The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km. The measurement is based on data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of \( \left( {6.5\pm 7.4\left( {\mathrm{stat}.} \right)_{-8.0}^{+8.3}\left( {\mathrm{sys}.} \right)} \right)\mathrm{ns} \) was measured corresponding to a relative difference of the muon neutrino velocity with respect to the speed of light \( {{{\left( {\upsilon -c} \right)}} \left/ {c} \right.}=\left( {2.7\pm 3.1\left( {\mathrm{stat}.} \right)_{-3.3}^{+3.4}\left( {\mathrm{sys}.} \right)} \right)\times {10^{-6 }} \). The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5 μs long extractions, was confirmed by a test performed at the end of 2011 using a short bunch beam allowing to measure the neutrino time of flight at the single interaction level.

The OPERA neutrino detector in the underground Gran Sasso Laboratory (LNGS) has been designed to perform the first detection of neutrino oscillations in direct appearance mode through the study of the $\nu_\mu\rightarrow\nu_\tau$ channel. The hybrid apparatus consists of an emulsion/lead target complemented by electronic detectors and it is placed in the high energy long-baseline CERN to LNGS beam (CNGS) 730 km away from the neutrino source. Runs with CNGS neutrinos were successfully carried out in 2008 and 2009. After a brief description of the beam, the experimental setup and the procedures used for the analysis of the neutrino events, we describe the topology and kinematics of a first candidate $\nu_\tau$ charged-current event satisfying the kinematical selection criteria. The background calculations and their cross-check are explained in detail and the significance of the event is assessed.The OPERA neutrino detector in the underground Gran Sasso Laboratory (LNGS) has been designed to perform the first detection of neutrino oscillations in direct appearance mode through the study of the $\nu_\mu\rightarrow\nu_\tau$ channel. The hybrid apparatus consists of an emulsion/lead target complemented by electronic detectors and it is placed in the high energy long-baseline CERN to LNGS beam (CNGS) 730 km away from the neutrino source. Runs with CNGS neutrinos were successfully carried out in 2008 and 2009. After a brief description of the beam, the experimental setup and the procedures used for the analysis of the neutrino events, we describe the topology and kinematics of a first candidate $\nu_\tau$ charged-current event satisfying the kinematical selection criteria. The background calculations and their cross-check are explained in detail and the significance of the event is assessed.The OPERA neutrino detector in the underground Gran Sasso Laboratory (LNGS) has been designed to perform the first detection of neutrino oscillations in direct appearance mode through the study of the νμ→ντ channel. The hybrid apparatus consists of an emulsion/lead target complemented by electronic detectors and it is placed in the high energy long-baseline CERN to LNGS beam (CNGS) 730 km away from the neutrino source. Runs with CNGS neutrinos were successfully carried out in 2008 and 2009. After a brief description of the beam, the experimental setup and the procedures used for the analysis of the neutrino events, we describe the topology and kinematics of a first candidate ντ charged-current event satisfying the kinematical selection criteria. The background calculations and their cross-check are explained in detail and the significance of the event is assessed

The OPERA experiment was designed to search for ${\nu }_{\mu }\to {\nu }_{\tau }$ oscillations in appearance mode, i.e., by detecting the $\tau$ leptons produced in charged current ${\nu }_{\tau }$ interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of the ${\nu }_{\mu }\to {\nu }_{\tau }$ appearance, achieved with four candidate events in a subsample of the data, was previously reported. In this Letter, a fifth ${\nu }_{\tau }$ candidate event, found in an enlarged data sample, is described. Together with a further reduction of the expected background, the candidate events detected so far allow us to assess the discovery of ${\nu }_{\mu }\to {\nu }_{\tau }$ oscillations in appearance mode with a significance larger than $5\sigma$.

The OPERA experiment was designed to study ${\nu }_{\mu }\to {\nu }_{\tau }$ oscillations in the appearance mode in the CERN to Gran Sasso Neutrino beam (CNGS). In this Letter, we report the final analysis of the full data sample collected between 2008 and 2012, corresponding to $17.97\times {10}^{19}$ protons on target. Selection criteria looser than in previous analyses have produced ten ${\nu }_{\tau }$ candidate events, thus reducing the statistical uncertainty in the measurement of the oscillation parameters and of ${\nu }_{\tau }$ properties. A multivariate approach for event identification has been applied to the candidate events and the discovery of ${\nu }_{\tau }$ appearance is confirmed with an improved significance level of $6.1\sigma$. $|\mathrm{\Delta }{m}_{32}^2|$ has been measured, in appearance mode, with an accuracy of 20%. The measurement of the ${\nu }_{\tau }$ charged-current cross section, for the first time with a negligible contamination from ${\overline{\nu }}_{\tau }$, and the first direct evidence for the ${\nu }_{\tau }$ lepton number are also reported.

The OPERA experiment is designed to search for ${\nu }_{\mu }\to {\nu }_{\tau }$ oscillations in appearance mode, i.e., through the direct observation of the $\tau$ lepton in ${\nu }_{\tau }$-charged current interactions. The experiment has taken data for five years, since 2008, with the CERN Neutrino to Gran Sasso beam. Previously, two ${\nu }_{\tau }$ candidates with a $\tau$ decaying into hadrons were observed in a subsample of data of the 2008–2011 runs. Here we report the observation of a third ${\nu }_{\tau }$ candidate in the ${\tau }^{-}\to {\mu }^{-}$ decay channel coming from the analysis of a subsample of the 2012 run. Taking into account the estimated background, the absence of ${\nu }_{\mu }\to {\nu }_{\tau }$ oscillations is excluded at the $3.4\sigma$ level.

Latest results of the OPERA experiment on nu-tau