Until the Large Hadron Collider (LHC) at CERN, near Geneva, is completed in about 2006, the Tevatron at Fermilab, near Chicago, will be the highest-energy accelerator available to particle physicists. But what then? The High-Energy Physics Advisory Panel has recently published a “White Paper” on planning for particle physics in the US. HEPAP, currently chaired by Fred Gilman of Carnegie Mellon University, serves as an advisory body to both the Department of Energy (DOE) and NSF.
Updating the 1998 report of a HEPAP planning subpanel, the new White Paper (http://hepserve.fnal.gov:8080/doe-hep/home.html) offers a current assessment, in a worldwide context, of where things stand now and what needs to be done in the next few years. The document is intended to serve as input for this summer’s Snowmass workshop (http://www.snowmass2001.org) on the future of high-energy physics, and for the 20-year plan that’s being prepared by a new DOE/NSF panel headed by Barry Barish (Caltech) and Jonathan Bagger (Johns Hopkins University). The report of that long-range planning panel is expected next fall.
Since the appearance of the 1998 subpanel report, there have been several important accomplishments: PEPII, the asymmetric B-factory at SLAC began running in 1999 and, by last fall, was already operating at its design luminosity. The Tevatron collider is just now getting under way again with greatly enhanced luminosity, after several years of shutdown to install its new “main injector” (see the photo) and a variety of other upgrades. At Cornell, the major upgrade of the CESR e+e− collider has also been completed. All these accomplishments, we are reminded, “were finished on schedule and on budget.”
The new main injector (foreground ring) at Fermilab should increase the luminosity of the Tevatron collider (background ring) by an order of magnitude for the run that’s just beginning.
The new main injector (foreground ring) at Fermilab should increase the luminosity of the Tevatron collider (background ring) by an order of magnitude for the run that’s just beginning.
Adequate utilization
Although the White Paper cites good reasons to believe that these facilities “are guaranteed to produce frontier physics results,” it expresses concern about funding for their use: “The shortfall of funds for operating the recently completed facilities will severely hamper their utilization.” The White Paper regards adequate funding for their operation, and for the research groups striving to extract the physics, as “the highest priority need.”
With regard to other large accelerators that will be needed, the White Paper calls R&D “the lifeblood of our science.” Arguing that current funding levels “are endangering the near- and far-term future of the field,” it urges that R&D toward new accelerators “should be increased substantially.”
The three leading options for accelerators with energies beyond the LHC and the LEP e+e− storage ring it is displacing are: an e+e− linear collider, a very large hadron collider (VLHC), and a muon collider. (See Maury Tigner’s article in Physics Today, January 2001, page 36.) Strong recent evidence for neutrino oscillation has focused attention on the notion that a useful first step toward a muon collider would be an intense neutrino source based on a muon storage ring.
The timeline for decisions by the international high-energy community will stretch over decades. “We expect that only one of each type of frontier facility will be built worldwide,” says the White Paper, “and that they will be built in different regions.”
‘The most pressing issue’
The e+e− linear collider concept is the most well developed, and the physics case for its construction is strong. Design work on various schemes for a collider in the 500-GeV regime is going on in the US, Europe, and Japan, and each of these regions is a potential host. The Germans, for example, are pushing for the superconducting design being developed at DESY in Hamburg. A decision is expected in two or three years. “The fundamental question is whether [the e+e−] machine is the desired candidate … that will restore the US to the energy frontier,” says the White Paper. “Making this decision is thus the most pressing issue before our community.”
A decision on the muon collider/neutrino source would come toward the end of the decade. Deciding about a VLHC will take longer. It will depend on what is discovered at the LHC. The feasibility of such a gargantuan machine, much bigger than the LHC, will also depend on R&D aimed at reducing the costs of both civil engineering and superconducting magnets. The White Paper foresees a decision early in the next decade.
At least one of these frontier accelerators should be built in the US, the White Paper argues. “The study of the fundamental issues bearing on the nature of matter … and the forces shaping the universe befits this nation…. Maintaining US leadership and training new generations [of high-energy physicists] demand an energy-frontier facility at home.”
