From cosmic OPERA to neutrino ballet
As the CNGS (CERN Neutrinos to Gran Sasso) project prepares to send its high intensity neutrino beam, some 730 km away in Italy, the OPERA collaboration is beginning to commission its electronic detectors in the underground Gran Sasso National Laboratory (LNGS).
OPERA is ready to come on stage. Based in the INFN Gran Sasso National Laboratory, 732 km from CERN, the experiment will commission its electronic detectors with the high intensity neutrino beam sent by CNGS (see Bulletin n°29-30/2006). The OPERA Collaboration, which comprises 170 physicists from 35 research institutes and universities worldwide, aims to clear up the mystery of neutrino oscillation.
The installation of the OPERA detector began in 2003 in Hall C of the underground laboratory at the LNGS. The detector is made of two identical Super Modules, each one containing one target section and one large-aperture spectrometer. The two Super Modules are now completed, following the installation of 5900 m2 of scintillator-strip detectors, 3050 m2 of resistive plate chambers, large planes of precision tracker using 8064 long drift tubes, and more than 2000 tonnes of iron for the magnets and the mechanical structure.
The main component of the OPERA detector is the Emulsion Cloud Chamber (ECC', which will allow the observation of the tau-neutrino through the topological signature of the decay of the charged tau particle produced when the neutrino interacts. The basic element of the ECC is a brick made of a sandwich of lead plates and sheets of nuclear emulsion sheets (10x13x7.5 cm3).The brick assembly machine, which is now being commissioned at LNGS, has the task of producing 200 000 bricks in one year. Filling the detector target with bricks is planned to start in August.
Data-taking with the electronic detectors began last December, recording muons in cosmic rays, and the final commissioning of all detectors continues smoothly. The first Super-Module is now ready for recording the CNGS neutrino interactions and the second will join suit in a few weeks.
As in any long-baseline neutrino experiment the timing of the beam must be defined with great accuracy, Thanks to a careful cross-calibration of the GPS system at CERN and LNGS, the synchronization between CERN and the LNGS experiments will be achieved with an accuracy better than 100 nanosecond. In fact, CNGS sends two bunches of neutrinos every six seconds, the two 10.5 microsecond long bunches being separated by 50 milliseconds. In order to reduce the background noise, the experiment has to select events exactly as a bunch passes through it.
Stay tuned for observations of the first neutrino from CERN in the LNGS laboratory at the end of August, with the first neutrino interactions in some bricks late in October. It will take more time to observe the interactions of tau-neutrinos but we will be ready.
