28 research outputs found
Electron Scattering From High-Momentum Neutrons in Deuterium
We report results from an experiment measuring the semi-inclusive reaction
where the proton is moving at a large angle relative to the
momentum transfer. If we assume that the proton was a spectator to the reaction
taking place on the neutron in deuterium, the initial state of that neutron can
be inferred. This method, known as spectator tagging, can be used to study
electron scattering from high-momentum (off-shell) neutrons in deuterium. The
data were taken with a 5.765 GeV electron beam on a deuterium target in
Jefferson Laboratory's Hall B, using the CLAS detector. A reduced cross section
was extracted for different values of final-state missing mass ,
backward proton momentum and momentum transfer . The data
are compared to a simple PWIA spectator model. A strong enhancement in the data
observed at transverse kinematics is not reproduced by the PWIA model. This
enhancement can likely be associated with the contribution of final state
interactions (FSI) that were not incorporated into the model. A ``bound neutron
structure function'' was extracted as a function of and
the scaling variable at extreme backward kinematics, where effects of
FSI appear to be smaller. For MeV/c, where the neutron is far
off-shell, the model overestimates the value of in the region of
between 0.25 and 0.6. A modification of the bound neutron structure
function is one of possible effects that can cause the observed deviation.Comment: 33 pages RevTeX, 9 figures, to be submitted to Phys. Rev. C. Fixed 1
Referenc
A Kinematically Complete Measurement of the Proton Structure Function F2 in the Resonance Region and Evaluation of Its Moments
We measured the inclusive electron-proton cross section in the nucleon
resonance region (W < 2.5 GeV) at momentum transfers Q**2 below 4.5 (GeV/c)**2
with the CLAS detector. The large acceptance of CLAS allowed for the first time
the measurement of the cross section in a large, contiguous two-dimensional
range of Q**2 and x, making it possible to perform an integration of the data
at fixed Q**2 over the whole significant x-interval. From these data we
extracted the structure function F2 and, by including other world data, we
studied the Q**2 evolution of its moments, Mn(Q**2), in order to estimate
higher twist contributions. The small statistical and systematic uncertainties
of the CLAS data allow a precise extraction of the higher twists and demand
significant improvements in theoretical predictions for a meaningful comparison
with new experimental results.Comment: revtex4 18 pp., 12 figure
Complete measurement of three-body photodisintegration of 3He for photon energies between 0.35 and 1.55 GeV
The three-body photodisintegration of 3He has been measured with the CLAS
detector at Jefferson Lab, using tagged photons of energies between 0.35 GeV
and 1.55 GeV. The large acceptance of the spectrometer allowed us for the first
time to cover a wide momentum and angular range for the two outgoing protons.
Three kinematic regions dominated by either two- or three-body contributions
have been distinguished and analyzed. The measured cross sections have been
compared with results of a theoretical model, which, in certain kinematic
ranges, have been found to be in reasonable agreement with the data.Comment: 22 pages, 25 eps figures, 2 tables, submitted to PRC. Modifications:
removed 2 figures, improvements on others, a few minor modifications to the
tex
eta-prime photoproduction on the proton for photon energies from 1.527 to 2.227 GeV
Differential cross sections for the reaction gamma p -> eta-prime p have been
measured with the CLAS spectrometer and a tagged photon beam with energies from
1.527 to 2.227 GeV. The results reported here possess much greater accuracy
than previous measurements. Analyses of these data indicate for the first time
the coupling of the etaprime N channel to both the S_11(1535) and P_11(1710)
resonances, known to couple strongly to the eta N channel in photoproduction on
the proton, and the importance of j=3/2 resonances in the process.Comment: 6 pages, 3 figure
Measurement of the Deuteron Structure Function F2 in the Resonance Region and Evaluation of Its Moments
Inclusive electron scattering off the deuteron has been measured to extract
the deuteron structure function F2 with the CEBAF Large Acceptance Spectrometer
(CLAS) at the Thomas Jefferson National Accelerator Facility. The measurement
covers the entire resonance region from the quasi-elastic peak up to the
invariant mass of the final-state hadronic system W~2.7 GeV with four-momentum
transfers Q2 from 0.4 to 6 (GeV/c)^2. These data are complementary to previous
measurements of the proton structure function F2 and cover a similar
