Measurements of light hadrons produced in heavy ion

Measurements of light hadrons produced in heavy ion collisions at RHIC energies indeed indicated the suppression of hadron production by over a factor of five in central Au+Au collisions [6]. Meanwhile, no suppression was observed for the same hadrons and high-energy direct photons in case of d+Au collisions [9,10]. It was the first experimental confirmation of jet-quenching and it allowed to estimate the Cilengitide manufacturer and color charge density in the formed medium associated with QGP. In spite of the fact that there are many theoretical models successfully describing the suppression of light hadrons in central heavy ion collisions, these models cannot explain a similar suppression of hadrons containing light quarks (u, d) and hadrons containing heavy quarks (c, b). It is clear that such a problem demands a deeper study of the jet-quenching effect, as well as systematical measurements of production and suppression of a wider sample of identified hadrons with different masses and quark content. Another important observation made at RHIC was the enhancement of baryon production with respect to mesons at intermediate transverse momentum in central heavy ion collisions [11]. The p/π ratio measured in central collisions of heavy ions in the transverse momentum range of 2–5 GeV/c was observed to be several times larger than the same ratio measured in p+p collisions at the same energy. For an explanation of this experimentally observed effect, called the baryon anomaly [12], hadron production mechanisms other than fragmentation need to be taken into account. Some existing models [13,14] try to explain this enhancement of baryon production through the recombination of structural quarks. In this scenario, three-quark baryons get a larger increase in transverse momentum than two-quark mesons. Recombination models assume a thermal source of partons is formed that can be associated with QGP. It should be noted that other alternative models explaining this effect also exist, including models based on hydrodynamic effects and radial flow evolution [15–17]. In such models, the difference between baryon and meson production is driven by the difference in particle masses. It is obvious that for a better understanding of dominating hadron production mechanisms, a systematic study of the production of different hadrons at intermediate transverse momentum is necessary, focusing on the production of baryons and mesons with similar masses. The experimental program of relativistic heavy ion collisions started at the Large Hadron Collider (LHC) at CERN (Switzerland) in 2010 [18]. All discoveries made at RHIC were confirmed by experiments at the LHC. In this work φ-mesons are considered the key instrument for studying the hot and dense matter produced in central heavy nuclei collision at the LHC. By mass and quark content this particle sits in between light (u, d) and heavy (c, b) hadrons. Measurements of φ-meson production in central heavy ion collisions will contribute to the systematic studies of the jet-quenching effect. Moreover, the mass of the φ-meson is similar to that of the proton, making it an ideal candidate for baryon anomaly studies. In this article measurements of φ-meson invariant production spectra in p+p collisions at = 2.76 TeV and in Pb+Pb collisions at = 2.76 TeV are presented. These results are used for calculating the nuclear modification factors for φ-mesons in Pb+Pb collisions at different centralities. The implications of the obtained results for the determination of the properties of the hot and dense medium and the dominating mechanisms of hadron production at different transverse momenta are discussed.
Measurement of the invariant production spectra of φ-mesons All results presented in this article were obtained by analyzing the data of the ALICE experiment at the LHC. A detailed description of the detector subsystems along with the discussion of the ALICE experimental program can be found in Ref. [19].