Two-particle angular correlation for charged particles emitted in Au+Au collisions at the center-of-mass of 200 MeV measured at RHIC energies revealed novel structures commonly referred to as a near-side ridge. The ridge phenomenon in relativistic A+A collisions is rooted probably in the initial conditions of the thermal evolution of the system. In this study we analyze the evolution of the bumping transverse structure of the energy density distribution caused by fluctuations of the initial density distributions that could lead to the ridge structures. We suppose that at very initial stage of collisions the typical one-event structure of the initial energy density profile can be presented as the set of longitudinal tubes, which are boost-invariant in some space-rapidity region and are rather thin. These tubes have very high energy density comparing to smooth background density distribution. The transverse velocity and energy density profiles at different times of the evolution till the chemical freeze-out (at the temperature T=165 MeV) willbe reached by the system are calculated for sundry initial scenarios.
We study time evolution of critical fluctuations of conserved charges near the QCD critical point in the context of relativistic heavy ion collisions. A stochastic diffusion equation is employed in order to describe the diffusion property of the critical fluctuation arising from the coupling of the order parameter field to conserved charges. We show that the diffusion property gives rise to a possibility of probing the early time fluctuations through the rapidity window dependence of the second-order cumulant and correlation function of conserved charges. It is pointed out that their non-monotonic behaviors as functions of the rapidity interval are robust experimental signals for the existence of the critical enhancement around the QCD critical point.
We look for fluctuations expected for the QCD critical point using an intermittency analysis in the transverse momentum phase space of protons produced around midrapidity in the 12.5% most central C+C, Si+Si and Pb+Pb collisions at the maximum SPS energy of 158$A$~GeV. We find evidence of power-law fluctuations for the Si+Si data. The fitted power-law exponent $phi_{2} = 0.96^{+0.38}_{-0.25}text{ (stat.)}$ $pm 0.16text{ (syst.)}$ is consistent with the va-lue expected for critical fluctuations. Power-law fluctuations had previously also been observed in low-mass $pi^+ pi^-$ pairs in the same Si+Si collisions.
We investigate the role of a finite surface tension during the time-evolution of fluctuations in the net-baryon density. The systems in this study undergo a temperature evolution across the phase transition in the critical region of the QCD phase diagram. The occuring non-equilibrium effects are discussed.
We present a quantitative study of vorticity formation in peripheral ultrarelativistic heavy ion collisions at sqrt(s)NN = 200 GeV by using the ECHO-QGP numerical code, implementing relativistic dissipative hydrodynamics in the causal Israel-Stewart framework in 3+1 dimensions with an initial Bjorken flow profile. We consider and discuss different definitions of vorticity which are relevant in relativistic hydrodynamics. After demonstrating the excellent capabilities of our code, which proves to be able to reproduce Gubser flow up to 8 fm/c, we show that, with the initial conditions needed to reproduce the measured directed flow in peripheral collisions corresponding to an average impact parameter b=11.6 fm and with the Bjorken flow profile for a viscous Quark Gluon Plasma with eta/s=0.1 fixed, a vorticity of the order of some 10^{-2} c/fm can develop at freezeout. The ensuing polarization of Lambda baryons does not exceed 1.4% at midrapidity. We show that the amount of developed directed flow is sensitive to both the initial angular momentum of the plasma and its viscosity.
We present a simple description of the energy density profile created in a nucleus-nucleus collision, motivated by high-energy QCD. The energy density is modeled as the sum of contributions coming from elementary collisions between localized charges and a smooth nucleus. Each of these interactions creates a sharply-peaked source of energy density falling off at large distances like $1/r^2$, corresponding to the two-dimensional Coulomb field of a point charge. Our model reproduces the one-point and two-point functions of the energy density field calculated in the framework of the color glass condensate effective theory, to leading logarithmic accuracy. We apply it to the description of eccentricity fluctuations. Unlike other existing models of initial conditions for heavy-ion collisions, it allows us to reproduce simultaneously the centrality dependence of elliptic and triangular flow.