Production In Heavy-ion Collisions Research Articles

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

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.

Light-nuclei production in heavy-ion collisions within a thermodynamical approach

We present results of simulations of light-nuclei production in relativistic heavy-ion collisions within updated Three-fluid Hydrodynamics-based Event Simulator Extended by UrQMD (Ultra-relativistic Quantum Molecular Dynamics) final State interactions (THESEUS). The simulations were performed for Pb+Pb and Au+Au collisions in the collision energy range of $\sqrt{s_{NN}}=$ 6.4--19.6 GeV. The light-nuclei production is treated within the thermodynamical approach on equal basis with hadrons. The only additional parameter related to the light nuclei is the energy density of late freeze-out that imitates afterburner stage of the collision because the light nuclei do not participate in the UrQMD evolution. This parameter is fixed from the condition of the best reproduction of the proton transverse-momentum spectrum after the UrQMD afterburner by that at the late freeze-out. The updated THESEUS results in not perfect, but 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 $N(t)\times N(p)/N^2(d)$, are also considered. The directed flow of light nuclei turns out to be more involved. Apparently, it requires explicit treatment of the afterburner evolution of light nuclei that violates the kinetic equilibrium. Imperfect reproduction of the light-nuclei data leaves room for medium effects in produced light nuclei.

Energy dependence of light hypernuclei production in heavy-ion collisions from a coalescence and statistical-thermal model perspective

A comparison of light hypernuclei production, from Ultra-relativistic Quantum Molecular Dynamics (UrQMD)$+\text{coalescence}$ and the thermal model, in heavy ion collisions over a wide range of beam energies and system sizes is presented. We find that both approaches provide generally similar results, with differences in specific details. Especially the ratios of hypertriton to $\mathrm{\ensuremath{\Lambda}}$ are affected by both the source radius $\mathrm{\ensuremath{\Delta}}r$ of the coalescence procedure as well as canonical effects. On the other hand, the double ratio ${S}_{3}$ is almost independent of canonical effects, which is in contrast to coalescence. Thus, both the beam energy dependence and centrality dependence of ${S}_{3}$ can be used to constrain the hypertriton source radius. To do so the currently available data are not yet sufficient. Elliptic flow is shown to be unaffected by the source size of the nuclei and an almost perfect mass scaling of the elliptic flow is observed. Our predictions further suggest that the existence of the H-dibaryon ($\mathrm{\ensuremath{\Lambda}}\mathrm{\ensuremath{\Lambda}}$) seems ruled out by ALICE data.

In-medium effects on hidden strangeness production in heavy-ion collisions

We study ϕ meson production in heavy-ion collisions from subthreshold energies of 1.23 A GeV up to RHIC energies within the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach where novel production channels for ϕ mesons based on a coupled channel T-matrix approach are implemented along with the collisional broadening of the ϕ meson spectral width in medium. Since ϕ meson production is closely related to the production of kaons and antikaons, antikaon properties are described via the self-consistent coupled-channel unitarized scheme within a SU(3) chiral Lagrangian (G-matrix) which incorporates explicitly the s− and p− waves of the kaon-nucleon interaction, while the in-medium modifications of kaons are accounted for via a kaon-nuclear potential, which is assumed to be proportional to the local baryon density.

Beauty Production in Heavy-ion Collisions with ALICE at the LHC

Beauty Production in Heavy-ion Collisions with ALICE at the LHC

Measurement of Light-nuclei Production in Heavy-ion Collisions by the STAR Experiment

In these proceedings, we present the measurements of centrality, transverse momentum and rapidity dependences of proton ($p$) and light nuclei ($d$ ($\overline{d}$), $t$, $^{3}\mathrm{He}$ ($\overline{^{3}\mathrm{He}}$), and $^{4}\mathrm{He}$) production in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV, and isobaric (Ru+Ru and Zr+Zr) collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV. The compound yield ratios in central collisions at 3 GeV are found to be larger than the transport model calculations. Furthermore, the kinetic freeze-out parameters at 3 GeV show a different trend compared to those of light hadrons ($\pi$, $K$, $p$) at higher energies.

Effects of high-momentum tail of nucleon momentum distribution on initiation of cluster production in heavy-ion collisions at intermediate energies

Based on the transport model isospin-dependent Boltzmann-Uehling-Uhlenbeck coupled with a phase-space coalescence afterburner, we studied the effects of the high-momentum tail (HMT) of nucleon momentum distribution in initialization in 197Au+197Au reactions at a beam energy of 400 MeV/nucleon with different impact parameters.We found remarkable impact parameter-dependent HMT effects on the fragment multiplicity distribution. The average neutron to proton ratio of produced isotopes is also affected by the HMT. The rapidity distributions of triton and 3He and their elliptic flows are all evidently affected by the HMT. All the effects of the HMT on the cluster production in heavy-ion collisions are centrality dependent.