The 30-km-long International Linear Collider (ILC) will collide electrons and positrons together at energies of at least 500 billion electron volts. Particle physicists will use the ILC to make detailed studies of the Higgs boson and any other new particles, such as supersymmetric particles, that might be discovered at the Large Hadron Collider (LHC). It is envisaged that the ILC will turn on by around the middle of the next decade, about eight years after the start up of the LHC, which is currently being built at CERN in Geneva.

The rival technologies are based on different types of cavities for the acceleration of the electrons and positrons in the collider. The DESY technology is based on superconducting cavities operating at 2 Kelvin, while the US/Japanese approach makes use of room temperature "X-band" technology. The two different technologies have been developed in parallel over the past decade but particle physicists have had to choose between them because the world can only afford one linear collider. That choice fell to a panel of 12 experts, known as the International Technology Recommendation Panel and chaired by Barry Barish of the California Institute of Technology.

"Both the 'warm' X-band technology and the 'cold' superconducting technology would work for a linear collider," Barish said. "The decision was not an easy one, because both technologies were well advanced and we knew the selection would have significant consequences for the participating laboratories. On the basis of our assessment, we recommended that the linear collider design be based on the superconducting technology."

Now that the ITRP has made its decision, particle physicists plan to carry out three more years of R&D and hope to complete an engineering design for the ILC by 2010. Construction of the collider could then begin, assuming that funding agencies and politicians can agree on where to build the machine. This timescale also assumes that the LHC finds evidence for the Higgs. If the Higgs is not seen at the LHC physicists may instead decide to opt for a higher-energy technology being developed at CERN. However, this technology is at an earlier stage of development and a collider based upon it would not be operational until about 2021.