Gluon Plasma Research Articles

Probing parton propagation in heavy-ion collisions with ALICE heavy-flavour measurements

Heavy quarks (charm and beauty) are valuable probes for investigating the properties of the quark–gluon plasma (QGP) formed in ultra-relativistic heavy-ion collisions, as they are mainly produced through hard-scattering processes prior to the formation of the QGP, and their number is conserved during the subsequent QGP evolution. Measurements of the nuclear modification factor RAA of charm and beauty hadrons allow us to characterise the in-medium energy loss of heavy quarks while traversing the QGP. Information on their diffusion and degree of participation in the collective motion of the medium can be obtained by measuring the elliptic-flow coefficient v2 of heavy-flavour particles. Complementary insights into heavy-quark fragmentation and energy redistribution can be obtained by measuring angular correlations involving heavy-flavour particles. In this contribution, the recently published results on the non-prompt v2 coefficient of D0 mesons are presented, comparing them with those of other particle species in Pb–Pb collisions at √SNN = 5.02 TeV. Additionally, we report the recent findings on the RAA of prompt D mesons and Λc+ baryons in Pb–Pb collisions at the same energy. Furthermore, we discuss the new Pb–Pb results on angular correlations between heavy-flavour decay electrons and charged particles in the same collision system.

Exploring medium properties using jet substructure measurements in pp and Pb–Pb collisions with ALICE

Various studies of jet substructure in heavy-ion collisions offer a consistent picture of QCD medium interactions and a diverse path towards further differentiating energy loss mechanisms. Some results, however, remain disjoint: the jet mass and jet angularities, including girth and thrust, are stronglycorrelated observables which have given seemingly conflicting answers on the angular quenching of jets traversing the quark–gluon plasma (QGP). ALICE has carried out new systematic measurements of these and other perturbativelycalculable angularities using consistent definitions, resolving the girth-mass problem, and revealing quenching effects at broad angles. Concurrently, applying Soft Drop grooming isolates the narrowing in the core of quenched jets. Grooming can also be employed to resolve medium scattering centers, with varying methods used to focus on regions of the splitting phase space. We present the first application of dynamical grooming in heavy-ion collisions to search for excess kT,g emissions as a signature of point-like scatters, providing new constraints on searches for in-medium Molière scattering. We also present a novel shift from studying jet-medium opacity from the angular perspective to a time-like one. By employing a new time reclustering strategy, we potentially enable a time-dependent study of jet substructure observables. We compare all results to assorted jet quenching models, providing new critical information on medium evolution as a function of angular, momentum, and time structure.

Search for anomalous chiral effects in heavy-ion collisions with ALICE

The interplay between the chiral anomaly and the strong magnetic or vortical fields created in noncentral heavy-ion collisions can lead to various anomalous chiral effects in the quark–gluon plasma, including the chiral magnetic effect (CME), the chiral magnetic wave (CMW), and the chiral vortical effect (CVE). In this proceeding, recent ALICE measurements of these effects are summarized. Utilizing Event Shape Engineering, fractions of CME and CMW signals extracted in Pb–Pb collisions at √SNN = 5.02 TeV are consistent with zero within uncertainties. The CVE is studied using azimuthal correlations between baryon pair Λ–p with Λ–h and h–h as reference. These measurements provide new insights into the experimental search for anomalous chiral effects in heavy-ion collisions.

Results from PHENIX

The PHENIX experiment at the Relatimay invistic Heavy Ion Collider has collected data scanning system sizes from p+p and 3He+Au to Au+Au and U+U at collision energies from √SNN = 7.7 to 510 GeV. The extensive measurements from these data improve our understanding of the Quark Gluon Plasma and the origin of the proton spin. PHENIX’s measurements of π0 mesons, photons, heavy flavor particles, and jets probe the formation of the QGP, and measurements of azimuthal anisotropies are sensitive to collective effects and the initial geometry of the collision. A selection of recent results from PHENIX with an emphasis on results from heavy ion collisions are discussed.

