Recent results of source function imaging from AGS through CERN SPS to RHIC

Abstract

Recent femtoscopic measurements involving the use of an imaging technique and a newly developed moment analysis are presented and discussed. We show that this new paradigm allows robust investigation of reaction dynamics for which the sound speed c s = 0 during an extended hadronization period. Source functions extracted for charged pions produced in Au+Au and Pb+Pb collisions show non-Gaussian tails for a broad selection of collision energies. The ratio of the RMS radii of these source functions in the out and side directions are found to be greater than 1, suggesting a finite emission time for pions.

Emission source functions in heavy ion collisions

“…The width ∆τ is interpreted then as mean emission duration time in the rest frame 4 . The break-up proper time τ 0 ∼ 9 fm/c and small but non-zero proper emission duration in the rest frame ∆τ ∼ 2 fm/c, at which simulations results are most close to the data, appear to be incompatible with the first order transition scenario [47,48], but can point to cross over phase transition [19]. Finite emission duration in the used parametrization (and, partly, the resonance decays contribution) leads to quite appreciable pion emission time differences in LCMS, with |∆t LCMS | ≈ 12 fm/c.…”

“…The tails observed in the pion source function can be interesting also in view of the activity devoted to the search of the phase transition between the QGP and the hadron gas, which could be expected to take place during the evolution of systems produced in the ultrarelativistic nuclear collisions [19]. The idea of such studies is that due to the soft To detail the interpretation of the extracted experimental data, one usually compares them with the results of calculations in different event generators, such as Therminator [20] or Hadronic Rescattering Calculations [21] (HRC).…”

“…The tails observed in the pion source function can be interesting also in view of the activity devoted to the search of the phase transition between the QGP and the hadron gas, which could be expected to take place during the evolution of systems produced in the ultrarelativistic nuclear collisions [19]. The idea of such studies is that due to the soft equation of state (leading to the speed of sound c s = ∂p ∂ǫ 1/2 s close to zero, c s ≈ 0), which system has at the 1 st order phase transition, its expansion should slow down and the lifetime should increase.…”

Bound for entropy and viscosity ratio of strange quark matter

“…In a recent paper Lacey has given a very lucid and colourful representation of viscosity bound for different fluids (see fig. 3 of [19]) which we summarize here. As the (T − T c )/T c varies from -0.5 to 0, η/s in (a) meson gas goes from 1.2 to 0.4, (b) water goes from 3.8 to 2.2 (c) liquid nitrogen from 3.4 to 0.8 and (d) liquid helium from 3.4 to 0.8.…”

“…We need to specify the average momentum P which we take from the Fermi distribution [1] this should be one for what is called the most perfect fluid, perhaps encountered in RHIC [19]. We see that the bound is nearly saturated at n B /n 0 ∼ 5 which is the surface of the star at T = 80 MeV.…”