identifiedparticle

An identified particle is a particle whose species has been determined by detector-based particle identification (PID). In high-energy collisions and fixed-target experiments, many particles are produced, but only some can be unambiguously labeled as electrons, muons, pions, kaons, or protons based on measurement.

PID relies on several observables. Specific energy loss (dE/dx) in tracking detectors helps separate species at given momentum. Time-of-flight systems provide velocity information. Cherenkov detectors (including RICH and aerogel variants) measure velocity via Cherenkov radiation. Calorimeters distinguish electrons from hadrons, and muon detectors identify muons. Transition radiation detectors aid high-momentum electron identification. These signals are often combined to maximize separation power across momentum ranges.

In analysis, information from multiple subsystems is combined into likelihood or Bayesian probabilities for particle species. Efficiencies and misidentification rates depend on momentum, angle, and detector configuration, and are calibrated with control samples or simulations. PID performance is summarized by efficiency curves and misID probabilities across momentum ranges.

Identified particles enable spectroscopy, yield measurements, and studies of hadronization and collective behavior in heavy-ion collisions. They are essential for reconstructing decays to final-state particles and for reducing background in precision measurements.

Experiments with extensive PID capabilities include large collider detectors and flavor factories such as those at the LHC and Belle II, which combine tracking, time-of-flight, Cherenkov, and calorimetric techniques to classify particle species over broad momentum ranges. The specific PID strategy varies by experiment and physics goal.