116 research outputs found
Phenomenological analysis of the CLAS data on double charged pion photo and electro- production
First comprehensive data on the evolution of nucleon resonance photocouplings
with photon virtuality Q^2 are presented for excited proton states in the mass
range from 1.4 to 2.0 GeV. N^* photocouplings were determined in
phenomenological analysis of CLAS data on 2 pi photo and electroproduction
within the framework of the JLAB-MSU phenomenological model.Comment: 10 pages, 7 figures (encapsulated postscript
Introducing GUNLAB a compact test facility for SRF photoinjectors
Superconducting radio frequency photoelectron injectors SRF photoinjectors are promising electron sources for high brightness accelerators with high average current and short pulse duration like FELs and ERLs. For the upcoming ERL project bERLinPro we want to test and commission different SRF photoinjectors, optimize the beam performance and examine photocathode materials in an independent test facility. Therefore we designed GunLab to characterize beam parameters from the SRF photoinjectors in a compact diagnostics beamline. The main challenge of GunLab is to characterize the full six dimensional phase space as a function of drive laser and RF parameters. Here we present design and estimated performance of GunLa
First measurement of coherent -meson photoproduction on deuteron at low energies
The cross section and decay angular distributions for the coherent \phi meson
photoproduction on the deuteron have been measured for the first time up to a
squared four-momentum transfer t =(p_{\gamma}-p_{\phi})^2 =-2 GeV^2/c^2, using
the CLAS detector at the Thomas Jefferson National Accelerator Facility. The
cross sections are compared with predictions from a re-scattering model. In a
framework of vector meson dominance, the data are consistent with the total
\phi-N cross section \sigma_{\phi N} at about 10 mb. If vector meson dominance
is violated, a larger \sigma_{\phi N} is possible by introducing larger t-slope
for the \phi N \to \phi N process than that for the \gamma N \to \phi N
process. The decay angular distributions of the \phi are consistent with
helicity conservation.Comment: 6 page
Measurement of Deeply Virtual Compton Scattering with a Polarized Proton Target
The longitudinal target-spin asymmetry A_UL for the exclusive
electroproduction of high energy photons was measured for the first time in
p(e,e'p\gamma). The data have been accumulated at Jefferson Lab with the CLAS
spectrometer using 5.7 GeV electrons and a longitudinally polarized NH_3
target. A significant azimuthal angular dependence was observed, resulting from
the interference of the Deeply Virtual Compton Scattering and Bethe-Heitler
processes. The amplitude of the sin(phi) moment is 0.252 +/- 0.042(stat) +/-
0.020(sys). Theoretical calculations are in good agreement with the magnitude
and the kinematic dependence of the target-spin asymmetry, which is sensitive
to the generalized parton distributions H and H-tilde.Comment: Modified text slightly, added reference
Light Vector Mesons in the Nuclear Medium
The light vector mesons (, , and ) were produced in
deuterium, carbon, titanium, and iron targets in a search for possible
in-medium modifications to the properties of the meson at normal nuclear
densities and zero temperature. The vector mesons were detected with the CEBAF
Large Acceptance Spectrometer (CLAS) via their decays to . The rare
leptonic decay was chosen to reduce final-state interactions. A combinatorial
background was subtracted from the invariant mass spectra using a
well-established event-mixing technique. The meson mass spectrum was
extracted after the and signals were removed in a nearly
model-independent way. Comparisons were made between the mass spectra
from the heavy targets () with the mass spectrum extracted from the
deuterium target. With respect to the -meson mass, we obtain a small
shift compatible with zero. Also, we measure widths consistent with standard
nuclear many-body effects such as collisional broadening and Fermi motion.Comment: 15 pages, 18 figures, 3 table
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