George Lolos

One of the main scientific questions - that remain partly answered- is the nature and behavior of the "glue" that holds the world's basic building blocks (protons and neutrons, or their constituent quarks) together. The foundation of subatomic physics is based on the premise that the quarks inside protons and neutrons are held together by exchanging a particle that acts as the nuclear “glue”, appropriately named "gluon".  The proton and neutron are then particles consisting of three quarks bound together, whereas quark-antiquark pairs are collectively known as mesons. The important and puzzling feature of this construction of nature - in a theory called Quantum Chromo Dynamics (QCD) - is that quarks are never found free, but only in the aforementioned triplet or pair states, a phenomenon known as “confinement”, a result of the very nature of the gluons. Indeed, the quarks inside protons would fly apart were it not for the strong nuclear force, which is carried by the gluons, just as the electromagnetic force is carried by the photons. Photons have no electric charge and cannot associate together; hence there are no atoms of light. But gluons carry a type of charge (so-called "colour" charge) and so they can “clump together”. The result of such an amalgamation is a “glueball”, a particle made up of nothing more than the force that holds nucleons together. Physicists have long sought experimental evidence for glueballs and for other exotic combinations of gluons and quarks that form new states of matter, known as "hybrids".

An understanding of the confinement mechanism in QCD requires a detailed mapping of the spectrum of hybrid mesons. There is good reason to expect beams of photons to yield hybrid mesons with quantum numbers not possible within the conventional picture of mesons, as bound states. At Jefferson Lab in Newport News, VA, and with the recent energy upgrade of the electron accelerator to 12 GeV, experiments have become possible to probe for such exotic states of matter that will push our understanding of the nature of confinement to a conclusion.  One such experiment that has its main objective the production and study of exotic hybrid mesons is GlueX and the UofR team has played a leading role in physics definition, its R&D and for construction of critical components of GlueX.  With the first delivery of beam into Hall D -that houses the GlueX experiment, we have now moved into the most exciting phase, after a long and challenging process that started in earnest in 2000, and within the next couple of years we expect to have the first conclusive results.  This will occupy the majority of research time for the foreseeable future.

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