Ultrarelativistic Heavy-ion Collisions Research Articles

Medium induced jet broadening in a quantum computer

QCD jets provide one of the best avenues to extract information about the quark-gluon plasma produced in the aftermath of ultra relativistic heavy ions collisions. The structure of jets is determined by multiparticle quantum interference hard to tackle using perturbative methods. When jets evolve in a QCD medium this interference pattern is modified, adding another layer of complexity. By taking advantage of the recent developments in quantum technologies, such effects might be better understood via direct quantum simulation of jet evolution. In this work, we introduce a precursor to such simulations. Based on the light-front Hamiltonian formalism, we construct a digital quantum circuit that tracks the evolution of a single hard probe in the presence of a stochastic color background. In terms of the jet quenching parameter $\hat q$, the results obtained using classical simulators of ideal quantum computers agree with known analytical results. With this study, we hope to provide a baseline for future in-medium jet physics studies using quantum computers.

Jet-perceived anisotropy revealed through high-p⊥ data

We explore to what extent, and how, high-p⊥ data and predictions reflect the shape and anisotropy of the QCD medium formed in ultrarelativistic heavy-ion collisions at LHC energies. To this end, we use our recently developed DREENA-A framework, which can accommodate any temperature profile within the dynamical energy loss formalism. We show that the ratio of high-p⊥v2 and (1−RAA) predictions reaches a well-defined saturation value, which is directly proportional to the time-averaged anisotropy of the evolving QGP, as seen by the jets.

Structure of $$^{128,129,130}$$Xe through multi-reference energy density functional calculations

Recently, values for the Kumar quadrupole deformation parameters of the nucleus $^{130}$Xe have been computed from the results of a Coulomb excitation experiment, indicating that this xenon isotope has a prominent triaxial ground state. Within a different context, it was recently argued that the analysis of particle correlations in the final states of ultra-relativistic heavy-ion collisions performed at the Large Hadron Collider (LHC) points to a similar structure for the adjacent isotope, $^{129}$Xe. In the present work, we report on state-of-the-art multi-reference energy density functional calculations that combine projection on proton and neutron number as well as angular momentum with shape mixing for the three isotopes $^{128,129,130}$Xe using the Skyrme-type pseudo-potential SLyMR1. Exploring the triaxial degree of freedom, we demonstrate that the ground states of all three isotopes display a very pronounced triaxial structure. Moreover, comparison with experimental results shows that the calculations reproduce fairly well the low-energy excitation spectrum of the two even-mass isotopes. By contrast, the calculation of $^{129}$Xe reveals some deficiencies of the effective interaction.

Event-shape engineering analysis of D meson in ultrarelativistic heavy-ion collisions

We describe the propagation of charm quarks in the quark-gluon plasma (QGP) by means of an event-by-event transport approach. In our calculations the non-perturbative interaction between heavy quarks and light partons has been taken into account through a quasi-particle approach with thermal light quark masses tuned to reproduce lQCD thermodynamics. We found that the flow observables v_2 and v_3 of D mesons are comparable with the experimental measurements for Pb + Pb collisions at 5.02 TeV in different ranges of centrality selections. The results are analyzed with event-shape engineering technique. The comparison of the anisotropic flow coefficients v_n with experimental data show a quite good agreement with experimental data for different flow vector q_2 selections, which confirms the strong coupling between charm quarks and light quarks in the QCD matter. Furthermore, we present here a novel study of the event-by-event correlations between flow harmonics of D mesons and soft hadrons at LHC energy with the event-shape engineering technique that can put further constraints on heavy quark transport coefficients toward a solid comparison between the phenomenological determination and the lattice QCD calculations.

