EMCal covers 110° in acceptance as shown on figure 2. It is composed of 11 SuperModules, each one being made of 288 different modules. Each module has 4 towers that allows to measure the energy with 12 672 electronique cables. Each tower has 77 layers of lead (1.44 mm) and scintillators (1.76 mm), corresponding to 20 radiation lenght. Modules are compressed to 1.2 kg/cm2 of pressure. To summarise : 4 towers make one module. 12 modules are aligned in a Strip Module and 24 Strip Modules are asembled to form a Super Module (SM). the figures below illustrate the structure.
The LPSC team took part in the system instllation : mecanical structures, assembly of the modules and super modules, configuration and test of the electronic and of the readout connections on the ALICE point 2 site.
The prototype performences have been studied in 2005 under a beam test at the Fermi National Accelerator Laboratory using electron beams of 4 to 66 GeV/c and the final electronic cards. Le signal obtained of 4.4 p.e./MeV is slightly above the simulated one. In addition the energy resolution of the order of is in agreement with simulations and physics needs.
The jet energy measurement uses the ALICE tracking reconstruction system for hadrons and the EMCal for the electromagnetic part. The energy resolution that is accessiblealso depends of othe rfactors like the acceptance cone definition for th signal or the lower limit in energy for charged particles especially for the background rejection. Simulations show that resoultions of the order of 25 to 30% can be obtained for jets of 100 GeV. The use of both the tracking system and the EMCal allows to reconstruct about 90% of the jet energy, while only 50% without the EMCal, for a jet of 100 GeV.