Improved linear Boltzmann transport model for hadron and jet suppression in ultra-relativistic heavy-ion collisions

TL;DR

The paper tackles the challenge of simultaneously describing hadron and full-jet suppression in ultrarelativistic heavy-ion collisions. It introduces two improvements to the linear Boltzmann transport framework: inserting in-medium transport at a medium scale $Q_M$ during vacuum parton showers and incorporating color flow so that medium-modified partons can form color-connected strings during hadronization. The results show that these changes modify the hadron-to-jet quenching ratio, enabling a unified description of $R_{AA}$ for hadrons and jets across flavors for $Q_M$ around $1-2$ GeV with tuned $oldsymbol{\alpha_s}$. They also explore the impact of color flow on hadronization, find that hadron $R_{AA}$ is more sensitive to color connections than jet $R_{AA}$, and discuss limitations such as non-perturbative effects and the need for coalescence and Bayesian parameter estimation.

Abstract

Jets serve as powerful tomographic probes of the quark-gluon plasma (QGP) created in relativistic heavy-ion collisions. While the expanding landscape of jet observables reveals multi-faceted aspects of jet-medium interactions, a precise and simultaneous description of the nuclear modification factors of hadrons and full jets still remains a challenge for theoretical models. In this work, we present two essential improvements to the linear Boltzmann transport (LBT) model to bridge this gap. First, instead of implementing in-medium parton transport after vacuum parton showers complete, we introduce a medium scale at which the parton transport is inserted into the vacuum parton showers, providing a more physical picture of parton-QGP interactions. Second, we incorporate color flow information into the LBT model, enabling string connections between partons whose configurations are correlated with the medium-modified parton showers before hadronization. We demonstrate that both improvements alter the predicted ratio of hadron to jet quenching, leading to a satisfactory description of the nuclear modification factors of hadrons and jets with different flavors within a unified framework.

Figures (5)

• Figure 1: (Color online) Schematic illustration of color flows in $1 \rightarrow 2$ parton splitting processes. The numbers indicate color indices, and the arrows pointing to the left represent anti-colors.
• Figure 2: (Color online) Schematic illustration of color flows in $2 \rightarrow 2$ parton scattering processes.
• Figure 3: (Color online) The nuclear modification factors of (a) inclusive jets and (b) charged hadrons in central Pb$+$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02TeV$, compared between using different medium scales. Experimental data are taken from the CMS CMS:2021vuiCMS:2016xef and ATLAS Aaboud:2018twu Collaborations.
• Figure 4: (Color online) The nuclear modification factors of (a) charged hadrons, (b) $D$ mesons, (c) $B$ mesons, (d) charged jets, (e) $D^0$-tagged jets, and (f) $b$-tagged jets in Pb$+$Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02TeV$, compared to experimental data from the CMS CMS:2021vuiCMS:2016xefCMS:2017qjwCMS:2017uoy, ATLAS Aaboud:2018twuATLAS:2022agz and ALICE ALICE:2023wazSheikh:2020sgf Collaborations.
• Figure 5: (Color online) The nuclear modification factors of inclusive jets and hadrons in central Pb$+$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02TeV$, compared between including and not including the color flow (CF) information in the Pythia string fragmentation. The experimental data are taken from the CMS CMS:2021vuiCMS:2016xef and ATLAS Aaboud:2018twu Collaborations.