New experimental results show that particles called muons can be bundled into beams suitable for high-energy collisions, opening the way to new physics.
Particle accelerators are best known for colliding matter to probe its composition, but they are also used to measure the chemical structure of drugs, treat cancers and make silicon microchips.
Current accelerators use protons, electrons and ions, but more powerful accelerators using muons – heavier cousins of electrons – have the potential to revolutionize the field. Muon accelerators would be both cheaper and smaller, and could therefore be built on the same sites as existing colliders while accessing even higher energies.
A new analysis of an experiment using a muon beam has demonstrated the success of one of the key technologies needed for muon accelerators. This paves the way for a muon collider to be developed more quickly than other types of accelerators using different particles.
The analysis was conducted by researchers at Imperial College London, as part of the Muon Ionization Cooling Experiment (MOUSE) collaboration, and the results are published today in Physics of nature.
The study’s first author, Dr Paul Bogdan Jurj, from the Department of Physics at Imperial College, said: “Our proof of principle is great news for the international particle physics community as it prepares for the next generation of high-energy accelerators. It is an important step towards the realisation of a muon collider, which could be integrated into existing sites, such as FermiLab in the US, where enthusiasm for this technology is growing.”
Powerful particle accelerators
The world’s most powerful particle accelerators, such as the Large Hadron Collider (LHC), collide particles called protons at high energies. These collisions produce new subatomic particles that physicists want to study, such as the Higgs boson and other bosons and quarks.
To achieve higher-energy collisions and access new discoveries and applications in physics, a much larger proton collider would need to be built. The LHC is shaped like a ring with a circumference of 27 km, and plans have been made to potentially build a collider of nearly 100 km.
However, the considerable cost and time required to build such a collider are leading some physicists to look for other solutions. Among the promising avenues are colliders capable of colliding muons.
Muon colliders would be more compact and therefore cheaper, and would achieve effective energies as high as those offered by the 100 km proton collider in a much smaller space. However, technological advances are needed to ensure that muon collisions can be sufficiently frequent.
Gathering the muons
The main challenge was to gather the muons into a small enough space so that once accelerated, they form a concentrated beam. This is essential to ensure that they collide with the beam of muons accelerating around the ring in the opposite direction.
The MICE collaboration has already produced such a beam using magnetic lenses and energy-absorbing materials to “cool” the muons. Initial analysis showed that this successfully moved the muons towards the center of the beam.
The new analysis of this experiment looked in more detail at the “shape” of the beam and the space it occupied. Thanks to this, the team was able to show that the beam had become more “perfect” thanks to the cooling: its size was reduced and the muons moved in a more organized way.
The experiment was carried out using the Science and Technology Facilities Council (STFC) MICE muon beamline ISIS Neutron and Muon Beam Facility at STFC’s Rutherford Appleton Laboratory in the UK. The team is now working with the International Muon Collider Collaboration to build the next stage of demonstrations.
Spokesperson for MICE collaboration Professor Ken Longfrom the Department of Physics at Imperial College, said: “The clearly positive result shown by our new analysis gives us the confidence to move forward with larger accelerator prototypes that put this technique into practice.”
Dr. Chris Rogersbased at STFC’s ISIS facility in Oxfordshire, led the MICE analysis team and is now leading the development of the muon cooling system for CERN’s Muon Collider. He said: “This is an important result that demonstrates the cooling performance of MICE in the clearest possible way. It is now imperative to move on to the next step, the Muon Cooling Demonstrator, in order to deliver the Muon Collider as quickly as possible.”
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