HYDRO + JETS (HYDJET++) event generator for Pb+Pb collisions at LHC

TL;DR

HYDJET++ is a Monte Carlo event generator that models heavy-ion collisions at LHC energies by combining soft hydro-like processes with jet descriptions, successfully reproducing various flow phenomena and correlations observed in Pb+Pb collisions.

Contribution

This paper introduces HYDJET++, a novel event generator that integrates soft and hard processes to simulate heavy-ion collisions at LHC energies, capturing complex flow and correlation phenomena.

Findings

Model reproduces azimuthal anisotropy and flow harmonics.

Explains violation of NCQ scaling at LHC.

Predicts ridge structure in dihadron correlations.

Abstract

The Monte Carlo event generator HYDJET++ is one of the few generators, designed for the calculations of heavy-ion collisions at ultrarelativistic energies, which combine treatment of soft hydro-like processes with the description of jets traversing the hot and dense partonic medium. The model is employed to study the azimuthal anisotropy phenomena, dihadron angular correlations and event-by-event (EbyE) fluctuations of the anisotropic flow in Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV. The interplay of soft and hard processes describes the violation of the mass hierarchy of meson and baryon elliptic and triangular flows at p_T > 2 GeV/c, the fall-off of the flow harmonics at intermediate transverse momenta, and the worsening of the number-of-constituent-quark (NCQ) scaling of elliptic/triangular flow at LHC compared to RHIC energies. The cross-talk of v_2 and v_3 leads to emergence of higher order harmonics in the model and to appearance of the ridge structure in dihadron angular correlations in a broad pseudorapidity range. HYDJET++ possesses also the dynamical EbyE fluctuations of the anisotropic flow. The model results agree well with the experimental data.