162 research outputs found
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
A precise extraction of the induced polarization in the 4He(e,e'p)3H reaction
We measured with unprecedented precision the induced polarization Py in
4He(e,e'p)3H at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2. The induced polarization
is indicative of reaction-mechanism effects beyond the impulse approximation.
Our results are in agreement with a relativistic distorted-wave impulse
approximation calculation but are over-estimated by a calculation with strong
charge-exchange effects. Our data are used to constrain the strength of the
spin independent charge-exchange term in the latter calculation.Comment: submitted to Physical Review Letter
Polarization Transfer in the 4He(e,e'p)3H Reaction at Q^2 = 0.8 and 1.3 (GeV/c)^2
Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H
reaction at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision.
The polarization-transfer coefficients are found to differ from those of the
1H(e,e' p) reaction, contradicting a relativistic distorted-wave approximation,
and favoring either the inclusion of medium-modified proton form factors
predicted by the quark-meson coupling model or a spin-dependent charge-exchange
final-state interaction. For the first time, the polarization-transfer ratio is
studied as a function of the virtuality of the proton
Study of the A(e,e') Reaction on H, H, C, Al, Cu and Au
Cross sections for the p()n process on H, H, C,
Al, Cu and Au targets were measured at the Thomas
Jefferson National Accelerator Facility (Jefferson Lab) in order to extract the
nuclear transparencies. Data were taken for four-momentum transfers ranging
from =1.1 to 4.8 GeV for a fixed center of mass energy of =2.14
GeV. The ratio of and was extracted from the measured
cross sections for H, H, C and Cu targets at = 2.15
and 4.0 GeV allowing for additional studies of the reaction mechanism. The
experimental setup and the analysis of the data are described in detail
including systematic studies needed to obtain the results. The results for the
nuclear transparency and the differential cross sections as a function of the
pion momentum at the different values of are presented. Global features
of the data are discussed and the data are compared with the results of model
calculations for the p()n reaction from nuclear targets.Comment: 28 pages, 19 figures, submited to PR
Scaling of the F_2 structure function in nuclei and quark distributions at x>1
We present new data on electron scattering from a range of nuclei taken in
Hall C at Jefferson Lab. For heavy nuclei, we observe a rapid falloff in the
cross section for , which is sensitive to short range contributions to the
nuclear wave-function, and in deep inelastic scattering corresponds to probing
extremely high momentum quarks. This result agrees with higher energy muon
scattering measurements, but is in sharp contrast to neutrino scattering
measurements which suggested a dramatic enhancement in the distribution of the
`super-fast' quarks probed at x>1. The falloff at x>1 is noticeably stronger in
^2H and ^3He, but nearly identical for all heavier nuclei.Comment: 5 pages, 4 figures, to be submitted to physical revie
Nuclear transparency and effective kaon-nucleon cross section from the A(e, e'K+) reaction
We have determined the transparency of the nuclear medium to kaons from
measurements on C, Cu, and Au targets.
The measurements were performed at the Jefferson Laboratory and span a range in
four-momentum-transfer squared Q=1.1 -- 3.0 GeV. The nuclear
transparency was defined as the ratio of measured kaon electroproduction cross
sections with respect to deuterium, (). We further
extracted the atomic number () dependence of the transparency as
parametrized by and, within a simple model assumption,
the in-medium effective kaon-nucleon cross sections. The effective cross
sections extracted from the electroproduction data are found to be smaller than
the free cross sections determined from kaon-nucleon scattering experiments,
and the parameter was found to be significantly larger than those
obtained from kaon-nucleus scattering. We have included similar comparisons
between pion- and proton-nucleon effective cross sections as determined from
electron scattering experiments, and pion-nucleus and proton-nucleus scattering
data.Comment: 7 pages, 5 figure
Measurement of Nuclear Transparency for the A(e,e' pi^+) Reaction
We have measured the nuclear transparency of the A(e,e' pi^+) process in
^{2}H,^{12}C, ^{27}Al, ^{63}Cu and ^{197}Au targets. These measurements were
performed at the Jefferson Laboratory over a four momentum transfer squared
range Q^2 = 1.1 - 4.7 (GeV/c)^2. The nuclear transparency was extracted as the
super-ratio of from data to a model of
pion-electroproduction from nuclei without pi-N final state interactions. The
Q^2 and atomic number dependence of the nuclear transparency both show
deviations from traditional nuclear physics expectations, and are consistent
with calculations that include the quantum chromodynamical phenomenon of color
transparency.Comment: 5 pages, 3 figs Changes to figure 2 and 3 (error band updated and
theory curves updated
New measurements of high-momentum nucleons and short-range structures in nuclei
We present new measurements of electron scattering from high-momentum
nucleons in nuclei. These data allow an improved determination of the strength
of two-nucleon correlations for several nuclei, including light nuclei where
clustering effects can, for the first time, be examined. The data also include
the kinematic region where three-nucleon correlations are expected to dominate.Comment: 5 pages, 3 figures. Results from JLab E02-01
Scaling study of the pion electroproduction cross sections and the pion form factor
The H()n cross section was measured for a range of
four-momentum transfer up to =3.91 GeV at values of the invariant
mass, , above the resonance region. The -dependence of the longitudinal
component is consistent with the -scaling prediction for hard exclusive
processes. This suggests that perturbative QCD concepts are applicable at
rather low values of . Pion form factor results, while consistent with the
-scaling prediction, are inconsistent in magnitude with perturbative QCD
calculations. The extraction of Generalized Parton Distributions from hard
exclusive processes assumes the dominance of the longitudinal term. However,
transverse contributions to the cross section are still significant at
=3.91 GeV.Comment: 6 pages, 3 figure
Probing Quark-Gluon Interactions with Transverse Polarized Scattering
We have extracted QCD matrix elements from our data on double polarized
inelastic scattering of electrons on nuclei. We find the higher twist matrix
element \tilde{d_2}, which arises strictly from quark- gluon interactions, to
be unambiguously non zero. The data also reveal an isospin dependence of higher
twist effects if we assume that the Burkhardt-Cottingham Sum rule is valid. The
fundamental Bjorken sum rule obtained from the a0 matrix element is satisfied
at our low momentum transfer.Comment: formerly "Nachtmann Moments of the Proton and Deuteron Spin Structure
Functions
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