226 research outputs found
New Measurements of the EMC Effect in Few-Body Nuclei
Measurements of the EMC effect show that the quark distributions in nuclei
are not simply the sum of the quark distributions of the constituent nucleons.
However, interpretation of the EMC effect is limited by the lack of a reliable
baseline calculation of the effects of Fermi motion and nucleon binding. We
present preliminary results from JLab experiment E03-103, a precise measurement
of the EMC effect in few-body and heavy nuclei. These data emphasize the
large-x region, where binding and Fermi motion effects dominate, and thus will
provide much better constraints on the effects of binding. These data will also
allow for comparisons to calculations for few-body nuclei, where the
uncertainty in the nuclear structure is minimized.Comment: Proceedings from talk at the Topical Group on Hadron Physics meeting,
Nashville Tennessee, October 22-24, 2006. 9 pages, 6 figure
Unique Electron Polarimeter Analyzing Power Comparison and Precision Spin-Based Energy Measurement
Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Moller, and Mott scattering, have been performed using the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility ( Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of the relative analyzing powers of the five polarimeters. This is the first time a precise comparison of the analyzing powers of Compton, Moller, and Mott scattering polarimeters has been made. Statistically significant disagreements among the values of the beam polarization calculated from the asymmetry measurements made with each polarimeter reveal either errors in the values of the analyzing power or failure to correctly include all systematic effects. The measurements reported here represent a first step toward understanding the systematic effects of these electron polarimeters. Such studies are necessary to realize high absolute accuracy (ca. 1%) electron polarization measurements, as required for some parity violation measurements planned at Jefferson Laboratory. Finally, a comparison of the value of the spin orientation exiting the injector that provides maximum longitudinal polarization in each experimental hall leads to an independent and very precise ( better than 10-4) absolute measurement of the final electron beam energy
Correlated Strength in Nuclear Spectral Function
We have carried out an (e,e'p) experiment at high momentum transfer and in
parallel kinematics to measure the strength of the nuclear spectral function
S(k,E) at high nucleon momenta k and large removal energies E. This strength is
related to the presence of short-range and tensor correlations, and was known
hitherto only indirectly and with considerable uncertainty from the lack of
strength in the independent-particle region. This experiment confirms by direct
measurement the correlated strength predicted by theory.Comment: 4 pages, 2 figures, accepted by Phys. Rev. Let
Longitudinal-Transverse Separations of Structure Functions at Low for Hydrogen and Deuterium
We report on a study of the longitudinal to transverse cross section ratio,
, at low values of and , as determined from
inclusive inelastic electron-hydrogen and electron-deuterium scattering data
from Jefferson Lab Hall C spanning the four-momentum transfer range 0.06 GeV. Even at the lowest values of , remains
nearly constant and does not disappear with decreasing , as expected. We
find a nearly identical behaviour for hydrogen and deuterium.Comment: 4 pages, 2 gigure
Atomic mass dependence of \Xi^- and \overline{\Xi}^+ production in central 250 GeV \pi^- nucleon interactions
We present the first measurement of the atomic mass dependence of central
\Xi^- and \overline{\Xi}^+ production. It is measured using a sample of 22,459
\Xi^-'s and \overline{\Xi}^+'s produced in collisions between a 250 GeV \pi^-
beam and targets of beryllium, aluminum, copper, and tungsten. The relative
cross sections are fit to the two parameter function \sigma_0 A^\alpha, where A
is the atomic mass. We measure \alpha = 0.924+-0.020+-0.025, for Feynman-x in
the range -0.09 < x_F < 0.15.Comment: 10 pages, revtex, 2 figures, submitted to Phys. Rev.
Separated Kaon Electroproduction Cross Section and the Kaon Form Factor from 6 GeV JLab Data
The () reaction was studied as a function of
the Mandelstam variable using data from the E01-004 (FPI-2) and E93-018
experiments that were carried out in Hall C at the 6 GeV Jefferson Lab. The
cross section was fully separated into longitudinal and transverse components,
and two interference terms at four-momentum transfers of 1.00, 1.36 and
2.07 GeV. The kaon form factor was extracted from the longitudinal cross
section using the Regge model by Vanderhaeghen, Guidal, and Laget. The results
establish the method, previously used successfully for pion analyses, for
extracting the kaon form factor. Data from 12 GeV Jefferson Lab experiments are
expected to have sufficient precision to distinguish between theoretical
predictions, for example recent perturbative QCD calculations with modern
parton distribution amplitudes. The leading-twist behavior for light mesons is
predicted to set in for values of between 5-10 GeV, which makes data
in the few GeV regime particularly interesting. The dependence at fixed
and of the longitudinal cross section we extracted seems consistent
with the QCD factorization prediction within the experimental uncertainty
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
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