy factorization in nucleus-nucleus collisions
We derive a high energy factorization theorem for inclusive gluon production
in A+A collisions. Our factorized formula resums i) all order leading
logarithms (g^2 \ln(1/x_{1,2}))^n of the incoming partons momentum fractions,
and ii) all contributions (g \rho_{1,2})^n that are enhanced when the color
charge densities in the two nuclei are of order of the inverse coupling--
\rho_{1,2}\sim g^{-1}. The resummed inclusive gluon spectrum can be expressed
as a convolution of gauge invariant distributions W[\rho_{1,2}] from each of
the nuclei with the leading order gluon number operator. These distributions
are shown to satisfy the JIMWLK equation describing the evolution of nuclear
wavefunctions with rapidity. As a by-product, we demonstrate that the JIMWLK
Hamiltonian can be derived entirely in terms of retarded light cone Green's
functions without any ambiguities in their pole prescriptions. We comment on
the implications of our results for understanding the Glasma produced at early
times in A+A collisions at collider energies.Comment: 55 pages, 14 postscript figure
Probing spectral properties of the QGP with real-time lattice simulations
We present a new method to obtain spectral properties of a non-Abelian gauge
theory in the region where occupation numbers are high. The method to measure
the (single-particle) spectral function is based on linear response theory and
classical-statistical lattice simulations. Although we apply it to a system far
from equilibrium in a self-similar regime, the extracted spectral function can
be understood within the hard thermal loop (HTL) formalism and can thus be
connected to thermal equilibrium at high temperatures. This allows us to obtain
quantities like the lifetime of quasiparticles that are beyond the leading
order and difficult to compute within HTL. The approach has the potential to
measure transport coefficients, to study the earliest stages of heavy-ion
collisions in a controlled way and it can be employed beyond the range of
validity of HTL.Comment: 5 pages, 2 figures, Proceedings of the International Conference on
Hard and Electromagnetic Probes of High-Energy Nuclear Collisions - Hard
Probes 201
Evolution of initial stage fluctuations in the glasma
We perform a calculation of the one- and two-point correlation functions of energy density and axial charge deposited in the glasma in the initial stage of a heavy ion collision at (mite proper time. We do this by describing the initial stage of heavy ion collisions in terms of freely evolving classical fields whose dynamics obey the linearized Yang-Mills equations. Our approach allows us to systematically resum the contributions of high momentum modes that would make a power series expansion in proper time divergent. We evaluate the field correlators in the McLerran-Venugopalan model using the glasma graph approximation, but our approach for the time dependence can be applied to a general four-point function of the initial color fields. Our results provide analytical insight into the preequilibrium phase of heavy ion collisions without requiring a numerical solution to the Yang-Mills equations.Peer reviewe
Higher-order corrections to exclusive heavy vector meson production
We present results for higher-order corrections to exclusive
production. This includes the first relativistic correction
of order in quark velocity, and next-to-leading order corrections in
for longitudinally polarized production. The relativistic
corrections are found to be important for a good description of the HERA data,
especially at small values of the photon virtuality. The next-to-leading order
results for longitudinal production are evaluated numerically. We also
demonstrate how the vector meson production provides complementary information
to the structure functions for extracting the initial condition for the
small- evolution of the dipole-proton scattering amplitude.Comment: Submission to SciPost, 6 pages, 2 figure
Effects of partial thermalization on HBT interferometry
Hydrodynamical models have generally failed to describe interferometry radii
measured at RHIC. In order to investigate this ``HBT puzzle'', we carry out a
systematic study of HBT radii in ultrarelativistic heavy-ion collisions within
a two-dimensional transport model. We compute the transverse radii and
as functions of for various values of the Knudsen number, which
measures the degree of thermalization in the system. For realistic values of
the Knudsen number estimated from data, we obtain ,
much closer to data than standard hydrodynamical results. Femtoscopic
observables vary little with the degree of thermalization. Azimuthal
oscillations of the radii in non central collisions do not provide a good probe
of thermalization.Comment: Proceedings for Quark Matter 2009, Knoxville, TN US
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