The physics potential of a new collider must be compelling.
The many design challenges of the accelerator technologies must be understood.
The costs to build and operate the collider must be thoroughly understood and compatible with realistic funding scenarios.
The role that such a new facility would have in the overall elementary particle physics program must be fully evaluated.
Furthermore, the United States government must be committed to significant support for such a facility, no matter where it is built.
The committee believes that early in the next decade, even before initial operations of the LHC, it may be possible for the U.S. community, in conjunction with the high-energy physics communities in Europe and Asia, to decide to pursue a particular technology and commit to building the next major collider facility. It is possible that discoveries in the intervening years will clarify the physics of electroweak symmetry breaking to the extent that one or more of the scenarios discussed could be eliminated.
Finally, the scale of particle physics accelerators is such that this facility will require strong international backing. Countries should rightly compete for the prize of having such a premier scientific instrument, but the commitment to an international collider facility means that we have to recognize and plan for the unfortunate possibility of no forefront accelerator in this country in the early decades of the next century. The management of the field of high-energy physics, both within and outside the United States, must allow and encourage truly international cooperation for all phases in the design and construction of such a facility, independent of its location. The groundbreaking progress that has been made in structuring the participation of U.S. physicists on the LHC project is an important step toward this goal.