372 research outputs found
PQCD Analysis of Parton-Hadron Duality
We propose an extraction of the running coupling constant of QCD in the
infrared region from experimental data on deep inelastic inclusive scattering
at Bjorken x -> 1. We first attempt a perturbative fit of the data that extends
NLO PQCD evolution to large x values and final state invariant mass, W, in the
resonance region. We include both target mass corrections and large x
resummation effects. These effects are of order O(1/Q^2), and they improve the
agreement with the Q^2 dependence of the data. Standard analyses require the
presence of additional power corrections, or dynamical higher twists, to
achieve a fully quantitative fit. Our analysis, however, is regulated by the
value of the strong coupling in the infrared region that enters through large x
resummation effects, and that can suppress, or absorb, higher twist effects.
Large x data therefore indirectly provide a measurement of this quantity that
can be compared to extractions from other observables.Comment: 10 pages, 3 figure
Value of alpha_s from deep-inelastic-scattering data
We report the value of obtained from QCD analysis of
existing data on deep-inelastic scattering of charged leptons off proton and
deuterium and estimate its theoretical uncertainties with particular attention
paid to impact of the high-twist contribution to the deep-inelastic-scattering
structure functions. Taking into account the major uncertainties the value
is obtained. An extrapolation of the LO--NLO--NNLO
results to the higher orders makes it possible to estimate .Comment: 9 pages, LATEX, 4 figures (EPS). Talk given at 16th International
Baldin Seminar on High-Energy Physics Problems: Relativistic Nuclear Physics
and Quantum Chromodynamics (ISHEPP 16), Dubna, Russia, 10-15 Jun 200; v2:
typos corrected, layout improved, 2 references adde
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
Off-shell effects in bound nucleons and parton distributions from H, H, H and He data
We report the results of a new global QCD analysis including deep-inelastic
scattering data off H, H, H, and He targets. Nuclear
corrections are treated in terms of a nuclear convolution approach with
off-shell bound nucleons. The off-shell (OS) corrections responsible for the
modification of the structure functions (SFs) of bound nucleons are constrained
in a global fit along with the proton parton distribution functions (PDFs) and
the higher-twist (HT) terms. We investigate the proton-neutron difference for
the OS correction and discuss our predictions for the SF ratio
and the corresponding PDF ratio in the proton, as well as their
correlations with the underlying treatment of the HT terms and of the OS
corrections. In particular, we find that the recent MARATHON data are
consistent with equal relative OS corrections for both the proton and the
neutron.Comment: Published version, 6 pages, 4 figure
Modeling power corrections to the Bjorken sum rule for the neutrino structure function F_1
Direct measurements of the the structure functions F_1^{nu p} and F_1^{nu n}
at a neutrino factory would allow for an accurate extraction of alpha_s from
the Q^2-dependence of the Bjorken sum rule, complementing that based on the
Gross-Llewellyn-Smith sum rule for F_3. We estimate the power (1/Q^2-)
corrections to the Bjorken sum rule in the instanton vacuum model. For the
reduced matrix element of the flavor-nonsinglet twist-4 operator
ubar_g_Gdual_gamma_gamma5_u - (u -> d) we obtain a value of 0.18 GeV^2, in good
agreement with the QCD sum rule calculations of Braun and Kolesnichenko. Our
result allows to reduce the theoretical error in the determination of alpha_s.Comment: 3 pages, 1 figure, uses iopart.cls. Proceedings of the 4th NuFact'02
Workshop "Neutrino Factories based on Muon Storage Rings", Imperial College,
London, July 1-6, 200
Parton distribution functions from the precise NNLO QCD fit
We report the parton distribution functions (PDFs) determined from the NNLO
QCD analysis of the world inclusive DIS data with account of the precise NNLO
QCD corrections to the evolution equations kernel. The value of strong coupling
constant \alpha_s^{NNLO}(M_Z)=0.1141(14), in fair agreement with one obtained
using the earlier approximate NNLO kernel by van Neerven-Vogt. The intermediate
bosons rates calculated in the NNLO using obtained PDFs are in agreement to the
latest Run II results.Comment: 8 pages, LATEX, 2 figures (EPS
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