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Register a new userTrace initial interaction from final state observable in relativistic heavy ion collisions
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In order to trace the initial interaction in ultra-relativistic heavy ion collision in all azimuthal directions, two azimuthal multiplicity-correlation patterns -- neighboring and fixed-to-arbitrary angular-bin correlation patterns -- are suggested. From the simulation of Au + Au collisions at 200 GeV by using the Monte Carlo models RQMD with hadron re-scattering and AMPT with and without string melting, we observe that the correlation patterns change gradually from out-of-plane preferential one to in-plane preferential one when the centrality of collision shifts from central to peripheral, meanwhile the anisotropic collective flow v_2 keeps positive in all cases. This regularity is found to be model and collision energy independent. The physics behind the two opposite trends of correlation patterns, in particular, the presence of out-of-plane correlation patterns at RHIC energy, are discussed.
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Investigation of momentum space correlations of particles produced in high energy reactions requires taking final state interactions into account, a crucial point of any such analysis. Coulomb interaction between charged particles is the most important such effect. In small systems like those created in e+e- or p+p collisions, the so-called Gamow factor (valid for a point-like particle source) gives an acceptable description of the Coulomb interaction. However, in larger systems such as central or mid-central heavy ion collisions, more involved approaches are needed. In this paper we investigate the Coulomb final state interaction for Levy-type source functions that were recently shown to be of much interest for a refined description of the space-time picture of particle production in heavy-ion collisions.
We investigate the two-particle intensity correlation function of $Lambda$ in relativistic heavy-ion collisions. We find that the behavior of the $LambdaLambda$ correlation function at small relative momenta is fairly sensitive to the interaction potential and collective flows. By comparing the results of different source functions and potentials, we explore the effect of intrinsic collective motions on the correlation function. We find that the recent STAR data gives a strong constraint on the scattering length and effective range of $LambdaLambda$ interaction as, $-1.8 mathrm{fm}^{-1} < 1/a_0 < -0.8 mathrm{fm}^{-1}$ and $3.5 mathrm{fm} < r_mathrm{eff} < 7 mathrm{fm}$, respectively,if $Lambda$ samples do not include feed-down contribution from long-lived particles. We find that feed-down correction for $Sigma^0$ decay reduces the sensitivity of the correlation function to the detail of the $LambdaLambda$ interaction. As a result, we obtain a weaker constraint $1/a_0 <-0.8$ fm$^{-1}$. Implication for the signal of existence of $H$-dibaryon is discussed. Comparison with the scattering parameters obtained from the double $Lambda$ hypernucleus may reveal in-medium effects in the $LambdaLambda$ interaction.
The particle momentum anisotropy ($v_n$) produced in relativistic nuclear collisions is considered to be a response of the initial geometry or the spatial anisotropy $epsilon_n$ of the system formed in these collisions. The linear correlation between $epsilon_n$ and $v_n$ quantifies the efficiency at which the initial spatial eccentricity is converted to final momentum anisotropy in heavy ion collisions. We study the transverse momentum, collision centrality, and beam energy dependence of this correlation for different charged particles using a hydrodynamical model framework. The ($epsilon_n -v_n$) correlation is found to be stronger for central collisions and also for n=2 compared to that for n=3 as expected. However, the transverse momentum ($p_T$) dependent correlation coefficient shows interesting features which strongly depends on the mass as well as $p_T$ of the emitted particle. The correlation strength is found to be larger for lighter particles in the lower $p_T$ region. We see that the relative fluctuation in anisotropic flow depends strongly in the value of $eta/s$ specially in the region $p_T <1$ GeV unlike the correlation coefficient which does not show significant dependence on $eta/s$.
In the present work we propose a new initial state model for hydrodynamic simulation of relativistic heavy ion collisions based on Bjorken-like solution applied streak by streak in the transverse plane. Previous fluid dynamical calculations in Cartesian coordinates with an initial state based on a streak by streak Yang-Mills field led for peripheral higher energy collisions to large angular momentum, initial shear flow and significant local vorticity. Recent experiments verified the existence of this vorticity via the resulting polarization of emitted $Lambda$ and $bar{Lambda}$ particles. At the same time parton cascade models indicated the existence of more compact initial state configurations, which we are going to simulate in our approach. The proposed model satisfies all the conservation laws including conservation of a strong initial angular momentum which is present in non-central collisions. As a consequence of this large initial angular momentum we observe the rotation of the whole system as well as the fluid shear in the initial state, which leads to large flow vorticity. Another advantage of the proposed model is that the initial state can be given in both [t,x,y,z] and $[tau, x, y, eta]$ coordinates, and thus can be tested by all 3+1D hydrodynamical codes which exist in the field.
We study charm production in ultra-relativistic heavy-ion collisions by using the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm quarks are produced by the PYTHIA event generator tuned to fit the transverse momentum spectrum and rapidity distribution of charm quarks from Fixed-Order Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses and widths are given by the Dynamical Quasi-Particle Model (DQPM), which reproduces the lattice QCD equation-of-state in thermal equilibrium. The relevant cross sections are calculated in a consistent way by employing the effective propagators and couplings from the DQPM. Close to the critical energy density of the phase transition, the charm quarks are hadronized into $D$ mesons through coalescence and/or fragmentation. The hadronized $D$ mesons then interact with the various hadrons in the hadronic phase with cross sections calculated in an effective lagrangian approach with heavy-quark spin symmetry. The nuclear modification factor $R_{AA}$ and the elliptic flow $v_2$ of $D^0$ mesons from PHSD are compared with the experimental data from the STAR Collaboration for Au+Au collisions at $sqrt{s_{NN}}$ =200 GeV and to the ALICE data for Pb+Pb collisions at $sqrt{s_{NN}}$ =2.76 TeV. We find that in the PHSD the energy loss of $D$ mesons at high $p_T$ can be dominantly attributed to partonic scattering while the actual shape of $R_{AA}$ versus $p_T$ reflects the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation. Also the hadronic rescattering is important for the $R_{AA}$ at low $p_T$ and enhances the $D$-meson elliptic flow $v_2$.
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