Particle production in small systems (proton-proton and proton-nucleus collisions) and in large systems (nucleus-nucleus collisions) at high-energy and high-density frontiers displays both similar or different behaviors. Comparing these behaviors is very useful for researchers to study the properties of particle productions and system evolutions.

At high-energy frontier, the Relativistic Heavy Ion Collider (RHIC) in the Brookhaven National Laboratory (BNL) and the Large Hadron Collider (LHC) in the European Organization for Nuclear Research (CERN) provide abundant data produced in small and large systems. These data include, but are not limited to, transverse momentum spectra, anisotropic flows, statistical or dynamical fluctuations of light flavor particles, heavy flavor particles, jets, and leptons. It is expected that the effect of cold nucleus or medium affects particle productions in large system, comparing with small system.

At the high-density frontier, the beam energy scan (BES) program and its second round (BESII) and fix target experiment at the RHIC, the BES at the Super Proton Synchrotron (SPS) in CERN, the Facility for Antiproton and Ion Research (FAIR) in Germany Center for Heavy Ion Research (GSI), and others performs nucleus-nucleus collisions at high density of baryon numbers around the expected critical point of hadronic matter transition to quark-gluon plasma (QGP). It is expected that the spectra of particles are different in small and large systems at the high-density frontier, and also at the high-energy frontier.

In small and large systems at high-energy and high-density frontiers, the features of particle production and system evolution attract high interest and are extensively studied both experimentally and theoretically. It is believed that the properties of particle production and system evolution in small and large systems at high-energy and high-density frontiers are different. These properties are related to those of early Universe considered to go through the stages of high-density and high-temperature.

In this Special Issue, we aim to collate original research articles as well as reviews on properties of particle production and system evolution in small and large systems at high-energy and high-density frontiers.

Potential topics include but are not limited to the following:

• Description of particle distributions and correlations, studies of statistical laws and dynamical properties of particle production
• Extraction of different quantities based on the particle spectra, correlations, and yield ratios
• Studies of the properties of particle production and system evolution in small and large systems at high-energy frontier
• Studies of the properties of particle production and system evolution in small and large system at high-density frontier
• Comparison of the properties of particle production and system evolution in small and large systems at high-energy and high-density frontiers