New measurements from Fermilab’s MINOS experiment suggest a difference in a key property of neutrinos and antineutrinos

Scientists of the MINOS experiment at the Department of Energy's Fermi National Accelerator laboratory have 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 ?m2 (''delta m squared''), is smaller by approximately 40 per cent for neutrinos than for antineutrinos.

However, there is a still a five per cent probability that ?m2 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 at the Neutrino 2010 conference in Athens, Greece, and in a seminar 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.''