We perform a global analysis of deep-inelastic $\textit{e}$ + $\textit{p}$ scattering data from HERA and transverse energy distributions in $\textit{p}$ + $\textit{p}$ and $\textit{p}$ + Pb collisions, alongside charged hadron multiplicities in Pb+Pb collisions at $$ \sqrt{s_{\textrm{NN}}}=5.02 $$ TeV from ALICE. Using a saturation-based initial state model grounded in high-energy QCD, we determine the early-time non-equilibrium shear viscosity to entropy density ratio $\textit{η/s}$ of the quark-gluon plasma. Our results provide new insights into the early-time transport properties of nuclear matter under extreme conditions.

Germany

Anton Andronic

Nicolas Borghini

Spain

Xiaojian Du

Christian Klein-Bösing

Renata Krupczak

United States

Hendrik Roch

Sören Schlichting

Constraining hot and cold nuclear matter properties from heavy-ion collisions and deep-inelastic scattering

Transverse momentum p T spectra and anisotropic flow distributions are studied for charmonia and charmed hadrons produced in Pb-Pb collisions and measured with the ALICE detector at the CERN Large Hadron Collider (LHC). The investigations are performed within the framework of the Statistical Hadronization Model with the transverse dynamics evaluated using predictions from relativistic viscous hydrodynamics as implemented in the computer codes MUSIC and FluiduM. With this essentially parameter-free approach good agreement is obtained for p T spectra in the range p T &lt; 10 GeV/c. The observed wide distribution in p T of anisotropic flow coefficients v2 and v3 for charmonia is also well reproduced, while their magnitude is generally somewhat over predicted. This finding may be connected to a difference in spatial distribution between light and charmed hadrons due to a different diffusion of light and heavy quarks in the hot fireball.

Peter Braun-Munzinger

Hjalmar Brunßen

Jana Crkovská

Johanna Stachel

Sweden

Vytautas Vislavicius

Martin Völkl

Transverse dynamics of charmed hadrons in ultra-relativistic nuclear collisions

The production of virtual photons is a very sensitive probe of the properties of the quark-gluon plasma. As they are experimentally detected by lepton pairs, they suffer from a large background arising from hadron decays. Light-flavour hadrons dominate at low invariant masses below m  ee  ~ 0.5 GeV and heavy flavours above. These contributions must therefore also be taken into account in experimental analyses at the LHC. In this paper, we calculate the direct contribution from virtual photons produced in the Drell-Yan process with an additional jet in POWHEG and find that it is significant at low invariant masses. We also simulate the background contributions from   <math> <mi>c</mi> <mover> <mi>c</mi> <mo>¯</mo> </mover> </math>  $$ c\overline{c} $$  and   <math> <mi>b</mi> <mover> <mi>b</mi> <mo>¯</mo> </mover> </math>  $$ b\overline{b} $$  production with POWHEG and quantify the theoretical uncertainties due to variations of the perturbative scales and parton distribution functions. We find larger relative and absolute uncertainties for the lighter c quarks than for heavier b quarks.

Tomáš Ježo

Michael Klasen

Alexander Neuwirth

Di-electron production at the LHC: unravelling virtual-photon and heavy-flavour contributions

This paper is a write-up of the ideas that were presented, developed and discussed at the fourth International Workshop on QCD Challenges from pp to AA, which took place in February 2023 in Padua, Italy. The goal of the workshop was to focus on some of the open questions in the field of high-energy heavy-ion physics and to stimulate the formulation of concrete suggestions for making progresses on both the experimental and theoretical sides. The paper gives a brief introduction to each topic and then summarizes the primary results.

Australia

Javira Altmann

France

Carlota Andres

Italy

Federico Antinori

Pietro Antonioli

Andrea Beraudo

Eugenio Berti

Livio Bianchi

Thomas Boettcher

Lorenzo Capriotti

Peter Christiansen

Czechia

Jesus Contreras Nuño

Leticia Cunqueiro Mendez

Cesar Silva

Andrea Dainese

Hans Dembinski

Brazil

Austria

David Dobrigkeit Chinellato

Andrea Dubla

Mattia Faggin

Chris Flett

Vincenzo Greco

Ilia Grishmanovskii

Jack Holguin

Finland

Yuuka Kanakubo

Dong Kim

Ramona Lea

South Korea

Su Lee

CERN

Saverio Mariani

Poland

Adam Matyja

Aleksas Mazeliauskas

Vincenzo Minissale

Andreas Morsch

Lucia Oliva

Luca Orusa

Petja Paakkinen

Daniel Pablos

Mexico

Guy Paić

Tanguy Pierog

Salvatore Plumari

Francesco Prino

Andrea Rossi

Lorenzo Sestini

Peter Skands

Olga Soloveva

Francesca Soramel

Alba Soto Ontoso

Martin Spousta

Andre Stahl Leiton

Jiayin Sun

Norway

Adam Takacs

Stefano Trogolo

Rosario Turrisi

Netherlands

Marta Verweij

Jing Wang

Klaus Werner

Valentina Zaccolo

China

Mingyu Zhang

Jianhui Zhu

Davide Zuliani

QCD challenges from pp to AA collisions: 4th edition

In relativistic nuclear collisions the production of hadrons with light (u,d,s) quarks is quantitatively described in the framework of the Statistical Hadronization Model (SHM). Charm quarks are dominantly produced in initial hard collisions but interact strongly in the hot fireball and thermalize. Therefore charmed hadrons can be incorporated into the SHM by treating charm quarks as ‘impurities’ with thermal distributions, while the total charm content of the fireball is fixed by the measured open charm cross section. We call this model SHMc and demonstrate that with SHMc the measured multiplicities of single charm hadrons in lead-lead collisions at LHC energies can be well described with the same thermal parameters as for (u,d,s) hadrons. Furthermore, transverse momentum distributions are computed in a blast-wave model, which includes the resonance decay kinematics. SHMc is extended to lighter collision systems down to oxygen-oxygen and includes doubly- and triply-charmed hadrons. We show predictions for production probabilities of such states exhibiting a characteristic and quite spectacular enhancement hierarchy.

Markus Köhler

Krzysztof Redlich

Denmark

The multiple-charm hierarchy in the statistical hadronization model

We propose a resolution of the discrepancy between the proton yield predicted by the statistical hadronization approach and data on hadron production in ultra-relativistic nuclear collisions at the LHC. Applying the S-matrix formulation of statistical mechanics to include pion-nucleon interactions, we reexamine their contribution to the proton yield, taking resonance widths and the presence of nonresonant correlations into account. The effect of multi-pion-nucleon interactions is estimated using lattice QCD results on the baryon-charge susceptibility. We show that a consistent implementation of these features in the statistical hadronization model, leads to a reduction of the predicted proton yield, which then quantitatively matches data of the ALICE collaboration for Pb-Pb collisions at the LHC.

Bengt Friman

Pok Man Lo

The thermal proton yield anomaly in Pb-Pb collisions at the LHC and its resolution