Ultrarelativistic Heavy-ion Collisions Research Articles

Dirac sea effects on heavy quarkonia decay widths in magnetized matter: A field theoretical model of composite hadrons

We study the partial decay widths of charmonium (bottomonium) states to $D\bar D (B\bar B)$ mesons in magnetized (nuclear) matter using a field theoretic model of composite hadrons with quark (and antiquark) constituents. These are computed from the mass modifications of the decaying and produced mesons, including the nucleon Dirac sea effects within a chiral effective model. The Dirac sea contributions are observed to lead to an rise (drop) in the quark condensates as the magnetic field is increased, an effect called the (inverse) magnetic catalysis. In the presence of a magnetic field, there are mixings of spin 0 (pseudoscalar) and spin 1 (vector) states (PV mixing) The nucleon Dirac sea effects are observed to be significant and the anomalous magnetic moments (AMMs) of the nucleons are observed to play an important role. For $\rho_B$=0, there is observed to be magnetic catalysis (MC) without and with AMMs, whereas, for $\rho_B=\rho_0$, the inverse magnetic catalysis (IMC) is observed when the AMMs are taken into account, contrary to MC, when the AMMs are ignored. The magnetic field effects on the heavy quarkonium decay widths should have observable consequences on the production of the hidden and open heavy flavour mesons from ultra-relativistic peripheral heavy ion collision experiments, at RHIC and LHC, where the produced magnetic fields are extremely large.

Generalized effective string rope model for the initial stages of ultrarelativistic heavy ion collisions

We present a Generalized Effective String Rope Model (GESRM) for the description of the initial state of relativistic heavy ion collisions. We start from the Effective String Rope Model (ESRM) and take into account fluctuations in the initial state following the Glauber Monte Carlo approach. Results from symmetric Au+Au collisions at different impact parameters and asymmetric A+Au head on collisions are presented at RHIC energies. The produced initial state is used as an initial condition for further hydrodynamical calculations.

Heavy quarkonia in a baryon asymmetric strongly magnetized hot quark matter

Recently there is a resurrection in the study of heavy quark bound states in a hot and baryonless matter with an ambient magnetic field but the matter produced at heavy-ion collider experiments is not perfectly baryonless, so we wish to explore the effect of small baryon asymmetry on the in-medium properties of the heavy quark bound states submerged in a strongly magnetized hot quark matter. Therefore, we have first given a revisit to the general covariant tensor structure of gluon self-energy in the above environment to compute the resummed propagator for gluons. This resummed propagator embodies the properties of medium, which gets translated into the (complex) potential between Q and Q¯ placed in the medium. We observe that the baryon asymmetry makes the real-part of potential slightly more attractive and weakens the imaginary-part. This opposing effects thus lead to the enhancement of binding energies and the reduction of thermal widths of QQ¯ ground states, respectively. Finally, the properties of quarkonia thus deciphered facilitate to compute the dissociation points of J/ψ and ϒ, which are found to have slightly larger values in the presence of baryon asymmetry. For example, J/ψ gets dissociated at 1.64Tc, 1.69Tc, and 1.75Tc, whereas ϒ is dissociated at 1.95Tc, 1.97Tc and 2.00Tc, for μ=0,60 and 100 MeV, respectively. This observation prevents early dissociation of quarkonia in the matter produced at ultrarelativistic heavy ion collisions with a small net baryon number, compared to the ideal baryonless matter.

Principal Component Analysis of azimuthal flow in intermediate-energy heavy-ion reactions

Principal Component Analysis (PCA) via Singular Value Decomposition (SVD) of large datasets is an adaptive exploratory method to uncover natural patterns underlying the data. Several recent applications of the PCA-SVD to event-by-event single-particle azimuthal angle distribution matrices in ultra-relativistic heavy-ion collisions at RHIC-LHC energies indicate that the sine and cosine functions chosen a priori in the traditional Fourier analysis are naturally the most optimal basis for azimuthal flow studies according to the data itself. We perform PCA-SVD analyses of mid-central Au+Au collisions at Ebeam/A=1.23 GeV simulated using an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model to address the following two questions: (1) if the principal components of the covariance matrix of nucleon azimuthal angle distributions in heavy-ion reactions around 1 GeV/nucleon are naturally sine and/or cosine functions and (2) what if any advantages the PCA-SVD may have over the traditional flow analysis using the Fourier expansion for studying the EOS of dense nuclear matter. We find that (1) in none of our analyses the principal components come out naturally as sine and/or cosine functions, (2) while both the eigenvectors and eigenvalues of the covariance matrix are appreciably EOS dependent, the PCA-SVD has no apparent advantage over the traditional Fourier analysis for studying the EOS of dense nuclear matter using the azimuthal collective flow in heavy-ion collisions.

