R&D for a muon accelerator
Alan Bross, group leader in the Fermilab Accelerator Physics Center and co-spokesperson of the Neutrino Factory and Muon Collider Collaboration, wrote this week's column.
Alan Bross works in the MuCool Test Area
When he first heard of the discovery of the muon in 1936, Isidor Rabi, a Nobel Prize winning physicist, asked, "Who ordered that?" At the time, the muon didn't fit into physicists' understanding of the subatomic world. Today we appreciate the important role that the muon plays in the Standard Model of particles and forces, and accelerator facilities around the world produce muons for experiments.
More and better experiments could be done if we can figure out how to create ultra-intense beams of muons and how to accelerate them. The applications are numerous. They include the search for lepton flavor violating processes, such as the decay of a muon into an electron and a photon, and the construction of a high-intensity muon accelerator that would drive a neutrino factory, the ultimate facility for studying neutrino mixing. Another application involves plans for an energy frontier muon collider that would smash positively and negatively charged muons into each other at energies that could exceed those of the most powerful electron-positron collider.
The members of the international Neutrino Factory and Muon Collider Collaboration are in full pursuit of these ideas. Comprised of scientists from Europe, Japan and the United States, the NFMCC is developing the concepts and technologies needed to produce and manipulate ultra-intense beams of muons.
The feasibility of a muon accelerator hinges on a technique known as muon ionization cooling. Working with members of the Fermilab Accelerator Division and the Particle Physics Division, the Fermilab NFMCC group carries out experiments on two important components necessary for muon ionization cooling: high-gradient, normal-conducting RF cavities and liquid-hydrogen absorbers. Our experiments take place at Fermilab's MuCool Test Area, located near the southern end of the Linac.
This spring, we will begin our first experiments using a proton beam extracted from the Linac, which will allow us to investigate how high-intensity particle beams affect those cavities and absorbers.
The Fermilab NFMCC group also participates in the Muon Ionization Cooling Experiment at the Rutherford Appleton Laboratory in the U.K. When fully operational, MICE will be the first experiment to demonstrate muon ionization cooling with a beam of muons. Fermilab has provided diagnostic tools for the MICE muon beam line and detector components for the MICE spectrometers.
We are also involved in the International Design Study for a Neutrino Factory where Fermilab's NFMCC group studies the front end of the neutrino factory and parts of the muon acceleration system. We are also investigating the feasibility of a low-energy neutrino factory and its corresponding neutrino detector.
There are still many challenges that we need to overcome before we have the technology to build a neutrino factory or a muon collider, but step by step, we are moving closer to our goal.