The study on the multiplicity dependence of ridge behavior in $pp$ collisions at $\sqrt{s}=13$ TeV at the LHC

Abstract

The long-range near-side ridge phenomenon in two-particle correlation is crucial for understanding the motion of partons after high-energy heavy-ion collisions. While it has been well explained by the hydrodynamic flow effect of the quark-gluon plasma (QGP) in heavy-ion collisions, the recent observation of the ridge structure in small systems has led to debates about the applicability of hydrodynamic models to explain the phenomenon since the collisions in small systems could not be sufficient to produce the medium required by the QGP matter. The Momentum Kick Model (MKM), on the other hand, explains the long-range near-side ridge phenomenon by the kinematic process; the high-momentum jet particles collide with medium partons, transfer their momentum to them (called the ``kick" process), and induce collective motion of the kicked-partons resulting in the ridge phenomenon. This MKM has successfully described the ridge structure in heavy-ion collisions at the RHIC. Furthermore, since the ridge phenomenon in small systems is prominent in high-multiplicity events, the MKM with multiplicity dependence (MKMwM) has been studied in $pp$ collisions at the LHC using a relationship between the number of kicked-partons and the multiplicity through an impact parameter. In this research, we extend the previous study with more recent experimental data-driven parameters and apply them to the new measurements that have a wider multiplicity range with $p_T$ and $ΔΦ$ bins at the LHC. Simultaneously, we not only provide a theoretical basis for the ridge behavior from the new measurements but also predict the ridge structure at the energies scheduled by the LHC in the upcoming Run 3 experiments.