Experimental overview on open-heavy flavours

Heavy flavours, i.e. charm and beauty quarks, are recognised as excellent probes of the colour-deconfined medium created in ultrarelativistic heavy–ion collisions, the quark–gluon plasma (QGP). In this document, the most recent measurements of heavy-flavour hadrons in heavy-ion collisions are summarised. Measurements of nuclear modification factors and angular anisotropies of open charm and beauty hadrons are reported to investigate the properties of the heavy-quark interactions in the QGP. A particular focus is given to the measurement of heavy-flavour baryons and hadrons with strangequark content for the study of the hadronisation mechanisms in both heavy–ion and proton–proton collisions. Finally, the polarisation of the charm vector mesons D*+ and J/ψ in heavy–ion collisions is 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.

The construction of the sPHENIX detector and status of its commissioning

sPHENIX is the first new major detector at RHIC in over twenty years. It is designed for pioneering studies of the Quark Gluon Plasma and Cold QCD phenomena using high-pT jet and heavy flavor probes with a broad kinematic reach and a capability to take large statistics sets of A+A, p+p and p+A data. sPHENIX construction was completed in April 2023. It was commissioned and took first Au+Au data in the RHIC 2023 Run. This paper describes the details of the detector design, challenges of sPHENIX construction, progress on the commissioning and first data from the RHIC 2023 run.

Equation of state of a hot-and-dense quark gluon plasma: Lattice simulations at real μB vs. extrapolations

The equation of state of the quark gluon plasma is a key ingredient of heavy ion phenomenology. In addition to the traditional Taylor method, several novel approximation schemes have been proposed with the aim of calculating it at finite baryon density. In order to gain a pragmatic understanding of the limits of these schemes, we compare them to direct results at μB > 0, using reweighting techniques free from an overlap problem. We use 2stout improved staggered fermions with 8 time-slices and cover the entire RHIC BES range in the baryochemical potential, up to μB/T = 3. This work is based on Ref. [1].

The Entropy of the Quark Gluon Plasma at Finite Temperature

In this paper we have calculated the thermal partition function of the thermo- dynamical system of Quark Gluon Plasma and also we have calculated the entropy of quark gluon plasma for the zero chemical potential at the thermal equilibrium condition.

Measurement of the radius dependence of charged-particle jet suppression in Pb–Pb collisions at [formula omitted

The ALICE Collaboration reports a differential measurement of inclusive jet suppression using pp and Pb–Pb collision data at a center-of-mass energy per nucleon–nucleon collision sNN=5.02 TeV. Charged-particle jets are reconstructed using the anti-kT algorithm with resolution parameters R=0.2, 0.3, 0.4, 0.5, and 0.6 in pp collisions and R=0.2, 0.4, 0.6 in central (0–10%), semi-central (30–50%), and peripheral (60–80%) Pb–Pb collisions. A novel approach based on machine learning is employed to mitigate the influence of jet background. This enables measurements of inclusive jet suppression in new regions of phase space, including down to the lowest jet pT≥40 GeV/c at R=0.6 in central Pb–Pb collisions. This is an important step for discriminating different models of jet quenching in the quark–gluon plasma. The transverse momentum spectra, nuclear modification factors, derived cross section, and nuclear modification factor ratios for different jet resolution parameters of charged-particle jets are presented and compared to model predictions. A mild dependence of the nuclear modification factor ratios on collision centrality and resolution parameter is observed. The results are compared to a variety of jet-quenching models with varying levels of agreement.

Mapping properties of the quark gluon plasma in Pb-Pb and Xe-Xe collisions at energies available at the CERN Large Hadron Collider

Mapping properties of the quark gluon plasma in Pb-Pb and Xe-Xe collisions at energies available at the CERN Large Hadron Collider

Soft and hard scales of the transverse momentum distribution in the color string percolation model

In color string models, the transverse momentum distribution (TMD) is obtained through the convolution of the Schwinger mechanism with the string tension fluctuations distribution. Considering a q-Gaussian distribution for these fluctuations, the TMD becomes a hypergeometric confluent function that adequately reproduces the characteristic scales at low and high p T values. In this approach, the hard scale of the TMD is a consequence of considering a heavy-tailed distribution for the string tension fluctuations whose width rises as , multiplicity or centrality increases. In this paper, we introduce broader information of the TMD in the color string percolation model by determining the color suppression factor, which now also depends on the parameters of the q-Gaussian. To this end, we analyze the reported data on pp and AA collisions at different center of mass energies, multiplicities, and centralities. In particular, for minimum bias pp collisions, we found that the q-Gaussian parameters and the effective temperature are monotonically increasing functions of the center of mass energy. Similar results are found for AA collisions as a function of the centrality at fixed . We summarize these results in a phase diagram that indicates the q-Gaussian parameters region allowing the quark–gluon plasma formation.