Non-equilibrium charmonium regeneration in strongly coupled quark-gluon plasma

The evaluation of quarkonium regeneration in ultrarelativistic heavy-ion collisions (URHICs) requires the knowledge of the heavy-quark phase space distributions in the expanding quark-gluon plasma (QGP) fireball. We employ a semi-classical charmonium transport approach where regeneration processes explicitly account for the time-dependent spectra of charm quarks via Langevin simulations of their diffusion. The inelastic charmonium rates and charm-quark transport coefficients are computed from the same charm-medium interaction. The latter is modeled by perturbative rates, augmented with a K-factor to represent nonperturbative interaction strength and interference effect. Using central 5.02 TeV Pb-Pb collisions as a test case we find that a good description of the measured J/ψ yield and its transverse-momentum dependence can be achieved if a large K≳5 is employed while smaller values lead to marked discrepancies. This is in line with open-charm phenomenology in URHICs, where nonperturbative interactions of similar strength are required. Our approach establishes a common transport framework for a microscopic description of open and hidden heavy-flavor (HF) observables that incorporates both nonperturbative and non-equilibrium effects, and thus enhances the mutual constraints from experiment on the extraction of transport properties of the QGP.

Dynamically groomed jet radius in heavy-ion collisions

We explore the ability of a recently proposed jet substructure technique, dynamical grooming, to pin down the properties of the quark-gluon plasma formed in ultrarelativistic heavy-ion collisions. In particular, we compute, both analytically and via Monte Carlo simulations, the opening angle ${\ensuremath{\theta}}_{g}$ of the hardest splitting in the jet as defined by dynamical grooming. Our calculation, grounded in perturbative QCD (pQCD), accounts for the factorization in time between vacuum-like and medium-induced processes in the double logarithmic approximation. We observe that the dominant scale in the ${\ensuremath{\theta}}_{g}$ distribution is the decoherence angle ${\ensuremath{\theta}}_{c}$ which characterizes the resolution power of the medium to propagating color probes. This feature also persists in strong coupling models for jet quenching. We further propose for potential experimental measurements a suitable combination of the dynamical grooming condition and the jet radius that leads to a pQCD-dominated observable with a very small sensitivity ($\ensuremath{\le}10%$) to medium response.

Upsilon decay widths in magnetized asymmetric nuclear matter

The in-medium partial decay widths of [Formula: see text] in magnetized asymmetric nuclear matter are studied using a field theoretic model for composite hadrons with quark (and antiquark) constituents. [Formula: see text] is the lowest bottomonium state which can decay to [Formula: see text] in vacuum. The medium modifications of the decay widths of [Formula: see text] to [Formula: see text] pair in magnetized matter arise due to the mass modifications of the decaying [Formula: see text] as well as of the produced [Formula: see text] and [Formula: see text] mesons. The in-medium masses of the open bottom meson in magnetized nuclear matter are computed from their interactions with the nucleons and the scalar mesons within a chiral effective model. The mass modification of the [Formula: see text] arises due to the medium modification of a scalar dilaton field, which is introduced in the model to simulate the gluon condensates of QCD. The effects of the anomalous magnetic moments for the proton and neutron are taken into consideration in the present investigation. The presence of the external magnetic field is observed to lead to different mass modifications within the [Formula: see text] as well as the [Formula: see text] doublets, even in isospin symmetric nuclear matter. This is due to the difference in the interactions of the proton and the neutron to the electromagnetic field. The charged [Formula: see text] mesons have additional contributions from the Landau energy levels, leading to positive shifts in their masses in the presence of a magnetic field. In the presence of an external magnetic field, there are contributions to the masses of the B, [Formula: see text] mesons and [Formula: see text] state (longitudinal component) due to the pseudoscalar meson–vector meson (PV) mixing ([Formula: see text], [Formula: see text] and [Formula: see text] mixings), which are also considered in this study. The PV mixing effects are observed to be the dominant contributions to the mass shifts of these mesons, which lead to appreciable modifications in the decay widths of [Formula: see text] to the neutral ([Formula: see text]) and the charged ([Formula: see text]) pairs in the presence of a magnetic field. These should have observable consequence in the production of open bottom mesons and bottomonium states at LHC and RHIC, where huge magnetic fields are produced in ultra-relativistic peripheral heavy-ion collisions.

