We investigate the difference between hadron resonance gas (HRG) calculations for chemical freeze-out parameters at fully and partly chemical equilibria. To this end, the results are compared with the particle ratios measured in central Au-Au collisions at a wide range of nucleon-nucleon center-of-mass energies, √ s N N = 7.7 − 200 GeV as offered by the STAR experiment. We restrict the discussion to STAR, because of large statistics and overall homogeneity of STAR measurements (one detector) against previous experiments. We find that the matter produced at these energies is likely in fully chemical equilibrium, which is consistent with recent lattice QCD results. The possible improvements by partial chemical equilibrium (γ S = 1) are very limited. We also discuss these results with the ones deduced from φ/π − and Ω − /π − ratios. These hadron ratios are sensitive to the degree of chemical equilibrium. Accordingly, the conclusion that the matter produced reaches fully chemical equilibrium in central Au-Au at RHIC energies is confirmed.

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At thermal equilibrium, different chemical freezeout conditions have been proposed so far. They have an ultimate aim of proposing a universal description for the chemical freezeout parameters (T ch and µ b ), which are to be extracted from the statistical fitting of different particle ratios measured at various collision energies with calculations from thermal models. A systematic comparison between these conditions is presented. The physical meaning of each of them and their sensitivity to the hadron mass cuts are discussed. Based on availability, some of them are compared with recent lattice calculations. We found that most of these conditions are thermodynamically equivalent, especially at small baryon chemical potential. We propose that further crucial consistency tests should be performed at low energies. The fireball thermodynamics is another way of guessing conditions describing the chemical freezeout parameters extracted from high-energy experiments. We endorse the possibility that the various chemical freezeout conditions should be interpreted as different aspects of one universal condition.

High Energy Physics (HEP), due to the vast and complex data expected from current and future experiments, is in need of powerful and efficient techniques for various analysis tasks. Genetic Programing (GP) is a powerful technique that can be used such complex tasks. In this paper, Genetic programing is used for modeling the functions that describe the pseudo-rapidity distribution of the shower particles for 12 C , 16 O , 28 Si and 32 S on nuclear emulsion and also to predict the distributions that are not present in the training set and matched them effectively. The proposed method shows a better fitting with experimental data. The GP prediction results prove a strong presence modeling in heavy ion collisions.

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A relatively new computational technique, namely gradient tree boosting (GTB), is presented for modeling the total cross sections of the scattering of positrons and electrons by alkali atoms in the low and intermediate energy regions. The calculations have been performed in the framework of gradient tree boosting (GTB). The GTB has been running based on the experimental data of the total collisional cross sections to produce the total cross sections for each alkali atom as a function of the incident energy of the projectile as well as the atomic number and the static dipole polarizability of the atom. Moreover our GTB model is used to predict the experimental data for total collisional cross sections that are not used in the training session. The calculated and predicted total collisional cross sections are compared with the experimental data. We find that the GTB technique shows a good match to the experimental data. To our knowledge, this is the first application of the GTB technique to the data of positron and electron collisions with alkali atoms at low and intermediate energies.

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