Hydrodynamic Collectivity in Proton--Proton Collisions at 13 TeV

Understand

In this paper, we investigate the hydrodynamic collectivity in proton--proton (pp) 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 ($K_S^0$, $\Lambda$).
• However, our model calculations show positive 4-particle cumulant $c_{2}\{4\}$ in high multiplicity pp collisions, and can not reproduce the negative $c_{2}\{4\}$ measured in experiment.
• Further investigations on the HIJING initial conditions show that the fluctuations of the second order anisotropy coefficient $\varepsilon_{2}$ increases with the increase of its mean value, which leads to a similar trend of the flow fluctuations.