PRESS RELEASE March 25, 2014

### THE FOURTH TRANSFORMATION OF NEUTRINOS

Now the scientists of the OPERA experiment can claim the observation of the extremely rare neutrino oscillation in the tau channel. The OPERA international experiment at the INFN Gran Sasso Laboratory (Italy) has detected a fourth tau neutrino. The neutrino indeed started its flight at CERN as muon neutrino and, after travelling 730 km through the Earth, it arrived at the Gran Sasso laboratory transformed into a tau neutrino. This important result was announced today during a seminar held at the Gran Sasso Laboratory. According to the head of the international research team, Giovanni De Lellis, from Federico II University and INFN in Naples, “The detection of the fourth tau neutrino is a very important confirmation of the previously seen events. This transition is now seen for the first time with a statistical significance exceeding the 4 sigma level: beyond the scientific jargon, this is equivalent to say that for the first time we have observed the extremely rare oscillation phenomenon of muon neutrinos to tau neutrinos, the aim of the OPERA project.” “If other tau neutrinos will be found in the data still to be analysed, an even higher significance level could be achieved. The important result reported today was made possible thanks to the dedication of all the researchers involved in the project”, De Lellis finally says. The international OPERA experiment (involving 140 physicists from 28 research institutes in 11 countries) was designed to observe this exceptionally rare phenomenon. Neutrino oscillations have been a poorly known phenomenon for several decades. More than 15 years ago, it was demonstrated that muon neutrinos produced in cosmic-ray interactions arrive at the Earth fewer than expected. The result reported today explains why: the “missing” neutrinos are indeed those muon neutrinos oscillating into tau neutrinos.

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13 August 2013 New paper "New results on $ν_μ\to ν_τ$ appearance with the OPERA experiment in the CNGS beam" is submitted to arXiv.

26 March 2013 A seminar at LNGS "New results from the OPERA experiment" by G.De Lellis will be broadcasted via http://streaming.lngs.infn.it/ at 14:30 of European time.

16 March 2013. New paper “Search for $ν_μ\rightarrow ν_e$ oscillations with the OPERA experiment in the CNGS beam” is submitted to JHEP and is available on arXive http://arxiv.org/abs/1303.3953 The new OPERA result sets new limits on the non-standard neutrino oscillation.

3 December 2012 After 5 years of operation the CNGS beam was stopped. In total it was 17.97 10**19 protons on target provided by the CNGS.

23 February 2012

The OPERA Collaboration, by continuing its campaign of verifications on the neutrino velocity measurement, has identified two issues that could significantly affect the reported result. The first one is linked to the oscillator used to produce the events time-stamps in between the GPS synchronizations. The second point is related to the connection of the optical fiber bringing the external GPS signal to the OPERA master clock. These two issues can modify the neutrino time of flight in opposite directions. While continuing our investigations, in order to unambiguously quantify the effect on the observed result, the Collaboration is looking forward to performing a new measurement of the neutrino velocity as soon as a new bunched beam will be available in 2012. An extensive report on the above mentioned verifications and results will be shortly made available to the scientific committees and agencies.

23 September 2011

The paper "Measurement of the neutrino velocity with the OPERA detector in the CNGS beam" is available online in the arXiv repository (arXiv:1109.4897):

PAPER

5 September 2011

The 2011 CNGS run started on March 18 and is well underway. The total number of pot accumulated so far is 3.96E19 corresponding to 23588 on-time events and 3947 candidate interactions in the target. The CNGS average efficiency since the beginning of the run is 78.5%.

18 June 2010

The paper "Observation of a first \nu_\tau candidate in the OPERA experiment in the CNGS beam" has been published in Physics Letters B (N. Agafonova et al., Phys.Lett. B691 (2010) 138); it is available online in the arXiv repository (arXiv:1006.1623):

PAPER

These results were presented by A. Ereditato in two special Seminars at the Gran Sasso laboratories (May 31) and at CERN (June 4). The slide of the Seminar can be found here

The corresponding press release from the OPERA Collaboration can be found here

18 May 2010

On May 31, 2010, starting from 3:00 pm, A. Ereditato will give a seminar entitled "Observation of events with decay topologies in the OPERA experiment". The seminar will take place in the "E. Fermi" auditorium of LNGS. It will also be given at CERN on June 4.

Abstract The OPERA experiment at LNGS is searching in the CERN CNGS beam for the first detection of muon- to tau-neutrino oscillations in appearance mode. The Collaboration has analyzed a sub-sample of the statistics collected in the 2008-2009 runs. We shall disclose first analysis results based on the detection of decay topologies.

26 November 2009

The 2009 CNGS run is over. From June 1 to November 23 CNGS accumulated 3.52 10^19 protons-on-target. The OPERA detector observed 21428 events on time with the beam and about 3700 interactions in the target.

20 August 2009

The 2009 CNGS run started on Monday June 1 with the OPERA detector fully operative. From June 1 to August 17 the CNGS accumulated 1.54 10^19 protons-on-target. By that time, OPERA has collected 9407 events on time with the beam and about 1600 candidate interactions in the target.

28 April 2009

L’Aquila earthquake of April 6th

On behalf of all its members, the OPERA Collaboration, which is rooted since 10 years in the community of L’Aquila, wishes to convey its deepest condolences to the families of the nearly 300 people who lost their lives in the dramatic earthquake of April the 6th. We express our heartful sympathy to all people that have lost their homes and are still suffering from the effects of this terrible event. We want to recognize with immense gratitude the care and commitment of our LNGS colleagues that – even in such difficult circumstances – have promptly restarted their activities to guarantee safety and full operation of all the experiments hosted in the Laboratories.

20-22 January 2009

OPERA MIZUNAMI Meeting

03 November 2008

The 2008 run is over. The CNGS beam delivered 1.78E19 protons on target. Corresponding to this statistics OPERA recorded about 10100 events correlated in time with the CNGS beam, among which 1700 candidates of neutrino interactions in the bricks.

13 October 2008

On Sunday 12th of October at 7pm, CNGS has integrated 1.23 10^19 protons on target. Opera has collected 6837 events on time with the beam and 1151 candidate neutrino interactions in the bricks.

14 September 2008

The CNGS 2008 run started on June 18th. Up to Sunday 14/9 CNGS has integrated 0.738 10^19 protons on target. Opera has collected 4085 events on time with the beam and 652 candidate neutrino interactions in the bricks.

## Attached documents

31 May 2010
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