Curtis A. Meyer Home Page

Professor Curtis A. Meyer
Department of Physics
Carnegie Mellon University
5000 Forbes Ave.
Pittsburgh, PA 15213

Wean Hall 8414
Phone: (412) 268-2745
Email: cme...@cmu.edu

Most of the visible mass of the universe is composed of protons and neutrons---particles which build up the cores of atoms. However, the protons and neutrons (nucleons) are themselves composed of more fundamental particles known as quarks and gluons and interestingly, these small constituents appear to be forever trapped inside their respective parent. An article in an August 2000 issue of the New York Times listed understanding confinement of quarks inside of protons and neutrons as one of the ten fundamental questions in physics to ponder for the 'next millennium or two'. While we believe that the theory of Quantum Chromodynamics, (QCD), can explain this confinement, an exact understanding of how QCD works has been extremely elusive. We know that QCD works under the extreme conditions found in high energy particle collisions, but our knowledge of what it is doing under normal conditions found in the every day world is quite limited. Using advances in high speed computing and experimental facilities that could soon be available at laboratories in the United States, scientists hope to go a long way in answering this question within the next decade.

In addition to the question of confinement, there has been a long-standing question on how the nominal three quarks inside of a nucleon behave. Are they free to bounce around like marbles in a fishbowl or are they somehow constrained to move together---what are the degrees of freedom inside the nucleon? This latter question can be answered by looking at what happens when the quarks inside a nucleon are excited, and thereby creating new particles. The spectrum of these particles is connected to the degrees of freedom. Surprising, the data seem to indicate that they are somehow constrained, but there are still crucial questions on our understanding of this spectrum. We are carrying out a large-scale effort to use new high-statistics data from Jefferson Lab to look in previously unexplored reactions to see if there are new particles to be found. The observation of even a small number of additional states could settle this question. First results which just appeared late in 2007 hint at new states, and we hope for more definitive results over the next year or so.

While the theory of QCD has been known for quite some time, we have only recently reached a point where we can start to understand confinement. Advances in a technique called lattice gauge QCD and significant improvements in computation power have combined to make the solution to QCD within reach. Lattice QCD solves QCD exactly in a discretized space-time world, but to do so, it requires massive computational power. Multi-teraflop computers are needed to allow theorists to do these calculations and to make detailed predictions for the spectrum of exotic hybrid mesons. Such computers are just now being put together. However, the final arbiter in determining which model of confinement is correct is experiment. So in parallel, experimenters are using recent developments in technology to carry out experiments that will map out the spectrum of this new type of matter with a focus on those hybrids that are distinctly different from normal mesons. They are the smoking gun unambiguous evidence of gluonic excitations. The GlueX experiment which will be built at Jefferson Lab is aimed at addressing these issues.