Ehab Abbas | Searcharxiv

arXiv2018

The Effect of Multiplicity Cut on Particle Ratios at 7 TeV Proton-Proton Collisions

The final state hadronic composition of proton-proton collisions at 7 TeV as a function of charged particle multiplicity density is studied. The thermal model is adjusted to match the experimental conditions in order to understand the effect of the experimental cuts on rapidity and multiplicity. This study indicates that the measured hadronic composition under a simultaneous cut on rapidity and multiplicity does not coincide with the fireball hadronic composition. Excluding proton to pion ratio, the adjusted model can explain the measured particle ratios. Therefore, the observed strangeness enhancement as a function of charged particle multiplicity density could be an effect of the experimental cuts.

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arXiv2014

Degree of Chemical Non-equilibrium in Central Au-Au Collisions at RHIC energies

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, \hbox{$\sqrt{s_{NN}}=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\neq 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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