We investigate the influence of global rotation on the chemical freeze-out parameters in ultra-relativistic heavy-ion collisions. Within the framework of the hadron resonance gas (HRG) model, the freeze-out parameters are determined using commonly employed freeze-out criteria, namely the fixed energy per particle and the scaled entropy density, extended here to include rotational effects. We find that the presence of rotation leads to a systematic shift of the chemical freeze-out curve toward lower temperatures in the <italic>T</italic>&#8211; <italic>&#956;<inf>B</inf></italic> phase diagram. The behavior of the electric charge and strangeness chemical potentials in the presence of rotation is also analyzed, providing the first systematic study of their rotational dependence within the HRG framework. Furthermore, we examine the impact of rotation on experimentally relevant observables, including hadron yield ratios and susceptibility ratios of conserved charges. Our results show that while particle yield ratios exhibit noticeable sensitivity to rotation, the conventional cumulant ratios remain comparatively less affected. This indicates that hadronic yield ratios may provide a more suitable observable for estimating the magnitude of rotational effects generated in heavy-ion collisions.

India

Nandita Padhan

Kshitish Kumar Pradhan

Arghya Chatterjee

Raghunath Sahoo

Vorticity-induced modifications of chemical freeze-out in heavy-ion collisions

The study of heavy-flavor hadrons is topical in the era of precision measurements, which is useful to test theories based on pQCD. The heavy-flavor hadrons are produced initially during heavy-ion or hadronic collisions and are one of the best probes to understand the initial stages of the collisions as well as the system evolution. In experiments, the heavy-flavor sectors are studied directly via their decay to different hadrons or di-leptons or via their semileptonic decay, which is accompanied by additional neutrinos. However, their measurement in experiments is resource intensive and requires input from different Monte Carlo event generators. In this study, we provide an independent method based on machine learning algorithms to separate such leptons coming from heavy-flavor semileptonic decays. We use pythia8 to generate events for this study, which gives a good qualitative and quantitative description of heavy-flavor production in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions. We use the xgboost model for this study, which is trained with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13.6</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>. We use <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mrow><mi>DCA</mi></mrow><mrow><mi>xy</mi></mrow></msub></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mrow><mi>DCA</mi></mrow><mrow><mi mathvariant="normal">Z</mi></mrow></msub></math>, and pseudorapidity as the input features to the machine. The ML model provides an accuracy of 98% for heavy-flavor decay electrons and almost 100% for heavy-flavor decay muons.

Kangkan Goswami

Suraj Prasad

Machine learning driven identification of heavy flavor decay leptons in proton-proton collisions at the Large Hadron Collider

The production of heavy quarks (charm and beauty) in high-energy hadronic and nuclear collisions provides an excellent testing ground for the theory of strong interactions and validates models based on quantum chromodynamics (QCD). In this work, prompt and nonprompt production of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mo>/</mo></mrow><mi>ψ</mi></math> in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> are studied as a function of the transverse spherocity using pythia8. <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mo>/</mo></mrow><mi>ψ</mi></math> is reconstructed via its electromagnetic decay to dielectrons and dimuons, in mid- and forward rapidity, respectively. Transverse spherocity, an event-shape observable, is used to distinguish hard-QCD events from the softer, isotropic ones. In pythia8, the production of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mo>/</mo></mrow><mi>ψ</mi></math> can be influenced by the average number of multiple parton interactions (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">⟨</mo><msub><mi>N</mi><mrow><mi>mpi</mi></mrow></msub><mo stretchy="false">⟩</mo></math>), owing to the underlying events, which have a dominant contribution to particle production at lower transverse momentum. Since transverse spherocity is correlated to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">⟨</mo><msub><mi>N</mi><mrow><mi>mpi</mi></mrow></msub><mo stretchy="false">⟩</mo></math>, this can serve as an experimentally accessible tool for event selection to study the underlying QCD processes influencing the prompt and nonprompt <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mo>/</mo></mrow><mi>ψ</mi></math> production. This study reveals the correlation between heavy-flavor production dynamics and topological event selection in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions using pythia8, whose relevance awaits experimental validation.

