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We review progress in the study of antinuclei, starting from Diracs equation and the discovery of the positron in cosmic-ray events. The development of proton accelerators led to the discovery of antiprotons, followed by the first antideuterons, demonstrating that antinucleons bind into antinuclei. With the development of heavy-ion programs at the Brookhaven AGS and CERN SPS, it was demonstrated that central collisions of heavy nuclei offer a fertile ground for research and discoveries in the area of antinuclei. In this review, we emphasize recent observations at Brookhavens Relativistic Heavy Ion Collider and at CERNs Large Hadron Collider, namely, the antihypertriton and the antihelium-4, as well as measurements of the mass difference between light nuclei and antinuclei, and the interaction between antiprotons. Physics implications of the new observations and different production mechanisms are discussed. We also consider implications for related fields, such as hypernuclear physics and space-based cosmic-ray experiments.
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Two-particle femtoscopy reveals the space-time substructure of the freeze-out configuration from heavy ion collisions. Detailed fingerprints of bulk collectivity are evident in space-momentum correlations, which have been systematically measured as a function of particle type, three-momentum, and collision conditions. A clear scenario, dominated by hydrodynamic-type flow emerges. Reproducing the strength and features of the femtoscopic signals in models involves important physical quantities like the Equation of State, as well as less fundamental technical details. An interesting approximate factorization in the measured systematics suggests that the overall physical freeze-out scale is set by final state chemistry, but the kinematic substructure is largely universal. Referring to previous results from hadron and lepton collisions, we point to the importance of determining whether these universal trends persist from the largest to the smallest systems. We review theoretical expectations for heavy ion femtoscopy at the LHC, and point to directions needing further theory and experimental work at RHIC and the LHC.
Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter $F$ and elliptic asymmetry coefficient $v_2$, for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive $F$ and negative $v_2$ of direct photons are illustrated and they seem to be anti-correlated to the corresponding free protons flow.
We present a subset of experimental results on charge fluctuation from the heavy-ion collisions to search for phase transition and location of critical point in the QCD phase diagram. Measurements from the heavy-ion experiments at the SPS and RHIC energies observe that total charge fluctuations increase from central to peripheral collisions. The net-charge fluctuations in terms of dynamical fluctuation measure $ u_{(+-,dyn)}$ are studied as a function of collision energy (sqsn) and centrality of the collisions. The product of $ u_{(+-,dyn)}$ and $langle N_{ch} rangle$ shows a monotonic decrease with collision energies, which indicates that at LHC energy the fluctuations have their origin in the QGP phase. The fluctuations in terms of higher moments of net-proton, net-electric charge and net-kaon have been measured for various sqsn. Deviations are observed in both $Ssigma$ and $kappasigma^2$ for net-proton multiplicity distributions from the Skellam and hadron resonance gas model for sqsn $<$ 39 GeV. Higher moment results of the net-electric charge and net-kaon do not observe any significant non-monotonic behavior as a function of collision energy. We also discuss the extraction of the freeze-out parameters using particle ratios and experimentally measured higher moments of net-charge fluctuations. The extracted freeze-out parameters from experimentally measured moments and lattice calculations, are found to be in agreement with the results obtained from the fit of particle ratios to the thermal model calculations.
The ultra-relativistic heavy-ion programs at the Relativistic Heavy Ion Collider and the Large Hadron Collider have evolved into a phase of quantitative studies of Quantum Chromodynamics at very high temperatures. The charm and bottom hadron production offer unique insights into the remarkable transport properties and the microscopic structure of the Quark-Gluon Plasma (QGP) created in these collisions. Heavy quarks, due to their large masses, undergo Brownian motion at low momentum, provide a window on hadronization mechanisms at intermediate momenta, and are expected to merge into a radiative-energy loss regime at high momentum. We review recent experimental and theoretical achievements on measuring a variety of heavy-flavor observables, characterizing the different regimes in momentum, extracting pertinent transport coefficients and deducing implications for the inner workings of the QGP medium.
We study the production of (hyper-)nuclei and di-baryons in most central heavy Ion collisions at energies of $E_{lab}=1-160 A$ GeV. In particular we are interested in clusters produced from the hot and dense fireball. The formation rate of strange and non-strange clusters is estimated by assuming thermal production from the intermediate phase of the UrQMD-hydro hybrid model and alternatively by the coalescence mechanism from a hadronic cascade model. Both model types are compared in detail. For most energies we find that both approaches agree in their predictions for the yields of the clusters. Only for very low beam energies, and for di-baryons including $Xi$s, we observe considerable differences. We also study the production of anti-matter clusters up to top RHIC energies and show that the observation of anti-$^4He$ and even anti-$^4_{Lambda}He$ is feasible. We have found a considerable qualitative difference in the energy dependence of the strangeness population factor $R_H$ when comparing the thermal production with the coalescence results.
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