Jet fragmentation via azimuthal angular correlations of electrons from heavy flavor decay in pp, p -Pb, and Pb-Pb collisions using PYTHIA8+Angantyr calculations

Measurements in heavy flavor azimuthal angular correlation provide insight into the production, propagation, and hadronization of heavy flavor jets in ultrarelativistic hadronic and heavy-ion collisions. These measurements across different colliding systems, such as $p\text{\ensuremath{-}}A$ and $A\text{\ensuremath{-}}A$, help us isolate the possible modification in particle production due to cold nuclear matter (CNM) effects and the formation of quark-gluon plasma (QGP), respectively. Jet correlation studies give direct access to the initial parton dynamics produced in these collisions. This article studies the azimuthal angular correlations of electrons from heavy flavor hadron decays in $pp, p$-Pb, and Pb-Pb collisions at $\sqrt{{s}_{NN}}=5.02$ TeV using $\text{PYTHIA8}+\text{Angantyr}$. We study the production of heavy flavor jets with different parton level processes, including multiparton interactions, different color reconnection prescriptions, and initial and final state radiation processes. In addition, we add the hadron-level processes, i.e., Bose-Einstein and rescattering effects, to quantify the effect due to these processes. The heavy flavor electron correlations are calculated in the different trigger and associated ${p}_{\mathrm{T}}$ intervals to characterize the impact of hard and soft scattering in the various colliding systems. The yields and the sigmas associated with the near-side (NS) and away-side (AS) correlation peaks are calculated and studied as a function of associated ${p}_{\mathrm{T}}$ for different trigger ${p}_{\mathrm{T}}$ ranges.

Jet fragmentation via azimuthal angular correlations of heavy flavors in pp collisions at s=7 TeV

Measurements in heavy-flavor azimuthal angular correlation provide insight into the production, propagation, and hadronization of heavy-flavor jets in ultrarelativistic hadronic and heavy-ion collisions. These measurements across different particle species help to isolate the possible modification in particle production and fragmentation due to different mass and quark contents. Jet correlation studies give direct access to the initial parton dynamics produced in these collisions. This article studies the azimuthal angular correlations of heavy-flavor hadrons (charm and beauty mesons and charm baryons) in $pp$ collisions at $\sqrt{s}=7$ TeV using pythia8. We study the production of heavy-flavor jets with different parton-level processes, including multiparton interactions and different color reconnection prescriptions. The heavy-flavor hadrons correlations are calculated in the different triggers and associated ${p}_{\mathrm{T}}$ intervals to characterize the impact of hard and soft scattering. The yields and the widths associated with the near-side (NS) and away-side (AS) correlation peaks are calculated and studied as a function of associated ${p}_{\mathrm{T}}$ for different trigger ${p}_{\mathrm{T}}$ ranges.

The medium-modified gto coverline{c} splitting function in the BDMPS-Z formalism

The formalism of Baier-Dokshitzer-Mueller-Peigné-Schiff and Zakharov determines the modifications of parton splittings in the QCD plasma that arise from medium-induced gluon radiation. Here, we study medium-modifications of the gluon splitting into a quark-anti-quark pair in this BDMPS-Z formalism. We derive a compact path-integral formulation that resums effects from an arbitrary number of interactions with the medium to leading order in the 1/{N}_c^2 expansion. Analyses in the N = 1 opacity and the saddle point approximations reveal two phenomena: a medium-induced momentum broadening of the relative quark-anti-quark pair momentum that increases the invariant mass of quark-anti-quark pairs, and a medium-enhanced production of such pairs. We note that both effects are numerically sizeable if the average momentum transfer from the medium is comparable to the quark mass. In ultra-relativistic heavy-ion collisions, this condition is satisfied for charm quarks. We therefore focus our numerical analysis on the medium modification of gto coverline{c} , although our derivation applies equally well to gto boverline{b} and to gluons splitting into light-flavoured quark-anti-quark pairs.

