Average transverse momenta of identified particles in relativistic nucleus-nucleus collisions

Abstract: [Background] The average transverse momentum of identified particle is an important observable in relativistic nucleus nucleus collision experiments. It can reflect the properties of hot matter created in the collisions and the characteristics of soft hadrons. [Purpose] It can also deepen our understanding and help to extract the information about the evolution of the collision system with systematic investigation. [Methods] By using the phenomenological linear and exponential functions, we studied the dependence of the average transverse momenta of identified particles produced at the midrapidity in relativistic nucleus nucleus collisions on the collision centrality, particle mass and the collision energy at given collision conditions, respectively, including the data from Au+Au, Cu+Cu, U+U collisions provided by the STAR Collaboration at the Relativistic Heavy Ion Collider (RHIC) and from Pb+Pb collisions provided by the ALICE Collaboration at the Large Hadron Collider (LHC). [Results & Conclusions] The systematic study shows that the good linear relationship between the average transverse momenta of identified particles and collision centrality is universal. Therefore, the collision centrality is a good physical quantity for studying the average transverse momenta of identified particles in relativistic nucleus nucleus collisions. It is also found that the fitting parameters of the linear function for the average transverse momentum with the collision centrality follow a power-law relationship with the collision energy, which is universal as well. For a given collision energy and collision centrality, it is found that the average transverse momenta of identified particles have a linear relationship with the particle mass qualitatively. Few data points of the identified particles deviate from the linear relationship which may be relevant with the details of their production mechanisms. Meanwhile, it is found that the average transverse momentum of a given identified particle follows an exponential relationship with the logarithm of the collision energy at a given collision centrality, which is also universal.