The ALICE Experiment
ALICE is the acronym for A Large Ion Collider Experiment, one of the largest experiments in the world devoted to research in the physics of matter at an infinitely small scale. Hosted at CERN, the European Laboratory for Nuclear Research, this project involves an international collaboration of more than 1200 physicists, engineers and technicians, including around 200 graduate students, from 132 physics institutes in 36 countries across the world. The collaboration includes several Italian Universities and INFN Sections, among them Alessandria, Bari, Bologna, Cagliari, Catania, LNF Frascati, Legnaro LNL, Padova, Salerno, La Sapienza Rome, Torino, Trieste, for a total of 200 physicists and technologists, including more than 20 PHD students.
ALICE is optimized to study heavy-ion collisions at a centre of mass energy of 2.76TeV per nucleon pair. The resulting temperature and energy density are expected to be high enough to produce quark–gluon plasma, a state of matter wherein quarks and gluons are free. Similar conditions are believed to existed a fraction of the second after the Big Bang, before quarks and gluons bound together to form hadrons and heavier particles.
The ALICE Detector
Located 50 m underground on the LHC ring, the ALICE detector is 16 m high, 26 m long, and weighs about 10 000 tons. The apparatus includes a magnetic solenoid and several detectors, the most part contained within the magnet and arranged in cylindrical symmetry around the axis of the LHC beams. This allows to detect, with high efficiency, the multitude of different particles produced in the ion-ion collisions at very high energy.
Starting from the volume close to the beam-interaction zone and moving radially outward, there are:
- the vertex detector, called Inner Tracking System (ITS), which measures the position of particle passage with a spatial resolution of a fraction of a millimetre. The ITS consists of six cylindrical layers of silicon detectors, respectively, two silicon pixels (SPD), two silicon drift (SDD) and two silicon microstrip (SSD)
- the Time Projection Chamber (TPC), which is a large volume filled with a gas as detection medium and is the main particle tracking device in ALICE
- the Time of Flight detector (TOF), which measures the particle flight time with time resolution of about 100 ps and covers a surface of 150 square meters
- the High Momentum Particle Identification Detector (HMPID), which is a RICH detector, to determine the speed of particles beyond the momentum range available through energy loss (in ITS and TPC, p = 600 MeV) and through time-of-flight measurements (in TOF, p = 1.2–1.4 GeV)
- the calorimeters as the spectrometer for photons (PHOS), which is a high-resolution electromagnetic calorimeter, and the electromagnetic calorimeter (EMCal), which is a lead-scintillator sampling calorimeter that covers almost the full length of the ALICE Time Projection Chamber
Besides the magnet there are the muon spectrometer, the detectors dedicated to the trigger and calorimetric measurements at small angles and the detectors dedicated to cosmic rays.
ALICE @ TRIESTE
The ALICE group in Trieste is mainly involved in the activities of the physics working group on light (PWG-LF) and heavy flavours (PWG-HF) with several data analyses (Resonances, Nuclei and Hypernuclei, D*) and it participates to the Inner Tracking System (ITS) detector project. It provides support to the maintenance and the daily operation of the ALICE Silicon Strip Detectors and of the ALICE Silicon Drift Detectors. Moreover, it is working at the preparation of the ALICE upgrade, in particular within the ITS upgrade project. The group is also engaged with the computing task of the ALICE experiment, mantaining the Trieste grid computing site and dealing with an interactive analysis facility on cloud computing.