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Low-Energy Photonuclear Studies The GW group has been involved in low-energy measurements (i.e., below pion threshold) related to few-body systems for several years in experiments at Saskatoon and Lund. An experiment at the Saskatchewan Accelerator Laboratory (SAL) to measure the simultaneous two-body breakup of 3He and 3H was led by Dr. Feldman [Fel95a] and the results are nearly ready for publication. A follow-up experiment at Lund on 3He is an extension to lower energy, and the GW group is an active part of the collaboration on that measurement. Dr. Feldman also has extensive experience in Compton scattering on the proton and the deuteron at SAL and is the spokesman for an earlier proposal [Fel95b] for elastic Compton scattering on deuterium, the results of which were recently published [Hor00]. Prior to our photofission measurements at JLab (Section IC2), we performed similar measurements at SAL [San99, San00]. This highly fruitful endeavor (three papers published plus one more in preparation) not only led to our JLab research in this area, but spawned the idea for an additional experiment at HIGS, listed below, to check whether a significant fraction of photofission events are accompanied by light particles, in seeming contradiction to QED calculations. We propose to continue these low-energy studies of Compton scattering, photo-disintegration of few-body systems, and photofission at the High Intensity Gamma Source (HIGS) located at Duke University. The Compton-backscattered photon beam from the Duke Free-Electron Laser has several distinct advantages: (1) ultrahigh photon flux, ultimately reaching 109 Hz, (2) 100% linearly polarized photon beam, with circular polarization obtainable after an upgrade, (3) monoenergetic beam, with ~1-2% energy resolution, and (4) extremely low background beam environment. Exploiting the high flux and polarization capabilities of the HIGS beam is central to our program of experiments proposed for this facility. One year ago, a group [Are02] of few-body theorists convened at the University of Trento to reflect on the alarming paradox that while significant advances in theory have taken place in the low-energy regime, fewer and fewer experimental facilities exist to exploit this theoretical progress. The HIGS facility is uniquely positioned to make substantial contributions to the field of low-energy few-nucleon physics. With this tool, and through the program outlined in this section, we are prepared to lead the next generation of high-precision experiments that can complement the recent progress on the theoretical front. In order to participate fully in the HIGS research program, we need to have a postdoc onsite at HIGS. To this end, the HIGS Lab has offered to cost-share such a position. |
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