467 research outputs found
Target Mass Corrections to Electro-Weak Structure Functions and Perturbative Neutrino Cross Sections
We provide a complete and consistent framework to include subasymptotic
perturbative as well as mass corrections to the leading twist (tau=2)
evaluation of charged and neutral current weak structure functions and the
perturbative neutrino cross sections. We revisit previous calculations in a
modern language and fill in the gaps that we find missing for a complete and
ready-to-use "NLO xi-scaling" formulary. In particular, as a new result we
formulate the mixing of the partonic and hadronic structure function tensor
basis in the operator approach to deep inelastic scattering. As an underlying
framework we follow the operator product expansion a la Georgi & Politzer that
allows the inclusion of target mass corrections at arbitrary order in QCD and
we provide explicit analytical and numerical results at NLO. We compare this
approach with a simpler collinear parton model approach to xi-scaling. Along
with target mass corrections we include heavy quark mass effects as a
calculable leading twist power suppressed correction. The complete corrections
have been implemented into a Monte Carlo integration program to evaluate
structure functions and/or integrated cross sections. As applications, we
compare the operator approach with the collinear approximation numerically and
we investigate the NLO and mass corrections to observables that are related to
the extraction of the weak mixing angle from a Paschos-Wolfenstein-like
relation in neutrino-iron scattering. We expect that the interpretation of
neutrino scattering events in terms of oscillation physics and electroweak
precision physics will benefit from our results.Comment: 26 pages, 5 figures, note added, to appear in PR
Next-to-Leading Order QCD Corrections to Charged Current Charm Production and the Unpolarized and Polarized Strange Sea at HERA
Charged current charm and D meson production is studied in detail as a means
of determining the unpolarized and polarized strange sea densities at HERA. All
analyses are performed in next-to-leading order QCD, including a calculation of
the so far unknown spin-dependent MSbar coefficient functions up to O(alpha_s).
It is shown that a decent measurement is possible in the unpolarized case,
provided a sufficient luminosity can be reached in the future, while for
longitudinally polarized beams it appears to be extremely challenging due to
limitations imposed on the expected statistical accuracy by the charm detection
efficiency.Comment: 34 pages, LaTeX, 7 eps figures, uses amssymb, axodraw (included) and
epsfig style
Open Heavy Flavor Production in QCD -- Conceptual Framework and Implementation Issues
Heavy flavor production is an important QCD process both in its own right and
as a key component of precision global QCD analysis. Apparent disagreements
between fixed-flavor scheme calculations of b-production rate with experimental
measurements in hadro-, lepto-, and photo-production provide new impetus to a
thorough examination of the theory and phenomenology of this process. We review
existing methods of calculation, and place them in the context of the general
PQCD framework of Collins. A distinction is drawn between scheme dependence and
implementation issues related to quark mass effects near threshold. We point
out a so far overlooked kinematic constraint on the threshold behavior, which
greatly simplifies the variable flavor number scheme. It obviates the need for
the elaborate existing prescriptions, and leads to robust predictions. It can
facilitate the study of current issues on heavy flavor production as well as
precision global QCD analysis.Comment: 13 pages, 10 figures, Proceedings of Ringberg Workshop: New Trends in
HERA Physics 2001, Munich, German
Treatment of Heavy Quarks in Deeply Inelastic Scattering
We investigate a simplified version of the ACOT prescription for calculating
deeply inelastic scattering from Q^2 values near the squared mass M_H^2 of a
heavy quark to Q^2 much larger than M_H^2.Comment: 14 pages, 5 figure
Polarized Parton Distribution in Neutrino Induced Heavy Flavor Production
In order to examine polarized strange quark distribution, semi-inclusive
D/\Dbar production in neutrino deep inelastic scattering is studied including
corrections. Cross section and spin asymmetry are
calculated by using various parametrizations of polarized parton distribution
functions. It is found that \Dbar production is promising to directly extract
the polarized strange sea.Comment: 3 pages, 2 figures. Talk given at the NuFact02 workshop, London, UK,
