1,484 research outputs found
Error Estimates on Parton Density Distributions
Error estimates on parton density distributions are presently based on the
traditional method of least squares minimisation and linear error propagation
in global QCD fits. We review the underlying assumptions and the various
mathematical representations of the method and address some technical issues
encountered in such a global analysis. Parton distribution sets which contain
error information are described.Comment: Latex, 12 pages, 5 figures. Needs iopart.cls and iopart12.clo.
Presented at New Trends in HERA Physics 2001, Ringberg Castle, Tegernsee,
Germany, June 17-22, 200
Charge dependent azimuthal correlations in Pb--Pb collisions at TeV
Separation of charges along the extreme magnetic field created in non-central
relativistic heavy--ion collisions is predicted to be a signature of local
parity violation in strong interactions. We report on results for charge
dependent two particle azimuthal correlations with respect to the reaction
plane for Pb--Pb collisions at TeV recorded in 2010 with
ALICE at the LHC. The results are compared with measurements at RHIC energies
and against currently available model predictions for LHC. Systematic studies
of possible background effects including comparison with conventional
(parity-even) correlations simulated with Monte Carlo event generators of
heavy--ion collisions are also presented.Comment: Published in the proceedings of "Quark Matter 2011", Annecy-Franc
Uncertainties on parton distribution functions from the ZEUS NLO QCD fit to data on deep inelastic scattering
An NLO QCD analysis of the ZEUS data on deep inelastic scattering
together with fixed-target data has been performed from which the gluon and
quark densities of the proton and the value of the strong coupling parameter,
, have been extracted. The study includes a full treatment of
the experimental systematic uncertainties, including point-to-point
correlations. Different ways of incorporating correlated systematic
uncertainties into the fit are discussed and compared.Comment: 8 pages, 1 figure. Invited talk at the Conference on Advanced
Statistical Techniques in Particle Physics, March 18-22 2002, Durham, U
Parton distributions from deep-inelastic-scattering data
We perform the analysis of existing light-targets deep-inelastic-scattering
(DIS) data in the leading-order (LO), next-to-leading-order (NLO), and
next-to-next-to-leading-order (NNLO) QCD approximations and extract PDFs
simultaneously with the value of the strong coupling constant and
the high-twist contribution to the structure functions. The main theoretical
uncertainties and experimental uncertainties due to all sources of experimental
errors in data are estimated, the latter generally dominate for the obtained
PDFs. The uncertainty in Higgs boson production cross section due to errors in
PDFs is % for the LHC and varies from 2% to 10% for the Fermilab
collider under variation of the Higgs boson mass from to . For the -boson production cross section the uncertainty is % for the both colliders. The value of is obtained, while the high-twist terms do
not vanish up to the NNLO as required by comparison to data
Determination of polarized parton distribution functions and their uncertainties
We investigate the polarized parton distribution functions (PDFs) and their
uncertainties by using the world data on the spin asymmetry A_1. The
uncertainties of the polarized PDFs are estimated by the Hessian method. The up
and down valence-quark distributions are determined well. However, the
antiquark distributions have large uncertainties at this stage, and it is
particularly difficult to fix the gluon distribution. The \chi^2 analysis
produces a positively polarized gluon distribution, but even \Delta g(x)=0
could be allowed according to our uncertainty estimation. In comparison with
the previous AAC (Asymmetry Analysis Collaboration) parameterization in 2000,
accurate SLAC-E155 proton data are added to the analysis. We find that the E155
data improve the determination of the polarized PDFs, especially the polarized
antiquark distributions. In addition, the gluon-distribution uncertainties are
reduced due to the correlation with the antiquark distributions. We also show
the global analysis results with the condition \Delta g(x)=0 at the initial
scale, Q^2=1 GeV^2, for clarifying the error correlation effects with the gluon
distribution.Comment: 9 pages, 15 eps figures, REVTeX, FORTRAN package is available at the
web site http://www-hs.phys.saga-u.ac.jp/aac.html. Replaced 3 eps figures in
Fig.
Hard probes in heavy ion collisions at the LHC: PDFs, shadowing and collisions
This manuscript is the outcome of the subgroup ``PDFs, shadowing and
collisions'' from the CERN workshop ``Hard Probes in Heavy Ion Collisions at
the LHC''. In addition to the experimental parameters for collisions at
the LHC, the issues discussed are factorization in nuclear collisions, nuclear
parton distributions (nPDFs), hard probes as the benchmark tests of
factorization in collisions at the LHC, and semi-hard probes as
observables with potentially large nuclear effects. Also, novel QCD phenomena
in collisions at the LHC are considered. The importance of the
program at the LHC is emphasized.Comment: The writeup of the working group "PDFs, shadowing and
collisions" for the CERN Yellow Report on Hard Probes in Heavy Ion Collisions
at the LHC, 121 pages. Subgroup convenors: K.J. Eskola, J.w. Qiu (theory) and
W. Geist (experiment). Editor: K.J. Eskol
High Q^2 Deep Inelastic Scattering at HERA
High Q^2 NC and CC cross-sections as measured at HERA can give information on
two distinct areas of current interest. Firstly, supposing that all the
electroweak parameters are well known, these cross-sections may be used to give
information on parton distributions at high x and high Q^2. Secondly, supposing
that parton distributions are well known, after evolution in Q^2 from the
kinematic regime where they are already measured, these cross-sections can be
used to give information on electroweak parameters in a process where the
exchanged boson is `spacelike' rather than `timelike'. WG1 addressed itself to
clarifying the limits of our present and possible future knowledge on both
these areas.Comment: 26 pages, 12 figures. Uses iopart.cls, iopart12.clo, axodraw.sty.
Report of WG1 of the 3rd UK Phenomenology Workshop on HERA Physics, Durham
1998. To be published in Journal of Physics
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