Grant: Subatomic Physics Envelope - Research Tools and Instruments

One of the central problems of modern physics research concerns our understanding of the building blocks of the atomic nucleus -- the protons, neutrons, and other particles (mesons) that bind them. Notable discoveries have indicated that these particles consist of yet more fundamental constituents, the quarks and gluons. While a very good theoretical framework (called Quantum Chromo-Dynamics, or QCD) is able to describe accurately how quarks and gluons interact at extremely high energies (or, equivalently, when the quarks are very close together), it has been very difficult to apply QCD to lower energy (longer distance) phenomena. The paradox is that the increasing complexity of the quark-gluon interaction as these particles become further apart is critically important to their confinement within the nuclear building blocks, but we cannot perform the QCD calculations necessary to confirm our understanding. One of the obstacles to our improved comprehension has been a lack of quality data, particularly for the Exclusive Reactions where the system responds coherently to the incoming probe, and so provides the clearest picture of the inner workings of QCD. Existing data in the Deep Inelastic Scattering regime are primarily inclusive in nature, where the system responds incoherently. The Super HMS spectrometer (SHMS), under construction in Jefferson Lab Hall C as part of a major upgrade of its facilities, will make Hall C the only facility in the world capable of exploring Exclusive Reactions up to Q^2~15 GeV^2, and it will do so at an unprecedented luminosity of 10^{39}/s/cm^2. Canadians lead important parts of this new experimental program, such as measurements of the charged pion form factor and scaling studies of pi+ and K+ production. Specifically, this proposal requests funds for the Heavy Gas Cerenkov detector, which is indispensable for these measurements. The Canadian-led experiments all require excellent pion identification, and this detector is solely responsible for providing that information. The detector work builds upon previously developed expertise and provides an excellent training ground for the next generation of scientists.