Of the award, approximately $99 million already approved by the National Science Board, the NSF's policy body, would go to LEPP. Up to $25 million, recommended by NSF program managers, would go to CHESS, with $2.44 million of this amount funded by the National Institutes of Health's National Institute for General Medical Sciences. Both research facilities share use of the Cornell Electron Storage Ring (CESR), the university's high-energy particle accelerator.
The expected awards indicate the NSF's approval of a major change in LEPP's 23-year investigation into the interactions of elementary particles. Physicists use the accelerator's particle detector, called CLEO, to observe the decays of particles containing quarks and to infer the laws governing them. Research at CESR and CLEO has provided much of the world's knowledge about the nature of the weak nuclear force -- one of the four fundamental forces in nature -- through the study of the b-quark. As of this summer, LEPP will begin switching its operations to lower energies to investigate the charm quark, known as c-physics.
In the new NSF Physics Division-funded project, LEPP physicists and their collaborators from 18 other universities will make precision measurements of the "strong force," which binds the quarks in the elementary particles, protons and neutrons. The studies will use the charm quark, which CESR will be able to produce in abundance. "There are important physics to be done here. There is a need for somebody in the world to do things that have never been done before," says LEPP director Maury Tigner.According to the theory of the strong force, there should exist new forms of matter, called gluonic matter, or "glueballs," involving the interactions of particles called gluons. Says Tigner, "We are in a very good position to be the first people to really nail that."
In the past, LEPP and CHESS have shared CESR simultaneously, with CHESS researchers using the powerful X-ray beams generated by magnetic structures in the ring. Investigation of charm physics requires operating CESR at low energy and the installation of 12 superconducting magnetic devices, called wigglers. When CESR is running at low energy it will not be able to generate sufficient X-rays for CHESS researchers. Thus LEPP and CHESS have decided to time-share the use of the accelerator, alternating periods of dedicated low-energy running for particle physics, with dedicated high-energy running for X-ray production.
With practice, the switching from low to high energy should be accomplished in days, or even a single day, using complex computer controls. Sol Gruner, director of CHESS, says the dedicated time on the machine "means that we can improve the quality of the X-ray beams by making them more brilliant, stable and of longer duration between refills of the machine. The total number of days we will be running will be roughly comparable to the historical average, but the beams will be of far better quality."
CHESS hosts roughly a thousand visits a year from scientists competing to use the intense X-ray beams generated by CESR. Their research includes the atomic structure and properties of electronic, structural, polymeric and biological materials, protein and virus crystallography, environmental science, radiography and microelemental analysis.
The LEPP program, indirectly, also will include work on the international linear collider, a 20-mile-long electron-positron accelerator being planned by several consortia. Cornell has taken the lead in organizing a national consortium that submitted a proposal to the NSF last September for about $1 million to support research on the collider. Although the agency has not yet approved that award, CESR's new research direction still will be highly relevant for the huge new collider. "Most of the radiation given off by the beam will be attributable to the superconducting wigglers, making this an ideal testing ground as a particle source for the new linear collider," says Tigner.
LEPP and CHESS also are collaborating with the Thomas Jefferson National Accelerator Facility (Jlab) in Virginia on the development of a novel type of future X-ray source based on superconducting accelerator technology largely developed at Cornell and demonstrated at Jlab. Dubbed the Energy Recovery Linac (ERL), it has the potential to produce brighter- and faster-pulse beams. A proposal for prototype ERL development has been submitted to the NSF and is awaiting a funding decision. Says Gruner, "We hope that this would lead to the development of a new X-ray source at Cornell that would be superior to any existing source."