Interplay of femtoscopic and charge-balance correlations

Correlations driven by the constraints of local charge conservation have been shown to provide insight into the chemical evolution and diffusivity of the high-temperature matter created in ultra-relativistic heavy ion collisions. Two-particle correlations driven by final-state interactions have allowed the extraction of critical femtoscopic space-time information about the expansion and dissolution of the same collisions. Whereas correlations from final-state interactions mainly appear at small relative momenta, a few tens of MeV/$c$, charge-balance correlations extend over a range of hundreds of MeV/$c$. In nearly all previous analyses, this separation of scales is used to focus solely on one class or the other. The purpose of this study is to quantitatively understand the degree to which correlations from final-state interactions distort the interpretation of charge-balance correlations and vice versa.

Probing the initial longitudinal density profile and electromagnetic field in ultrarelativistic heavy-ion collisions with heavy quarks

Heavy quarks are valuable probes of the electromagnetic field and the initial condition of the quark-gluon plasma (QGP) matter produced in high-energy nuclear collisions. Within an improved Langevin model that is coupled to a (3+1)-dimensional viscous hydrodynamic model, we explore the origin of the directed flow coefficient ($v_1$) of heavy mesons and their decay leptons, and its splitting ($\Delta v_{1}$) between opposite charges. We find that while the rapidity dependence of the heavy flavor $v_1$ is mainly driven by the titled energy density profile of the QGP with respect to the longitudinal direction at the RHIC energy, it is dominated by the electromagnetic field at the LHC energy. The $\Delta v_{1}$ serves as a novel probe of the spacetime evolution profile of the electromagnetic field. Our results of $D$ mesons and their decay electrons are consistent with the available data at RHIC and LHC, and our predictions on the heavy flavor decay muons can be further tested by future measurements.

Production of Omega NN and Omega Omega N in ultra-relativistic heavy-ion collisions

Even though lots of Lambda -hypernuclei have been found and measured, multi-strangeness hypernuclei consisting of Omega are not yet discovered. The studies of multi-strangeness hypernuclei help us further understand the interaction between hyperons and nucleons. Recently the Omega N and Omega Omega interactions as well as binding energies were calculated by the HAL-QCD’s lattice Quantum Chromo-Dynamics (LQCD) simulations and production rates of Omega -dibaryon in Au + Au collisions at RHIC and Pb + Pb collisions at LHC energies were estimated by a coalescence model. The present work discusses the production of more exotic triple-baryons including Omega , namely Omega NN and Omega Omega N as well as their decay channels. A variation method is used in calculations of bound states and binding energy of Omega NN and Omega Omega N with the potentials from the HAL-QCD’s results. The productions of Omega NN and Omega Omega N are predicted by using a blast-wave model plus coalescence model in ultra-relativistic heavy-ion collisions at sqrt{s_{NN}} = 200 GeV and 2.76 TeV. Furthermore, plots for baryon number dependent yields of different baryons (N and Omega ), their dibaryons and hypernuclei are made and the production rate of a more exotic tetra-baryon (Omega Omega NN) is extrapolated.

Deuteron production in ultrarelativistic heavy-ion collisions: A comparison of the coalescence and the minimum spanning tree procedure

The formation of deuterons in heavy-ion collisions at relativistic energies is investigated by employing two recently advanced models---the minimum spanning tree (MST) method and the coalescence model---by embedding them in the parton-hadron quantum molecular dynamics (PHQMD) and the ultrarelativistic quantum molecular dynamics (UrQMD) transport approaches. While the coalescence mechanism combines nucleons into deuterons at the kinetic freeze-out hypersurface, the MST identifies the clusters during the different stages of time evolution. We find that both clustering procedures give very similar results for the deuteron observables in the UrQMD as well as in the PHQMD environment. Moreover, the results agree well with the experimental data on deuteron production in Pb$+$Pb collisions at $\sqrt{{s}_{NN}}=8.8$ GeV (selected for the comparison of the methods and models in this study). A detailed investigation shows that the coordinate space distribution of the produced deuterons differs from that of the free nucleons and other hadrons. Thus, deuterons are not destroyed by additional rescattering.

