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Jet substructure in heavy-ion collisions is a rapidly evolving area with lots of intriguing new measurements. This contribution presents a selection of recent jet-substructure measurements from experiments at the LHC, in particular, soft-drop groomed radii of jets and reclustered large-radius jets from ATLAS, jet axis difference and generalized jet angularities from ALICE, as well as dijet shapes and b-jet shapes from the CMS experiment.

In the recent decades of high energy physics research, it was demonstrated that strongly interacting quark-gluon plasma (sQGP) is created in ultra-relativistic nucleus–nucleus collisions. Investigation and understanding of properties of the hadronic matter is among the important goals of NA61/SHINE collaboration at CERN SPS. Mapping of the phase diagram is achieved by varying the collision energy ($5\mathrm{\text{GeV}}<\sqrt{s_{\mathrm{\text{NN}}}}<17\mathrm{\text{GeV}}$) and by changing the collision system ($\mathrm{\text{p}}+\mathrm{\text{p}}$, $\mathrm{\text{p}}+\mathrm{\text{Pb}}$, $\mathrm{\text{Be}}+\mathrm{\text{Be}}$, $\mathrm{\text{Ar}}+\mathrm{\text{Sc}}$, $\mathrm{\text{Xe}}+\mathrm{\text{La}}$, $\mathrm{\text{Pb}}+\mathrm{\text{Pb}}$).

We report on the measurement of femtoscopic correlations in intermediate systems at intermediate SPS energies. Interpreting the results of measurements within the symmetric Lévy source formalism, we discuss the values of Lévy source parameters as a function of average pair transverse mass. One of the physical parameters is particularly important, the Lévy exponent $\alpha$, which describes the shape of the source and may be related to the critical exponent $\eta$ in the proximity of the critical point. Therefore, measuring it may shed light on the location of the critical endpoint of the QCD phase diagram.

Studying heavy-flavor production in high-energy heavy-ion collisions (HIC) can enhance our comprehension of parton interactions with the quark-gluon plasma (QGP) created in these collisions. Due to their significant mass, heavy quarks (charm and bottom) are mainly generated during the initial phase of HIC when hard scatterings are prevalent, and experience the entire evolution of the QGP. One way to study heavy quarks is through the measurement of electrons from heavy-flavor hadron decay, heavy-flavor electrons (HFE). In this contribution, we present the analysis of HFE at low transverse momentum ($p_{\mathrm{\text{T}}}$) in Au+Au collisions at $\sqrt{s_{\mathrm{\text{NN}}}}=54.4$GeV using data taken in 2017 by the STAR experiment. The strong HFE suppression was already observed in the central Au+Au collisions at $\sqrt{s_{\mathrm{\text{NN}}}}=200$GeV. Measuring heavy-flavor quark nuclear modification factors below the RHIC top energy offers new insights on the in-medium energy loss, especially the collisional energy loss which is dominant at low $p_{\mathrm{\text{T}}}$.

In high-energy physics, quantum statistical correlation measurements are very important for getting a good picture of how a particle-emitting source is structured in space and time, as well as its thermodynamic properties and inner dynamics. It is necessary to take into account the various final state effects since they have the potential to alter the observed femtoscopic correlation functions. Protons are affected mostly by the strong interaction, whereas other charged particles are mostly influenced by the Coulomb interaction. The interaction of the particles under investigation with the fireball or the expanding cloud of the other particles in the final state might also have significant consequences. This may case the trajectories of the particles to shift. This phenomenon can be viewed as an Aharonov–Bohm effect since the pair’s alternate tracks reveal a closed loop with an internal field. We investigate a numerical solution for a toy model to study the modifications of Bose–Einstien correlation function strength, which is sensitive to this effect.

