339 research outputs found
New results on SIDIS SSA from Jefferson Lab
We present studies of single-spin and double-spin asymmetries in
semi-inclusive electroproduction of pions using the CEBAF 6 GeV polarized
electron beam. Kinematic dependences of single and double spin asymmetries have
been measured in a wide kinematic range at CLAS with a polarized NH target.
Significant target-spin and asymmetries have been
observed. The hypothesis of factorization has been tested with -dependence
of the double spin asymmetry.Comment: 4 pages, 6 figure
New measurement of charge asymmetry from HERA
After presenting the recent measurements of neutral current cross section in
DIS at HERA, we explain the effect of the interference at the
electro-weak scale, visible on these data. Then, the beam charge difference
is measured and the interference itself is extracted. Results are
discussed in the context of perturbative QCD.Comment: 4 pages, 3 figures, proceedings of the International Workshop on
Positrons at Jefferson Lab (March 25-27, 2009), Thomas Jefferson National
Accelerator Facility, Newport News, V
Axial structure of the nucleon
We review the current status of experimental and theoretical understanding of the axial nucleon structure at low and moderate energies. Topics considered include (quasi)elastic (anti)neutrino-nucleon scattering, charged pion electroproduction off nucleons and ordinary as well as radiative muon capture on the proton
Phenomenological analysis of the CLAS data on double charged pion photo and electro- production
First comprehensive data on the evolution of nucleon resonance photocouplings
with photon virtuality Q^2 are presented for excited proton states in the mass
range from 1.4 to 2.0 GeV. N^* photocouplings were determined in
phenomenological analysis of CLAS data on 2 pi photo and electroproduction
within the framework of the JLAB-MSU phenomenological model.Comment: 10 pages, 7 figures (encapsulated postscript
Measurement of Unpolarized and Polarized Cross Sections for Deeply Virtual Compton Scattering on the Proton at Jefferson Laboratory with CLAS
This paper reports the measurement of polarized and unpolarized cross sections for the ep→e′p′γ reaction, which is composed of deeply virtual Compton scattering (DVCS) and Bethe-Heitler (BH) processes, at an electron beam energy of 5.88 GeV at the Thomas Jefferson National Accelerator Facility using the Large Acceptance Spectrometer CLAS. The unpolarized cross sections and polarized cross section differences have been measured over broad kinematics, 0.10 \u3c xB \u3c 0.58, 1.0 \u3c Q2 \u3c4.8 GeV2 and 0.09\u3c−t \u3c2.00 GeV2. The results are found to be consistent with previous CLAS data, and these new data are discussed in the framework of the generalized parton distribution approach. Calculations with two widely used phenomenological models are approximately compatible with the experimental results over a large portion of the kinematic range of the data
Quasifree Pion Electroproduction from Nuclei in the Region
We present calculations of the reaction in the
distorted wave impulse approximation. The reaction allows for the study of the
production process in the nuclear medium without being obscured by the details
of nuclear transition densities. First, a pion electroproduction operator
suitable for nuclear calculations is obtained by extending the Blomqvist-Laget
photoproduction operator to the virtual photon case. The operator is gauge
invariant, unitary, reference frame independent, and describes the existing
data reasonably well. Then it is applied in nuclei to predict nuclear cross
sections under a variety of kinematic arrangements. Issues such as the effects
of gauge-fixing, the interference of the resonance with the
background, sensitivities to the quadrupole component of the
excitation and to the electromagnetic form factors, the role of final-state
interactions, are studied in detail. Methods on how to experimentally separate
the various pieces in the coincidence cross section are suggested. Finally, the
model is compared to a recent SLAC experiment.Comment: 27 pages in REVTEX, plus 22 PS figures embedded using psfig.sty
(included), uuencode
Effective role of unpolarized nonvalence partons in Drell-Yan single spin asymmetries
We perform numerical simulations of the Sivers effect from single spin
asymmetries in Drell-Yan processes on transversely polarized protons. We
consider colliding antiprotons and pions at different kinematic conditions of
interest for the future planned experiments. We conventionally name "framework
I" the results obtained when properly accounting for the various flavor
dependent polarized valence contributions in the numerator of the asymmetry,
and for the unpolarized nonvalence contribution in its denominator. We name
"framework II" the results obtained when taking a suitable flavor average of
the valence contributions and neglecting the nonvalence ones. We compare the
two methods, also with respect to the input parametrization of the Sivers
function which is extracted from data with approximations sometimes
intermediate between frameworks I and II. Deviations between the two approaches
are found to be small except for dilepton masses below 3 GeV. The Sivers effect
is used as a test case; the arguments can be generalized to other interesting
azimuthal asymmetries in Drell-Yan processes, such as the Boer-Mulders effect.Comment: 13 pages, 9 figures in eps forma
Precision Studies of QCD in the Low Energy Domain of the EIC
The manuscript focuses on the high impact science of the EIC with objective
to identify a portion of the science program for QCD precision studies that
requires or greatly benefits from high luminosity and low center-of-mass
energies. The science topics include (1) Generalized Parton Distributions, 3D
imagining and mechanical properties of the nucleon (2) mass and spin of the
nucleon (3) Momentum dependence of the nucleon in semi-inclusive deep inelastic
scattering (4) Exotic meson spectroscopy (5) Science highlights of nuclei (6)
Precision studies of Lattice QCD in the EIC era (7) Science of far-forward
particle detection (8) Radiative effects and corrections (9) Artificial
Intelligence (10) EIC interaction regions for high impact science program with
discovery potential. This paper documents the scientific basis for supporting
such a program and helps to define the path toward the realization of the
second EIC interaction region.Comment: 103 pages,47 figure
A new highly segmented start counter for the CLAS detector
The design, construction and performance of a highly segmented Start Counter are described. The Start Counter is an integral part of the trigger used in photon beam running with CLAS in Hall B at the Thomas Jefferson National Accelerator Facility (TJNAF). The Start Counter is constructed of 24 2.2-mm-thick single-ended scintillation paddles, forming a hermetic hexagon around the target region. This device measures the interaction time of the incoming photon in the target by detecting the outgoing particles. The counter provides complex trigger topologies, shows good efficiency and achieved a time resolution of 350 ps
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