Dr. Matthias Burkardt, Distinguished Achievement Professor
Ph.D., Erlangen, Germany (1989)
Department of Physics
Office: Gardiner Hall 258A
MSC 3D
New Mexico State University
PO Box 30001
Las Cruces, NM
880038001
Phone: 5756461928
FAX: 5756461934
Email: burkardt@nmsu.edu


About
Research Interests:
My primary research interest is in nonperturbative strong interaction physics and the
quark/gluon (=parton) structure of hadrons and nuclei. I am particularly interested in
understanding the role of nonperturbative Quantum Chromo Dynamics (QCD) from
medium energy to highenergy scattering experiments.
Within this area, the main focus of my recent research has been to better understand
what one can actually learn from these experiments and/or related calculations. More
specifically, even though mathematical expressions in terms of matrix elements of complicated
operators exist to describe the outcome of a certain experiment, the complicated
nature of these matrix elements often obscures the intuitive physical interpretation of
results from both experiments as well as numerical simulations.
 Generalized Parton Distributions (GPDs):
These correlation functions were
originally introduced to parameterize the quark/gluon aspects of nucleon structure
in highenergy Compton scattering. It was also recognized that these very abstract
GPDs play a role in other observables. What I was able to demonstrate is that
GPDs themselves are interesting: By taking a suitable Fourier transform they
provide a 3 dimensional image of the nucleon, where one axis corresponds to the
quark or gluon momentum and the other two axes correspond to the location of
the quark/gluon in the transverse plane.
 SingleSpin Asymmetries (SSAs):
When a nucleon target is polarized transversly
relative to an incoming electron beam, many hadrons produced in a collision
tend to show a leftright asymmetry in their distribution relative to the nucleon
spin direction. One of the aspects that is remarkable about such SSAs is that
they persist at high energies and that they normally exhibit very stable patterns
(e.g. as a function of the beam energy). Theoretical calculations of SSAs depend
simultaneously on several aspects of hadron structure (interference between complex
phases, orbital angular momentum, final state interactions) that makes the
interpretation of the SSAs mysterious. What I found is that there is a simple
semiclassical interpretation for the origin of these SSAs that has to do with the
transverse deformation of the distribution of quarks and gluons in a transversely
polarized target and that there is a qualitative connection between GPDs and
SSAs. This observation now allows turning things around and takeing a measured
SSA and deducing what the deformation in the target nucleon must have been.
 Transverse Force on Quarks:
Certain observables in highenergy polarized
electronnucleon scattering (longitudinalbeam/ transversetarget doublespin
asymmetries) are sensitive to correlations between quarks and gluons at the same
position. Being a multiparton correlation function, these matrix elements have
eluded a simple physics interpretation for a long time. Recently, I realized that,
in a semiclassical sense, these correlation functions can teach us something about
the color Lorentz forces that act on a quark in a nucleon after it has been struck
by a highenergy photon. This novel interpretation now provides fresh momentum
for both measurements as well as numerical calculations for these observables.
 I continue to search for ’simple pictures’ and to indentify the physical interpretation
for complicated observables.
Publications
List of publications and recent invitated talks