Measurement of the nuclear modification factor for muons from charm and bottom hadrons in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

Heavy-flavour hadron production provides information about the transport properties and microscopic structure of the quark–gluon plasma created in ultra-relativistic heavy-ion collisions. A measurement of the muons from semileptonic decays of charm and bottom hadrons produced in Pb+Pb and pp collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV with the ATLAS detector at the Large Hadron Collider is presented. The Pb+Pb data were collected in 2015 and 2018 with sampled integrated luminosities of 208μb−1 and 38μb−1, respectively, and pp data with a sampled integrated luminosity of 1.17pb−1 were collected in 2017. Muons from heavy-flavour semileptonic decays are separated from the light-flavour hadronic background using the momentum imbalance between the inner detector and muon spectrometer measurements, and muons originating from charm and bottom decays are further separated via the muon track's transverse impact parameter. Differential yields in Pb+Pb collisions and differential cross sections in pp collisions for such muons are measured as a function of muon transverse momentum from 4 GeV to 30 GeV in the absolute pseudorapidity interval |η|<2. Nuclear modification factors for charm and bottom muons are presented as a function of muon transverse momentum in intervals of Pb+Pb collision centrality. The bottom muon results are the most precise measurement of b quark nuclear modification at low transverse momentum where reconstruction of B hadrons is challenging. The measured nuclear modification factors quantify a significant suppression of the yields of muons from decays of charm and bottom hadrons, with stronger effects for muons from charm hadron decays.

The Effect of Strong Magnetic Field on Heavy Quarkonia in a Hot Medium Using Nikiforov-Uvarov Method

The influence of temperature and a constant strong magnetic field on the quarkonium heavy meson spectrum is explored as a result of recent research suggesting that a strong magnetic field can be formed at primary stage in ultrarelativistic heavy ion collisions (URHIC). Debye screen potential is used in non-relativistic models, and the states are termed as charmonium &amp; bottominum. In order to better understand the current findings, a comparison has been made in recent studies. Therefore, the number of flavor and magnetic field play an essential role in hot medium.

Modification of Z0 leptonic invariant mass in ultrarelativistic heavy ion collisions as a measure of the electromagnetic field

An extraordinary strong magnetic field, eB0≈1018 Gauss, is expected to be generated in non-central ultrarelativistic heavy ion collisions and it is envisaged to induce several effects on hot QCD matter including the possibility of local parity and local charge conjugation and parity symmetry violations. A direct signature of such e.m. fields and a first quantitative measurement of its strength and lifetime are still missing. We point out that both the mean value of leptonic invariant mass of Z0 boson, reconstructed by its decaying lepton pairs, and the relative width are modified in relativistic heavy ion collisions due to the presence of strong initial e.m. fields. We propose a measurement of the leptonic invariant mass of Z0 as a novel probe of the strength of the By. Both shifts could be up to about few hundred MeV and are found to depend on the integral of By over the time duration quadratically (approximate). Hence it provides a novel and clear probe of electromagnetic fields, which can be tested experimentally.

Resummed Relativistic Dissipative Hydrodynamics

In this review, we present the motivation for using relativistic anisotropic hydrodynamics to study the physics of ultrarelativistic heavy-ion collisions. We then highlight the main ingredients of the 3+1D quasiparticle anisotropic hydrodynamics model including the underlying symmetry assumptions and present phenomenological comparisons with experimental data at different collision energies. These comparisons show that anisotropic hydrodynamics can describe many bulk observables of the quark-gluon plasma.

Simple model to include initial-state and hot-medium effects in the computation of quarkonium nuclear modification factor

Quarkonium suppression is one of the more useful observables to obtain information about the hot medium created in ultrarelativistic heavy-ion collisions. In this manuscript, we discuss a simple way to implement both the initial-state effects and the hot-medium evolution, and to compute the quarkonium nuclear modification factor if the survival probability for a bound state at a given energy density is known. Based on the Glauber model, the temperature of the evolving medium and the centrality dependence of the nuclear modification factor will be analysed.

