An important activity toward advancing accelerator capability is research and development for a high luminosity muon collider. Muons have important properties compared to electrons and protons when considering a possible next step for a high energy physics facility. Since radiation by muons is much suppressed compared to electrons, it is feasible to consider a relatively compact circular collider in the TeV energy range for muons. However the muon, like the electron, is a point particle and therefore can explore the same physics regime as protons with approximately ten times higher energy. Accordingly the muon collider has attracted increasing interest over the past couple of years. Since the muon is an unstable particle there are many new facets of accelerator physics and technology that need to be examined before one can say with confidence that such a device will work.
The International Muon Ionization Cooling Experiment (or MICE) is a high energy physics experiment dedicated to observing ionization cooling of muons for the first time. Such cooling is a necessary step toward a muon collider. Cooling is a process whereby the emittance of a beam is reduced in order to reduce the beam size, so that more muons can be accelerated in smaller aperture accelerators and with fewer focussing magnets. This might enable the construction of high intensity muon accelerators, for example for a Neutrino Factory or Muon Collider, which potentially can attain higher energies than electron-positron colliders.
Researchers looking for a method of cooling muons designed the MICE experiment to test the effectiveness of a technique called ionization cooling. Ionization cooling takes place when muons are sent through an absorber in which they lose momentum via ionization energy loss. They are then reaccelerated in a linear accelerator where their energy is restored only in the forward direction. MICE will use a single particle beam, with not more than one muon passing through the detector about every 10 nanoseconds. The experiment needs to balance the cooling from energy loss with the heating from multiple scattering of the muons.
The Muon Ionization Cooling Experiment will make detailed measurements of muon ionization cooling using a newly constructed low-energy muon beam at the Rutherford Appleton Laboratory (RAL). The experiment is a single particle experiment and utilizes many detector techniques from high energy physics experiments. To characterize and monitor the muon beamline, newly developed scinitillating fiber profile monitors and scintillator paddle rate monitors are employed. In order to monitor the purity of the beam and tag the arrival time of individual muons, a dual aerogel Cherenkov system is used, and a plastic scintillator time-of-flight system will be used.
See the two images for the complete 2 pages of the Project Otcomes Report. We have developed Cherenkov light detectors with high density aerogel,as shown in Figure 1, to measure the speeds of sub-atomic particles (pions, muons, and electrons). We wish to ID muons for the Muon Ionization Cooling Experiment (MICE) at the Rutherford Lab in the UK. MICE uses liquid hydrogen to slow the motion of muons in all directions and then restores the forward motion with radio frequency electric fields. This leads tonarrow bunches of muons which can be collided at high energies toexplore the Higgs Boson and the energy frontier. This is the intellectual merit and broader impact of the work. In aerogel, a silicon dioxide foam, the speed of light is slower than in a vacuum. If a sub-atomic particle exceeds this speed, Cherenkov light is emitted, similar to a sonic boom from a jet airplane. High density aerogel is new. We can now measure particles moving at 90% the speed of light or 168,000 miles per second. Combining the speed of an electrically charged particle with its trajectory in a magnet leads to a measure of its mass. Pions, muons, and electrons all have different masses. The liquid hydrogen at our MICE experiment must be contained. To do this Mississippi has fabricated aluminum windows with a central thickness of only 0.007 inches. This allows muons to pass into the hydrogen with minimal scattering. The windows are fabricated on a computer controlled lathe with a precision machined backing plate. A non-contact method of measuring window thickness with the radiation sources, Cesium-137 and Thallium-204, has been developed as shown in Figure 2. Mississippi has been working to accelerate muons in very fast ramping rings of magnets to effective energies up to 25 times higher than the Large Hadron Collider in Switzerland at a similar cost, once a muon source exists [1]. As electric fields increase the speed of a muon, the magnet field is ramped to stay in synch. Figure 3 shows a prototype magnet. The 1.8 Tesla magnetic field observed is five times stronger than a refrigerator magnet. [1] http://arxiv.org/pdf/1207.7354.pdf and http://arxiv.org/pdf/1207.6730.pdf
