News from the Muon Collider 2011 conference

Fermilab theorist Chris Hill wrote this week’s column.

Chris Hill

During the last week of June, roughly 100 physicists met in the thin air of Telluride, Colo., to contemplate the construction and physics goals of a muon collider. This new type of particle collider would be one of the most complex devices ever created by humans. It would employ a short-lived particle, the muon, which disintegrates in a mere 2 millionths of a second. That’s just long enough to use the particle as a probe to unveil the secrets of nature.

The muon collider plans and designs are still conceptual, and we won’t be building such a machine for at least 20 years. Undaunted, the scientists at Telluride trekked on to identify and solve the multifarious issues that revolve around three topics:

  • creating a large number of muons and antimuons for the collider using the proposed Project X accelerator
  • cooling these particles to form small packets that can be accelerated to an energy of up to 2 TeV
  • making the muons and antimuons collide head on at 4 TeV in a complex and robust particle detector

For the detector design, the challenge is to differentiate between the particles coming from actual muon-antimuon collisions and the enormous background created by particles coming from muon decays. At the Telluride meeting, scientists reported a feasible solution: a detector that utilizes fast timing and clever geometry to deal with the ferocious backgrounds. Major, more detailed, studies need to be done before this type of detector becomes a reality.

Theorists provided a list of the “top six” key physics questions to explore 20 years from now, when a muon collider exists. The list includes:

  • studying a very heavy, beyond-the-Standard Model Higgs boson, via WW scattering, which would be difficult to detect at the LHC
  • probing in depth the collider production of dark matter particles
  • studying a Z’-boson, should the LHC find evidence of such a particle. If it exists, a Z’ boson will act as an amplifier for new physics, and this would reduce the stringent technological requirements for muon cooling and background reduction.

The muon collider complex would fit on the Fermilab site and could be built in functional stages, beginning with the Project X proton accelerator. The next stage would be the construction of a large muon storage ring, or neutrino factory, followed by the construction of the muon collider itself. Staging distributes the costs over many years and many sub-projects and might be the way for the United States to once more host experiments at the Energy Frontier.

Participants in the Muon Collider 2011 conference. The conference co-chairs were Marco Battaglia, Berkeley Lab/UC Santa Cruz; Estia Eichten, Fermilab; and Robert Palmer, Brookhaven. Ron Lipton chaired Fermilab’s organizing committee.