Where did all the matter in the universe come from? This is one of the biggest mysteries in fundamental physics and exciting results released on 15 June 2011 from a team including researchers at the University of Warwick at the international T2K neutrino experiment in Japan could be an important step towards resolving this puzzle.
The intriguing results indicate a new property of the enigmatic particles known as neutrinos.
There are three types of neutrinos (called flavours) – one paired by particle interactions with the familiar electron (called the electron neutrino), and two more paired with the electron’s heavier cousins, the muon and tau leptons. Previous experiments around the world have shown that these different flavours of neutrinos can spontaneously change into each other, a phenomenon called “neutrino oscillation”.
Two types of oscillations have already been observed but in its first full period of operation, the T2K experiment has already seen evidence for a new type of oscillation (the appearance of electron neutrinos in a muon neutrino beam). If confirmed, this means that we have now observed that neutrinos can oscillate in every way possible.
This observation is of particular interest because it opens the possibility of being able to test whether the oscillations of neutrinos and their anti-particles (called anti-neutrinos) could be different. If the oscillations of neutrinos and anti-neutrinos are different, it would be an example of what physicists call CP-violation and this could be the key to explaining why there is more matter than anti-matter in the universe (an excess which could not happen within the known laws of physics).
The experiment ran from January 2010 until 11th March this year, when it was dramatically interrupted by the Japanese earthquake. Fortunately, the multinational T2K team were unharmed and their highly sensitive detectors were largely undamaged. Six clean electron neutrino events are observed in the data taken before the earthquake, while in the absence of oscillations there should only have been 1.5 +/- 0.3. Even though such an excess could only happen by chance about one time in a hundred, that is not good enough to confirm a new physics discovery, so this is called an “indication”.
Dr Gary Barker from the University of Warwick said: “The T2K project has given us an intriguing hint that this third neutrino oscillation channel is present in nature – our job now is to collect much more data and work to further understand our detector in order to reach levels of precision that will put the conclusion beyond doubt.”
Prof. Takashi Kobayashi of the KEK Laboratory in Japan and spokesperson for the T2K experiment, said “It shows the power of our experimental design that with only 2% of our design data we are already the most sensitive experiment in the world for looking for this new type of oscillation”.
STFC is the UK sponsor of particle physics and supports the UK universities involved in the T2K experiment.
In this projected diagram of cylinder-shaped Super-Kamiokande, each coloured dot shows a photomultiplier that detected light (these photomultipliers are mounted on the inside wall of the detector). Electron neutrinos which subsequently induce electromagnetic showers to eventually emit Cherenkov light that is detected in a ring-shaped structure.
Notes for Editors
The experiment is a huge undertaking with over 500 scientists from 12 countries. The UK has invested £14.3M in the T2K project.
There are three elements to the experiment:
1. A beam of muon neutrinos is produced at the Japan Proton Accelerator Research Center in
2. The neutrinos then pass through a complex set of near detectors located 280 meters from the target in order to determine the neutrino beam’s composition and properties before the neutrinos have a chance to oscillate. 8 STFC-supported institutions (listed below) were involved in the production of a variety of components for these near detectors.
3. The neutrinos then fly under the ground for 295 km across Japan to the mammoth Super Kamiokande neutrino detector (a tank of 50,000 tons of ultra-pure water surrounded by sensitive optical detectors which can see the very faint flashes of light emitted by the very rare interactions of passing neutrinos with the water). This is capable of telling muon neutrinos from electron neutrinos with high precision, and is thus ideal for looking for the appearance of a small fraction of electron neutrinos appearing in the muon neutrino beam, the key signature of this new type of oscillation.
T2K UK collaboration and contacts
- STFC Daresbury Laboratory – Prof. Dave Wark
- STFC Rutherford Appleton Laboratory – Dr Alfons Weber
- University of Warwick – Dr Gary Barker
- Imperial College
London– Prof. Dave Wark
- Lancaster University – Prof. Peter Ratoff
- Liverpool University – Prof. Christos Touramanis
- Queen Mary University London – Dr Francesca Di Lodovico
- Sheffield University – Dr Lee Thompson
- University of Oxford – Dr Giles Barr
About STFC The Science and Technology Facilities Council is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar.STFC operates or hosts world class experimental facilities including:
- in the UK; ISIS pulsed neutron source, the Central Laser Facility, and LOFAR. STFC is also the majority shareholder in Diamond Light Source Ltd.
- overseas; telescopes on
La Palmaand Hawaii
It enables UK researchers to access leading international science facilities by funding membership of international bodies including European Laboratory for Particle Physics (CERN), the Institut Laue Langevin (ILL), European Synchrotron Radiation Facility (ESRF) and the European Southern Observatory (ESO). STFC is one of seven publicly-funded research councils. It is an independent, non-departmental public body of the Department for Business, Innovation and Skills (BIS). www.stfc.ac.uk
For further information please contact:
Peter Dunn, Head of Communications
Communications Office, University House,
University of Warwick, Coventry, CV4 8UW, United Kingdom
Tel: +44 (0)24 76 523708 Mobile/Cell: +44 (0)7767 655860
PR82 16h June 2011