Production In Heavy-ion Collisions Research Articles

Flavor-independent yield of high- pT hadrons from nuclear collisions

Data on high-pT hadron production in heavy ion collisions at Feynman xF=0 indicate at universality of the observed nuclear suppression. Our analysis of the production mechanisms demonstrates important role of the color transparency effects which make the survival probability of a quark-antiquark dipole independent of the quark flavor, provided that the hadron wave function is formed outside the medium. The latter condition imposes restrictions on the range of pT, which should be sufficiently high to make the nuclear suppression universal. We also found that the in-medium broadening rate q^ (frequently called transport coefficient) significantly depends on the quark flavor, diminishing for heavy quarks. Published by the American Physical Society 2024

GPU-based computing analysis for charged-particle production in heavy ion collisions

The innovation of this paper lies in the introduction of GPU acceleration, which has greatly speeded up the projects progress. It begins by offering a brief overview of the research history on quark-gluon plasma (QGP) and the corresponding research tool, heavy ion collisions. The paper mainly focuses on data analysis of a significant process within the hadronic collisions, namely, the charged-particle production. The investigation of this process is an integral part of QGP research, as it occurs promptly after the formation of QGP. By applying the tracklet method to the datasets collected by ALICE detector, an estimate of the charged-particle multiplicity density is presented. The finding then suggests a positive correlation between the number of participating nucleons in the collision and the normalized charged-particle multiplicity density. Notably, this dependence on centrality is similar to the research conducted by the ALICE collaboration, but derived from a distinct dataset. It indicates that there should be an underlying mechanism behind the intriguing phenomenological trend waiting for further exploration. These studies have the potential to enhance the understanding of quantum chromodynamics (QCD) and provide insights into the true nature of the universe.

Far-from-equilibrium slow modes and momentum anisotropy in an expanding plasma

The momentum distribution of particle production in heavy-ion collisions encodes information about thermalization processes in the early-stage quark-gluon plasma. We use kinetic theory to study the far-from-equilibrium evolution of an expanding plasma with an anisotropic momentum-space distribution. We identify slow and fast degrees of freedom in the far-from-equilibrium plasma from the evolution of moments of this distribution. At late times, the slow modes correspond to hydrodynamic degrees of freedom and are naturally gapped from the fast modes by the inverse of the relaxation time, τR−1. At early times, however, there are an infinite number of slow modes with a gap inversely proportional to time, τ−1. From the evolution of the slow modes we generalize the paradigm of the far-from-equilibrium attractor to vector and tensor components of the energy-momentum tensor, and even to higher moments of the distribution function that are not part of the hydrodynamic evolution. We predict that initial-state momentum anisotropy decays slowly in the far-from-equilibrium phase and may persist until the relaxation time. Published by the American Physical Society 2024

Novel approach to light-cluster production in heavy-ion collisions

Novel approach to light-cluster production in heavy-ion collisions

Thermal dilepton production in heavy-ion collisions at beam-energy-scan (BES) energies

The lepton pair production rate at finite temperature and at nextto-leading-order (NLO) is calculated for quark-gluon plasma at non-zero net baryon density. Yields are obtained using a (3+1)D multicomponent simulation capable of reproducing hadronic observables measured in the RHIC Beam Energy Scan (BES). Spectra of intermediate invariant mass dileptons are compared with measurements from the STAR collaboration. The result of a study where the temperature information obtained from the dilepton spectrum from heavyion collisions performed at different energies and centralities is presented.

Mechanisms for cluster production in heavy-ion collisions near midrapidity

The formation of weakly bound clusters and hypernuclei in the hot and dense environment at midrapidity is a surprising phenomenon observed experimentally in heavy-ion collisions, spanning from low SIS to ultra-relativistic LHC energies. This occurrence, often referred to as the ’ice in a fire’ puzzle, has prompted the exploration of three distinct approaches to elucidate cluster formation: the potential mechanism, involving cluster formation throughout the entire heavy-ion collision via potential interactions between nucleons; the kinetic mechanism, entailing deuteron production through catalytic hadronic reactions; and coalescence at kinetic freeze-out. In this context, we discuss the observables sensitive to the mechanism of cluster production, utilizing a microscopic transport Parton-Hadron-Quantum Molecular (PHQMD) approach.

Electromagnetic probes in heavy-ion collisions

Electromagnetic probes such as photons and dileptons (l+l−) are a unique tool to study the space-time evolution of the hot and dense matter created in heavy-ion collisions, since they are emitted at all stages of the collision with negligible final-state interactions. In this article, the latest results on soft photon (real and virtual) production in heavy-ion collisions are presented.

Experimental overview: Quarkonium production in relativistic particle collisions

Quarkonium provides a golden probe of the formation of the Quark Gluon Plasma (QGP). Its production in heavy-ion collisions can be affected by an interplay of different phenomena such as medium-induced dissociation and heavy-quark (re)combination in the QGP, and cold nuclear matter effects due to the presence of the nucleus. The measurement of quarkonium states in different collision systems and beam energies allows to gain further insights on these effects and probe the properties of the QGP. In these proceedings, an overview of the main experimental quarkonium measurements in proton-proton, protonnucleus and nucleus-nucleus collisions is presented, giving emphasis on the most recent results from the Large Hadron Collider and Relativistic Heavy Ion Collider experiments shown at the 2023 Quark Matter conference.

