One of last year’s surprise results came from the MINOS (Main Injector Neutrino Oscillation Search) experiment in the US, which suggested that neutrinos and their antimatter counterparts, antineutrinos, might have different masses – an idea that goes against most commonly accepted theories of how the subatomic world works. At Lepton Photon 2011, however, the MINOS collaboration presented updated results. These constitute the world’s best measurement of muon neutrino and antineutrino mass comparisons and bring the masses more closely together.
Since the result announced in June 2010, the experiment has nearly doubled its data set, from 100 antineutrino events to 197 events. While the new results are only about 1 σ away from the previous results, the combination rules out concerns that the previous result could have arisen from detector or calculation errors. Instead, the combined results point to a statistical fluctuation that has lessened as more data have been collected.