Particles multiplicity based on rapidity in Landau and artificial neural network (ANN) models

In this paper, artificial neural network (ANN) model is used to estimate the multiplicity per rapidity for charged pions and kaons observed in various high-energy experiments from central [Formula: see text] heavy-ion collisions with energies ranging from 2–200 GeV, and then compared to available experimental data, including RHIC-BRAHMS experiment, and covering the energy range of the future accelerator facilities at NICA and FAIR. We also used Landau hydrodynamical approach, which has a better description for the evolution of hot and dense matter produced in ultra-relativistic heavy-ion collisions. The approach is fitted to both results estimated from experiment and ANN simulation. We noted that the Landau model accurately reproduces the entire range of multiplicity per rapidity for all created particles at all energies. Also ANN model can reproduce the multiplicity per rapidity very well for all the considered particles. This encourages us to use ANN model to predict the multiplicity per rapidity for [Formula: see text] particles at energies [Formula: see text] and [Formula: see text] GeV.

Towards solving the puzzle of high temperature light (anti)-nuclei production in ultra-relativistic heavy ion collisions

The creation of loosely bound objects in heavy ion collisions, e.g. light clusters, near the phase transition temperature (Tch≈155 MeV) has been a puzzling observation that seems to be at odds with Big Bang nucleosynthesis suggesting that deuterons and other clusters are formed only below a temperature T≈0.1−1 MeV. We solve this puzzle by showing that the light cluster abundancies in heavy ion reactions stay approximately constant from chemical freeze-out to kinetic freeze-out. To this aim we develop an extensive network of coupled reaction rate equations including stable hadrons and hadronic resonances to describe the temporal evolution of the abundancies of light (anti-)(hyper-)nuclei in the late hadronic environment of an ultrarelativistic heavy ion collision. It is demonstrated that the chemical equilibration of the light nuclei occurs on a very short timescale as a consequence of the strong production and dissociation processes. However, because of the partial chemical equilibrium of the stable hadrons, including the nucleon feeding from Δ resonances, the abundancies of the light nuclei stay nearly constant during the evolution and cooling of the hadronic phase. This solves the longstanding contradiction between the thermal fits and the late stage coalescence (and the Big Bang nucleosynthesis) and explains why the observed light cluster yields are compatible with both a high chemical production temperature and a late state emission as modeled by coalescence. We also note in passing that the abundancies of the light clusters in the present approach are in excellent agreement with those measured by ALICE at LHC.

Direct Photon Production in High-Energy Heavy Ion Collisions within the Integrated Hydrokinetic Model

The results on description of direct photon yields, transverse momentum spectra, and flow harmonics, measured in ultrarelativistic heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) for different collision centrality classes, analyzed within the Integrated Hydrokinetic Model (iHKM) are reviewed. The iHKM simulation results, corresponding to the two opposite approaches to the matter evolution treatment at the final stage of the system’s expansion within the model, namely, the chemically equilibrated and the chemically frozen evolution, are compared. The so-called “direct photon puzzle” is addressed, and its possible solution, suggesting the account for additional photon emission at confinement, is considered.

Hadron production within a full transport approach with statistical hadronization mechanism at RHIC and LHC energies

We present for the first time results on final hadron production, with and without strangeness content, in Ultrarelativistic Heavy Ion Collisions at RHIC and LHC center of mass energies obtained combining a full 3+1D relativistic Boltzmann transport approach with a statistical hadronization mechanism. The non-perturbative interaction between quarks and gluons is described by means of a quasi-particle approach that permits to have an Equation of State close to lattice QCD. The resulting framework naturally includes both shear and bulk viscous effects. The 3+1D full transport evolution is converted to hadrons by mean of a realistic freeze-out hypersurface considering all known hadron resonances and by performing resonance decays. We present results on charged-hadron multiplicity, identified-particle spectra and identified-particle elliptic flow of π, K and p produced at RHIC and LHC energies for different centralities.