851 research outputs found
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
A global DGLAP analysis of nuclear PDFs
In this talk, we shortly report results from our recent global DGLAP analysis
of nuclear parton distributions. This is an extension of our former
EKS98-analysis improved with an automated minimization procedure and
uncertainty estimates. Although our new analysis show no significant deviation
from EKS98, a sign of a significantly stronger gluon shadowing could be seen in
the RHIC BRAHMS data.Comment: Talk given at EPS HEP 200
Black Hole Production at LHC: String Balls and Black Holes from pp and Lead-lead Collisions
If the fundamental planck scale is near a TeV, then parton collisions with
high enough center-of-mass energy should produce black holes. The production
rate for such black holes at LHC has been extensively studied for the case of a
proton-proton collision. In this paper, we extend this analysis to a lead-lead
collision at LHC. We find that the cross section for small black holes which
may in principle be produced in such a collision is either enhanced or
suppressed, depending upon the black hole mass. For example, for black holes
with a mass around 3 TeV we find that the differential black hole production
cross section, d\sigma/dM, in a typical lead-lead collision is up to 90 times
larger than that for black holes produced in a typical proton-proton collision.
We also discuss the cross-sections for `string ball' production in these
collisions. For string balls of mass about 1 (2) TeV, we find that the
differential production cross section in a typical lead-lead collision may be
enhanced by a factor up to 3300 (850) times that of a proton-proton collision
at LHC.Comment: Added some discussion, final version to appear in Phys. Rev. D (rapid
communications
CGC and initial state effects in Heavy Ion Collisions
A brief review of the phenomenological studies in the field of heavy ion
collisions based on the Color Glass Condensate theory and, in particular, of
those relying in the use of the BK equation including running coupling effects
is presented.Comment: 6 pages, 5 figures. Contribution to the proceedings of the Hot Quarks
2010 Conference. June 21-26, La Londe Les Maures, Franc
Non-equilibrium initial conditions from pQCD for RHIC and LHC
We calculate the initial non-equilibrium conditions from perturbative QCD
(pQCD) within Glauber multiple scattering theory for AGeV and
ATeV. At the soon available collider energies one will
particularly test the small region of the parton distributions entering the
cross sections. Therefore shadowing effects, previously more or less
unimportant, will lead to new effects on variables such as particle
multiplicities , transverse energy production , and the
initial temperature . In this paper we will have a closer look on the
effects of shadowing by employing different parametrizations for the shadowing
effect for valence quarks, sea quarks and gluons. Since the cross sections at
midrapidity are dominated by processes involving gluons the amount of their
depletion is particularly important. We will therefore have a closer look on
the results for , , and by using two different
gluon shadowing ratios, differing strongly in size. As a matter of fact, the
calculated quantities differ significantly.Comment: typo in ref's removed, ack's added, no change in result
Effects of shadowing on Drell-Yan dilepton production in high energy nuclear collisions
We compute cross sections for the Drell-Yan process in nuclear collisions at
next-to-leading order (NLO) in \alpha_s. The effects of shadowing on the
normalization and on the mass and rapidity dependence of these cross sections
are presented. An estimate of higher order corrections is obtained from
next-to-next-to-leading order (NNLO) calculation of the rapidity-integrated
mass distribution. Variations in these predictions resulting from choices of
parton distribution sets are discussed. Numerical results for mass
distributions at NLO are presented for RHIC and LHC energies, using appropriate
rapidity intervals. The shadowing factors in the dilepton mass range 2 < M < 10
GeV are predicted to be substantial, typically 0.5 - 0.7 at LHC, 0.7 - 0.9 at
RHIC, and approximately independent of the choice of parton distribution sets
and the order of calculation.Comment: 13 pages, 9 eps figure
Hard Parton Rescatterings and Minijets in Nuclear Collisions at LHC
The average number of minijets and the corresponding transverse energy
produced in heavy ion collisions are evaluated by including explicitly
semi-hard parton rescatterings in the dynamics of the interaction. At the LHC
semi-hard rescatterings have a sizable effect on global characteristics of the
typical inelastic event. An interesting feature is that the dependence on the
cutoff which separates soft and hard parton interactions becomes less critical
after taking rescatterings into account.Comment: 14 pages, 3 figures. Enlarged discussion in sect.1 and 4; 1 figure
added. To be published in Phys.Rev.
Fading out of J/psi color transparency in high energy heavy ion peripheral collisions
We provide predictions for the J/psi coherent production in the peripheral
heavy ion collisions at LHC and at RHIC using the leading twist model of
nuclear shadowing based on the QCD factorization theorem for diffraction and
the HERA hard diffraction data. We demonstrate that for the LHC kinematics this
model leads to a bump-shape distribution in rapidity which is suppressed
overall as compared to the expectations of the color transparency regime by a
factor 6. This is significantly larger suppression than that expected within
the impact parameter eikonal model. Thus we show that the interaction of
spatially small wave package for which the total cross section of interaction
with nucleons is small is still strongly shadowed by nuclear medium in high
energy processes.Comment: 13 pages, 7 figure
DGLAP analyses of nPDF: constraints from data
We explain how the constraints from present experimental data can be used to
obtain the nPDF in the framework of LO DGLAP evolution. We will also compare
the only two available sets of this type and comment on the important
information that neutrino factories could provide.Comment: 1 pages, 1 postscript figure. Invited talk at the NuFact'02 workshop
(Neutrino Factories based on Muon Storage Rings), London, July 200
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