If we build it, they will come

June 6, 2003

The UK must grab its chance to become home of a neutrino factory, argues Ken Long

What is a neutrino? An academic question, perhaps, but one that bears on some of the most fundamental questions in particle physics and cosmology today. To reveal the true nature of the neutrino, measurements of exquisite precision must be performed, which require vast numbers of the sub-atomic particles. With world-leading expertise in relevant technologies, the UK has a unique opportunity to lead the international work that could ultimately produce a "neutrino factory" capable of meeting demand for the mysterious particles.

Recent experimental results in Japan and Canada have shown that the widely accepted "standard model" description of the neutrino is wrong. Instead, they imply that the particles have mass and that one particular type of neutrino can change into another as it travels through space. The consequences of these observations are far-reaching - not only will the standard model have to be modified, but it may be that neutrinos form a significant part of the "dark matter" known to make up most of the universe. Furthermore, the interactions of the neutrinos produced in the big bang may have been responsible for the removal of essentially all anti-matter from existence.

To create a high-intensity neutrino beam, a number of other particles must be produced first. A high-power proton beam is collided with a metal target. This produces an enormous number of particles called pions. The pions are captured and then decay to produce muons. Muons, in turn, decay to produce neutrinos.

The key is to create a muon beam of unprecedented brilliance that can be compressed, accelerated and finally injected into the storage ring. One essential task will be to shrink this muon beam using a technique called ionisation cooling. So far, this technique has not been demonstrated in principle or in practice. The Muon Ionisation Cooling Experiment collaboration had been formed to take on this challenge. The work will be carried out by an international team of 150 physicists drawn from Europe, the US and Japan, using an existing experimental facility at the Rutherford Appleton Laboratory in Oxfordshire.

The UK has a fantastic opportunity. The Isis accelerator at RAL has the world's highest current-density proton beam. Thus, it may prove to be an ideal place to site the neutrino factory. The UK has a proven record in the provision of high-power particle beams and in the development of novel detector technologies. While the neutrino factory itself is a long-term goal, the work required to make it a reality has already begun. The UK needs a sustained research-and-development programme targeted on the technologies that underpin the facility; the source of the high-power proton beam, the high-power target and the ionisation-cooling channel.

The world-class science, the chance to develop a new technique for particle physics and the real possibility that the neutrino factory could be hosted at RAL have lead to a great deal of excitement in the UK particle physics community and strong support from research councils and government.

Clearly, if such a facility were sited at RAL, it would have a tremendous impact on local and national industry. A modest investment in a focused R&D programme over the next five to ten years will establish the UK as a leader of the international neutrino factory community and will put us in a strong position to lead the effort.

Ken Long is reader in physics at Imperial College London.

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