The world’s two most mature proposals for a collider complementary to the Large Hadron Collider are joining collaborative forces.
The two proposed electron-positron collider projects, the Compact Linear Collider Study and the International Linear Collider, have traditionally been viewed as casual rivals--both in the running to be built as the future complement to CERN’s proton-smashing machine, the LHC.
Now CLIC and the ILC are joining organizational forces under the linear collider umbrella. The new organizational structure, announced in February by the International Committee for Future Accelerators (ICFA) Chair Pier Oddone, is still in its very early stages, but those involved hope to finalize the governance framework by July, implementing the new plan gradually over the following year. The plan is for ICFA, which currently oversees the ILC Global Design Effort, to establish a Linear Collider Board, which would in turn govern CLIC, the ILC, and a third program that focuses on detector research for both machines.
“As we move into the next phase in the evolution of linear colliders it is important to bring the ILC and CLIC efforts under unified leadership,” Oddone said.
A milestone in that evolution is the fulfillment of a longstanding mandate by the ILC Global Design Effort to deliver its ILC Technical Design Report, which it will do by the end of the year.
“The new structure is the logical next step,” said ILC Steering Committee Chair Jonathan Bagger. Not only is the ILC soon to submit its technical design, but the LHC data, which will determine a good deal of the physics case for a future linear collider, are coming in fast and furious.
“With the LHC results pouring in, the physics situation is changing rapidly,” Bagger said. “The new governance structure will be able to react quickly to whatever the LHC discovers.”
The confluence of the separate R&D efforts has been progressing steadily and informally for a number of years, a natural move given that both machines are linear accelerators: researchers can coordinate in overlapping technological areas.
“Under the new organization, the natural technical programs will work together as now, with the only real difference being a joint top management that can set joint responsibilities and determine priorities,” said GDE Director Barry Barish.
Also, both machines would make electrons and positrons collide, so scientists on both projects can continue to cooperate on the physics and detector R&D, again, guided by LHC results.
The LHC is typically described as a discovery machine, colliding protons to search for the celebrated Higgs boson and other particles and forces predicted by theoretical models. An electron-positron collider would serve as a precision machine, colliding elementary particles to measure in detail how the Higgs boson couples to other particles and look for new subatomic phenomena. The precision measurements would be sensitive to physics far beyond the energy reach of the accelerator itself and point the way to additional discoveries.
The primary technological difference between the two collider candidates is the way they accelerate particles. The ILC uses cold, superconducting structures to accelerate particles to between 0.5 and 1 teraelectronvolts of energy. CLIC uses warm, normal-conducting structures to accelerate particles to between 0.5 and 3 TeV.
Another stark difference between the two proposed machines is the maturity of their designs. The ILC is ripe for construction: the imminent release of its technical design indicates that, in principle, it could be built immediately. On the other hand, CLIC has another five to ten years of development and system tests before construction could start.
Yet the greatest challenge of the organizational unification could be a cultural one. At this stage, CLIC is a CERN-centered collaboration with international participation. The ILC program, on the other hand, is a global program whose governance is shared across multiple laboratories and regions.
“To find a common way forward, there will have to be more of an appreciation of a linear collider as a global endeavor,” said CLIC leader Steinar Stapnes. “Many are already involved in both projects, so for them it will reflect their actual working situation. For others, it will be a learning process.”
Most in the community agree that all the organizational charting, planning and growing pains will be worth it when the LHC data finally arrive, clarifying the prospect of the future of particle physics.
“I can't wait for the LHC results to come in,” Bagger said, echoing an oft-repeated refrain in linear collider circles. “They’ll help answer old questions, and point the way to new ones every bit as exciting as what has come before.”