348 research outputs found
Shadowing and Antishadowing in Neutrino Deep Inelastic Scattering
The coherence of multiscattering quark nuclear processes leads to shadowing
and antishadowing of the electromagnetic nuclear structure functions in
agreement with measurements. This picture leads to substantially different
antishadowing for charged and neutral current processes, particularly in
anti-neutrino reactions, thus affecting the extraction of the weak-mixing angle
.Comment: 4 pages, 1 figure, Prepared for the International Conference on QCD
and Hadronic Physics, Beijing, China, June 16-20 200
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
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
Interplay of Soft and Hard Interactions in Nuclear Shadowing at High and Low x
Nuclear shadowing corrections are dominated by soft interaction and grow as
function of more slowly than the single scattering term, which has an
essential contribution from hard interaction. Therefore, we predict vanishing
nuclear shadowing at very low provided that is high and fixed. At the
same time, at medium and low , nuclear shadowing grows with as is
well known for soft hadronic interactions.Comment: Latex file, 8 pages including 4 Postscript figures. To appear in the
Proceedings of the Workshop on Future Physics at HERA, DESY, September 25,
1995 -- May 31, 199
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
Flavor and Charge Symmetry in the Parton Distributions of the Nucleon
Recent calculations of charge symmetry violation(CSV) in the valence quark
distributions of the nucleon have revealed that the dominant symmetry breaking
contribution comes from the mass associated with the spectator quark
system.Assuming that the change in the spectator mass can be treated
perturbatively, we derive a model independent expression for the shift in the
parton distributions of the nucleon. This result is used to derive a relation
between the charge and flavor asymmetric contributions to the valence quark
distributions in the proton, and to calculate CSV contributions to the nucleon
sea. The CSV contribution to the Gottfried sum rule is also estimated, and
found to be small
The sigma term and the quark number operator in QCD
We discuss the relationship of the forward matrix element of the operator
, related to the so-called sigma term, to the quark number. We
show that in the naive quark model in the canonical formalism these quantities
coincide in the limit of small average quark momenta. In the QCD parton model
defined through light-front quantization this result is preserved at leading
perturbative order but it receives radiative corrections. We analyze the
theoretical and phenomenological consequences of this result, which provides a
bridge between a current algebra quantity, the sigma term, and a deep-inelastic
quantity, the parton number.Comment: 30 pages, 1 figure, DFTT-92-6 (April 1993
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
TACTIC : The TRIUMF Annular Chamber for Tracking and Identification of Charged particles
An in-depth characterization of the TACTIC detector was performed using data from a 148Gd alpha source and some test runs with a stable ion beam. The detector is an active target time-projection chamber with a blind central region for maximizing beam tolerance and GEM-based electron amplification, equipped with a modern digitizing data acquisition system allowing the recording of full signals. The system was developed to study the reaction 8Li(α,n)11B, which is important for bridging the mass 8 gap in scenarios of low 4He density like Inhomogeneous Big Bang Nucleosynthesis and the production of r-process seeds in supernovae. Both energy resolution and tracking accuracy were found to agree with theoretical predictions and Geant4 simulations. The 8Li beam rate capability of the system is predicted to be of the order of 105s-1, several orders of magnitude higher than most previous measurements of the same reaction, while still maintaining a high detection efficiency of 70% to 80 %
Nuclear Antishadowing in Neutrino Deep Inelastic Scattering
The shadowing and antishadowing of nuclear structure functions in the
Gribov-Glauber picture is due respectively to the destructive and constructive
interference of amplitudes arising from the multiple-scattering of quarks in
the nucleus. The effective quark-nucleon scattering amplitude includes Pomeron
and Odderon contributions from multi-gluon exchange as well as Reggeon
quark-exchange contributions. We show that the coherence of these
multiscattering nuclear processes leads to shadowing and antishadowing of the
electromagnetic nuclear structure functions in agreement with measurements.
This picture leads to substantially different antishadowing for charged and
neutral current reactions, thus affecting the extraction of the weak-mixing
angle . We find that part of the anomalous NuTeV result for
could be due to the nonuniversality of nuclear antishadowing for
charged and neutral currents. Detailed measurements of the nuclear dependence
of individual quark structure functions are thus needed to establish the
distinctive phenomenology of shadowing and antishadowing and to make the NuTeV
results definitive.Comment: 38 pages, 15 figure
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