Physics programme of the ALICE 3 experiment for the LHC Runs 5 and 6

Ultrarelativistic heavy-ion collisions are used to study the physics of strongly interacting matter under extreme conditions, similar to those of the early universe. In such collisions a deconfined state of quarks and gluons, the quark-gluon plasma (QGP), is formed. Nuclear collisions at the LHC provide access to the highest-temperature, longest-lived experimentally accessible QGP. After three years of Long Shutdown and intensive installation of detector and accelerator upgrades, ALICE is about to take data at a peak Pb–Pb collision rate of 50 kHz to further characterize the properties of the QGP. Even after the ambitious scientific programme for the upcoming Runs 3 and 4, open questions will remain. Therefore, a next-generation LHC heavy-ion experiment ALICE 3 is proposed for the 2030s. It should give access to next-level measurements of electromagnetic probes and heavy-flavour hadrons, including multi-charm states and exotic hadrons, inaccessible in the LHC Runs 3 and 4.

Medium-modifications of g → cc splitting

We study medium-modifications of the gluon splitting into a quark and anti-quark pair. Applying the Baier-Dokshitzer-Mueller-Peigné-Schiff and Zakharov (BDMPS-Z) formalism, we derive a path-integral formula for the in-medium g → qq¯ splitting function in the close-to-eikonal limit. Our analysis shows that there are two qualitatively different medium effects: transverse momentum broadening of qq¯ pairs and enhanced production of such pairs. We note that both effects are numerically sizeable if the average momentum transfer from the medium to the parton is at the quark mass scale. In ultra-relativistic heavy-ion collisions, this condition is realized by charm quarks, therefore we focus our numerical analysis on the medium-modifications of g → cc¯ splitting.

Resonance production and interaction from low to high energy

Measurements of short-lived hadronic resonances are used to probe the properties of the hadronic phase in ultra-relativistic heavy-ion collisions. Since these resonances have lifetimes comparable to that of the produced fireball, they are sensitive to the competitive re-scattering and regeneration effects in the hadronic gas, which modifies the observed particle momentum distributions and yields after hadronization. With different masses, quantum numbers, and quark content, hadronic resonances can provide insight into processes that determine the shapes of particle momentum spectra, strangeness production, and the possible onset of collective effects. The system size and collision-energy dependence of resonance production will be presented.

Charmonium, Bc and X(3872) Transport at the LHC

We deploy a kinetic-rate equation to evaluate the transport of J/ψ, ψ(2S), Bc and X (3872) in ultrarelativistic heavy-ion collisions and compare their production yields to experimental data from the Large Hadron Collider. The rate equation has two main transport parameters: the equilibrium limit and reaction rate for each state. The temperature-dependent equilibrium limits include charm- and bottom-quark fugacities based on their initial production. The reaction rates for charmonia, bottomonia and Bc rely on charm- and bottomquark masses and binding energies from a thermodynamic T-matrix approach. For the X (3872) particle, internal structure information is encoded in reaction rates and initial conditions in the hadronic phase via two different scenarios: a loosely bound hadronic molecule vs. a compact tetraquark.

Impact of the electromagnetic field on Z0 leptonic invariant mass in ultrarelativistic heavy ion collisions

The extraordinary strong magnetic field generated in ultrarelativistic heavy ion collisions makes it possible to investigate many novel effects in the hot QCD matter, and a direct probe of it thus becomes an urgent task in the field. Here we report a new way to probe it, where the leptonic invariant mass distribution of Z0 boson will be modified in the presence of the magnetic field due to the Lorentz force on the lepton pairs from the decay of Z0 boson. It is found that the magnetic field can decrease the mean value of Z0 leptonic invariant mass and increase its width, and both shifts approximately depend on the integral of the magnetic field over its time duration quadratically.

QCD sum rule analysis of heavy quarkonium states in magnetized matter: Effects of magnetic and inverse magnetic catalysis

