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Effects of Subnucleonic Fluctuations on the Longitudinal Dynamics of Heavy-Ion Collisions

Oscar Garcia-Montero, Sören Schlichting, Jie Zhu

TL;DR

The paper investigates how subnucleonic fluctuations shape the longitudinal dynamics in heavy-ion collisions. It employs a hybrid framework that couples the rapidity-resolved McDipper initial state with (3+1)D viscous hydrodynamics (CLVisc), exploring several fluctuation scenarios including nucleon, hotspot, and thickness fluctuations. The analysis shows good agreement with data for charged-hadron and net-proton multiplicities, as well as directed flow and flow decorrelations, with subnucleonic fluctuations enhancing the even component of $v_1$ and the decorrelation signal, particularly at mid- to central rapidities; peripheral collisions reveal missing quark-sector fluctuations in fragmentation regions. The work demonstrates the importance of nucleon substructure for longitudinal observables and motivates future refinements such as valence-quark fluctuations, a more realistic pre-equilibrium stage, and hadronic afterburners for quantitative precision.

Abstract

It is well understood that subnuclear fluctuations in the initial state of heavy-ion collisions have an important impact on the creation of long-range correlations in the transverse plane. This is also true for the creation of particle correlations along the beam direction, which can be measured in particle detectors, e.g. through longitudinal decorrelation observables. In this work, we study the emergence of long-range rapidity structures in Pb+Pb collisions using a hybrid model connecting the 3D resolved {\Dipper} initial state model to a (3+1)D viscous hydrodynamics framework CLVisc. We include different sources of fluctuations at the (sub-)nucleon level and present the effects of their inclusion on the longitudinal structure of relevant observables, focusing in this proceedings paper on charged hadron multiplicities, baryon stopping, directed flow and flow decorrelation. We find remarkable agreement to the experimental data regarding directed flow and the rapidity resolved charge particle multiplicity.

Effects of Subnucleonic Fluctuations on the Longitudinal Dynamics of Heavy-Ion Collisions

TL;DR

The paper investigates how subnucleonic fluctuations shape the longitudinal dynamics in heavy-ion collisions. It employs a hybrid framework that couples the rapidity-resolved McDipper initial state with (3+1)D viscous hydrodynamics (CLVisc), exploring several fluctuation scenarios including nucleon, hotspot, and thickness fluctuations. The analysis shows good agreement with data for charged-hadron and net-proton multiplicities, as well as directed flow and flow decorrelations, with subnucleonic fluctuations enhancing the even component of and the decorrelation signal, particularly at mid- to central rapidities; peripheral collisions reveal missing quark-sector fluctuations in fragmentation regions. The work demonstrates the importance of nucleon substructure for longitudinal observables and motivates future refinements such as valence-quark fluctuations, a more realistic pre-equilibrium stage, and hadronic afterburners for quantitative precision.

Abstract

It is well understood that subnuclear fluctuations in the initial state of heavy-ion collisions have an important impact on the creation of long-range correlations in the transverse plane. This is also true for the creation of particle correlations along the beam direction, which can be measured in particle detectors, e.g. through longitudinal decorrelation observables. In this work, we study the emergence of long-range rapidity structures in Pb+Pb collisions using a hybrid model connecting the 3D resolved {\Dipper} initial state model to a (3+1)D viscous hydrodynamics framework CLVisc. We include different sources of fluctuations at the (sub-)nucleon level and present the effects of their inclusion on the longitudinal structure of relevant observables, focusing in this proceedings paper on charged hadron multiplicities, baryon stopping, directed flow and flow decorrelation. We find remarkable agreement to the experimental data regarding directed flow and the rapidity resolved charge particle multiplicity.
Paper Structure (5 sections, 3 figures)

This paper contains 5 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Model Description
  3. Hydrodynamic evolution: CLVisc
  4. Results
  5. Conclusions and Outlook

Figures (3)

  • Figure 1: (Left) Charged hadron multiplicity distribution as a function of pseudorapidity $\eta$ for Pb-Pb collisions at 2.76 TeV compared to ALICE data ALICE:2015bpk. (Right) Net-proton multiplicity for same system. For readability only the 5-10,20-30 and 40-50% centrality classes are presented.
  • Figure 2: Odd (left) and even (right) components of directed flow $v_1(\eta)$ of charged hadrons compared with ALICE data ALICE:2013xri for the 10-20% centrality class.
  • Figure 3: Directed flow $v_1(\eta)$ of charged hadrons compared with ALICE data ALICE:2016tlx. Subnucleonic hotspots enhance the even component, improving agreement with experiment.