In high-energy heavy-ion physics experiments, a state of matter is created that existed in the early Universe: the quark-gluon plasma. This strongly interacting matter exists in today’s experiments only within a range of a few femtometers and for a duration of a few femtometers per speed of light, making its resolution with optical tools impossible. However, there is a method that allows for a closer look into the structure of the quark-gluon plasma: femtoscopy. Initially used in astronomy, femtoscopy is based on the quantum mechanical indistinguishability of identical particles, which causes them to arrive at detectors in a correlated manner. The measurable correlation is related to the space–time structure of the particle-emitting source, which in heavy-ion physics is the quark-gluon plasma created in collisions. For free particles, a relatively simple relationship exists between the source and the correlation (essentially a Fourier transform). However, this relationship becomes complex when accurately accounting for the repulsive Coulomb interaction between final-state electrically charged particles. Our paper presents a new method that is more precise than previously used ones, yet less computationally demanding, especially for the exotic source function shapes. Mathematically, the method is interesting because it exactly handles many emerging integrals and limits. Practically, it is ready for use in experimental analyses.

The Average Phase Space Density (APSD) of very high energy nuclear collisions at the total "freeze-out" temperature offers an indirect but convenient tool to assess the merit and worth of the pionisation models. We have attempted to apply here a specific multiple production model with a view to estimating the APSD of pions for a set of sulphur-induced ultrarelativistic heavy-ion collisions in a unified manner, to compare them finally with the experiment-based results of NA35 and NA44-groups at CERN and also with the calculational results based on the thermal model. The specific implications of the present approach have also been pointed out in the end.

We present analytical results for the equation of state for hot gluon plasma obtained with an effective perturbation based on hard thermal loops resummation theory. The effective two-loop results depend on Debye screening and finite width of gluons as physical parameters. Considering next-to-leading Debye mass and finite width effects, we find the equation of state to be in good agreement with recent lattice results for T≳2T_c.

We consider one-loop effective action of SU(3) QCD with a most general constant chromomagnetic (chromoelectric) background which has two independent Abelian field components. The effective potential with a pure magnetic background has a local minimum only when two Abelian components and of color magnetic field are orthogonal to each other. The nontrivial structure of the effective action has important implication in estimating quark–gluon production rate and p_T-distribution in quark–gluon plasma. In general the production rate depends on three independent Casimir invariants, in particular, it depends on the relative orientation between chromoelectric fields.

A complete expression for the p_T-distribution of the gluon production rate in the homogeneous chromoelectric field has been obtained. Our result contains a new additional term proportional to the singular function . We demonstrate that the presence of this term is consistent with the dual symmetry of QCD effective action and allows to reproduce the known result for the total imaginary part of the effective action after integration over transverse momentum.

In continuation of our previous works, we attempt here to understand the nature of data on direct photon and neutral pion production in the latest RHIC experiments at for all the different interactions studied therein from the viewpoint of a nonstandard outlook and approach as described in Refs. 4 and 5 here. It is found that the proposed model could account for the data-sets with a fair degree of success.

The shear viscosity of quark–gluon plasma (QGP) at leading logarithm order at finite temperature and chemical potential in weakly coupled limit is studied by solving transport equations. The result shows that the chemical potential effect adds a positive μ²/T² correction to the pure temperature case and thus increases the shear viscosity.

Quark matter both in terrestrial experiment and in astrophysics is briefly reviewed. Astrophysical quark matter could appear in the early Universe, in compact stars, and as cosmic rays. Emphasis is put on quark star as the nature of pulsars. Possible astrophysical implications of experiment-discovered sQGP are also concisely discussed.

We propose the enhancement of Λ_c yield in heavy ion collisions at RHIC and LHC as a novel signal for the existence of diquarks in the strongly coupled quark-gluon plasma produced in these collisions as well as in the Λ_c. Assuming that stable bound diquarks can exist in the quark-gluon plasma, we argue that the yield of Λ_c would be increased by two-body collisions between [ud] diquarks and c quarks, in addition to normal three-body collisions among u, d and c quarks. A quantitative study of this effect based on the coalescence model shows that including the contribution of diquarks to Λ_c production indeed leads to a substantial enhancement of the Λ_c/D ratio in heavy ion collisions.

In this letter we propose a new method of calculating the equation of state (EOS) of quasi-particle model of quark–gluon plasma at finite chemical potential. In the quasi-particle model the quark propagator has the form of a free quark propagator with a temperature and density dependent effective mass. From this quark propagator the EOS at finite chemical potential is calculated using the model-independent formula proposed in Refs. 16 and 17. A comparison between our EOS and the cold, perturbative EOS of QCD proposed in Ref. 23 is made.

