After more than three years of research and the passage of billion of billions of particles travelling from one part of the Alps to another, the metamorphosis of a neutrino has been directly observed for the first time ever, at the Gran Sasso National Laboratories of the Italian National Institute for Nuclear Physics (Istituto Nazionale di Fisica Nucleare - INFN) in Gran Sasso (LNGS). This metamorphosis consists of the transformation of one type of neutrino into another, a result that will pave the way for New Physics, although it will obviously have to be confirmed by additional observations of "mutating" neutrinos such as this first one.

The phenomenon was observed by the international collaboration OPERA (Oscillation Project with Emulsion-tRacking Apparatus). Neutrinos are "shot" from the European laboratory of CERN in beams directed to the Gran Sasso: in a mere 2.4 milliseconds they travel 732 kilometres beneath the Earth's crust to the core of the Gran Sasso Mountain in the Abruzzo Region and, during their journey, there is the possibility that some of them “change” their nature. The observation of this “mutation” was made possible by a fruitful collaboration between the OPERA researchers, CERN and the INFN Laboratories in Gran Sasso, within the CNGS neutrino beam project.

A single candidate neutrino that turned (in particle physics is called “oscillation”) from a muon neutrino into a tau neutrino was detected by the OPERA scientists, who since 2007 have observed several thousands of “normal” muon neutrinos sent by CERN and received at LNGS. This observation is a strong evidence that neutrinos have mass and that they can oscillate, passing from one “family” to another. That neutrinos can transform themselves was first proposed around the mid-20th century by the Italian physicist Bruno Pontecorvo, who was part of Enrico Fermi's group of researchers “Via Panisperna Boys”. In the Standard Model developed by physicists to explain the Universe, neutrinos do not have mass; it will thus be necessary to rectify this model, to provide new explanations, and to begin new research, which could have diverse implications in Cosmology, Astrophysics, and Particle Physics.

For 15 years a number of experiments have revealed the neutrino oscillation through disappearance of neutrinos coming from the atmosphere, the Sun, and other sources. However, this is the likely the first time that a neutrino that has oscillated from one type into another has been directly observed. It is as if, after having learned of a crime, the victim's body has finally been found.

Source: INFN Website