Keith Griffioen
Professor of Physics
Department of Physics
College of William and Mary
P.O. Box 8795
Williamsburg, VA 23187-8795
Office Phone: 757-221-3537
Fax: 757-221-3540
Email: griff at physics
Ever since the discovery of
quarks, high-energy electron
scattering experiments have provided increasingly
more accurate data on how these quarks combine to form
nucleons. (neutrons and protons).
Our present knowledge is extensive but incomplete.
We do not yet know precisely the size of the proton, where its
spin comes from, and just how three quarks with masses of a few MeV,
and the massless gluons that hold them together,
can make a proton with a mass of 938 MeV. The
strong nuclear force
is interesting and challenging because there are
three different "charges", dubbed "red", "green", and "blue,"
instead of the single charge for the electric force.
Consequently, the math is extremely difficult to solve, but
the resulting proton is intriguing, complex, and surprising.
My experimental research, which is primarily done using the
CLAS Spectrometer
at
Jefferson Lab,
involves three-dimensional
imaging of the proton and neutron to understand how the quarks
and gluons are distributed in space, in momentum, in spin
orientation, and in quark flavor (up, down, and strange).
Such a program involves a number of different electron-scattering and
photon absorption experiments with various combinations of
spin polarized beams and targets. The computational
techniques for solving quantum chromodynmaics, the theory
of the strong interaction, have become accurate enough so that
theory and experiment can now become joint partners in understanding
the proton. We hope to discover exciting surprises about the
proton and neutron's internal structure in the coming years.
The MAMI electron accelerator at the University of
Mainz provides beams of photons and electrons at high intensity but much lower beam
energies than at Jefferson Lab. Therefore, targeted, short experiments using MAMI play a unique role
in understanding the proton's structure. A measurement of the deuteron charge radius has been completed, and
precision tests of the Standard Model are being developed.
From the rapid orbits of outer stars in galaxies and the strength of gravitational lensing we can quantify the dark matter
in the universe, even as we have no clue as to what it might be. Many experiments are currently searching for
dark matter.
If dark matter interacts with its own force, the force-carrier may be like the photon we know, except massive. The
HPS experiment
at Jefferson Lab's Hall B, is currently searching for the dark photon.
Publications
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