Aswathy Menon Kavumpadikkal Radhakrishnan

Finland

Neelkamal Mallick

Topological production of charmonia with event-shape engineering in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> using pythia8

The universality of electric charge as a quantum number allows thermoelectric properties to manifest across diverse systems, starting from a hot quantum chromodynamic matter in heavy-ion collisions at a high energy scale to semiconductors in condensed matter systems at a low energy scale. In this work, we explore the emergence of magneto-transport phenomena, specifically the magneto-Thomson and transverse Thomson effects, in a hot and dense hadronic medium produced in relativistic heavy-ion collisions at the Relativistic Heavy Ion Collider and Large Hadron Collider energies. These phenomena arise due to the combined influence of temperature gradients and non-zero baryon chemical potential, particularly in the presence of an external magnetic field. Using the relativistic Boltzmann transport equation within the relaxation time approximation, we analyze the behavior of the hadronic medium considering different frameworks of hadron resonance gas models. The presence of external magnetic fields breaks the isotropy of the thermoelectric transport coefficient matrix, giving rise to new components of the Thomson coefficient, namely, magneto-Thomson and transverse Thomson coefficients. For the first time, we estimate the magneto-Thomson and transverse Thomson coefficients, which originate from the temperature dependence of the magneto-Seebeck coefficient and Nernst coefficient, respectively, in hadron gas under the influence of a static and time-varying magnetic field. Our findings provide a novel perspective on the higher-order thermoelectric properties of the hot and dense hadronic medium in the context of heavy-ion collisions.

Kamaljeet Singh

Magneto-Thomson and transverse Thomson effects in an interacting hadron gas in the presence of an external magnetic field

We investigate the general susceptibilities in the charm sector by using the van der Waals hadron resonance gas model (VDWHRG).We argue that the ideal hadron resonance gas, which assumes no interactions between hadrons, and the excluded volume hadron resonance gas, which includes only repulsive interactions, fail to explain the lattice quantum chromodynamics (lQCD) data at very high temperatures. In contrast, the VDWHRG model, incorporating both attractive and repulsive interactions, extends the degree of agreement with lQCD up to nearly 180 MeV. We estimate the partial pressure in the charm sector and study charm susceptibility ratios in a baryon-rich environment, which is tricky for lQCD due to the fermion sign problem. Our study further solidifies the notion that the hadrons should not be treated as noninteracting particles, especially when studying higher order fluctuations, but rather one should consider both attractive and repulsive interactions between the hadrons.

Mexico

Dushmanta Sahu

Partial pressure and susceptibilities of the charmed sector in the van der Waals hadron resonance gas model

The gradients act as invisible engines of transport, converting microscopic imbalances into macroscopic flows and, thus, providing deep insights into the dynamics of physical systems. Thermal gradients do not merely drive the flow of heat, but they also set the microscopic constituents of the system into motion. In such scenarios, the constituents of the system not only transport energy, but also diffuse collectively under the influence of these gradients. For the very first time, we present a first-principles investigation of the Soret and Dufour effects in hot and dense QCD matter. We use the relativistic Boltzmann transport equation under the relaxation time approximation. By incorporating chemical potential and temperature gradients into the kinetic theory framework, we derive explicit expressions for the Dufour coefficient, which quantifies the heat flow due to concentration gradients, and the Soret coefficient, which describes the particle diffusion induced by thermal gradients. These coupled-transport phenomena are traditionally studied in multicomponent classical systems at low energy scales. In this study, we follow quasiparticle models for the deconfined phase and the hadron resonance gas model for the confined hadronic phase in the context of heavy-ion collisions. This study provides novel insights into the thermodiffusion and diffusion-thermo phenomena and opens avenues for incorporating such effects in hydrodynamic modeling and transport simulations of QCD matter.

Soret and Dufour effects in hot and dense QCD matter

The behavior of vector mesons in extreme environments provides a unique probe of non-perturbative Quantum Chromodynamics. We investigate the conditions for Bose-Einstein condensation (BEC) of spin-1 <italic>&#961;</italic> mesons in dense rotating hadronic matter, a regime relevant to the peripheral heavy-ion collisions and the interiors of rapidly rotating neutron stars. When the <italic>&#961;</italic> meson chemical potential ( <italic>&#956;<inf>&#961;</inf></italic>) approaches its effective mass ( <math altimg='si1.svg'><msubsup><mi>m</mi><mi>&#961;</mi><mo>*</mo></msubsup></math>), a phase transition to BEC occurs. We demonstrate that this transition is non-trivially influenced by global rotation, which couples to the spin of the <italic>&#961;</italic> mesons, leading to a macroscopic spin alignment of the condensate along the axis of rotation. This interplay between condensation and rotation results in distinct polarization patterns, which can serve as a possible signature of a BEC in experiments. The results suggest that rapidly rotating neutron stars may harbor an anisotropic, spin-polarized <italic>&#961;</italic>-condensed phase, which could impact their equation of state.

