ATLAS is one of the general-purpose detectors at the Large Hadron Collider (LHC), the accelerator built at CERN, in which protons collide against protons with a total centre-of-mass energy of 14 TeV, the highest ever achieved in a laboratory. It investigates a wide range of physics, including the search for the Higgs boson, extra dimensions, and new particles that could make up dark mater. The ATLAS detector (22 meters high and 44 meters long) is a very complex apparatus, made up of several subsystems, built on dozens of laboratories around the world.
IFAE is a major player in ATLAS. Our institute was a focal point in the assembly of one of the largest sub-detectors, the Hadron Calorimeter, or TileCal (short for Tile Calorimeter). This sub-detector consists of three “barrels”. IFAE produced one complete barrel, made of 64 modules, each weighting 12 tons, plus one spare. IFAE also designed and fabricated the TileCal calibration electronics. TileCal was the first detector installed in the cavern of the ATLAS experiment. Once in place, extensive tests of the electronic readout and of the calibration systems were carried out, in which IFAE had and still has a major role.
In addition to the work on the detector, IFAE is heavily involved in other aspects of the ATLAS experiment, among them contributions to the ATLAS trigger system, in particular to the Event Filter Infrastructure, Trigger Operations and Integrations Tasks and Level-1 and Level-2 Trigger Studies. It is also responsibility of IFAE the operation of a Tier2 centre of analysis and Monte Carlo simulation in a distributed way, in collaboration with IFIC in Valencia and UAM in Madrid. The analysis of data will be done at IFAE Tier3 centre.
Finally, IFAE is heavily involved in the upgrade of the ATLAS pixel detector. The pixel upgrade efforts are two folded: in the short term an insertable pixer layer (IBL) will be mounted on the beam-pipe to attenuate the performance degradation of the current detector due to radiation damage. In the longer term, the super-LHC luminosity upgrade will require a complete replacement of the current pixel system. The IFAE group is working on the characterization and sensor-readout chip integration of the new pixel sensor technologies for ATLAS, as well as the construction of the IBL.
The LHC will provide excellent opportunities to search for physics beyond the Standard Model (SM), in particular for supersymmetry (SUSY). If supersymmetric particles indeed exist and are not very massive they will be produced in sufficient amount at the LHC for them to be discovered. But before any claim of discovery can be made, one must be sure that all backgrounds are well understood. There are at present many uncertainties in the properties and cross-sections of the standard processes at the LHC energies, which will be resolved from data. Among all the SM processes, Z-boson plus jets and top-quark pair-production might be dominant backgrounds for many SUSY searches. These two processes are being studied in detail at IFAE.