ALICE through the phase transition

While proton-proton collisions will be the principal diet of CERN's LHC machine, heavy-ion collisions will also be on the menu. The ALICE experiment will be ready and waiting. Another of ALICE's TDRs concerns the experiment's inner tracking system (ITS). This is the innermost layer of the detector, responsible for tracking emerging particles where their density will be at its highest. ALICE physicists have been working with colleagues from fellow LHC experiment LHCb to develop silicon pixel chips for the inner two layers of the ITS.The result is a chip with 50 x 425 mu m cells; a prototype detector based on this chip is being tested this year.The ITS has six layers, all using silicon technology, and about 10 million digital and 2 million analogue readout channels to digest the huge number of particles produced in LHC lead-ion collisions. The collaboration has opted for a hybrid ITS structure combining sensors, electronics and mechanical support. Beam tests so far have indicated that the ITS should achieve position resolution better than 20 mu m. Surrounding the ITS is the core of the ALICE detector - its time projection chamber (TPC). (0 refs).