Matter, Anti-matter and MICE

Matter and anti-matter are believed to have been created in equal amounts when the Universe came in to existence at the Big Bang, and yet in the Universe today there is only matter. The quest to understand more about the mysterious neutrino particle which is thought to be responsible for this phenomenon has taken a major step forward. The Muon Ionisation Cooling Experiment (MICE) project, an accelerator research experiment for a major component of a future Neutrino Factory, has achieved an important milestone with the successful transport of a beam of muon particles along the MICE muon beam.

Professor Ken Long of Imperial College London, and spokesperson for MICE UK, said “Observing the first particles to pass through the MICE Muon Beam was an immensely exciting moment and represents the culmination of a fantastic, international team effort. It really marks the end of the beginning; we can now begin to tune up the beam and work towards the demonstration of ionisation cooling.”

Observations of atmospheric and solar neutrinos have shown that they change state (oscillate), between three forms - electron, tau and muon - during their journey across the Earth or from the Sun to the Earth. This discovery is extremely significant since oscillations can only occur if neutrinos have mass and yet the Standard Model of particle physics, on which our current understanding of how our Universe was created and is held together rests, assumes that neutrinos have no mass. The fact that neutrinos change state implies that they have mass and therefore that the Standard Model is wrong or incomplete. Results from experiments such as those from the SuperKamiokaNDE experiment in Japan and the Sudbury Neutrino Observatory in Canada detecting atmospheric neutrinos produced by cosmic rays, as well as neutrinos from the Sun, discovered that neutrinos do have mass after all.

To study the mysterious neutrino in detail requires a new way of generating very high intensity beams of high energy neutrinos of known characteristics (composition, energy) by storing muons in a decay ring with long straight sections pointing to large detectors hundreds or thousands of kilometres away. A Neutrino Factory is the answer. The Neutrino Factory will allow experiments of exquisite precision to be mounted, thus allowing the characteristics of the neutrino to be explored with unprecedented accuracy, reshaping our understanding of the structure of nature and the forces that bind it together. Studies have shown that such a Neutrino Factory can be built, but that there are a number of technical challenges to be solved before a technical design can be completed. A major challenge is presented by the fact that muons decay in about 2 millionths of a second and ionisation cooling is the only technique that can cool the muons fast enough, enabling muon beams of the required intensity to be delivered by the Neutrino Factory.

The technologies required for ionisation cooling will be demonstrated by MICE proving that muons can be assembled into ‘bunches’ in which the muons are going in the same direction and have roughly the same energy. Such ‘cold’ bunches can be made of small enough size to allow the muon beam to be accelerated and stored.

The MICE project is a major collaboration involving scientists and engineers from across the world, with collaborators in UK, the US, Switzerland, Italy, Bulgaria, The Netherlands, China and Japan. The UK teams include the Science and Technology Facilities Council Rutherford Appleton Laboratory (RAL) and Daresbury Laboratory (DL). The collaboration is designing, building and testing a section of realistic cooling channel on a beam line on the ISIS facility at RAL. Achieving this will give confidence that a full ionisation cooling channel, consisting of a large number of cooling sections, can be designed and built economically. In order to demonstrate the cooling performance, it will be necessary to characterise the muon beam going in and out of the cooling section with unprecedented accuracy.

Professor Alain Blondel of University of Geneva, Switzerland, MICE Collaboration Spokesperson said, “Developing new particle accelerator technologies is vital for progress in science in general and particle physics in particular. The MICE collaboration was set-up in 2001 to demonstrate ionisation cooling, which has never been done before, with the hope of seeing first beam in 2004. As usual things have taken longer than expected, with many political, financial, technical and even human difficulties. The collaboration has held together beautifully, everybody pulling their end and working very hard, with the tireless support from our big funding agencies, RAL and the ISIS team. Congratulations and gratitude should go to all of them. The recent successes represent the first small steps in our still long march towards the demonstration of ionisation cooling in 2010.“

Dr Andrew Taylor, Director ISIS added, "The high intensity proton synchrotron that we use as the driver for the ISIS neutron source could not have been possible without the development and research within the particle physics community over the past decades.

