Average transverse momentum of identified particles in pp collisions

Based on the experimental data of the average transverse momentum \langle p_\rm T\rangle of identified particles produced in the midrapidity of proton-proton (pp) collisions from the STAR and PHENIX Collaborations at the Relativistic Heavy Ion Collider (RHIC) and the ALICE Collaboration at the Large Hadron Collider (LHC), covering collision energies of 62.4,200 GeV, 0.9, 2.76, 5.02, 7, 8 and 13 TeV, their dependences of the particle mass, the pseudorapidity density distribution of charged particles and collision energy are systematically analyzed by using empirical formulas, respectively. The results indicate that the \langle p_\rm T\rangle of identified particles has a linear relationship with both particle mass and the logarithm of the collision energy \ln\sqrts and has a power-law relationship with the pseudorapidity density distribution of charged particles. It is worth noting that two distinct linear trends are observed for the \langle p_\rm T\rangle of identified particles versus particle mass, one for mesons and the other for baryons, at all the collision energies studied. Meanwhile, the fitting parameters for the \langle p_\rm T\rangle of identified particles versus particle mass follow a power-law relationship with the collision energy \sqrts , while those from the pseudorapidity density distribution of charged particles and the logarithm of the collision energy have a linear relationship with particle mass. Moreover, the meson-baryon divisions have been observed for all of them. These phenomena are different from those observed for the \langle p_\rm T\rangle of identified particles in relativistic nucleus-nucleus(A-A) collisions. Therefore, the \langle p_\rm T\rangle of identified particles could serve as a probe to study the similarities and differences in pp collisions and A-A collisions.