For instance, there has been a vivid debate on whether one can
understand
the intrinsic angular momentum - the spin - of a nucleon as a sum of
the
spins of the quarks which are inside it. Several experiments have
investigated
this question over the past 40 years by scattering polarized (spin-oriented)
high-energy
electrons, positrons and muons from polarized nucleon targets. I have been
actively involved
in a large program of experiments at the Stanford Linear Accelerator
Center
(SLAC, in California). Five of these experiments have been completed
and
their data published. Since the 1990's, I am leading a complementary
program using the CLAS spectrometer in Hall B of the Thomas Jefferson
National Accelerator Facility (JLab) in nearby Newport News. The
combined
information of these experiments allows us to understand the
transition
from the small-distance structure of nucleons (quasi-free quarks) to
its
static properties (magnetic moment and spin). Presently, my group is preparing for a new round of experiments with an improved detector (CLAS12), new polarized target, and the energy-upgraded (from 6 GeV to 11 GeV) continuous electron beam at Jefferson Lab.
Another part of my research program uses the unique facilities
of
JLab (continuous electron beam combined with the large acceptance
spectrometer
CLAS) to study the differences of the quark structure of bound and free
nucleons. As part of this program, I am leading an experimental program
(called
"BONuS") that measures, for the first time, the (unpolarized) structure
function for a (nearly) free neutron, undistorted by nuclear binding
effects. The 6 GeV version of this experiment, as well as an experiment
(E6) that gives us information on how this free neutron structure
becomes distorted if the neutron gets very close to another nucleon,
have been concluded and the results published. Now the BONuS
collaboration is focussing on the definitive run at 11 GeV, scheduled
for 2018 with CLAS12.
I am part of the Experimental Nuclear Physics group at ODU that has
built six large detector components (drift chambers) for CLAS and
then again another 5 drift chambers for CLAS12, in
preparation
for these and other experiments. We are also leading the effort to
build the polarized target for CLAS12 and the recoil detector ("RTPC")
for BONuS12. The research of the Experimental
Nuclear
Physics Group at ODU is being sponsored by the U.S. Department of
Energy and the National Science Foundation (for construction projects)
and typically involves 6 faculty, 2-3 postdoctoral research associates,
a
dozen graduate students and several undergraduate students.
Here is a writeup
in the "Courier" explaining my research "for the interested
layperson".
For my lecture "The Structure of the Neutron" on September 28th,
2004, click here.
And here is a recent
presentation to ODU graduate students. For a list of recent publications, click here.