298 research outputs found
The Generalized Parton Distributions program at Jefferson Lab
The Generalized Parton Distributions (GPD) have drawn a lot of interest from
the theoretical community since 1997, but also from the experimental community
and especially at Jefferson Lab. First, the results for Deeply Virtual Compton
Scattering (DVCS) at 4.2 GeV beam energy have recently been extracted from CLAS
data. The single spin asymmetry shows a remarkably clean sine wave despite the
rather low Q2 achievable at this energy. Two new dedicated DVCS experiments
using 6 GeV beam will run in 2003 and 2004 in Hall A and Hall B respectively.
Both experiments will yield very accurate results over a wide range of
kinematics, and allow for the first time a precise test of the factorization of
the DVCS process. Assuming the Bjorken regime is indeed reached, these
experiments will allow the extraction of linear combinations of GPD's and put
strong constraints on the available phenomenological models. Upon successful
completion of both experiments, a wider experimental program at 6 GeV can be
envisioned, using for instance Deuterium targets trying to nail down the
neutron and deuteron GPD's. In addition, resonances can be probed using
DeltaVCS where one produces a resonance in the final state. Finally, the 12 GeV
upgrade of Jefferson Lab extends the available kinematical range, and will
allow us to perform a complete, high precision GPD program using various
reactions among which, Deeply Virtual Meson Electroproduction (DVMP) and DVCS.Comment: Proceeding of "Exclusive Processes at High Momentum Transfer"
workshop, May 2002, Jefferson Lab, US
Results on Deeply Virtual Compton Scattering at Jefferson Lab
After about 10 years of growing interest for Generalized Parton Distributions
come the first results from dedicated experiments, using the golden Deeply
Virtual Compton Scattering process. After a short introduction, we will explain
the experimental methodology andshow results of the Hall A E00-110 experiment,
which aimed at measuring helicity-dependent photon electroproduction cross
sections. We will enphasize how this experiment provided the first stringent
tests of the scaling property of this process, allowing for the first time a
model-independent extraction of a linear combination of Generalized Parton
Distributions. We will also describe the Hall B E01-113 experiment which
measured the photon electroproduction beam spin asymmetry over a wide
kinematical range. The summary will include an outlook on the next generation
of experiments which are already planned at Jefferson Lab at 6 GeV, but also
after the planned 12 GeV upgrade.Comment: Proceedings of SPIN'06 Symposium in Kyoto, Japa
On timelike and spacelike deeply virtual Compton scattering at next to leading order
We study timelike and spacelike virtual Compton scattering in the generalized
Bjorken scaling regime at next to leading order in the strong coupling
constant, in the medium energy range which will be studied intensely at JLab12
and in the COMPASS-II experiment at CERN. We show that the Born amplitudes get
sizeable O(\alpha_s) corrections and, even at moderate energies, the gluonic
contributions are by no means negligible. We stress that the timelike and
spacelike cases are complementary and that their difference deserves much
special attention
The low Q
The JLAB EIC (JLEIC) design includes a chicane after the interaction point to detect electron associated with production of quasi-real photon at the interaction. This chicane layout can also be used for Compton polarimetry to measure the electron beam polarization. This proceeding will present the layout of the low Q2 chicane and the implementation and current R&D of a Compton polarimeter which would be located in the middle of this chicane
Precision Measurement of the Proton and Deuteron Spin Structure Functions g\u3csub\u3e2\u3c/sub\u3e and Asymmetries A\u3csub\u3e2\u3c/sub\u3e
We have measured the spin struction functions g2(p) and g(2)(d) and the virtual photon asymmetries A(2)(p) and A(2)(d) over the kinetmatic range 0.02 less than or equal to x less than or equal to 0.8 and 0.7 less than or equal to Q2 less than or equal to 20 GeV2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and (LiD)-Li-6 targets. Our measured g2 approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d(2)(p) and d(2)(n) are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule if there is no pathological behavior as x --\u3e 0. The Efremov-Leader-Teryaev integral is consistent with zero within our measured kinematic range. The absolute value of A2 is significantly smaller than the A2 \u3c √ R(1 +A1)/2 limit
Exclusive Neutral Pion Electroproduction in the Deeply Virtual Regime
We present measurements of the ep->ep pi^0 cross section extracted at two
values of four-momentum transfer Q^2=1.9 GeV^2 and Q^2=2.3 GeV^2 at Jefferson
Lab Hall A. The kinematic range allows to study the evolution of the extracted
hadronic tensor as a function of Q^2 and W. Results will be confronted with
Regge inspired calculations and GPD predictions. An intepretation of our data
within the framework of semi-inclusive deep inelastic scattering has also been
attempted
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