1,234 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
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
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
-Pb deep inelastic scattering
Nuclear-medium effects in the weak structure functions and
in the charged current neutrino and antineutrino induced deep
inelastic reactions in Pb have been studied. The calculations have been
performed in a theoretical model using relativistic nuclear spectral functions
which incorporate Fermi motion, binding and nucleon correlations.
We also consider the pion and rho meson cloud contributions calculated from a
microscopic model for meson-nucleus self-energies. Using these structure
functions, the results for the differential cross section have been obtained
and compared with the CERN Hybrid Oscillation Research apparatUS (CHORUS) data.
The results for the ratios ,
, ,
, and (i=2,3)
have also been obtained and a few have been compared with some of the
phenomenological fits.Comment: 19Pages, 12 Fig
Nuclear corrections of parton distribution functions
We report global analysis results of experimental data for nuclear
structure-function ratios F_2^A/F_2^{A'} and proton-nucleus Drell-Yan
cross-section ratios sigma_{DY}^{pA}/sigma_{DY}^{pA'} in order to determine
optimum parton distribution functions (PDFs) in nuclei. An important point of
this analysis is to show uncertainties of the distributions by the Hessian
method. The results indicate that the uncertainties are large for gluon
distributions in the whole x region and for antiquark distributions at x>0.2.
We provide a code for calculating any nuclear PDFs at given x and Q^2 for
general users. They can be used for calculating high-energy nuclear reactions
including neutrino-nucleus interactions, which are discussed at this workshop.Comment: 1+6 pages, LaTeX, 10 eps files, espcrc2.sty, to be published in Nucl.
Phys. B Supplements, Proceedings of the Third International Workshop on
Neutrino-Nucleus Interactions in the Few GeV Region (NuInt04), Gran Sasso,
Italy, March 17-21, 2004. Nuclear PDF library is available at
http://hs.phys.saga-u.ac.jp/nuclp.htm
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
- …