and can significantly enhance the recorded yields of vector mesons. For this purpose, 250,000 CPUs are installed right on the detector to identify candidates for high-momentum tracks and analyse the energy deposition associated with them as quickly as possible (while the signals are still being created in the detector). This information is sent to a global tracking unit, which combines all of the information to search for electron–positron track pairs within only 6 μs. To develop such a Transition Radiation Detector (TRD) for ALICE many detector prototypes were tested in mixed beams of pions and electrons. Particle identification with ALICE ALICE also wants to know the identity of each particle, whether it is an electron, or a proton, a kaon or a pion. Charged hadrons (in fact, all stable charged particles) are unambiguously identified if their mass and charge are determined. The mass can be deduced from measurements of the momentum and of the velocity. Momentum and the sign of the charge are obtained by measuring the curvature of the particle's track in a magnetic field. To obtain the particle velocity there exist four methods based on measurements of time-of-flight and ionization, and on detection of transition radiation and Cherenkov radiation. Each of these methods works well in different momentum ranges or for specific types of particle. In ALICE all of these methods may be combined in order to measure, for instance, particle spectra. In addition to the information given by ITS and TPC, more specialized detectors are needed: the TOF measures, with a precision better than a tenth of a billionth of a second, the time that each particle takes to travel from the vertex to reach it, so that one can measure its speed. The high momentum particle identification detector (HMPID) measures the faint light patterns generated by fast particles and the TRD measures the special radiation very fast particles emit when crossing different materials, thus allowing to identify electrons. Muons are measured by exploiting the fact that they penetrate matter more easily than most other particles: in the forward region a very thick and complex absorber stops all other particles and muons are measured by a dedicated set of detectors: the muon spectrometer. Time of Flight Charged particles are identified in ALICE by Time-Of-Flight (TOF). TOF measurements yield the velocity of a charged particle by measuring the flight time over a given distance along the track trajectory.