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We propose a new method to investigate the existence and location of the conjectured high-temperature critical point of strongly interacting matter via contours of constant entropy density. By approximating these lines as a power series in the baryon chemical potential $\mu_B$, one can extrapolate them from first-principle results at zero net-baryon density, and use them to locate the QCD critical point, including the associated first-order and spinodal lines. As a proof of principle, we employ currently available continuum-extrapolated first-principle results from the Wuppertal--Budapest collaboration to find a critical point at a temperature and a baryon chemical potential of $T_c = 114.3 \pm 6.9$ MeV and $\mu_{B,c} = 602.1 \pm 62.1$ MeV, respectively. We advocate for a more precise determination of the required expansion coefficients via lattice QCD simulations as a means of pinpointing the location of the critical endpoint in the phase diagram of strongly interacting matter.

The PYTHIA8/ANGANTYR model for heavy ion collisions was recently updated with a mechanism for \textitglobal colour reconnection. The colour reconnection model used is QCD colour algebra inspired and enhances baryon production due to the formation of string junctions. In this paper, we present updates to the junction formation and string fragmentation mechanisms, connected to heavy quark fragmentation. This allows for the simulation of heavy quark fragmentation, using junction formation, in heavy ion collisions. The framework is validated for proton collisions, and we show results for charm baryon production in proton-lead collisions.

We present the results from our investigation of angular correlations between baryon pairs in the PYTHIA8 event generator. We show how colour reconnection models and hadronization mechanisms influence such angular correlations and in particular address the effect of gluons on the baryon production mechanism in the Lund string fragmentation model. We conclude by discussing the new theoretical ideas in comparison with the ALICE pp collision results for the baryon angular correlations. We propose a hypothesis for suppressing baryons produced in gluon jets and show how that may influence the angular correlations.

This review aims at providing an extensive discussion of modern constraints relevant for dense and hot strongly interacting matter. It includes theoretical first-principle results from lattice and perturbative QCD, as well as chiral effective field theory results. From the experimental side, it includes heavy-ion collision and low-energy nuclear physics results, as well as observations from neutron stars and their mergers. The validity of different constraints, concerning specific conditions and ranges of applicability, is also provided.

We present an updated version of the QCD-based colour reconnection model in PYTHIA8, where we constrain the range in impact parameter for which reconnections are allowed. In this way, we can introduce more realistic colour reconnections in the Angantyr model for heavy ion collisions, where previously only reconnections within separate nucleon sub-collisions have been allowed. We investigate how the new impact parameter constraint influences final states in pp collisions, and retune parameters of the multi-parton interaction parameters in PYTHIA to compensate so that minimum bias data are reproduced. We also study multiplicity distributions in pA collisions and find that, in order to counteract the loss in multiplicity due to the introduction of global colour reconnections, we need to modify some parameters in the Angantyr model while keeping the parameters tuned to pp fixed. With Angantyr we can then extrapolate to AA collisions without further parameter tuning and retaining a reasonable description of the basic multiplicity distributions.

We present a new model for building up complete exclusive hadronic final states in high energy nucleus collisions. It is a direct extrapolation of high energy pp collisions (as described by PYTHIA), and thus bridges a large part of the existing gap between heavy ion and high energy physics phenomenology. The model is inspired by the old Fritiof model and the notion of wounded nucleons. Two essential features are the treatment of multi-parton interactions and diffractive excitation in each NN sub-collision. Diffractive excitation is related to fluctuations in the nucleon partonic sub-structure, and fluctuations in both projectile and target are here included for the first time. The model is able to give a good description of general final-state properties such as multiplicity and transverse momentum distributions, both in pA and AA collisions. The model can therefore serve as a baseline for understanding the non-collective background to observables sensitive to collective behaviour. As PYTHIA does not include a mechanism to reproduce the collective effects seen in pp collisions, such effects are also not reproduced by the present version of Angantyr. Effects of high string density, shown to be able to reproduce e.g. higher strangeness ratios and the ridge in pp, will be added in future studies