The next-generation collider may be a 100-kilometer accelerator ring, the construction of which will cost at least $10 billion. At the same time, the prospects for discovering with the new collider something comparable in importance to the discovery of the Higgs boson in 2012 are very, very vague. But, it is quite possible that for immersion into the depths of physics of tiny particles, scientists will not even need such a grandiose and expensive construction, for this there will be a fairly new technology in which particles are used that have never been used before in accelerators of any type.
All modern accelerators and colliders can operate with a fairly limited set of elementary particles, mainly protons, electrons and positrons (antielectrons). These charged particles, dispersed to high speeds and energies, collide with each other or with the target material in the region surrounded by highly sensitive detectors, which make it possible to establish the sequence and parameters of the decay process of these particles into secondary particles. But, each of the types of particles used today has its positive and negative sides.
Protons, for example, consist of smaller particles called quarks, and therefore, when protons decay, they get such a saturated “soup” of secondary particles in which it is very difficult to trace the occurrence of interesting scientific phenomena. Electrons and positrons are simpler, “point” particles, but they produce secondary radiation when their direction of movement changes. Because of this, the effective accelerators of these particles must be straight and have a long length.
In the world of elementary particles there are particles such as muons, they, like electrons, are primitive particles, only 200 times larger, and they practically do not radiate (lose energy) during a change in direction of motion. However, muons have their own problems that make it difficult to work with these particles. Muons live a very short time, they decay into other particles 2 microseconds after they occur. In addition, to obtain muons, a proton beam directed to the target from a certain material is used, and when protons collide, not only muons are produced, but also particles called pions, which immediately decay into muons, forming a stream of random muon “sprays” around the forming beam.
Recently, physicists working as part of the MICE experiment (Muon Ionization Cooling Experiment), announced the success, which was the result of 20 years of experimental and theoretical research. They managed to get a stable muon beam using a method called ionization cooling.
This method allows you to capture muons moving in random directions and direct them through a special cooling device, which consists of 12 superconducting electromagnets that produce fields that envelop a 22-liter container filled with liquid hydrogen. The walls of this container have aluminum windows through which muons pass, which give their energy to hydrogen atoms by ionizing the latter. And as a result of complex processes occurring inside the container, on its other side there appears a directed and fairly well focused beam consisting of muons. After that, the muons of the beam can be accelerated using magnets and radio frequency resonance cavities to the energies required for physical experiments.
The ionization cooling method was developed by theoretical physicists in the late 1970s and early 1980s. But only at the present time there were technologies that allowed its practical implementation. “This was an extremely complex problem, considering the types and shapes of magnetic fields that must be generated for the ionization cooler to work,” says Chris Rogers, physicist, “It was only in the early 2000s that the design of the ionization cooler and “This was dictated by the interest of science in neutrinos, in subatomic particles that practically do not interact with ordinary matter. Muons decay into neutrinos and the muon beam can be considered as a source of these particles”.
Note that the experimental setup of the MICE experiment began work in 2012, and the data collection process was completed in 2017. And the subsequent analysis of the vast array of data collected has taken the past two years. The results of the analysis made it possible to determine the parameters of the muon beam before and after the ionization cooler, and these parameters indicate that the expected effect is indeed present, completely suppressing the random movement of individual muons.
The lack of a workable ionization cooler was a problem that prevented scientists from creating a muon accelerator. Now, having received this device at their disposal, scientists can begin to design a muon collider, which will allow them to peer into such areas of particle physics that are beyond the capabilities of traditional colliders and linear accelerators.