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The size and evolution of the matter created in a relativistic heavy-ion collision strongly depend on collision geometry, defined by centrality. Experimentally the centrality of collisions can be characterized by the measured multiplicities of the produced particles at midrapidity or by the energy measured in the forward rapidity region, which is sensitive to the spectator fragments. This serves as a proxy for the true collision centrality, as defined by the impact parameter in the models of collisions. In this work, the procedure for centrality determination based on Monte-Carlo sampling of spectator fragments has been proposed. The validity of the procedure has been checked using the fully reconstructed DCM-QGSM-SMM model events and published data from the NA61/SHINE experiment. [ABSTRACT FROM AUTHOR]

Pre-equilibrium emissions affect the production of excited systems in nuclear reactions, thus modifying their properties which enter as input parameters in the comparison with statistical models. In this contribution, we discuss this subject referring to recent results from experiments performed at Legnaro National Laboratories (Italy) with the GARFIELD apparatus complemented with other detectors. [ABSTRACT FROM AUTHOR]

High-energy heavy-ion collisions offer the unique possibility to study fundamental properties of nuclear matter in the laboratory, which are relevant for our understanding of the structure of compact stellar objects and the dynamics of neutron star mergers. Of particular interest are the nuclear matter equation of state (EOS), the in-medium modifications of hadrons and the degrees of freedom of matter at high densities and temperatures. Pioneering experiments exploring the EOS for symmetric matter were performed at the SIS18 accelerator of GSI, measuring, as function of beam energy, the collective flow of protons and of light fragments and subthreshold strangeness production. These data were reproduced by various microscopic transport model calculations, providing, up to date, the best constraint for the EOS of symmetric matter with an incompressibility of about 200 MeV for densities up to twice the saturation density. This article reviews the experimental results on subthreshold kaon production together with the theoretical interpretation and gives a brief outlook towards future experiments at higher densities. [ABSTRACT FROM AUTHOR]

The first measurement of the production of pions, kaons, (anti-)protons and ϕ mesons at midrapidity in Xe–Xe collisions at s NN = 5.44 TeV is presented. Transverse momentum ( p T ) spectra and p T -integrated yields are extracted in several centrality intervals bridging from p–Pb to mid-central Pb–Pb collisions in terms of final-state multiplicity. The study of Xe–Xe and Pb–Pb collisions allows systems at similar charged-particle multiplicities but with different initial geometrical eccentricities to be investigated. A detailed comparison of the spectral shapes in the two systems reveals an opposite behaviour for radial and elliptic flow. In particular, this study shows that the radial flow does not depend on the colliding system when compared at similar charged-particle multiplicity. In terms of hadron chemistry, the previously observed smooth evolution of particle ratios with multiplicity from small to large collision systems is also found to hold in Xe–Xe. In addition, our results confirm that two remarkable features of particle production at LHC energies are also valid in the collision of medium-sized nuclei: the lower proton-to-pion ratio with respect to the thermal model expectations and the increase of the ϕ -to-pion ratio with increasing final-state multiplicity. [ABSTRACT FROM AUTHOR]

Based on the recent success of the Angantyr model in describing multiplicity distributions of the hadronic final state in high energy heavy ion collisions, we investigate how far one can go with a such a string-based scenario to describe also flow effects measured in such collisions. For this purpose we improve our previous so-called shoving model, where strings that are close in space-time tend to repel each other in a way that could generate anisotropic flow, and we find that this model can indeed generate such flows in AA collisions. The flow generated is not quite enough to reproduce measurements, but we identify some shortcomings in the presented implementation of the model that, when fixed, could plausibly give a more realistic amount of flow. [ABSTRACT FROM AUTHOR]

