Unexpected difference between neutrinos and antineutrinos suggested at MINOS
15 Jun 2010 09:36 AM
An international team of scientists from the MINOS experiment at the Fermi National Accelerator laboratory (Fermilab) yesterday, 14 June, announced the world’s most precise measurement to date of the parameters that govern antineutrino oscillations, the back-and-forth transformations of antineutrinos from one type to another. This result provides information about the difference in mass between different antineutrino types. The measurement showed an unexpected variance in the values for neutrinos and antineutrinos. This mass difference parameter, called Δm2 (“delta m squared”), is smaller by approximately 40 percent for neutrinos than for antineutrinos.
However, there is a still a five percent probability that Δm2 is actually the same for neutrinos and antineutrinos. With such a level of uncertainty, MINOS physicists need more data and analysis to know for certain if the variance is real.
Neutrinos and antineutrinos behave differently in many respects, but the MINOS results, presented today at the Neutrino 2010 conference in Athens, Greece and in a colloquium at Fermilab, are the first observation of a potential fundamental difference that established physical theory could not explain.
“Everything we know up to now about neutrinos would tell you that our measured mass difference parameters should be very similar for neutrinos and antineutrinos,” said MINOS co-spokesperson Rob Plunkett. “If this result holds up, it would signal a fundamentally new property of the neutrino-antineutrino system. The implications of this difference for the physics of the universe would be profound.”
“We do know that a difference of this size in the behaviour of neutrinos and antineutrinos could not be explained by current theory,” said MINOS co-spokesperson Jenny Thomas of University College London. "While the neutrinos and antineutrinos do behave differently on their journey through the Earth, the Standard Model predicts the effect is immeasurably small in the MINOS experiment. Clearly, more antineutrino running is essential to clarify whether this effect is just due to a statistical fluctuation or the first hint of new physics.”
The NUMI beam is capable of producing intense beams of either antineutrinos or neutrinos. This capability allowed the experimenters to measure the unexpected mass difference parameters. The measurement also relies on the unique characteristics of the MINOS detector, particularly its magnetic field, which allows the detector to separate the positively and negatively charged muons resulting from interactions of antineutrinos and neutrinos, respectively. MINOS scientists have also updated their measurement of the standard oscillation parameters for muon neutrinos, providing an extremely precise value of Δm2.
Muon antineutrinos are produced in a beam originating in Fermilab's Main Injector. The antineutrinos’ extremely rare interactions with matter allow most of them to pass through the Earth unperturbed. A small number, however, interact in the MINOS detector, located 735 km away from Fermilab in Soudan, Minnesota. During their journey, which lasts 2.5 milliseconds, the particles oscillate in a process governed by a difference between their mass states.
UK groups at the University College London, Universities of Cambridge, Oxford and Sussex and the STFC Rutherford Appleton Laboratory are participating in MINOS, funded by the Science and Technology Facilities Council.
Notes for Editors:
Graphics and images are available at: http://www.fnal.gov/pub/presspass/press_releases/MINOS_photos/2010.html
Media contacts:
Rhianna Wisniewski
Fermilab,
Tel +1-630-840-6733
Email rhianna@fnal.gov
Professor Jenny Thomas (at the conference in Greece)
University College London
Tel: +44 7919 107 359
Email: jthomas@hep.ucl.ac.uk
Julia Maddock
STFC Press Office
Tel +44 7901 514975
Email Julia.maddock@stfc.ac.uk
MINOS
The MINOS experiment involves more than 140 scientists, engineers, technical specialists and students from 30 institutions, including universities and national laboratories, in five countries: Brazil, Greece, Poland, the United Kingdom and the United States. Funding comes from: the Department of Energy and the National Science Foundation in the U.S., the Science and Technology Facilities Council in the U.K; the University of Minnesota in the U.S.; the University of Athens in Greece; and Brazil's Foundation for Research Support of the State of São Paulo (FAPESP) and National Council of Scientific and Technological Development (CNPq).
Fermilab
Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operated under contract by Fermi Research Alliance, LLC.
Science and Technology Facilities Council
The Science and Technology Facilities Council ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange.
The Council has a broad science portfolio including Astronomy, Particle Physics, Particle Astrophysics, Nuclear Physics, Space Science, Synchrotron Radiation, Neutron Sources and High Power Lasers. In addition the Council manages and operates three internationally renowned laboratories:
• The Rutherford Appleton Laboratory, Oxfordshire
• The Daresbury Laboratory, Cheshire
• The UK Astronomy Technology Centre, Edinburgh
The Council gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics (CERN), the Institute Laue Langevin (ILL), European Synchrotron Radiation Facility (ESRF), the European organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA). It also funds UK telescopes overseas on La Palma, Hawaii and in Chile, and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at Jodrell Bank Observatory.
The Council distributes public money from the Government to support scientific research.