OPERA's overture


When neutrinos interact, they mainly produce one muon and a shower of hadrons. Here we see two interactions in the heart of the OPERA detector: one in the steel plates of the first magnet (left), the other in the target's scintillation counters (right).

OPERA's opening score has been played at the Gran Sasso Laboratory in Italy, and it's in perfect harmony with the melody of the CNGS neutrino beam from CERN, 730 kilometres away. OPERA's overture was played on 18 August 2006, when the first tracks, corresponding to interactions with CNGS neutrinos, were recorded in its detectors.

To the great satisfaction of the teams on both of the Alps, the quality of the CNGS beam is fully in line with expectations, as are the first tracks observed by OPERA, which records data with hardly any down time. Over a five-day period, a little over 300 interactions correlated with the CNGS beam were identified, just as predicted. During this first run it has been possible to verify the correct operation of the electronic detectors (4000 m2 of RPC, 6000 m2 of scintillation strips, 2 magnets) in global mode data taking with an overall efficiency of 95% to check the synchronisation of the OPERA and CNGS clocks and to test the algorithms governing the selection of interesting events.

OPERA is now ready to enter the next phase, aimed at observing neutrino interactions in the emulsions of the detector's 200000 bricks, which will be produced and installed over the coming months. OPERA's ultimate aim is to observe oscillations from muon-neutrinos into tau-neutrinos (see Bulletin No. 30/2003). The long search for oscillations starts in earnest at the end of October and will last at least 5 years.