Abstract
In this paper, we investigate the hydrodynamic collectivity in proton–proton (p–p) collisions at 13 TeV, using iEBE-VISHNU hybrid model with HIJING initial conditions. With properly tuned parameters, our model simulations can remarkably describe all the measured 2-particle correlations, including integrated and differential elliptic flow coefficients for all charged and identified hadrons (KS0, Λ). However, our model calculations show positive 4-particle cumulant c2{4} in high multiplicity pp collisions, and can not reproduce the negative c2{4} measured in experiment. Further investigations on the HIJING initial conditions show that the fluctuations of the second order anisotropy coefficient ε2 increases with the increase of its mean value, which leads to a similar trend of the flow fluctuations. For a simultaneous description of the 2- and 4- particle cumulants within the hydrodynamic framework, it is required to have significant improvements on initial condition for pp collisions, which is still lacking of knowledge at the moment.
Highlights
One of the main goal of the heavy-ion program at Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) is to create a novel state of matter, the Quark-Gluon Plasma (QGP), and study its properties
The anisotropic flow, that evaluates the anisotropy of the momentum distribution of final produced particles, is sensitive to both initial state fluctuations and the QGP transport properties [1,2,3,4,5,6,7]
Various unexpected phenomena have been observed in these small systems, especially in the high multiplicity region
Summary
One of the main goal of the heavy-ion program at Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) is to create a novel state of matter, the Quark-Gluon Plasma (QGP), and study its properties. With the four sets of parameters listed, we calculate the integrated flow harmonics v2, v3 and v4 in pp collisions at 13 TeV, using iEBE-VISHNU model with HIJING initial conditions. IEBE-VISHNU with HIJING initial conditions can describe the measured 2-particle correlations for both charged and identified hadrons, it fails to reproduce the negative c2{4} as measured by CMS and ATLAS with the standard cumulant method [37] and three-subevent method [61] (0.3 < pT < 3.0 GeV).
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