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Sub-Panel Pushes New Linear Collider for High-energy Physics Research

By Richard M. Todaro

The US should take the lead in the next generation of high-energy physics research by funding the construction at home of an electron-positron linear collider, and it should commit to "vigorous long-term" research and development on a range of other particle accelerator projects, according to the recommendations of a draft report issued by a government advisory panel.

Declaring that "particle physics stands at the threshold of a new era of discovery," the draft report states that such projects have the potential to answer some of the most profound questions ranging from the existence of the Higgs particle (believed to give fermionic particles like leptons and quarks their mass), to the existence of various higher dimensions (as predicted in string theory), to the exact nature of the mysterious dark matter and dark energy (which are believed to fill the Universe and hold the key to its ultimate fate).

The report by the joint Department of Energy (DOE) and National Science Foundation's High-Energy Physics Advisory Panel (HEPAP) was released in late October, and a final report is scheduled for January 2002 release. Written by the HEPAP Sub-Panel on Long-Range Planning for US High-Energy Physics, the report is intended to serve as a 20-year road map that will prioritize what the panel feels are the most important projects for the international high-energy physics community.

Because the US Government provides so much money to high-energy physics research - about $700 million from the Department of Energy and another $50 million to $80 million from the National Science Foundation (NSF) for this year alone, according to statistics provided this past summer from the two organizations - the panel's priorities will help determine how large amounts of research dollars and human capital will be spent in the future. In the case of projects that the draft report "cannot recommend funding for.at this time," the individuals involved were very concerned and are now anxiously waiting to see what the final report states.

Jonathan Bagger of the Johns Hopkins University, co-chair of the HEPAP sub-panel, said the two key elements in the draft report were the 20-year roadmap and five specific recommendations, chief of which is the call for construction of a linear collider in the US. As part of the roadmap, the draft report calls for the creation of a "Particle Physics Project Prioritization Panel," dubbed simply "P5," in order to prioritize certain intermediate-term projects.

Listed among the top priorities in the report's roadmap is the Large Hadron Collider presently under construction at CERN in Switzerland and scheduled to become operational in 2006. The LHC is a circular machine that will smash protons into other protons at energies of 14 Tera-electron volts, seven times more powerful than the Fermilab Tevatron, which is currently the world's highest energy accelerator.

The report envisions a linear collider to be operational around 2012. There are at present several proposals for linear colliders being developed in different parts of the world, including a Japanese-Asian one, a German-European one, and an American one dubbed the Next Linear Collider.

"We give our highest recommendation to participation in such a machine, wherever it is built," said Barry Barish of Caltech, the other co-chair of the HEPAP long-range planning sub-panel that issued the report. "There is now a worldwide consensus on this priority."

As for what comes next, there are a variety of proposals for an assortment of new machines and new projects, including another proton-proton collider with energies an order of magnitude above that of the LHC.

"Beyond the LHC and the linear collider are other proposals, including a Very Large Hadron Collider (VLHC), a Muon Collider, a Neutrino Factory and a third generation linear collider called CLIC," said Bagger. "Our report strongly supports research and development toward these efforts as well. VLHC energies could be 100 to 200 Tera-electron volts, but we really don't know."

One project for which the draft report does not recommend immediate funding is the BTeV experiment at Fermilab, which is designed to probe for new quark physics at the electro-weak scale by studying "flavor changing processes" and probing for CP violation. With a price tag of $250 million and its funding not yet approved, the draft report states "we regret that we cannot recommend funding BTeV as a line item at this time."

Sheldon Stone of Syracuse University, one of the two lead scientists on the BTeV project, said he was told that HEPAP has no intention of killing the experiment and that the wording of the final report will show this.

"I was totally shocked by what they said, but then they said they didn't mean that," Stone said. "This is a draft and we shouldn't be discussing details until the final report comes out in January."

Bagger said that his panel left open the possibility for future BTeV funding.

"Our panel had some very carefully written words that we couldn't recommend that BTeV be funded in the very near future, but certainly the door would be open for funding down the line."

The five recommendations of the subpanel are that:

  • The US undertake a broad program of research "focused on the frontiers of matter, energy, space, and time" that includes a commitment to sharing intellectual insights, providing highly scientifically and technologically trained individuals to the economy, and developing new technologies to improve society.
  • The high-energy physics community follows the 20-year road map outlined in the report that prioritizes what facilities to build and projects to fund in a "balanced program to maximize scientific opportunity" and that includes creation of a panel that will update the roadmap as necessary.
  • The US take the leadership through the DOE and the NSF and the involvement of the full particle physics community in building a "high-energy, high-luminosity, electron-positron linear collider."
  • The US prepare a bid to host this linear collider, and that its site "take full advantage of the resources and infrastructure available at SLAC and Fermilab."
  • There be "vigorous, long-term research and development aimed toward future high-energy accelerators" and "development of particle detectors and information technology" for international collaboration.

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