Two teams developing rival designs for an international linear collider will continue with their own separate blueprints – even though both teams are joining forces at the organizational level. Barry Barish, head of the design effort for the International Linear Collider (ILC), told that both the ILC and the rival Compact Linear Collider (CLIC) will remain distinct projects despite the recent creation of a Linear Collider Board that will govern the development of the two designs. But given the costs of building such a machine, which will be the successor to CERN's Large Hadron Collider (LHC), only one such design is likely to be built and the new organizational structure will not result in one joint proposal.

Most of the R&D design for CLIC, which could measure precisely any of the new particles that the LHC might discover, is being carried out at CERN. Both it and the ILC will collide electrons with positrons, but while the ILC will use superconducting technology to collide particles with energies of about 500 GeV, CLIC will collide particles at 1 TeV or more using a novel "two beam" acceleration technique.

The ILC design is more mature than CLIC's and is, in principle, ready for construction whereas some of CLIC's concepts have not yet been proven and would need to be demonstrated over the coming 5 to 10 years. "The two groups already work together on mutual technical problems, but this will enable joint planning, including preparations for any comparisons in the future," says Barish. "There can only be one possible linear collider in the world, preparations are expensive and need to be co-ordinated."

Joint leadership

Under the new structure, the directorate of the two design teams will report into a linear collider director, a new position that has yet to be appointed. The director will then report into the Linear Collider Board, which will oversee the preparation of a collider proposal that will then report to the International Committee for Future Accelerators chaired by Fermilab boss Pier Oddone. The Linear Collider Board will consist of 16 members – a chair plus five representatives each from Europe, Asia and the Americas – who have not yet been chosen. "Clearly, joint leadership can help bring this all together as a global project best matched to the science," says Barish.

"I think this is an excellent development, which I have been supporting for some time," says theoretical physicist John Ellis from Kings College London, who is on the CLIC steering committee. "There are many technical issues in common between CLIC and the ILC such as civil engineering, beam delivery and detector design, that it makes great sense to work together"

Indeed, deciding which design to go for will depend on what physics the LHC discovers over the coming years. "If the ILC parameters match the science coming from CERN, it will be the obvious choice; but if it is crucial to go well beyond 1 TeV, then the ILC is impractical and CLIC represents a possible solution on a longer timescale to go as high as maybe 3 TeV," says Barish.

The ILC team is expected to release its technical design report by the end of the year.