July 1-6, 200
Determination of fragmentation functions and their application to exotic-hadron search
We discuss studies on determination of fragmentation functions and an
application to exotic-hadron search by using characteristic differences between
favored and disfavored functions. The optimum fragmentation functions are
determined for pion, kaon, and proton in the leading order (LO) and
next-to-leading order (NLO) of the running coupling constant alpha_s by global
analyses of hadron-production data in electron-positron annihilation. Various
parametrization results are much different in disfavored-quark and gluon
fragmentation functions; however, we show that they are within uncertainties of
the determined functions by using the Hessian method for uncertainty
estimation. We find that the uncertainties are especially large in the
disfavored-quark and gluon fragmentation functions. NLO improvements are
explicitly shown in the determination by comparing uncertainties of the LO and
NLO functions. Next, we propose to use differences between favored and
disfavored fragmentation functions for determining internal quark
configurations of exotic hadrons. We make a global analysis for f_0 (980) for
finding its internal configuration; however, uncertainties are too large to
specify the structure at this stage.Comment: 8 pages, LaTeX, 7 eps files, Progress of Theoretical Physics,
Supplement in press. Proceedings of New Frontiers in QCD 2010 - Exotic Hadron
Systems and Dense Matter -, Jan.18 - Mar.19, 2010, Kyoto, Japa
Uncertainties of the CJK 5 Flavour LO Parton Distributions in the Real Photon
Radiatively generated, LO quark (u,d,s,c,b) and gluon densities in the real,
unpolarized photon, calculated in the CJK model being an improved realization
of the CJKL approach, have been recently presented. The results were obtained
through a global fit to the experimental F2^gamma data. In this paper we
present, obtained for the very first time in the photon case, an estimate of
the uncertainties of the CJK parton distributions due to the experimental
errors. The analysis is based on the Hessian method which was recently applied
in the proton parton structure analysis. Sets of test parametrizations are
given for the CJK model. They allow for calculation of its best fit parton
distributions along with F2^gamma and for computation of uncertainties of any
physical value depending on the real photon parton densities. We test the
applicability of the approach by comparing uncertainties of example
cross-sections calculated in the Hessian and Lagrange methods. Moreover, we
present a detailed analysis of the chi^2 of the CJK fit and its relation to the
data. We show that large chi^2/DOF of the fit is due to only a few of the
experimental measurements. By excluding them chi^2/DOF approx 1 can be
obtained.Comment: 28 pages, 8 eps figures, 2 Latex figures; FORTRAN programs available
at http://www.fuw.edu.pl/~pjank/param.html; table 10, figure 10 and section 6
correcte
CJK- Improved LO Parton Distributions in the Real Photon and Their Experimental Uncertainties
A new analysis of the radiatively generated, LO quark (u,d,s,c,b) and gluon
densities in the real, unpolarized photon, improved in respect to our paper
[1], is presented. We perform four new global fits to the experimental data for
F2^gamma, two using a standard FFNS approach and two based on ACOT(chi) scheme
[2], leading to the FFNS(CJK) and CJK models. We also present the analysis of
the uncertainties of the new CJK 2 parton distributions due to the experimental
errors, the very first such analysis performed for the photon. This analysis is
based on the Hessian method, for a comparison for chosen cross-sections we use
also the Lagrange method.Comment: Prepared for Photon 2003: International Conference on the Structure
and Interactions of the Photon (Including the 15th International Workshop on
Photon-Photon Collisions), Frascati (Italy), 7-11 April 2003; 10 pages, Latex
using espcrc2 style, 1 tex and 5 postscript figures; FORTRAN programs
available at http://www.fuw.edu.pl/~pjank/param.htm
Overview of Hard processes at RHIC: high-pt light hadron and charm production
An overview of the experimental results on high-pt light hadron production
and open charm production is presented. Data on particle production in
elementary collisions are compared to next-to-leading order perturbative QCD
calculations. Particle production in Au+Au collisions is then compared to this
baseline.Comment: 9 pages, 6 figures, Strange Quark Matter 200
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