Particle Identification in the ALICE Experiment

The particle identification capabilities of the ALICE experiment are unique among the four major LHC experiments. The working principles and excellent performance of the central barrel detectors in a high-multiplicity environment are presented as well as two physics examples: the extraction of transverse momentum spectra of charged pions, kaons, protons, and the observation of the 4He-nucleus. 1. PID detectors and performance The ALICE experiment is exploiting almost all known techniques for particle identification (PID). The particle identification of the Inner Tracking System (ITS) and the Time Projection Chamber (TPC) are based on the specific energy loss per unit path length of a particle which depends for a given momentum only on its charge and rest mass. Thus, the simultaneous measurement of track momentum (or rigidity) and signal amplitude in a sensitive detector volume allows to identify particles. The measured mean energy deposit of a track is denoted as dE/dx hereafter. In practice, it can be described with parameterizations of the well-known Bethe-Bloch formula. Particle identification via dE/dx needs to be supplemented by additiona