ampt

AMPT, short for A Multi-Phase Transport model, is a Monte Carlo event generator used to simulate relativistic heavy-ion collisions and related high-energy processes. It provides a phenomenological description of the space-time evolution from the early partonic stage to the final hadronic state, enabling comparisons with experimental data on particle yields, spectra, and collective flow.

AMPT comprises several interacting components that represent consecutive stages of a collision. Initial conditions are taken from HIJING, producing partons and excited strings. In the partonic phase, a parton cascade (ZPC) handles scatterings among quarks and gluons. The model offers two hadronization schemes: in the default version, strings fragment into hadrons via PYTHIA; in the string-melting version, strings are converted to partons and hadronize through quark coalescence. The final hadrons then undergo hadronic rescattering described by the ART transport model. The framework thus spans multiple phases from parton production to hadronization and hadronic interaction.

AMPT has two main modes that cater to different physics questions. The default mode emphasizes string fragmentation, while the string-melting mode emphasizes partonic degrees of freedom and quark coalescence, which can affect flow observables and particle correlations. The model is controlled by parameters such as the parton scattering cross section, the strong coupling, and the screening mass, which influence the dynamics of the partonic and hadronic phases.

AMPT has been used to study a range of observables across energies from SPS to the LHC, including charged-particle multiplicities, transverse momentum spectra, and flow coefficients like v2 and v3. It remains a widely cited tool for interpreting heavy-ion data and exploring aspects of quark-gluon plasma formation, despite its phenomenological nature and model dependencies.