Strangeness at High Temperatures: From Hadrons to Quarks

Abstract

Appropriate combinations of up to fourth order cumulants of net strangeness fluctuations and their correlations with net baryon number and electric charge fluctuations, obtained from lattice QCD calculations, have been used to probe the strangeness carrying degrees of freedom at high temperatures. For temperatures up to the chiral crossover separate contributions of strange mesons and baryons can be well described by an uncorrelated gas of hadrons. Such a description breaks down in the chiral crossover region, suggesting that the deconfinement of strangeness takes place at the chiral crossover. On the other hand, the strangeness carrying degrees of freedom inside the quark gluon plasma can be described by a weakly interacting gas of quarks only for temperatures larger than twice the chiral crossover temperature. In the intermediate temperature window these observables show considerably richer structures, indicative of the strongly interacting nature of the quark gluon plasma.PACS numbers: 11.10. Wx, 11.15.Ha, 12.38.Aw, 12.38.Gc, 12.38.Mh, 24.60.Ky, 25.75.Gz, 25.75.Nq Introduction.-Strangeness has played a crucial role [1] in the experimental and theoretical investigations of the deconfined phase, namely the Quark Gluon Plasma (QGP) phase, of Quantum Chromodynamics (QCD) at high temperatures. Experimental results from the Relativistic Heavy Ion Collider and the Large Hadron Collider suggest that the QGP has been created during the highly energetic collisions of heavy nuclei [2]. Experimental results showing enhanced production and large collective flow of strange hadrons [3] strongly indicate that deconfined strange quarks existed inside the QGP, despite the absence of real strange quarks within the initially colliding nuclei. However, theoretical understanding of the deconfinement of strangeness remains unclear. A-priori it is not unreasonable to expect that the heavier strange quark may not be largely influenced by the chiral symmetry of QCD and the deconfinement of the strange quarks may not take place at the chiral crossover temperature (T c ). Based on the observations that, compared to the light up and down quarks, the net strange quark number fluctuations [4,5] show a much smoother behavior across the chiral crossover region, it has been suggested [6] that the deconfinement crossover for the strange quarks may take place at a temperature larger than T c . Consequently strange hadronic bound states may exist inside the QGP for temperatures T T c [7].Moreover, the nature of the deconfined QGP for moderately high temperatures also remains elusive. An intriguing open question is whether in this temperature regime the QGP is a strongly coupled medium lacking a quasi-particle description [2] or consists of other degrees of freedom such as colored bound states [8] or massive colored quasi-particles [9]. Knowledge regarding the behav-

Three-loop HTLpt thermodynamics at finite temperature and chemical potential

“…[9][10][11], and [139]. As we can see from this figure, for the fourth order susceptibility there is very good agreement with available lattice data.…”

“…At this time, the most reliable method to calculate the QCD thermodynamic functions at finite temperature and zero chemical potential is lattice gauge theory (see e.g. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]). Importantly, lattice QCD can be used to probe the behavior of QCD matter near the transition temperature where QCD matter undergoes a phase transition from the hadronic phase to the deconfined QGP phase.…”

Fluctuations of conserved charges in relativistic heavy ion collisions: An introduction

“…This result suggests that the medium is well described by the hadronic degrees of freedom up to near T c , but the non-hadronic physics shows up around T c . Similar ideas are applied to investigate the flavor hierarchy in the breakdown of the HRG model [81,84,87]. These studies suggest that fluctuations are useful observables to understand quasi-particle properties in the medium although they are static quantities.…”

Electrical conductivity and charge diffusion in thermal QCD from the lattice

“…[62], where a continuum extrapolated lattice QCD calculation was performed (see, however, ref. [63]). …”