Lowmultiplicity

Lowmultiplicity refers to events in particle collisions or decays that produce a small number of final-state particles. In practice, the term is used when the multiplicity N, the count of charged or all final-state particles within a defined detector acceptance, is low (for example a few tracks). The precise threshold depends on the experiment and the analysis, and distinctions are made between inclusive multiplicity (any number of particles) and exclusive multiplicity (exactly N particles). Measurements often use reconstructed charged-particle tracks with certain transverse momentum and pseudorapidity limits, and may supplement with neutral-energy information from calorimeters.

Low-multiplicity events arise in several contexts. Elastic scattering and two-body decays inherently produce few final-state particles. Diffractive and exclusive production processes in hadron colliders can yield events with only a handful of visible particles. Quantum electrodynamics processes, such as lepton-pair production in electron-positron or proton-proton collisions, also populate the low-multiplicity region. The characterization of these events is sensitive to detector acceptance, triggering, and pile-up, requiring careful corrections and background estimation.

Applications and implications include detector calibration and performance studies, tuning of event generators, and background estimation for high-multiplicity analyses. Low-multiplicity data help validate theoretical models of soft QCD and diffraction and provide baselines for understanding more complex final states. Analyses must account for reconstruction efficiencies and model dependence when interpreting multiplicity distributions.