Spin distributions for several evaporation residues populated in the 16 O+ 154 Sm system have been measured at projectile energy ≈ 6.2 MeV/A by using the charged particle– γ -coincidence technique. The measured spin distributions of the evaporation residues populated through incomplete fusion associated with ‘fast’ α and 2 α -emission channels are found to be entirely different from fusion–evaporation channels. It is observed that the mean input angular momentum for the evaporation residues formed in incomplete fusion channel is relatively higher than that observed for evaporation residues in complete fusion channels. The feeding intensity profile of evaporation residues populated through complete fusion and incomplete fusion have also been studied. The incomplete fusion channels are found to have narrow range feeding only for high spin states, while complete fusion channels are strongly fed over a broad spin range and widely populated. Comparison of present results with earlier data suggests that the mean input angular momentum values are relatively smaller for spherical target than that of deformed target using the same projectile and incident energy highlighting the role of target deformation in incomplete fusion dynamics. [ABSTRACT FROM AUTHOR]

The Large Hadron Collider accelerates and collides both proton beams and lead beams to the highest energies available in the laboratory. One of the most important global characteristics of such collisions is the multiplicity of produced particles. The ATLAS detector registers passage of charged particles using silicon detectors over a pseudorapidity range of about 5 pseudorapidity units. Several methods of reconstruction of the charged particle multiplicity and angular distribution were developed. These methods range from the full reconstruction of particles and their momenta to an estimate of the number of charged particles based on counting hits registered in a single layer of the Pixel detector. First results obtained from experimental data for p+p interactions and performance studies for heavy ion collisions based on Monte Carlo simulations are discussed. [ABSTRACT FROM AUTHOR]

A selection of experimental results from the PHOBOS Collaboration relevant for probing high-energy nuclear collisions with high transverse momentum particles is presented. The inclusive yields of charged particles and comparisons between nuclear and elementary collisions already reveal a large amount of parton energy loss in the hot and dense medium created in heavy ion collisions. Remarkable scaling and factorization features are observed, unifying the data taken at various collision energies, centralities and nuclear sizes. To further analyze the nature of the energy loss, a measurement of pseudorapidity (Δ η) and azimuthal angle (Δ φ) correlations between high transverse momentum charged hadrons ( p T>2.5 GeV/ c) and all associated charged particles is presented at both short-range (small Δ η) and long-range (large Δ η) over a continuous detector acceptance covering −4<Δ η<2. Various near- and away-side features of the correlation structure are discussed as a function of centrality in Au + Au collisions at $\sqrt{s_{NN}}=200$ GeV. The results provide new information about the longitudinal (Δ η) extent of the near-side ‘ridge’ structure, first observed by the STAR Collaboration over a narrower η range. In central Au + Au collisions the ridge structure extends to at least Δ η=4, and its strength completely diminishes as collisions become more peripheral. [ABSTRACT FROM AUTHOR]

A large set of experimental data was analyzed in terms of characteristic signatures of different interaction as well as product emission scenarios. The analysis confirms that the reaction cross-section appears still dominated by dissipative binary reactions involving the survival of well-defined projectile-and target-like fragments. Consistent with such a "gentle" collision scenario are the Galilei-invariant velocity distributions of charged products featuring statistical emission from two fully accelerated projectile- and target-like fragments. On the other hand, the Galilei-invariant velocity plots reveal the presence of a third effective emission source with velocity intermediate between the velocities of projectile- and target-like fragments. Fragments emitted from the intermediate-velocity source appear to be produced dynamically in the overlap zone of the projectile and target nuclei. The experimental multidimensional joint distributions of neutrons and charged reaction products were found to exhibit several different types of prominent correlation patterns. It makes them a useful tool for probing reactions scenarios, different from the traditional approach of interpreting inclusive yields of individual reaction products. [ABSTRACT FROM AUTHOR]

The study of heavy ion collisions at the Large Hadron Collider (LHC) represents an opportunity to study partonic matter at center-of-mass energies a factor of ∼ 27 times higher than currently possible. This dramatic increase in energy will allow the creation of strongly interacting matter at the highest energy density ever produced in the laboratory. The Compact Muon Solenoid (CMS) detector is ideally suited to study the rich physics of Quantum Chromodynamics and the strong interaction in this new energy region. A brief overview of the heavy ion physics capabilities of the CMS detector is presented. [ABSTRACT FROM AUTHOR]

A status of the ALICE experiment is given. Details on the advancement of the major projects, together with results of recent performance tests are presented. PACS: 25.70.Ef – 21.60.Gx – 27.30.+t [ABSTRACT FROM AUTHOR]