Computation of quarkonium dissociation and recombination rates in quark–gluon plasma using Bateman equation

The quarkonium yield productions in the relativistic Heavy-Ion Collisions and their modifications within the Quark–Gluon Plasma (QGP) produced in the collisions have been investigated for more than four decades. Similarly, phenomenological model studies with various themes have been performed to comprehend the features of the QGP medium along with its associated particle production. This paper proposes a model that combines the effects of color screening, gluon-induced dissociation, and recombination on quarkonium production in heavy-ion collisions involving ([Formula: see text] ions) at a center-of-mass energy of [Formula: see text][Formula: see text]TeV. Unlike the Boltzmann transport rate equations of dissociation and recombination, the rate equations are decoupled and solved individually using a method involving Bateman solution ensuring the dissociation and recombination of heavy quarks within the QGP medium are accounted well.

Collision integral with momentum-dependent potentials and its impact on pion production in heavy-ion collisions

Collision integral with momentum-dependent potentials and its impact on pion production in heavy-ion collisions

Probing the high-density symmetry energy from subthreshold hyperon production in heavy-ion collisions

The hyperon dynamics in heavy-ion collisions near threshold energy has been investigated within the quantum molecular dynamics transport model. The isospin and momentum dependent hyperon-nucleon potential and the threshold energy correction on the hyperon elementary cross section are included in the model. It is found that the high-density symmetry energy is dependent on the isospin ratios Σ−/Σ+ and Ξ−/Ξ0, in particular in the domain of high kinetic energies. The isospin diffusion in heavy-ion collisions influences the neutron/proton ratio in the high-density region. The Σ−/Σ+ ratio depends on the stiffness of symmetry energy, in particular at the beam energy below the threshold value (Eth=1.58 GeV), i.e., the kinetic energy spectra of the single ratios, excitation functions and energy spectra of the double ratios in the isotopic reactions of 108Sn + 112Sn, 112Sn + 112Sn, 124Sn + 124Sn and 132Sn + 124Sn. The double strangeness ratio Ξ−/Ξ0 weakly depends on the symmetry energy because of the hyperon-hyperon collision mainly contributing the Ξ production below the threshold energy (Eth = 3.72 GeV).

Top quark and vector meson production in heavy ion collisions at CMS

Heavy ion collisions are rich and complex systems that involve different aspects of QCD and electromagnetic phenomena. From head-on collisions to the case in which the nuclei miss each other, many of QCD and photo-induced probes are being actively investigated. In this contribution we briefly discuss both of these different topics and some of the CMS results on top quark production and vector meson photo-production, as well as the physics motivation to study these processes are presented.

Dissociation rates and recombination likelihood of bottomonium states in heavy-ion collisions at sNN=5.02 TeV

In the medium of relativistic heavy-ion collisions, dissociation of the quarkonium and its survival have been studied to understand the properties of Quark Gluon Plasma (QGP). The coupled rates of dissociation and recombination reactions in QGP are commonly solved with the Boltzmann transport equation in which the formation and dissociation reactions compete with each other. Since the dissociation of newly formed bound-states is not accounted in the Boltzmann equation, a framework of decoupled rates is developed to assess the combined effect of gluon-induced dissociation and recombination (though it is small for [Formula: see text]) together with color screening on bottomonium production in heavy-ion collisions at center of mass energy [Formula: see text][Formula: see text]TeV. To calculate the recombination rates, we have employed an effective method of Bateman solution which ensures the correlated effect between the recombination and the dissociation of the newly combined bottomonium in the QGP medium. The modifications of bottomonium have been estimated in an inflating QGP with the constraints matching with the dynamics of [Formula: see text] collision events at LHC.

Unraveling gluon jet quenching through [formula omitted] production in heavy-ion collisions

Jet quenching has long been regarded as one of the key signatures for the formation of quark-gluon plasma in heavy-ion collisions. Despite significant efforts, the separate identification of quark and gluon jet quenching has remained as a challenge. Here we show that J/ψ in high transverse momentum (pT) region provides a uniquely sensitive probe of in-medium gluon energy loss since its production at high pT is particularly dominated by gluon fragmentation. Such gluon-dominance is first demonstrated for the baseline of proton-proton collisions within the framework of leading power non-relativistic quantum chromodynamics factorization formalism. We then use the linear Boltzmann transport model combined with hydrodynamics for the simulation of jet-medium interaction in nucleus-nucleus collisions. The satisfactory description of experimental data on both nuclear modification factor RAA and elliptic flow v2 reveals, for the first time, that the gluon jet quenching is the driving force for high pTJ/ψ suppression. This novel finding is further confirmed by the data-driven Bayesian analyses of relevant experimental measurements, from which we also obtain the first quantitative extraction of the gluon energy loss distribution in the quark-gluon plasma.

