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Register a new userThe effect of partonic wind on charm quark correlations in high-energy nuclear collisions
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In high-energy collisions, massive heavy quarks are produced back-to-back initially and they are sensitive to early dynamical conditions. The strong collective partonic wind from the fast expanding quark-gluon plasma created in high-energy nuclear collisions modifies the correlation pattern significantly. As a result, the angular correlation function for D$bar{rm D}$ pairs is suppressed at the angle $Deltaphi=pi$. While the hot and dense medium in collisions at RHIC ($sqrt{s_{NN}}=200$ GeV) can only smear the initial back-to-back D$bar {rm D}$ correlation, a clear and strong near side D$bar{rm D}$ correlation is expected at LHC ($sqrt{s_{NN}}=5500$ GeV).
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We study the nuclear stopping in high energy nuclear collisions using the constituent quark model. It is assumed that wounded nucleons with different number of interacted quarks hadronize in different ways. The probabilities of having such wounded nucleons are evaluated for proton-proton, proton-nucleus and nucleus-nucleus collisions. After examining our model in proton-proton and proton-nucleus collisions and fixing the hadronization functions, it is extended to nucleus-nucleus collisions. It is used to calculate the rapidity distribution and the rapidity shift of final state protons in nucleus-nucleus collisions. The computed results are in good agreement with the experimental data on $^{32}mbox{S} + ^{32}mbox{S}$ at $E_{lab} = 200$ AGeV and $^{208}mbox{Pb} + ^{208}mbox{Pb}$ at $E_{lab} = 160$ AGeV. Theoretical predictions are also given for proton rapidity distribution in $^{197}mbox{Au} + ^{197}mbox{Au}$ at $sqrt{s} = 200$ AGeV (BNL-RHIC). We predict that the nearly baryon free region will appear in the midrapidity region and the rapidity shift is $langle Delta y rangle = 2.22$.
We consider the SU(2) Glasma with gaussian fluctuations and study its evolution by means of classical Yang-Mills equations solved numerically on a lattice. Neglecting in this first study the longitudinal expansion we follow the evolution of the pressures of the system and compute the effect of the fluctuations in the early stage up to $tapprox 2$ fm/c, that is the time range in which the Glasma is relevant for high energy collisions. We measure the ratio of the longitudinal over the transverse pressure, $P_L/P_T$, and we find that unless the fluctuations carry a substantial amount of the energy density at the initial time, they do not change significantly the evolution of $P_L/P_T$ in the early stage, and that the system remains quite anisotropic. We also measure the longitudinal fields correlators both in the transverse plane and along the longitudinal direction: while at initial time fields appear to be anticorrelated in the transverse plane, this anticorrelation disappears in the very early stage and the correlation length in the transverse plane increases; on the other hand, we find that the longitudinal correlator decreases for a small longitudinal separation while being approximately constant for larger separation, which we interpret as a partial loss of longitudinal correlation induced by the dynamics.
We propose to measure azimuthal correlations of heavy-flavor hadrons to address the status of thermalization at the partonic stage of light quarks and gluons in high-energy nuclear collisions. In particular, we show that hadronic interactions at the late stage cannot significantly disturb the initial back-to-back azimuthal correlations of DDbar pairs. Thus, a decrease or the complete absence of these initial correlations does indicate frequent interactions of heavy-flavor quarks and also light partons in the partonic stage, which are essential for the early thermalization of light partons.
Measurements of heavy flavor quark (charm and bottom) correlations in heavy ion collisions are instrumental to understand the flavor dependence of energy loss mechanisms in hot and dense QCD media. Experimental measurements of these correlations in baseline $p$+$p$ collisions are crucial to understand the contributions of perturbative and non-perturbative QCD processes to the correlation functions and further help in interpreting correlation measurements in heavy ion collisions. In this paper, we investigate $D$-$bar{D}$ meson correlations and $D$ with one particle from $D$ meson decay daughter correlations using PYTHIA Event Generator in $p$ + $p$ collisions at $sqrt{s}$ = 200, 500 and 5500 GeV. Charm/bottom events are found to contribute mainly to the away side/near side pattern of $D$-electron correlations, respectively. In the energy region of RHIC, $D$-$bar{D}$ correlations inherit initial $c$-$bar{c}$ correlations and $Brightarrow DX$ decay contribution is insignificant. Furthermore, Bottom quark correlations are suggested to be applicable at LHC energy, as the bottom contributions on $D$ related correlations are relatively large.
In this paper, we give an account of the peripheral-tube model, which has been developed to give an intuitive and dynamical description of the so-called ridge effect in two-particle correlations in high-energy nuclear collisions. Starting from a realistic event-by-event fluctuating hydrodynamical model calculation, we first show the emergence of ridge + shoulders in the so-called two-particle long-range correlations, reproducing the data. In contrast to the commonly used geometric picture of the origin of the anisotropic flow, we can explain such a structure dynamically in terms of the presence of high energy-density peripheral tubes in the initial conditions. These tubes violently explode and deflect the near radial flow coming from the interior of the hot matter, which in turn produces a two-ridge structure in single-particle distribution, with approximately two units opening in azimuth. When computing the two-particle correlation, this will result in characteristic three-ridge structure, with a high near-side ridge and two symmetric lower away-side ridges or shoulders. Several anisotropic flows, necessary to producing ridge + shoulder structure, appear naturally in this dynamical description. Using this simple idea, we can understand several related phenomena, such as centrality dependence and trigger-angle dependence.
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