Taking shape in the Italian Gran Sasso underground laboratory is a large module for the Imaging Cosmic And Rare Underground Signals (ICARUS) detector.
ICARUS uses the liquid argon time projection chamber idea initially proposed by Carlo Rubbia in 1977 which combines the advantages of visible particle tracks (like a bubble chamber) with the flexibility of fully electronic data acquisition. The drift time of electrons released by ionization drift over long distances can be picked up via an arrangement of readout wires giving simultaneous imaging in different views.
A large continuously active detector could be used to record neutrino interactions from terrestrial beams sent over long distances, from atmospheric and solar neutrinos, or from particles from cosmic and atmospheric sources. Track chambers provided important milestones in neutrino physics history, and the hope is that this tradition will continue with the new technique. In addition the detector could also monitor for proton decay.
From 1991 until 1995, a 3 t prototype chamber at CERN demonstrated proof of the principle. With the ultimate goal of building a 5000 t detector, a stepwise strategy foresaw:
* developing the infrastructure needed to build and operate a large detector;
* acquiring the in situ safety experience with a still modest liquid argon volume; and
* evaluating a definitive and practical engineering choice for the final phase.
For this, the most efficient and economical approach was to build and test a module of intermediate size outside Gran Sasso before moving it underground for final assembly. The module thus has to be transportable, which limited its size to about 600 t (twin sub-modules of 3.9 x 4.2 m and a length of 19 m).
As well as testing design and logistics, such an intermediate detector would at the same time be an important first step in the ICARUS scientific programme, with a target mass close to that of the Japanese Kamiokande detector, but with the advantages of the new technology. En route to this T600 prototype, a 10 m3 (15 t) prototype built by Air Liquide was first shipped to INFN Pavia for cryogenic testing and to check operation of the inner wire chamber at liquid argon temperatures before trials in situ at Gran Sasso. Track lengths of up to 4 m have been achieved. Assembly and tests of the T600 module are taking place during this year at Pavia prior to initial cooldown. Much longer tracks are hoped for and expected.
T600 modules could be piled up, lego fashion, for the 5000 t detector. Another objective is “ICANOE” (ICARUS for a Neutrino Oscillation Experiment) to intercept the neutrino beam from CERN at Gran Sasso (January p5).
Initially a CERN-Italian venture, ICARUS has grown to also involve groups from the US (UCLA), Switzerland (ETH Zurich), China (Beijing) and Poland.