The strongest electromagnetic fields in nature are created in high energy nuclear collisions and expected to change the dynamic scattering processes in the early stage. The magnetic field effect on the Drell-Yan process is investigated in this work. The single photon decay into quark pairs and lepton pairs in an external magnetic field leads to a significant Drell-Yan suppression in low and intermediate invariant mass region. The calculation up to the Landau level <math altimg='si1.svg'><mi>n</mi><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mn>1</mn></math> is complete in the energy region <math altimg='si2.svg'><mi>s</mi><mo linebreak='goodbreak' linebreakstyle='after'>&lt;</mo><mn>2</mn><mo stretchy='false'>/</mo><mn>3</mn><mi>n</mi><mo stretchy='false'>(</mo><mi>e</mi><mi>B</mi><mo stretchy='false'>)</mo></math>, and the enlarged phase space at higher landau levels may enhance the dilepton spectrum in the high mass region.

China

Shile Chen

Germany

Jiaxing Zhao

Pengfei Zhuang

Suppressed Drell-Yan process by an external magnetic field

Motivated by the work of Cardoso et al. (2022) <cross-ref refid='br0150' id='crf0030'>[15]</cross-ref> on black holes in galaxies, we derive a new black hole solution surrounded by a Dekel-Zhao (DZ) dark matter profile. The derived metric, influenced by DZ profile parameters, exhibits two distinct regimes: for <math altimg='si1.svg'><mi>r</mi><mo>&#8810;</mo><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math> ( <math altimg='si2.svg'><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math> is a characteristic radius), exponential corrections dominate, producing significant deviations from the Schwarzschild solution near dense cores, while for <math altimg='si3.svg'><mi>r</mi><mo>&#8811;</mo><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math>, these corrections vanish, restoring the Schwarzschild metric at large distances. These findings ensure consistency with general relativity in vacuum. The black hole shadow and deflection angle are analyzed, demonstrating that the shadow radius increases with black hole mass ( <math altimg='si4.svg'><msub><mrow><mi>M</mi></mrow><mrow><mi mathvariant='normal'>BH</mi></mrow></msub></math>), while higher central densities ( <math altimg='si5.svg'><msub><mrow><mi>&#961;</mi></mrow><mrow><mi mathvariant='normal'>ch</mi></mrow></msub></math>) result in smaller shadows, reflecting the environmental impact of dense dark matter halos. Photon dynamics reveal how DZ profiles modify critical impact parameters and effective potentials, with gravitational lensing effects highly sensitive to the characteristic radius ( <math altimg='si2.svg'><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math>). Smaller <math altimg='si2.svg'><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math> values lead to larger deflection angles due to stronger gravitational effects near compact cores. This work highlights the significance dark matter profiles in shaping black hole observables, providing a theoretical foundation for future observational studies and advancing the understanding of dark matter-black hole interactions in astrophysical and cosmological contexts.

Türkiye

Ali Övgün

Philippines

Reggie C. Pantig

Black hole in the Dekel-Zhao dark matter profile

The rotation effect on the QCD properties is an open question. We study the dynamic gluon mass in a dense QCD matter, the rotation is introduced by taking a covariant transformation between the flat and curved spaces. The law of causality which restricts the rotation strength of the system is carefully considered in the calculation. We find that the rotation effect is not monotonous. Overall, it behaves like an anti-screening effect, reflecting in the decreasing gluon mass, but the strength changes with the rotation. For a QCD matter with low baryon density, the screening effect in the flat space can be completely canceled by the rotation, and gluons are confined in a strongly rotating matter. When the rotation is extremely high, the matter approaches to a weakly interacting gas.

Guojun Huang

Yin Jiang

Rotation induced color confinement

We study the system size dependence of heavy quark (HQ) observables at a center-of-mass energy of <math><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>5.02</mn></mrow></math> TeV to explore whether it can provide further constraints on the physical processes which are involved: energy loss of HQs in the quark gluon plasma (QGP), hadronization, and hadronic rescattering. We use the EPOS4HQ approach to study <math><mi>p</mi><mo>−</mo><mi>p</mi></math> and 0–10% central O-O, Ar-Ar, Kr-Kr, and Pb-Pb reactions and investigate in detail the momentum change of heavy quarks from creation until their detection as part of a hadron as well as the enhancement of heavy baryon production at low <math><msub><mi>p</mi><mi>T</mi></msub></math>. We investigate furthermore the origin and the system size dependence of the azimuthal correlations between the heavy quark <math><mi>Q</mi></math> and the heavy antiquark <math><mover><mi>Q</mi><mo>¯</mo></mover></math> and how one can bypass the problem that correlations are washed out due to the combinatorial background. We conclude that a systematic study of the system size dependence of the momentum loss allows separating the momentum loss due to the passage through the QGP from the momentum change due to hadronization, and that the <math><mrow><mi>Q</mi><mover><mi>Q</mi><mo>¯</mo></mover></mrow></math> correlations yield insight into the different pQCD processes in which the heavy quarks are created.

France

Joerg Aichelin

Pol Bernard Gossiaux

Klaus Werner

System-size dependence of energy loss and correlations of heavy mesons at energies available at the CERN Large Hadron Collider

The magnetic field created in high energy nuclear collisions will affect the QCD dynamical processes, such as the heavy quark production which happens in the initial stage of the collisions. We calculate in a strong magnetic field the heavy quark production cross section of the process   <math> <mi>gg</mi> <mo>→</mo> <mi>Q</mi> <mover> <mi>Q</mi> <mo>¯</mo> </mover> </math>  $$ gg\to Q\overline{Q} $$  at leading order and the corresponding transverse momentum distribution in nucleus-nucleus collisions. In comparison to the QED process, the heavy quark production is dominated by the unique QCD channel with gluon self-interaction. Due to the dimension reduction of quark phase space in a strong magnetic field, the production is concentrated in a very narrow energy region above the threshold. Since the rotational invariance is broken in a magnetic field, the production becomes anisotropic.

