Investigating the Speed of Sound of the Medium formed by Heavy-Ion collisions at the LHC



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The Quark-Gluon Plasma (QGP) is a phase of matter that is believed to be created shortly after the Big Bang, an extremely hot and dense matter where quarks and gluons become deconfined from their typical hadronic states. A Large Ion Collider Experiment (ALICE) at the Large Hadron Collider (LHC) and the experiments at the Relativistic Heavy Ion Collider (RHIC) have obtained experimental evidence of QGP formation generated through relativistic heavy ion collisions with ultra-relativistic energies. They have provided a tool to study the phase transition from hadronic matter to this deconfined phase of quarks and gluons. This dissertation results from studies at the Large Hadron Collider in Geneva, Switzerland, in which nuclei collide to study matter under the most extreme conditions on earth. It's been a big open challenge to obtain an experimental determination of the temperature reached in a heavy-ion collision and also the determination of other thermodynamic quantities, such as the entropy, which gives access to the number of degrees of freedom. Recent endeavors in determining the temperature of the medium formed in heavy-ion collisions made it possible to empirically measure other thermodynamic quantities, such as the speed of sound. The speed of sound is a fundamental property of any material. It is directly related to the thermodynamic properties of the QGP and the hot hadronic matter produced by the QGP after the phase transition. It also plays a fundamental role in exploring the equation of state (EOS). This dissertation uses the data from heavy-ion collisions from the ALICE detector, in Pb-Pb collisions at (\sqrt{s_{N N}}=5.02) TeV and Xe-Xe collisions at (\sqrt{s_{N N}}=5.44) TeV. Two methods were explored to extract the speed of sound experimentally in ultra-central collisions. i.e. the two nuclei collide head-on. The values obtained are consistent with predictions from Lattice QCD at temperatures of around T=150 MeV.



QGP (Quark-Gluon plasma), LHC (Large hadron collider)