Abstract
The OPERA experiment at the Gran Sasso underground laboratory is searching for νμ → ντ oscillations in appearance mode in the CNGS neutrino beam. Four ντ candidate events have been found so far, using a sub-sample of data from the 2008-2012 runs. Given the number of analysed events and the low background, νμ → ντ oscillations are established with a significance of 4.2 σ. In this paper the data analysis is discussed, with emphasis on the background constraints obtained using dedicated data-driven control samples. We present also the analysis of the τ neutrino and electron neutrino data in the framework of the 3+1 sterile neutrino model. The measurement of the muon charge ratio in the collected cosmic ray sample is also reported.
Highlights
After more than 60 years since the first direct observation of anti-νe from reactors, neutrinos are still the least known particles of the Standard Model, which foresees the existence of three neutrinos, one for each charged lepton
The muon spectrometers were composed of an iron-core dipole magnet with drift tubes used as precision trackers and 22 layers of resistive plate chambers (RPC) inside the magnetized iron
The OPERA experiment was designed to observe νμ → ντ oscillations through τ appearance in a pure νμ beam
Summary
After more than 60 years since the first direct observation of anti-νe from reactors, neutrinos are still the least known particles of the Standard Model, which foresees the existence of three neutrinos, one for each charged lepton. Even if the absolute mass scale has not yet been measured, the two ∆m2 values are well known from neutrino oscillation experiments, as well as the mixing matrix, all except for the phase. Nowadays there are many experiments that have observed neutrino oscillations, both from natural (solar and atmospheric) and artificial (nuclear reactors and neutrino beams) sources. This paper is a review of the latest results from the OPERA experiment, designed to observe, on a muon neutrino beam, oscillations in tau neutrinos induced by ∆m2atm and θ23 , the parameters. It is worth noticing that, thanks to the use of nuclear emulsions, OPERA is a unique experiment, able to identify the CC interactions of all the three neutrino flavors (νe , νμ , and ντ )
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