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Research Projects
Study of Medium Modifications
Jefferson Lab Experiment E-01-112 "Photoproduction of
Vector Mesons off Nuclei",
C. Djalali, M. Kossov, and D. Weygand spokespeople.
- Jefferson Lab Experiment E-03-104 "Probing the Limits of the
Standard Model of Nuclear Physics with the 4He(e,e'p)3H Reaction",
R. Ent, R. Ransome, S. Strauch, and P. Ulmer spokespeople. (pdf)
Experiment E03-104 ran in Hall A from October 3 to November 9, 2006
and analysis is now underway. Michael Paolone from the University of
South Carolina is the Ph.D. student analyzing the data. The goal of
the experiment was to measure the recoil proton polarizations after
scattering electrons from 4He in quasielastic kinematics
and for low missing momenta at Q2 values of 0.8 and 1.3
(GeV/c)2. The observables include the polarization-transfer
coefficients perpendicular and along the three-momentum-transfer
direction, P'x and P'z, as well as the induced
polarization, Py, normal to the electron scattering
plane. The ratio P'x/P'z is expected to be
sensitive to the ratio of the proton electromagnetic form factors,
GE/GM, in the dense nuclear medium;
Py is sensitive to final-state interactions. Measuring
both, the polarization-transfer ratio for 4He and
1H, allows us to determine the double ratio R =
(P'x/P'z)4He /
(P'x/P'z)1H and compare
the reaction on the bound proton directly with that on the free
proton. Experiment E03-104 is an extension of E93-049. The latter
experiment found reasonable agreement between data and calculation
only after inclusion of medium-modified nucleon form factors as
predicted by the quark-meson coupling (QMC) model /citeref:lu.
Although, in principle, conventional DWIA calculations could be
improved at the cost of added complexity, the inclusion of
medium-modified nucleons may offer a more economical description of
nuclei. However, the uncertainties of the previous
data do not yet allow a definite conclusion.
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Baryon Spectroscopy and Meson Photoproduction
Jefferson Lab Experiment E-98-109 "Photoproduction of phi Mesons
with Linearly Polarized Photons", P. Cole, J. Mueller, and D. Tedeschi
spokespeople
(pdf)
Jefferson Lab Experiments E-03-105 "Pion Photoproduction
from a Polarized Target", N. Benmouna, W. Briscoe, G. O'Rielly,
I. Strakovski, and S. Strauch spokespeople
(ps)
E-06-013 "Measurement of &pi+&pi-
Photoproduction in Double-Polarization Experiments using CLAS", M. Bellis, V. Crede, and S. Strauch
spokespeople.
(pdf)
E03-105 will study single-pion photoproduction reactions, p(&gamma,
&pi+)n and p(&gamma, p)&pi0, with polarized
beam and longitudinally as well as transversely polarized target using
the CLAS detector at Jefferson Lab Hall B. The experiment will
measure two single- (T and P ) and three double-polarization
observables (G, F , and H ); experiment E01-104 will measure the
double-polarization observable E. The data will greatly constrain
partial-analyses wave and reduce model-dependent uncertainties in the
extraction of nucleon resonance properties, providing a new bench-
mark for comparisons with QCD-inspired models. The measurement will
span cos(&thetacm) from -0.9 to 0.9 in a center-of-mass
energy range above 1300 MeV and up to 2150 MeV.
Jefferson Lab Experiment E-04-010 "Search for Exotic
Cascades with CLAS Using an Untagged Virtual Photon Beam",
R. Gothe, M. Holtrop, E. Smith, and S. Stepanyan spokespeople
(pdf)
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Few-Body Physics
Jefferson Lab Experiment E-05-103 "Low Energy Deuteron
Photodisintegration", R. Gilman, A. Sarty, and S. Strauch
spokespeople.
(pdf)
We propose to study deuteron photodisintegration recoil
polarization observables in the region E&gamma ≈ 400
MeV. This is an energy range in which the available hadronic
calculations are starting to disagree with the available data, in
particular for the induced polarization py. This
disagreement is the most prominent precursor for the breakdown of
these calculations in the GeV region. But the existing polarization
data are arguably lousy. Our goal is to provide a high quality,
systematic data set that might allow theoretical studies to identify
what elements are missing from the calculations.
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Detector Developements
CLAS12 FTOF System
The Time-of-Flight System (FTOF) will be a major component of the
CLAS12 forward detector, used to measure the time-of-flight of
charged particles. This system will be comprised of the current CLAS
TOF spectrometer and a newly developed detector layer to improve the
timing resolution. This new detector layer will consist of an array of
414 scintillator paddles of lengths from 32 cm to 372 cm and will be
mounted on the available support structure. The FTOF system will be
the primary tool for charged hadron identification in the CLAS12
detector.
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