Heavy flavor production under a strong magnetic field

Understanding the polarization property of  $$J/\psi $$  <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math>   is critical to constrain its production mechanism. In addition, the polarization of  $$J/\psi $$  <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math>   can reveal the impact of strong electromagnetic and vorticity fields in relativistic heavy ion collisions. In this study, we analyzed the yield and polarization of  $$J/\psi $$  <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math>   in relativistic heavy ion collisions at different centrality and transverse momentum regions, using three different reference frames: the Collins–Soper frame, the helicity frame, and the event plane frame. The polarization of initially produced  $$J/\psi $$  <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math>   is determined by the NRQCD calculation and is similar to that of pp collisions. However, both unpolarization and transverse polarization are considered for the regenerated  $$J/\psi $$  <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math>  . Our results indicate that the polarization at high  $$p_T$$  <math> <msub> <mi>p</mi> <mi>T</mi> </msub> </math>   is similar to that observed in pp collisions. However, at low  $$p_T$$  <math> <msub> <mi>p</mi> <mi>T</mi> </msub> </math>  , where regenerated  $$J/\psi $$  <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math>   dominates, it is likely that the polarized charm quarks in the rotational QGP medium are responsible for this phenomenon. Our study supplies a baseline for future research on the effects of strong electromagnetic and vorticity fields on  $$J/\psi $$  <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math>   polarization.

Baoyi Chen

$$J/\psi $$  <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math>   polarization in relativistic heavy ion collisions

The static properties and dynamic evolution of bottomonium states in a hot QCD medium are investigated through the Schrödinger equation with complex heavy quark potentials, which have been presented recently in a lattice QCD study and with three different extractions. This approach builds a direct connection between the in-medium heavy quark potentials from the lattice QCD to the experimental observables. The yields and nuclear modification factors  $$R_{AA}$$  <math> <msub> <mi>R</mi> <mrow> <mi>AA</mi> </mrow> </msub> </math>   of bottomonium in Pb–Pb collisions at  $$\sqrt{s_\textrm{NN}}=5.02$$  <math> <mrow> <msqrt> <msub> <mi>s</mi> <mtext>NN</mtext> </msub> </msqrt> <mo>=</mo> <mn>5.02</mn> </mrow> </math>   TeV are calculated in this work. Our results show a large suppression of the bottomonium yield in heavy ion collisions due to the large imaginary potential. To understand bottomonium  $$R_{AA}$$  <math> <msub> <mi>R</mi> <mrow> <mi>AA</mi> </mrow> </msub> </math>   based on lattice QCD potentials, we propose a formation time for bottomonium states and find that experimental data can be well explained with the heavy quark potential extracted by the Padé fit, which shows no color screening in the real part potential.

United Kingdom

Ge Chen

Bottomonium evolution with in-medium heavy quark potential from lattice QCD

Employing the recently developed EPOS4HQ event generator, we study the production of different heavy-flavor mesons in relativistic heavy-ion collisions at BNL Relativistic Heavy Ion Collider and CERN Large Hadron Collider energies. The transverse momentum spectra, yield ratio, nuclear modification factor, and elliptic flow can be well described in the EPOS4HQ framework. We furthermore analyze the processes which modify these observables as compared to <math><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions and are at the origin of the experimentally determined nuclear modification factor <math><msub><mi>R</mi><mrow><mi>A</mi><mi>A</mi></mrow></msub></math>.

Poland

Vitalii Ozvenchuk

Heavy-flavor hadron production in relativistic heavy ion collisions at energies available at BNL RHIC and at the CERN LHC in the EPOS4HQ framework

Heavy-flavor hadrons produced in ultrarelativistic heavy-ion collisions are a sensitive probe for studying hadronization mechanisms of the quark-gluon-plasma. In this paper, we survey how different transport models for the simulation of heavy-quark diffusion through a quark-gluon plasma in heavy-ion collisions implement hadronization and how this affects final state observables. Utilizing the same input charm-quark distribution in all models at the hadronization transition, we find that the transverse-momentum dependence of the nuclear modification factor of various charm hadron species has significant sensitivity to the hadronization scheme. In addition, the charm-hadron elliptic flow exhibits a nontrivial dependence on the elliptic flow of the hadronizing partonic medium.

Jörg Aichelin

Italy

Andrea Beraudo

Shanshan Cao

United States

Wenkai Fan

Min He

Vincenzo Minissale

Taesoo Song

Ivan Vitev

Ralf Rapp

Steffen Bass

Elena Bratkovskaya

Vincenzo Greco

Salvatore Plumari

Hadronization of heavy quarks

The creation of a quark-gluon plasma (QGP) is expected in heavy-ion collisions. It came as a surprise that proton-proton collisions at ultrarelativistic energies show as well a “QGP-like” behavior and signs of the creation of a fluid, although the corresponding system size is not more than a few cubic femtometers. Even more surprisingly, also heavy-flavor particles seem to be part of the fluid or at least interact with it. In this paper, we will investigate in a quantitative way this “collective behavior” of heavy flavor, by employing the newly developed EPOS4HQ approach, which has proven to be compatible with basic experimental data of light-flavor hadrons. We will investigate all observables, which may manifest collectivity, as particle spectra, elliptic flow, baryon-to-meson ratios, and two-particle correlations, and compare the results with experimental data. We will try to disentangle initial-state effects, those being due to interactions between charm quarks and plasma partons, and final-state effects (hadronization).

Heavy flavor as a probe of hot QCD matter produced in proton-proton collisions