1,352 research outputs found
Color fluctuation approximation for multiple interactions in leading twist theory of nuclear shadowing
The leading twist theory of nuclear shadowing predicts the shadowing
correction to nuclear parton distributions at small by connecting it to the
leading twist hard diffraction in electron-nucleon scattering. The
uncertainties of the predictions are related to the shadowing effects resulting
from the interaction of the hard probe with nucleons. We argue that
the pattern of hard diffraction observed at HERA allows one to reduce these
uncertainties. We develop a new approach to the treatment of these multiple
interactions, which is based on the concept of the color fluctuations and
accounts for the presence of both point-like and hadron-like configurations in
the virtual photon wave function. Using the developed framework, we update our
predictions for the leading twist nuclear shadowing in nuclear parton
distributions of heavy nuclei at small .Comment: 16 pages, 4 figures. Revised to address the Referee's comments.
Matches the published version, PLB 687 (2010) 167
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
The Effect of Shadowing on Initial Conditions, Transverse Energy and Hard Probes in Ultrarelativistic Heavy Ion Collisions
The effect of shadowing on the early state of ultrarelativistic heavy ion
collisions is investigated along with transverse energy and hard process
production, specifically Drell-Yan, , and production. We
choose several parton distributions and parameterizations of nuclear shadowing,
as well as the spatial dependence of shadowing, to study the influence of
shadowing on relevant observables. Results are presented for Au+Au collisions
at GeV and Pb+Pb collisions at TeV.Comment: Submitted to Phys. Rev.
Estimation of Collision Impact Parameter
We demonstrate that the nuclear collision geometry (i.e. impact parameter)
can be determined with 1.5 fm accuracy in an event-by-event analysis by
measuring the transverse energy flow in the pseudorapidity region with a minimal dependence on collision dynamics details at the LHC
energy scale. Using the HIJING model we have illustrated our calculation by a
simulation of events of nucleus-nucleus interactions at the c.m.s energy from 1
up to 5.5 TeV per nucleon and various type of nuclei.Comment: 6 pages, 3 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
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
Angular pattern of minijet transverse energy flow in hadron and nuclear collisions
The azimuthal asymmetry of minijet system produced at the early stage of
nucleon-nucleon and nuclear collisions in a central rapidity window is studied.
We show that in pp collisions the minijet transverse energy production in a
central rapidity window is essentially unbalanced in azimuth due to asymmetric
contributions in which only one minijet hits the acceptance window. We further
study the angular pattern of transverse energy flow generated by semihard
degrees of freedom at the early stage of high energy nuclear collisions and its
dependence on the number of semihard collisions in the models both including
and neglecting soft contributions to the inelastic cross section at RHIC and
LHC energies as well as on the choice of the infrared cutoff.Comment: 25 LaTeX pages, 11 figures embedded with epsf; expanded versio
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
Jets in 200 GeV p+p and d+Au collisions from the STAR experiment at RHIC
Full jet reconstruction in heavy-ion collisions is a promising tool for the
quantitative study of properties of the dense medium produced at RHIC.
Measurements of d+Au collisions are important to disentangle initial state
nuclear effects from medium-induced kT broadening and jet quenching. Study of
jet production and properties in d+Au in combination with similar studies in
p+p is an important baseline measurement needed to better understand heavy-ion
results. We present mid-rapidity inclusive jet pT spectra and di-jet
correlations (kT) in 200 GeV p+p and d+Au collisions from the 2007-2008 RHIC
run. We discuss the methods used to correct the data for detector effects and
for background in d+Au collisions.Comment: 4 pages, 5 figures. To appear in Hot Quarks 2010 conference
proceeding
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