67 research outputs found
Photodisintegration of He into p+t
The two-body photodisintegration of He into a proton and a triton has
been studied using the CEBAF Large-Acceptance Spectrometer (CLAS) at Jefferson
Laboratory. Real photons produced with the Hall-B bremsstrahlung-tagging system
in the energy range from 0.35 to 1.55 GeV were incident on a liquid He
target. This is the first measurement of the photodisintegration of He
above 0.4 GeV. The differential cross sections for the He
reaction have been measured as a function of photon-beam energy and
proton-scattering angle, and are compared with the latest model calculations by
J.-M. Laget. At 0.6-1.2 GeV, our data are in good agreement only with the
calculations that include three-body mechanisms, thus confirming their
importance. These results reinforce the conclusion of our previous study of the
three-body breakup of He that demonstrated the great importance of
three-body mechanisms in the energy region 0.5-0.8 GeV .Comment: 13 pages submitted in one tgz file containing 2 tex file and 22
postscrip figure
Exclusive electroproduction on the proton at CLAS
The reaction has been measured, using the 5.754
GeV electron beam of Jefferson Lab and the CLAS detector. This represents the
largest ever set of data for this reaction in the valence region. Integrated
and differential cross sections are presented. The , and
dependences of the cross section are compared to theoretical calculations based
on -channel meson-exchange Regge theory on the one hand and on quark handbag
diagrams related to Generalized Parton Distributions (GPDs) on the other hand.
The Regge approach can describe at the 30% level most of the features
of the present data while the two GPD calculations that are presented in this
article which succesfully reproduce the high energy data strongly underestimate
the present data. The question is then raised whether this discrepancy
originates from an incomplete or inexact way of modelling the GPDs or the
associated hard scattering amplitude or whether the GPD formalism is simply
inapplicable in this region due to higher-twists contributions, incalculable at
present.Comment: 29 pages, 29 figure
First Measurement of Beam-Recoil Observables Cx and Cz in Hyperon Photoproduction
Spin transfer from circularly polarized real photons to recoiling hyperons
has been measured for the reactions and
. The data were obtained using the CLAS
detector at Jefferson Lab for center-of-mass energies between 1.6 and 2.53
GeV, and for . For the , the
polarization transfer coefficient along the photon momentum axis, , was
found to be near unity for a wide range of energy and kaon production angles.
The associated transverse polarization coefficient, , is smaller than
by a roughly constant difference of unity. Most significantly, the {\it
total} polarization vector, including the induced polarization ,
has magnitude consistent with unity at all measured energies and production
angles when the beam is fully polarized. For the this simple
phenomenology does not hold. All existing hadrodynamic models are in poor
agreement with these results.Comment: 28 pages, 18 figures, Submitted to Physical Review
Claudins in lung diseases
Tight junctions are the most apically localized part of the epithelial junctional complex. They regulate the permeability and polarity of cell layers and create compartments in cell membranes. Claudins are structural molecules of tight junctions. There are 27 claudins known, and expression of different claudins is responsible for changes in the electrolyte and solute permeability in cells layers. Studies have shown that claudins and tight junctions also protect multicellular organisms from infections and that some infectious agents may use claudins as targets to invade and weaken the host's defense. In neoplastic diseases, claudin expression may be up- or downregulated. Since their expression is associated with specific tumor types or with specific locations of tumors to a certain degree, they can, in a restricted sense, also be used as tumor markers. However, the regulation of claudin expression is complex involving growth factors and integrins, protein kinases, proto-oncogens and transcription factors. In this review, the significance of claudins is discussed in lung disease and development
A measurement of the differential cross section for the reaction from deuterium
We report a measurement of the differential cross section for the process from the CLAS detector at Jefferson Lab in Hall B for
photon energies between 1.0 and 3.5 GeV and pion center-of-mass (c.m.) angles
() between 50 and 115. We confirm a previous
indication of a broad enhancement around a c.m. energy () of 2.2 GeV
at in the scaled differential cross section, . Our data show the angular dependence of this enhancement
as the scaling region is approached in the kinematic region from 70 to
105.Comment: 6 pages, 3 figures. submitted to PR
First measurement of target and double spin asymmetries for polarized e- polarized p --> e p pi0 in the nucleon resonance region above the Delta(1232)
The exclusive channel polarized proton(polarized e,e prime p)pi0 was studied
in the first and second nucleon resonance regions in the Q2 range from 0.187 to
0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer
(CLAS). Longitudinal target and beam-target asymmetries were extracted over a
large range of center-of-mass angles of the pi0 and compared to the unitary
isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model
DMT. A strong sensitivity to individual models was observed, in particular for
the target asymmetry and in the higher invariant mass region. This data set,
once included in the global fits of the above models, is expected to place
strong constraints on the electrocoupling amplitudes A_{1/2} and S_{1/2} for
the Roper resonance N(1400)P11, and the N(1535)S11 and N(1520)D13 states.Comment: 13 pages, 13 figure
Separated Structure Functions for the Exclusive Electroproduction of and Final States
We report measurements of the exclusive electroproduction of and
final states from a proton target using the CLAS detector at the
Thomas Jefferson National Accelerator Facility. The separated structure
functions , , , and were
extracted from the - and -dependent differential cross sections
taken with electron beam energies of 2.567, 4.056, and 4.247 GeV. This analysis
represents the first separation with the CLAS detector, and
the first measurement of the kaon electroproduction structure functions away
from parallel kinematics. The data span a broad range of momentum transfers
from GeV and invariant energy from GeV, while spanning nearly the full center-of-mass angular range of the
kaon. The separated structure functions reveal clear differences between the
production dynamics for the and hyperons. These results
provide an unprecedented data sample with which to constrain current and future
models for the associated production of strangeness, which will allow for a
better understanding of the underlying resonant and non-resonant contributions
to hyperon production.Comment: 61 pages, 26 figures, 5 table
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