The Time-Of-Flight detector of ALICE at LHC: construction, test and commissioning with cosmic rays

After several years of research and development the Time-Of-Flight detector of ALICE (A Large Ion Collider Experiment) has been constructed and is presently fully installed and operative in the experimental area located at the interaction point n.2 of the LHC (Large Hadron Collider) at CERN. Particle identification in ALICE is essential, as many observables are either mass or flavour dependent, therefore many different techniques are used to cover the largest possible momentum range. As said, the TOF (Time- Of-Flight) detector, of which a comprehensive review is given in Chapter 2, is dedicated to hadron identification at medium momenta. The detector exploits the novel technology based on the Multigap Resistive Plate Chamber (MRPC) which guarantees the excellent performance required for a very large time-of-flight array. The construction of the ALICE TOF detector has required the assembly of a large number of MRPC detectors which has been successfully carried out thanks to a careful mass production controlled by strict quality assurance procedures. The uniformity in the production and in detector performance are stressed in Chapter 3 which focuses on the quality assurance tests performed during all the phases of the construction of the detector. In Chapter 3 the online data quality monitor tools for the TOF detector are also presented. The fourth chapter aims at presenting the first results obtained with cosmic rays during the global commissioning phase of ALICE along with a brief description of the first data-taking experience.