We briefly discuss the possible decoherence observed at the LHC emphasizing that the value of the average transverse momentum at can be interpreted as a manifestation of the deviation from the mechanism of the transient state of rotating matter.

Heavy quarkonium states are considered as one of the key observables for the study of the phase transition from a system made of hadrons towards a Quark–Gluon Plasma (QGP). In the last 25 years, experiments at CERN and Brookhaven have studied collisions of heavy ions looking for a suppression of charmonia/bottomonia, considered as a signature of the phase transition. After an introduction to the main concepts behind these studies and a short review of the SPS and RHIC results, I will describe the results obtained in Pb–Pb collisions by the ALICE experiment at the LHC. The ALICE findings will be critically compared to those of lower energy experiments, to CMS results, and to model calculations. The large cross-sections for heavy-quark production at LHC energies are expected to induce a novel production mechanism for charmonia in heavy-ion collisions, related to a recombination of pairs along the history of the collision and/or at hadronization. The occurrence of such a process at the LHC will be discussed. Finally, prospects for future measurements will be shortly addressed.

This is a continuation of recent studies of ϒ(nS) production at the LHC in pp collisions. Our previous studies were for rapidity y = -1 to 1 for the CMS detector, while the present study is for y = 2.5 to 4.0 at the LHC.

Based on an analogy with topologically ordered new state of matter in condensed matter systems, we propose a low energy effective field theory for a parity conserving liquid-like quark–gluon plasma (QGP) around critical temperature in quantum chromodynamics (QCD) system. It shows that below a QCD gap which is expected several times of the critical temperature, the QGP behaves like topological fluid. Many exotic phenomena of QGP near the critical temperature discovered at Relativistic Heavy Ion Collision (RHIC) are more readily understood by the suggestion that QGP is a topologically ordered state.

Transverse momentum $(p_T)$ distributions of primary charged particles were compared to simulations using the Ultra Relativistic Quantum Molecular Dynamics (UrQMD) transport model and the HIJING 1.0 model in minimum bias p–Pb collisions at $\sqrt{s_{NN}}=5.02\mathrm{\text{TeV}}$ in the pseudorapidity $(\eta )$ regions: $\eta <0.3$, $0.3<\eta <0.8$ and $0.8<\eta <1.3$ and in the transverse momentum range $0.5<p_T<20\mathrm{\text{GeV}}/c$. The simulated distributions were then compared with the ALICE data and it was observed that UrQMD predicts systematically higher yields than HIJING 1.0. Both codes cannot describe the experimental data in the range of $0.5<p_T<20\mathrm{\text{GeV}}/c$, though in the region of $p_T>5\mathrm{\text{GeV}}/c$ the model predictions are very close to the experimental results for particles with $\left|\eta \right|<0.3$, $0.3<\eta <0.8$. The ratio of the yield at forward pseudorapidity to that at $\left|\eta \right|<0.3$ was also studied. It was observed that the predictions of the models depend on $\eta$. In the experiment there is no essential difference of yields for particles from the intervals of $\left|\eta \right|<0.3$, $0.3<\eta <0.8$ and $0.8<\eta <1.3$. The differences are significant for the models where the ratios are systematically less than 1. This means that the results are not connected to a medium effect but reflect the Cronin effect. We are led to conclude that the codes cannot take into account satisfactorily the leading effect due to the asymmetric p–Pb fragmentation.

Transverse momentum distributions and nuclear modification factor of integrated charged particles yield produced in p+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV are investigated in mid-rapidity regions of $-0.5<y<0$ at one event multiplicity class 0–5% in the transverse momentum range of $0<p_T<$20 GeV/c. Simulations with EPOS-1.99, EPOS-LHC and QGSJETII-04 are compared with the ALICE data. All three models are in good agreement with each other up to $p_T\sim$3 GeV/c for transverse momentum distributions but after that QGSJETII-04 overpredicts the experimental data. EPOS-LHC seems to describe the experimental data quite well as compared to the other two models. The ratios of the kaons to pions and protons to pions are also presented where again EPOS-LHC provides good agreement with the ALICE data. In case of the nuclear modification factor, for (anti) pions and (anti) kaons, the model distribution is around 1, whereas it is greater than 1 in case of (anti) protons which shows Cronin enhancement.