Emergent spin polarization from <italic>&#961;</italic> meson condensation in rotating hadronic matter

Thermoelectric phenomena are traditionally associated with the interconversion of thermal and electrical energy in many-body systems. In the context of high-temperature quantum chromodynamics (QCD) matter produced in relativistic heavy-ion collisions, thermoelectric responses can provide insight into the evolving microscopic dynamics and the redistribution of effective degrees of freedom across the phase transition region. In this work, for the first time, we present a phenomenological study of the thermoelectric figure of merit ( <italic>ZT</italic>) in hot QCD matter, with a particular focus on its behavior across the hadronic and quark-gluon plasma phases. Using model-based calculations for the electrical conductivity, Seebeck coefficient, and thermal conductivity, we analyze the temperature dependence of <italic>ZT</italic> and identify characteristic features near the QCD phase transition temperature. Our results indicate that <italic>ZT</italic> exhibits nontrivial behavior near the transition region, reflecting the changing transport properties and active degrees of freedom in the medium. This phenomenological study of the thermoelectric figure of merit provides a complementary perspective to traditional transport studies and may provide critical insights for advancing the understanding of QCD matter through the transition region.

Thermoelectric figure of merit and the deconfinement phase transition

Pion condensation in ultrarelativistic collisions presents a compelling theoretical phenomenon with significant implications for the dynamics of hadronic matter. Various theoretical frameworks offer insight into the nature of high-temperature Bose-Einstein condensation (BEC). The present study investigates the dissipative behavior of a relativistic pion gas undergoing BEC in ultrarelativistic heavy-ion collisions. Further, we obtain viscosity (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math>), bulk viscosity (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ζ</mi></math>), and speed of sound (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>c</mi><mi>s</mi></msub></math>) by employing the Boltzmann transport equation with the relaxation time approximation. Findings show a substantial drop in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi><mo>/</mo><mi>s</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ζ</mi><mo>/</mo><mi>s</mi></math> with the fractional increase in condensation. This effect is becoming more evident in larger systems approaching the thermodynamic limit. Alongside the reduction in viscosities, the speed of sound also decreases with increasing condensation, indicating a softening of the equation of state. The analysis of finite-size effects reveals that larger systems exhibit more pronounced signatures of BEC. These results suggest that pion condensation can influence the hydrodynamic evolution of the hadronic phase in heavy-ion collisions, with consequential implications for interpreting collective flow observables and the underlying equation of state.

Captain R. Singh

Bose-Einstein condensation and dissipative dynamics in a relativistic pion gas

RHIC and LHC have injected <math altimg='si2.svg'><mrow><msup><mrow /><mn>16</mn></msup><mrow><mi mathvariant='normal'>O</mi></mrow></mrow></math> nuclei in their accelerator complexes with a focus on investigating collectivity and the origin of quark-gluon plasma signatures in small collision systems. The <math altimg='si2.svg'><mrow><msup><mrow /><mn>16</mn></msup><mrow><mi mathvariant='normal'>O</mi></mrow></mrow></math> nuclei are known to possess clusters of <math altimg='si1.svg'><mi>&#945;</mi></math>-particles ( <math altimg='si19.svg'><mrow><msup><mrow /><mn>4</mn></msup><mrow><mi mathvariant='normal'>H</mi></mrow><mi>e</mi></mrow></math>) inside the nucleus. This paper attempts to study the clustered-nuclear-geometry dependence of anisotropic flow coefficients such as elliptic flow ( <math altimg='si20.svg'><msub><mi>v</mi><mn>2</mn></msub></math>) and triangular flow ( <math altimg='si21.svg'><msub><mi>v</mi><mn>3</mn></msub></math>), which are sensitive to the nuclear geometry of colliding nuclei. The study is performed in pO and OO collisions at <math altimg='si6.svg'><mrow><msqrt><msub><mi>s</mi><mrow><mrow><mi mathvariant='normal'>N</mi></mrow><mi>N</mi></mrow></msub></msqrt><mo linebreak='goodbreak'>=</mo><mn>9.61</mn></mrow></math> TeV and 7 TeV respectively, employing a hybrid model encompassing IP-Glasma + MUSIC + iSS + UrQMD. The results of the clustered nuclear geometry are compared with those of the Woods&#8211;Saxon nuclear profile. Both initial and final state anisotropies are estimated. This study is thus one of its first kind, where the study of anisotropic flow coefficients for pO and OO collisions is presented using a hybrid hydrodynamics model. While the effect of <math altimg='si1.svg'><mi>&#945;</mi></math>-clustering in pO is found to be small, it is significant for each observable studied in OO collisions. It is also observed that the magnitude of this effect has a noteworthy dependence on the size of the 4He.