An aerogel RICH detector for the next generation heavy-ion experiment at LHC

The ALICE collaboration is proposing a new apparatus, ALICE 3, to investigate the Quark Gluon Plasma (QGP) properties. In this context, conceptual studies for the development of a RICH detector for ALICE 3 are ongoing. The proposed baseline layout is a proximity-focusing RICH, using aerogel (refractive index n= 1.03 at λph= 400 nm) as Cherenkov radiator and a layer of Silicon Photomultipliers (SiPM) for the photon detection. A multi-layer (focusing) aerogel layout, with increasing refractive index, is also considered. If good time resolution of ≈ 20 ps can be achieved in the SiPM photons detectors, they can be able to identify charged hadrons via TOF measurements. The detector specifications and performance, obtained by means of dedicated Monte Carlo simulation, are presented. The R&D challenges related to the proposed design are also discussed.

Viscous QCD medium effects on the bottom quark transport coefficients

The bottom quark transport coefficients, i.e., drag and diffusion coefficients, have been studied for the collisional and soft gluon radiative processes within the viscous QCD medium. The thermal medium effects are incorporated using the effective fugacity quasiparticle model (EQPM). Both the shear and bulk viscous effects at leading order are embedded through the near-equilibrium distribution functions of the quark–gluon plasma (QGP) constituent quasiparticles. The transport coefficients’ dependence on the bottom quark’s initial momentum and QGP temperature have been investigated. The relative dominance of the radiative over the collisional process for the bottom quark seems to occur at a higher initial momentum compared to that of the charm quark. In contrast, the effect of the viscous corrections seems to be more for the charm quark. Furthermore, we also investigate the validity of the Einstein fluctuation–dissipation theorem for our analysis.

Effect of a Wake-Field on the Dissociation of Quarkonium in Collisional Quark–Gluon Plasma

We have studied wake effects on the dissociation of heavy quarkonia states J/ψ and Y by introducing an in-medium modification to the inter-quark potential. The wakes in the quark–gluon plasma were modeled using linear response theory using a dynamic dielectric function obtained from kinetic theory (Boltzmann equation) with a Bhatnagar–Gross–Krook (BGK) collision term. The in-medium modified potential was used to investigate the dissociation character depending on various parameters such as the velocity of quarkonium moving through the medium and the collision frequency. We have also calculated critical values of the dissociation temperature. Modifications of the dissociation energy due to wake-field effects were found.

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.

Holographic energy loss near critical temperature in an anisotropic background

We study the energy loss of a quark moving in a strongly coupled quark gluon plasma under the influence of anisotropy. The heavy quark drag force, diffusion coefficient, and jet quenching parameter are calculated using the Einstein–Maxwell-dilaton model, where the anisotropic background is characterized by an arbitrary dynamical parameter A. Our findings indicate that as the anisotropic factor A increases, the drag force and jet quenching parameter both increase, while the diffusion coefficient decreases. Additionally, we observe that the energy loss becomes more significant when the quark moves perpendicular to the anisotropy direction in the transverse plane. The enhancement of the rescaled jet quenching parameters near critical temperature T c , as well as drag forces for a fast-moving heavy quark is observed, which presents one of the typical features of quantum chromodynamics phase transition.

Probing universal dynamics with topological data analysis in a gluonic plasma

Probing universal dynamics with topological data analysis in a gluonic plasma

Thermodynamic and cosmological parameters of early stages of the universe

The early Universe was characterized by the presence of heavy particles that decoupled at different temperatures leading to different phases of the Universe. This had some consequences on the time evolution of the thermodynamic and the cosmological parameters characterizing each phase of the early Universe. In this study, we derive the analytic expressions of the equations governing the time evolution of these parameters using the equations of state of the MIT bag model describing the quark–gluon plasma era. In addition, using the equations of state derived from considering the recent results of the lattice QCD simulations, we solve numerically the differential equation governing the time evolution of the energy density in the early Universe. The time evolution of the parameters under concern including the energy density, entropy density, temperature, pressure in addition to Hubble parameter and scale factor can then be estimated as will be presented in this work.

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.