There have been impressive advances in our understanding of nuclear physics that have resulted from the use of the electromagnetic probe over the last decade. Furthermore, the prospects for future advances have never been brighter. This is due in no small measure to the fact that this decade has also been characterized (for our particular subfield) by a very substantial investment in new facilities. Three major new facilities have come into operation. The 4 GeV, cw accelerator, CEBAF, is presently being commissioned, and research operations will begin shortly using a broad array of new experimental facilities. The 1 GeV Bates South Hall Ring project is also in the commissioning phase, and major new instrumentation has been constructed to provide new capabilities for research at these lower energies. The Laser Electron Gamma Source (LEGS) at BNL began operation in 1990, and has provided polarized photon beams of remarkable quality with energies up to 330 MeV.
These facilities provide us with the wide-ranging, complementary capabilities needed to mount a broad attack on major open questions in nuclear and strong interaction physics. They do so by taking advantage of the unique precision of the electromagnetic probe with the added insights provided by the ability to measure exclusive reactions over a broad range of momentum and energy transfer and to exploit the spin degrees of freedom in these reactions. CEBAF, with its unique combination of high energy, high intensity, and high duty factor, will open broad new experimental avenues for investigation. The lower beam energies and the use of the internal target technique in the Bates stretcher ring will provide an excellent complement to the CEBAF capabilities. Finally, the LEGS facility continues to offer unmatched capability for experiments carried out with highly-polarized real photons.
To realize the anticipated return on the very substantial investment that we have made over the last decade in developing these new capabilities, it is now essential that these facilities be operated in an optimum manner. The participants in the Town Meeting on Electromagnetic Physics (and others in the subfield with whom we have discussed the situation) were unanimous in stressing that the most important need of the subfield for the next decade is the realization of the research program we have all worked so hard to put in place.
Therefore, it is our highest priority recommendation that the NSAC Long Range Plan begin by providing the resources necessary to ``run the program" properly. This will require:
To be specific, proper utilization of these facilities
implies:
The Town Meeting and the community have also been presented with a highly
cost-effective proposal from CEBAF that will double its energy for a cost
of about $30M. This proposal takes advantage of the excellent performance
of the superconducting linac technology and free space available in the
linac tunnels. 25%more cryomodules can be installed, and the performance
of the existing cryomodules and beam transport system upgraded in an
evolutionary manner that causes no disruption in the operation of the
facility. The higher energy will extend the physics reach of CEBAF to
include the scaling regime, and meson spectroscopy. It also allows access
to the high behavior of exclusive processes, the onset of color
transparency, and a number of other important new areas.
The electromagnetic physics community endorses the scientific merit of increasing the maximum energy available from CEBAF into the 8-10 GeV regime in an evolutionary manner during the decade covered by the new Long Range Plan. Access to this higher-energy regime will open important new scientific opportunities.