In-medium masses of the $1S$ and $1P$ states of heavy quarkonia are investigated in the magnetized asymmetric nuclear medium, accounting for the Dirac sea effects, using a combined approach of chiral effective model and QCD sum rule method. Masses are calculated from the in-medium scalar and twist-2 gluon condensates, calculated within the chiral model. The gluon condensate is simulated through the scalar dilaton field, $\ensuremath{\chi}$ introduced in the model through a scale-invariance breaking logarithmic potential. Contribution of the Dirac sea is incorporated through the nucleonic tadpole diagrams. Treating the scalar fields as classical, the dilaton field, $\ensuremath{\chi}$, the isoscalar nonstrange $\ensuremath{\sigma}(\ensuremath{\sim}(⟨\overline{u}u⟩+⟨\overline{d}d⟩))$, strange $\ensuremath{\zeta}(\ensuremath{\sim}⟨\overline{s}s⟩)$ and isovector $\ensuremath{\delta}(\ensuremath{\sim}(⟨\overline{u}u⟩\ensuremath{-}⟨\overline{d}d⟩))$ fields, are obtained by solving their coupled equations of motion as derived from the chiral model Lagrangian. The effects of magnetic field are incorporated through the Dirac sea as well as the Landau energy levels of the protons, and the anomalous magnetic moments of the nucleons. The scalar fields modify appreciably with magnetic field due to the Dirac sea contribution. In-medium masses of the charmonium and bottomonium ground states are observed to have significant modifications with magnetic field due to the effects of (inverse) magnetic catalysis. In presence of an external magnetic field, there is mixing between the longitudinal component of the vector and the pseudoscalar mesons (PV mixing) in both quarkonia sectors, leading to a rise (drop) of the masses of $J/{\ensuremath{\psi}}^{||}({\ensuremath{\eta}}_{c})$ and ${\mathrm{\ensuremath{\Upsilon}}}^{||}(1S)({\ensuremath{\eta}}_{b})$ states. These might show in the experimental observables, e.g., the dilepton spectra in the noncentral, ultrarelativistic heavy ion collision experiments at RHIC and LHC, where the produced magnetic field is huge.

Electromagnetic interaction of low transverse momentum charged leptons with heavy nuclei in ultra-peripheral ultra-relativistic heavy-ion collisions

The photon–photon interaction in ultra-relativistic heavy-ion collision is a source of the charged lepton pairs. The photon-photon fusion leads to the lepton creation in broad configuration space around the “collision” point. Those created close to heavy nuclei may undergo strong electromagnetic interaction with them. The impact parameter space distributions of electrons/positrons and charged muons are calculated within the b-space EPA model of such collisions. The evolution of e^+/e^- and mu ^+/mu ^- distributions due to the electromagnetic interaction of leptons with nuclei is studied, and the distortion of rapidity and transverse momentum distributions are shown. A part of the analysis is independent of the production model. We show the first exploratory results for the reaction Pb + Pb at sqrt{s_{NN}} = 17.3 GeV (SPS) and 200 GeV (RHIC) energies. We provide results for selected creation points and when integrating over their positions as dictated by the b-space EPA model. We observe sizeable effects for e^+ / e^- and much smaller effects for mu ^+ / mu ^-. We predict a possible sizeable accumulation of leptons with rapidities close to the beam rapidity. The EM effects lead to asymmetry in the production of e^+ and e^- or mu ^+ and mu ^-.

Study of Bulk Properties of Strange Particles in Au+Au Collisions at sNN = 54.4 GeV.

We analyzed the transverse momentum pT spectra of various strange hadrons KS0, Λ(Λ¯) and Ξ-(Ξ¯+) at mid-rapidity (y) in different centrality intervals from Au+Au collisions at sNN= 54.4 GeV. The pT spectra of these strange hadrons are investigated by the Tsallis-like distribution, which satisfactorily fits the experimental data. The bulk properties of the medium produced in ultra-relativistic heavy-ion collisions at the kinetic freeze-out are reflected by measuring the hadron spectra. The effective temperature T, transverse flow velocity βT, and mean pT along with other parameters that are strongly dependent on centrality and particle specie are extracted. The effective temperature of multi-strange particle (Ξ-(Ξ¯+)) is larger as compared to singly-strange particles Λ(Λ¯) and KS0. Furthermore, the kinetic freeze-out temperature T, transverse flow velocity βT. and mean pT (⟨pT⟩) show a decreasing trend towards lower centrality, while the entropy parameter q increases from central to peripheral collisions. In addition, a positive correlation of ⟨pT⟩ and T and a negative correlation of q and T are also reported.

Flow correlations from a hydrodynamics model with dynamical freeze-out and initial conditions based on perturbative QCD and saturation

We extend the applicability of the hydrodynamics, perturbative QCD and saturation -based EKRT (Eskola-Kajantie-Ruuskanen-Tuominen) framework for ultrarelativistic heavy-ion collisions to peripheral collisions by introducing dynamical freeze-out conditions. As a new ingredient compared to the previous EKRT computations we also introduce a nonzero bulk viscosity. We compute various hadronic observables and flow correlations, including normalized symmetric cumulants, mixed harmonic cumulants, and flow--transverse-momentum correlations, and compare them against measurements from the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC) . We demonstrate that the inclusion of the dynamical freeze-out and bulk viscosity allows a better description of the measured flow coefficients in peripheral collisions and enables the use of an extended centrality range when constraining the properties of QCD matter in the future.

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.