Deep learning assisted jet tomography for the study of Mach cones in QGP

Mach cones are expected to form in the expanding quark-gluon plasma (QGP) when energetic quarks and gluons traverse the hot medium at a velocity faster than the speed of sound in high-energy heavy-ion collisions. The shape of the Mach cone and the associated diffusion wake are sensitive to the initial jet production location and the propagation direction of the parton shower relative to the radial flow because of the distortion caused by the collective expansion of the QGP and the large density gradient. The shape of jet-induced Mach cones and their distortions in heavy-ion collisions provide a unique and direct probe of the dynamical evolution and the equation of state of QGP. However, it is difficult to identify the Mach cone and the diffusion wake in current experimental measurements of final hadron distributions because they are averaged over all possible initial jet production locations and parton-shower propagation directions. To overcome this difficulty, we develop a deep learning assisted jet tomography which uses the full information of the final hadrons from jets to localize the initial jet production positions. This method can help to constrain the initial regions of jet production in heavy-ion collisions and enable a differential study of Mach-cones with different path lengths and orientations relative to the radial flow of the QGP in heavy-ion collisions.

Universal energy dependence of measured temperatures for baryons produced in heavy-ion collisions

From the data on baryon production in heavy-ion collisions it is shown that a set of measurable functions exist, one for each baryon type, that depend exponentially on transverse momenta up to the maximum values detected for all collision energies ranging from the low end of RHIC BES to the high end of CERN LHC. The implied temperatures satisfy a scaling law in collision energy with a universal exponent for all baryon types which is the novel discovery. A self-similar thermal source is implied. Furthermore, it is shown how the scaling behavior depends on centralities. Those features in the data are related to simple properties of light and strange quarks by use of the recombination model. Prediction of $\phi$ meson production is made and then verified by existing data.

A Monte Carlo Study of Hyperon Production with the MPD and BM@N Experiments at NICA

Study of the strangeness production in heavy-ion collisions is one of the most important parts of the physics program of the BM@N and MPD experiments at the NICA accelerator complex. With collision energies sNN of 2.3–3.3 GeV in the fixed target mode at BM@N and 4–11 GeV in the collider mode at MPD, the experiments will cover the region of the maximum net baryon density and provide high-statistics complementary data on different physics probes. In this paper, some results of Monte Carlo studies of hyperon production with the BM@N and MPD experiments are presented, demonstrating their performance for investigation of the objects with strangeness.

Photons production in heavy-ion collisions as a signal of deconfinement phase

The photon production due to conversion of two gluons into a photon, $$gg\rightarrow \gamma $$ , in the presence of the background gauge fields is studied within the specific mean-field approach to QCD vacuum. In this approach, mean field in the confinement phase is represented by the statistical ensemble of almost everywhere homogeneous abelian (anti-)self-dual gluon configurations, while the deconfined phase can be characterized by the purely chromomagnetic fields. The probability of gluon conversion of two gluons into a photon vanishes in the confinement phase due to the randomness of the background field configurations. The anisotropic strong electromagnetic field, generated in the collision of relativistic heavy ions, serves as a catalyst for deconfinement with the appearance of an anisotropic purely chromomagnetic mean field. Respectively, deconfined phase is characterized by nonzero probability of the conversion of two gluons into a photon with strongly anisotropic angular distribution.

Study of Isothermal Compressibility and Speed of Sound in the Hadronic Matter Formed in Heavy-Ion Collision Using Unified Formalism

The thermodynamical quantities and response functions are useful to describe the particle production in heavy-ion collisions as they reveal crucial information about the produced system. While the study of isothermal compressibility provides an inference about the viscosity of the medium, speed of sound helps in understanding the equation of state. With an aim towards understanding the system produced in the heavy-ion collision, we have made an attempt to study isothermal compressibility and speed of sound as function of charged particle multiplicity in heavy-ion collisions at sNN = 2.76 TeV, 5.02 TeV, and 5.44 TeV using unified formalism.

Light-Nuclei Production in Heavy-Ion Collisions at sNN = 6.4 – 19.6 GeV in THESEUS Generator Based on Three-Fluid Dynamics

Light-nuclei production in relativistic heavy-ion collisions is simulated within an updated Three-fluid Hydrodynamics-based Event Simulator Extended by UrQMD (Ultra-relativistic Quantum Molecular Dynamics) final State interactions (THESEUS). The simulations are performed in the collision energy range of sNN= 6.4–19.6 GeV. The light-nuclei are produced within the thermodynamical approach on an equal basis with hadrons. Since the light nuclei do not participate in the UrQMD evolution, the only additional parameter related to the light nuclei, i.e., the energy density of late freeze-out, is used for the imitation of the afterburner stage of the collision. The updated THESEUS provides a reasonable reproduction of data on bulk observables of the light nuclei, especially their functional dependence on the collision energy and light-nucleus mass. Various ratios, d/p, t/p, t/d, and N(t)×N(p)/N2(d), are also considered. Imperfect reproduction of the light-nuclei data leaves room for medium effects in produced light nuclei.