We report the first measurement of the (e,e′p) reaction cross-section ratios for Helium-3 (He3), Tritium (H3), and Deuterium (d). The measurement covered a missing momentum range of ...40≤pmiss≤550MeV/c, at large momentum transfer (〈Q2〉≈1.9 (GeV/c)2) and xB>1, which minimized contributions from non quasi-elastic (QE) reaction mechanisms. The data is compared with plane-wave impulse approximation (PWIA) calculations using realistic spectral functions and momentum distributions. The measured and PWIA-calculated cross-section ratios for He3/d and H3/d extend to just above the typical nucleon Fermi-momentum (kF≈250 MeV/c) and differ from each other by ∼20%, while for He3/H3 they agree within the measurement accuracy of about 3%. At momenta above kF, the measured He3/H3 ratios differ from the calculation by 20%−50%. Final state interaction (FSI) calculations using the generalized Eikonal Approximation indicate that FSI should change the He3/H3 cross-section ratio for this measurement by less than 5%. If these calculations are correct, then the differences at large missing momenta between the He3/H3 experimental and calculated ratios could be due to the underlying NN interaction, and thus could provide new constraints on the previously loosely-constrained short-distance parts of the NN interaction.
Multiple sclerosis (MS) is a disabling inflammatory demyelinating disease of the central nervous system (CNS) that primarily affects young adults. Available therapies can inhibit the inflammatory ...component of MS but do not suppress progressive clinical disability. An alternative approach would be to inhibit mechanisms that drive the neuropathology of MS, which often includes the death of oligodendrocytes, the cells responsible for myelinating the CNS. Identification of molecular mechanisms that mediate the stress response of oligodendrocytes to optimize their survival would serve this need. This study shows that the neurotrophic cytokine leukemia inhibitory factor (LIF) directly prevents oligodendrocyte death in animal models of MS. We also demonstrate that this therapeutic effect complements endogenous LIF receptor signaling, which already serves to limit oligodendrocyte loss during immune attack. Our results provide a novel approach for the treatment of MS.
The generalized forward spin polarizabilities gamma(0) and delta(LT) of the neutron have been extracted for the first time in a Q2 range from 0.1 to 0.9 GeV2. Since gamma(0) is sensitive to nucleon ...resonances and delta(LT) is insensitive to the Delta resonance, it is expected that the pair of forward spin polarizabilities should provide benchmark tests of the current understanding of the chiral dynamics of QCD. The new results on delta(LT) show significant disagreement with chiral perturbation theory calculations, while the data for gamma(0) at low Q2 are in good agreement with a next-to-leading-order relativistic baryon chiral perturbation theory calculation. The data show good agreement with the phenomenological MAID model.
Basic instrumentation for Hall A at Jefferson Lab Arrington, J.; Averett, T.; Beise, E.J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2004, Letnik:
522, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro- and photo-induced reactions at very high luminosity and good momentum and angular ...resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2×10
−4. A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of
10
38
cm
−2
s
−1
. The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium.
Measurements of elastic electron scattering data within the past decade have highlighted two-photon exchange contributions as a necessary ingredient in theoretical calculations to precisely evaluate ...hydrogen elastic scattering cross sections. This correction can modify the cross section at the few percent level. In contrast, dispersive effects can cause significantly larger changes from the Born approximation. The purpose of this experiment is to extract the carbon-12 elastic cross section around the first diffraction minimum, where the Born term contributions to the cross section are small to maximize the sensitivity to dispersive effects. The analysis uses the LEDEX data from the high resolution Jefferson Lab Hall A spectrometers to extract the cross sections near the first diffraction minimum of
12
C at beam energies of 362 MeV and 685 MeV. The results are in very good agreement with previous world data, although with less precision. The average deviation from a static nuclear charge distribution expected from linear and quadratic fits indicate a 30.6% contribution of dispersive effects to the cross section at 1 GeV. The magnitude of the dispersive effects near the first diffraction minimum of
12
C has been confirmed to be large with a strong energy dependence and could account for a large fraction of the magnitude for the observed quenching of the longitudinal nuclear response. These effects could also be important for nuclei radii extracted from parity-violating asymmetries measured near a diffraction minimum.
Here, we report the first measurement of the (e, e' p) three-body breakup reaction cross sections in helium-3 (3He) and tritium (3H) at large momentum transfer ($\langle{Q^2}\rangle$ ≈ 1.9 (GeV/c)2) ...and xB > 1 kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta 40 ≤ pmiss ≤ 500 MeV/c that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab-initio calculations. Overall good agreement, within ±20%, is observed between data and calculations for the full pmiss range for 3H and for 100 ≤ pmiss ≤ 350 MeV/c for 3He. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at pmiss > 250 MeV/c and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of 3He plus 3H, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire pmiss range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of 500 MeV/c.
We report the first measurement of the
(
e
,
e
′
p
)
three-body breakup reaction cross sections in helium-3 (
3
He
) and tritium (
3
H
) at large momentum transfer
⟨
Q
2
⟩
≈
1.9
(
GeV
/
c
)
2
...and
x
B
>
1
kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta
40
≤
p
miss
≤
500
MeV
/
c
that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab initio calculations. Overall good agreement, within
±
20
%
, is observed between data and calculations for the full
p
miss
range for
3
H
and for
100
≤
p
miss
≤
350
MeV
/
c
for
3
He
. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at
p
miss
>
250
MeV
/
c
and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of
3
He
plus
3
H
, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire
p
miss
range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of
500
MeV
/
c
.
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