343 research outputs found
On parton distributions beyond the leading order
The importance of properly taking into account the factorization scheme
dependence of parton distribution functions is emphasized. A serious error in
the usual handling of this topic is pointed out and the correct procedure for
transforming parton distribution functions from one factorisation scheme to
another recalled. It is shown that the conventional and
DIS definitions thereof are ill-defined due to the lack of distinction between
the factorisation scheme dependence of parton distribution functions and
renormalisation scheme dependence of the strong coupling constant . A
novel definition of parton distribution functions is suggested and its role in
the construction of consistent next-to-leading order event generators briefly
outlined.Comment: PRA-HEP-93/05, Latex, 10 pages and 2 Postscript figures appended at
the end of this fil
\bar u - \bar d asymmetry - a few remarks
We make a few remarks on possible sources of uncertainties of the asymmetry obtained by different methods and comment on its possible
verification in the future. In addition we comment on its present
understanding.Comment: 3 pages, a talk at the 7th International Workshop on Deep Inelastic
Scattering and QCD (DIS99), Zeuthen, April 199
Liquid Xenon Detectors for Positron Emission Tomography
PET is a functional imaging technique based on detection of annihilation
photons following beta decay producing positrons. In this paper, we present the
concept of a new PET system for preclinical applications consisting of a ring
of twelve time projection chambers filled with liquid xenon viewed by avalanche
photodiodes. Simultaneous measurement of ionization charge and scintillation
light leads to a significant improvement to spatial resolution, image quality,
and sensitivity. Simulated performance shows that an energy resolution of <10%
(FWHM) and a sensitivity of 15% are achievable. First tests with a prototype
TPC indicate position resolution <1 mm (FWHM).Comment: Paper presented at the International Nuclear Physics Conference,
Vancouver, Canada, 201
On QCD -evolution of Deuteron Structure Function for
The deep-inelastic deuteron structure function (SF) in the
covariant approach in light-cone variables is considered. The and
-dependences of SF are calculated. The QCD analysis of generated data both
for non-cumulative ranges was performed. It was
shown that -evolution of SF is valid for ranges and
for the same value of QCD scale parameter . It was
found the -dependence of SF for the ranges is essentially different.Comment: LaTeX, 10 pages, 2 Postscript figure
Omega Meson Cloud and the Proton's Light Anti-Quark Distribution
We use the meson cloud model of the nucleon to calculate distribution
functions for and in the proton.
Including the effect of the omega meson cloud, with a coupling constant
, allows a reasonably good description of the data.Comment: 6 pages, 2 figures, LaTe
EPS09 - Nuclear PDFs and Their Uncertainties at NLO
In this talk, we present our recent next-to-leading order (NLO) nuclear
parton distribution functions (nPDFs), which we call EPS09. As an extension to
earlier NLO analyses, we supplement the deep inelastic scattering and Drell-Yan
dilepton data by inclusive midrapidity pion measurements from RHIC in order to
reduce the otherwize large freedom in the nuclear gluon densities. Our
Hessian-type error analysis leading to a collection of nPDF error sets, is the
first of its kind among the nPDF analyses.Comment: 4 pages, 4 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
The Flavor Asymmetry of the Nucleon Sea
We re-examine the effects of anti-symmetry on the anti-quarks in the nucleon
sea arising from gluon exchange and pion exchange between confined quarks.
While the effect is primarily to suppress anti-down relative to anti-up quarks,
this is numerically insignificant for the pion terms.Comment: To appear in Phys. Rev.
Color Transparency via Coherent Exclusive rho Production
We examine the potential of the COMPASS experiment at CERN to study color
transparency via exclusive coherent vector meson production in hard
muon-nucleus scattering. It is demonstrated that COMPASS has high sensitivity
to test this important prediction of perturbative QCD.Comment: Feasibility study for COMPASS collaboration, 3 pages, no figures, 1
table. This contribution is based on talk presented at the Workshop on Spin
Physics, Trento, Italy, July 2001. The conference www site is
http://ECTstar.ect.it/contents.html The proceedings of the workshop will be
published as a special issue of Nuclear Physics B (proc suppl), eds. S Bass,
A De Roeck and A Deshpande. A more complete 26 page feasibility study with 7
figures and 3 tables is available as A. Sandacz et al., hep-ex/0106076
Revision of 26 Sept. for Ref. 11 modificatio
Testing the meson cloud in the nucleon in Drell-Yan processes
We discuss the present status of the \bar u-\bar d asymmetry in the nucleon
and analize the quantities which are best suited to verify the asymmetry. We
find that the Drell-Yan asymmetry is the quantity insensitive to the valence
quark distributions and very sensitive to the flavour asymmetry of the sea. We
compare the prediction of the meson cloud model with different experimental
data including the Fermilab E772 data and recent data of the NA51 Collaboration
at CERN and make predictions for the planned Drell-Yan experiments.Comment: written in ReVTeX, 26 pages + 10 PS-figure
Shadowing in neutrino deep inelastic scattering and the determination of the strange quark distribution
We discuss shadowing corrections to the structure function in neutrino
deep-inelastic scattering on heavy nuclear targets. In particular, we examine
the role played by shadowing in the comparison of the structure functions
measured in neutrino and muon deep inelastic scattering. The importance of
shadowing corrections in the determination of the strange quark distributions
is explained.Comment: 22 pages, 7 figure
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