It's a great pleasure to be able to return the favour and use ISIS as a test bed for the development of key technologies that are steps on the way to building a Neutrino Factory that may one day be built on the Rutherford Appleton Laboratory."

Notes for editors

Image and caption

• Image - Some of the MICE team assembled at RAL in front of the dipole.
  From left to right: Tony Jones, Danny Lordan, Alain Blondel, Paul Sinclair, Mike Zisman, George Sim, Chris Nelson, Paul Kyberd, Cyril Locket, Eamonn Capocci, Ashok Jamdagni, Matt Hills and Paul Barclay.

Contacts

• Natalie Bealing
  STFC Press Office
  Tel: + 44 (0)1235 445484
  
  
• Professor Alain Blondel
  University of Geneva
  Tel: + 41 76 487 4058
  
  
• Professor Ken Long
  Imperial College
  Tel: + 44 (0)207 5947812 or
  Tel: + 44 (0)1235 445646 (RAL)

The MICE collaboration consists of 150 scientists from the UK, continental Europe, the US and Japan. UK collaborators are from Brunel University, Glasgow University, University of Lancaster and the Cockcroft Institute, University of Liverpool, Imperial College London, University of Oxford and the John Adama Institute, STFC Rutherford Appleton Laboratory, STFC Daresbury Laboratory and University of Sheffield.

The MICE team has completed several significant steps in realising the experiment during 2008. The mechanical installation and test of the pion production target in the ISIS proton synchrotron accelerator has been completed, the pion decay line has been built and beam counters and other equipment are installed in the experimental hall. Recently, the first particles have been transported through the MICE Muon Beam itself. Over the coming months, the MICE spectrometer system will be installed and experiments will finally begin. The cooling channel will be built over the next two to three years, culminating in the demonstration of ionisation cooling and exploration of a vital technique for the future Neutrino Factory.

Observations of atmospheric and solar neutrinos have shown that they change state (oscillate), between three forms - electron, tau and muon - during their journey across the earth or from the Sun to the Earth. This discovery is extremely significant since oscillations can only occur if neutrinos have mass. The Standard Model of particle physics, on which our current understanding of how our Universe was created and is held together rests, assumes that neutrinos have no mass. The fact that neutrinos change state implies that they have mass and therefore that the Standard Model is wrong or incomplete; new particles and/or new conservation laws are required to accommodate the fact that neutrinos have mass.

1. The Standard Model of Particle Physics is built on the fact that the elementary building blocks of matter are divided into three generations of two kinds of particle quarks and leptons. The leptons consist of the charged electron, muon and tau, together with three electronically neutral particles the electron neutrino, the muon neutrino and the tau neutrino. The Standard Model predicts that neutrinos have no mass.
   
   
2. Ionisation cooling is the only technique that can cool the muons fast enough muons decay in about 2 millionths of a second. ‘Cooling’ refers to the idea that a cloud of muons that all have different energies and directions looks like a hot gas, whereas when they all have about the same energy and move in the same direction, they look like a cool gas. In ionisation cooling, the energy of the muon is reduced by passage through matter (liquid hydrogen) and one component of the energy is restored by acceleration with radiofrequency electric fields. While there is no doubt that this works, the efficiency of this cooling technique requires detailed knowledge of the behaviour of muons in many materials for example, in the windows of the vessel that contains the liquid hydrogen.
   
   
3. The physics motivation for the Neutrino Factory is the study of the properties of neutrinos. In the wake of the spectacular observation of cosmic neutrinos, which gained the Nobel Prize for Physics in 2002 for Ray Davis and Masatoshi Koshiba, it was also discovered that neutrinos have mass and undergo, over astronomical distances, a quantum phenomenon called neutrino oscillations. Much of the excitement arises because there is the possibility within the neutrino oscillation phenomenon that there could be a significant difference between the properties of neutrinos and antineutrinos, and that this might be related to the observation that in the Universe today there is no antimatter, although in the Big Bang, matter and antimatter would have been created in equal amounts. A Neutrino Factory would be the most powerful source of neutrinos suitable for these experiments. The discovery of an asymmetry in the properties of neutrinos and antineutrinos would be one of the most exciting discoveries of the 21st Century.

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