My Research Program
My experimental research program is centered on the boundary between nuclear and elementary particle physics. The last 50 years have brought ample evidence that the building blocks of the nucleus - protons and neutrons - are made up from point-like particles called quarks. While the basic properties and interactions of quarks are well understood, it is still an open question how quarks combine to make up a nucleon (a proton or neutron) - i.e., what the quark wave function of a nucleon is - and how the quark substructure of nucleons influences and is influenced by the forces that bind them into nuclei.

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.

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