OPERA.html

An appearance experiment to search for n_m-n_toscillations in the CERN to LNGS beam

OPERA is a long baseline neutrino oscillation experiment designed to detect the appearance of n_t a in pure n_m beam in the parameters region indicated by the anomaly in the fluxes of neutrinos produced by cosmic ray interactions in the atmosphere. The detector target of 1.8 kilotons is made of foils of lead interleaved with films of nuclear photographic emulsion. The high spatial resolution of the emulsion technology is exploited to detect unambiguously the decay vertices of the t^- lepton produced in charged current n_t interactions with the lead nuclei. The detector is installed at the Laboratori Nazionali del Gran Sasso (LNGS) in a cavern excavated under the Gran Sasso in the Italian Abruzzes. The cavern is in the line of sight of the CNGS beam of neutrinos originated from CERN, Geneva, at a distance of 730 km. The commissioning of the beam and the electronic components of the detector has taken place in August 2006. The filling of the target has started in October 2006 and is due to be completed by mid-2007. The data taking is planned to last for five years.

The OPERA physics goal
At the nominal value of ∆m²₂₃ = 2.5 10^-3 eV² and full n_m-n_tmixing (sin²2q₂₃=1), as measured by the Super-Kamiokande atmospheric neutrino experiment, OPERA will observe about than 20 n_t CC interactions after 5 years of data taking, with an estimated background of only 1 event. The probability to establish the oscillation signal at a 4-sigma level is of 99.9%.

At the same value of ∆m², OPERA will lower down the upper limit on the mixing angle sin²2q₁₃ of the sub-dominant oscillation channel n_m-n_e from 0.14, as mesured by the CHOOZ reactor neutrino experiment, to 0.06.

The OPERA detector
OPERA is a massive hybrid detector consisting of two identical super-modules. Each super-module has a 0.9-kton instrumented target followed by a 10x8 m² magnetic muon spectrometer. One target is the repetition of 31 6.7x6.7 m² modules each including a proper target wall followed by a dual X-Y plane of scintillator strips trackers for event location in the target. A wall is an assemblage of 8.3kg bricks made of 56 1-mm thick lead sheets, that provide the necessary mass, interleaved with 57 nuclear emulsion films that provide the necessary sub-millimetre high resolution.

Bricks in which a neutrino interaction has occured, typically 30 per day, are identified by the event reconstruction in the trackers. They will be extracted, disassembled and the emulsion films scanned and analysed by a battery of high speed high resolution automatic microscopes in order to locate the interaction vertex and search for candidates of the t^- lepton decay topology.

1. The brick in which the interaction takes place is identified by electronic detectors and extracted from the target by a robot.

2. The primary interaction vertex is searched for in emulsion sheets by automatic high speed, high resolution microscopes.

3. Secondary vertices compatible with the decay of a t^- lepton are searched for at a distance shorter than some millimetres from the primary vertex.

4. The candidates n_tinteraction are analysed using the emulsion and the electronic data.

The Target Trackers are the main contribution of our IIHE-ULB group to the OPERA detector. They have been constructed in collaboration with the universities of Bern and Neuchâtel, with the IN2P3/CNRS laboratories of IReS, Strasbourg and LAL Orsay and with JINR Dubna.

Picture to the left: the 64 6.7m×25mm×10mm scintillator strips forming one TT module. The light signals produced by the strips are collected and guided at both ends by a wavelength shifting optical fibre, where they are read by 64-channel multianode PM tubes.
Central picture: one TT tracker made of two planes. The front plane made of 4 horizontal modules is seen while the back plane of 4 vertical modules is hidden.
Picture to the right: side view of one the two targets. Each of the 31 tracker planes follows an empty target wall of 52 trays. Each tray will be loaded with 64 8.3 kg bricks.

Click here for technical details on the scintillator strips target trackers: parts, materials, construction, performances, assembly of the OPERA detector.

IIHE-ULB Brussels
Sofia
IRB Zagreb

LAPP Annecy, IPNL Lyon, LAL Orsay, IReS Strasbourg

Hamburg, Münster, Rostock

Technion Haifa
LNGS Assergi, Bari, Bologna, LNF Frascati, L’Aquila, Naples, Padova, Rome, Salerno

Toho Funabashi, Aichi Karia, Kobe, Nagoya, Utsunomiya

JINR Dubna, INR Moscow, ITEP Moscow, LPI Moscow, SINP Moscow, Obninsk

Gyeongsang Jinju

Bern, Neuchâtel, ETH Zurich

METU Ankara

These are short (in English) and long (in French) presentations of the elusive neutrino from their discovery to recent results on oscillation.

The official OPERA Collaboration site where copies of all presentations to conferences and public documents are available.

The site of the Neutrino Oscillation Industry where links to all the neutrinos experiments sites and related sites in the domain of astrophysics and cosmology can be found.

The Neutrino Unbound site provides, among many things, a very comprehensive list of publications on neutrino physics and astrophysics.