two-dimensional region of Q2 and Bjorken variable x. Determination of the
deuteron F2 over a large x interval including the quasi-elastic peak as a
function of Q2, together with the other world data, permit a direct evaluation
of the structure function moments for the first time. By fitting the Q2
evolution of these moments with an OPE-based twist expansion we have obtained a
separation of the leading twist and higher twist terms. The observed Q2
behaviour of the higher twist contribution suggests a partial cancellation of
different higher twists entering into the expansion with opposite signs. This
cancellation, found also in the proton moments, is a manifestation of the
"duality" phenomenon in the F2 structure function
Exclusive meson electroproduction from hydrogen at CLAS
The longitudinal and transverse components of the cross section for the reaction were measured in Hall B at Jefferson
Laboratory using the CLAS detector. The data were taken with a 4.247 GeV
electron beam and were analyzed in a range of from 0.2 to 0.6 and of
from 1.5 to 3.0 GeV. The data are compared to a Regge model based on
effective hadronic degrees of freedom and to a calculation based on Generalized
Parton Distributions. It is found that the transverse part of the cross section
is well described by the former approach while the longitudinal part can be
reproduced by the latter.Comment: 6 pages, 4 figure
Tensor Polarization of the phi meson Photoproduced at High t
As part of a measurement of the cross section of meson photoproduction
to high momentum transfer, we measured the polar angular decay distribution of
the outgoing in the channel in the
center-of-mass frame (the helicity frame). We find that s-channel helicity
conservation (SCHC) holds in the kinematical range where -channel exchange
dominates (up to GeV for =3.6 GeV). Above this
momentum, -channel production of a meson dominates and induces a
violation of SCHC. The deduced value of the coupling constant lies in
the upper range of previously reported values.Comment: 6 pages; 5 figure
Measurement of the - and -Dependence of the Asymmetry on the Nucleon
We report results for the virtual photon asymmetry on the nucleon from
new Jefferson Lab measurements. The experiment, which used the CEBAF Large
Acceptance Spectrometer and longitudinally polarized proton (NH) and
deuteron (ND) targets, collected data with a longitudinally
polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present
paper, we concentrate on our results for and the related ratio
in the resonance and the deep inelastic regions for our lowest
and highest beam energies, covering a range in momentum transfer from
0.05 to 5.0 GeV and in final-state invariant mass up to about 3 GeV.
Our data show detailed structure in the resonance region, which leads to a
strong --dependence of for below 2 GeV. At higher , a
smooth approach to the scaling limit, established by earlier experiments, can
be seen, but is not strictly --independent. We add
significantly to the world data set at high , up to . Our data
exceed the SU(6)-symmetric quark model expectation for both the proton and the
deuteron while being consistent with a negative -quark polarization up to
our highest . This data setshould improve next-to-leading order (NLO) pQCD
fits of the parton polarization distributions.Comment: 7 pages LaTeX, 5 figure
Beam Spin Asymmetries in DVCS with CLAS at 4 .8 GeV
We report measurements of the beam spin asymmetry in Deeply Virtual Compton
Scattering (DVCS) at an electron beam energy of 4.8 GeV using the CLAS detector
at the Thomas Jefferson National Accelerator Facility. The DVCS beam spin
asymmetry has been measured in a wide range of kinematics, 1(GeV/c)
(GeV/c), , and 0.1 (GeV/c)
(GeV/c), using the reaction \pEpX. The number of
H and H events are separated in
each bin by a fit to the line shape of the H
distribution. The validity of the method was studied in detail using
experimental and simulated data. It was shown, that with the achieved missing
mass squared resolution and the available statistics, the separation of DVCS-BH
and events can reliably be done with less than 5% uncertainty. The
- and -dependences of the moments of the asymmetry are
extracted and compared with theoretical calculations
Proton source size measurements in the eA â e'ppX reaction
Two-proton correlations at small relative momentum
q
were studied in the
e
A
(
3
H
e
,
4
H
e
,
C
,
F
e
)
â
e
âČ
p
p
X
reaction at
E
0
=
4.46
â
â
G
e
V
using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small
q
was found to be in accordance with theoretical expectations. Sizes of the emission region were extracted, and proved to be dependent on
A
and on the proton momentum. The size of the two-proton emission region for He was measured in
e
A
reactions for the first time