746 research outputs found
Charge Symmetry Violation Corrections to Determination of the Weinberg Angle in Neutrino Reactions
We show that the correction to the Paschos-Wolfenstein relation associated
with charge symmetry violation in the valence quark distributions is
essentially model independent. It is proportional to a ratio of quark momenta
that is independent of Q^2. This result provides a natural explanation of the
surprisingly good agreement found between our earlier estimates within several
different models. When applied to the recent NuTeV measurement, this effect
significantly reduces the discrepancy with other determinations of the Weinberg
angle.Comment: 7 pages, no figures; expanded discussion of N.ne.Z correction
Erratum: Next-to-leading order supersymmetric QCD predictions for associated production of gauginos and gluinos [Phys. Rev. D 62, 095014 (2000)]
Errors in the published version of the paper are corrected, and new figures
are provided.Comment: 3 pages, latex, 4 figure
Parton Distributions in the Valon Model
The parton distribution functions determined by CTEQ at low are used as
inputs to test the validity of the valon model. The valon distributions in a
nucleon are first found to be nearly independent. The parton distribution
in a valon are shown to be consistent with being universal, independent of the
valon type. The momentum fractions of the partons in the valon add up
separately to one. These properties affirm the validity of the valon model. The
various distributions are parameterized for convenient application of the
model.Comment: 9 pages + 9 figures in ep
Quasi Stable Black Holes at the Large Hadron Collider
We adress the production of black holes at LHC and their time evolution in
space times with compactified space like extra dimensions. It is shown that
black holes with life times of hundred fm/c can be produced at LHC. The
possibility of quasi-stable remnants is discussed.Comment: 4 pages, 3 figures, typos removed, omitted factors included, accepted
for publicatio
Charm quark and D^* cross sections in deeply inelastic scattering at DESY HERA
A next-to-leading order Monte Carlo program for the calculation of heavy
quark cross sections in deeply inelastic scattering is described. Concentrating
on charm quark and D^*(2010) production at HERA, several distributions are
presented and their variation with respect to charm quark mass, parton
distribution set, and renormalization-factorization scale is studied.Comment: 15 pages including 8 figures. Uses Latex, Revtex, and psfig.
References added - others updated. Several sentences/words added for clarity.
Results/conclusions unchanged. To appear in Phys. Rev.
Monte Carlo integration on GPU
We use a graphics processing unit (GPU) for fast computations of Monte Carlo
integrations. Two widely used Monte Carlo integration programs, VEGAS and
BASES, are parallelized on GPU. By using plus multi-gluon production
processes at LHC, we test integrated cross sections and execution time for
programs in FORTRAN and C on CPU and those on GPU. Integrated results agree
with each other within statistical errors. Execution time of programs on GPU
run about 50 times faster than those in C, and more than 60 times faster than
the original FORTRAN programs.Comment: 6 pages, 2 figure
Calculation of HELAS amplitudes for QCD processes using graphics processing unit (GPU)
We use a graphics processing unit (GPU) for fast calculations of helicity
amplitudes of quark and gluon scattering processes in massless QCD. New HEGET
({\bf H}ELAS {\bf E}valuation with {\bf G}PU {\bf E}nhanced {\bf T}echnology)
codes for gluon self-interactions are introduced, and a C++ program to convert
the MadGraph generated FORTRAN codes into HEGET codes in CUDA (a C-platform for
general purpose computing on GPU) is created. Because of the proliferation of
the number of Feynman diagrams and the number of independent color amplitudes,
the maximum number of final state jets we can evaluate on a GPU is limited to 4
for pure gluon processes (), or 5 for processes with one or more
quark lines such as and . Compared with the usual
CPU-based programs, we obtain 60-100 times better performance on the GPU,
except for 5-jet production processes and the processes for which
the GPU gain over the CPU is about 20
Hera Events, Tevatron Jets, and the Uncertainty On Quarks At Large X
The recently reported excess of events at HERA compared to QCD calculations
impels us to examine all possible Standard Model explanations before invoking
``new physics''. We explore the possibility of adding an unusual, but small,
component of additional quarks at large x (beyond x>0.75) as a way to increase
the predicted SM cross-section in the HERA kinematic region by the QCD
evolution feed-down effect. We describe various scenarios under which this can
be achieved while maintaining good global fits to all established data sets.
This implies a much larger SM uncertainty than commonly assumed. In addition,
the modified parton distributions provide another possible mechanism to account
for the CDF high-pt jet excess which occurs at similar x and Q^2 values.Comment: 13 page Latex, 8 ps figures, replaced with modifications to the tex
Strange-Beauty Meson Production at Colliders
The production rates and transverse momentum distributions of the
strange-beauty mesons and at colliders are calculated
assuming fragmentation is the dominant process. Results are given for the
Tevatron in the large transverse momentum region, where fragmentation is
expected to be most important.Comment: Minor changes in the discussion section. Also available at
http://www.ph.utexas.edu/~cheung/paper.htm
Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon
There are two mechanisms for the generation of an asymmetry between the
strange and anti-strange quark distributions in the nucleon: nonperturbative
contributions originating from nucleons fluctuating into virtual baryon-meson
pairs such as and , and perturbative contributions
arising from gluons splitting into strange and anti-strange quark pairs. While
the nonperturbative contributions are dominant in the large- region, the
perturbative contributions are more significant in the small- region. We
calculate this asymmetry taking into account both nonperturbative and
perturbative contributions, thus giving a more accurate evaluation of this
asymmetry over the whole domain of . We find that the perturbative
contributions are generally a few times larger in magnitude than the
nonperturbative contributions, which suggests that the best region to detect
this asymmetry experimentally is in the region . We find that
the asymmetry may have more than one node, which is an effect that should be
taken into account, e.g. for parameterizations of the strange and anti-strange
quark distributions used in global analysis of parton distributions.Comment: 14 pages, 4 figures, figures comparing theoretical calculations with
NNPDF global analysis added, accepted for publication in EPJ
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