The observation of a second neutrino tau interaction at the INFN Gran Sasso Laboratory was announced by the OPERA Collaboration during the 25th Neutrino Conference, in Kyoto, earlier this month. This result follows on from the first observation, made in 2010.
With this new result the OPERA detector is back on track to its original motivations, after a noisy excursion over the measurement of the neutrino time of flight. The OPERA experiment was designed to search for the rare events of neutrino oscillations, according to which muon neutrinos moving along their path transform into a different type, the so-called tau neutrino.
The accelerators at CERN produce a beam of muon neutrinos, which are sent towards the Gran Sasso Laboratory. Thanks to their extremely rare interactions with matter, neutrinos arrive practically unperturbed at Gran Sasso, having crossed 730 km of rock. The 1250 ton OPERA apparatus – which has been taking data since 2008 – acts like a photographic camera, recording interactions of tau neutrinos: thereby being able to demonstrate the oscillation phenomenon.
Obtained after the collection and analysis, with micrometric accuracy, of several thousands of neutrino interactions, the detection of this second event is an important step towards the accomplishment of the final goal of the experiment.
The news of this second interaction arrived at the Kyoto conference together with the confirmation – from OPERA and three other experiments at Gran Sasso (Borexino, ICARUS and LVD) – that the neutrino time of flight is consistent with the speed of light.