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Register a new userParton Distributions at Hadronization from Bulk Dense Matter Produced at RHIC
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We present an analysis of $Omega$, $Xi$, $Lambda$ and $phi$ spectra from Au+Au collisions at $sqrt{s_{NN}}=200$ GeV in terms of distributions of effective constituent quarks at hadronization. Consistency in quark ratios derived from various hadron spectra provides clear evidence for hadron formation dynamics as suggested by quark coalescence or recombination models. We argue that the constituent quark distribution reflects properties of the effective partonic degrees of freedom at hadronization. Experimental data indicate that strange quarks have a transverse momentum distribution flatter than that of up/down quarks consistent with hydrodynamic expansion in partonic phase prior to hadronization. After the AMPT model is tuned to reproduce the strange and up/down quark distributions, the model can describe the measured spectra of hyperons and $phi$ mesons very well where hadrons are formed through dynamical coalescence.
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The rapidity densities in Au-Au collisions at center-of-mass energies 200 and 130 A GeV measured at Relativistic Heavy-Ion Collider by STAR and PHENIX collaborations are analyzed within the statistical hadronization model at chemical freeze-out. We find that the model can describe the experimental rapidity densities well. The corresponding chemical freeze-out parameters are determined and they are seen to be in agreement with what we expect from our previous analyzes at lower beam energies at AGS and SPS.
The charged particles produced in heavy ion collisions consist of two parts: One is from the freeze-out of hot and dense matter formed in collisions. The other is from the leading particles. In this paper, the hot and dense matter is assumed to expand according to the hydrodynamic model including phase transition and decouples into particles via the prescription of Cooper-Frye. The leading particles are as usual supposed to have Gaussian rapidity distributions with the number equaling that of participants. The investigations of this paper show that, unlike low energy situations, the leading particles are essential in describing the pseudorapidity distributions of charged particles produced in high energy heavy ion collisions. This might be due to the different transparencies of nuclei at different energies.
The longitudinal asymmetry arises in relativistic heavy ion collisions due to fluctuation in the number of participating nucleons. This asymmetry causes a shift in the center of mass rapidity of the participant zone. The rapidity shift as well as the longitudinal asymmetry have been found to be significant at the top LHC energy for collisions of identical nuclei. We study the longitudinal asymmetry and its effect on charged particle rapidity distribution and anisotropic flow parameters at relatively lower RHIC energies using a model calculation. The rapidity shift is found to be more pronounced for peripheral collisions, smaller systems and also for lower beam energies due to longitudinal asymmetry. A detailed study has been done by associating the average rapidity shift to a polynomial relation where the coefficients of this polynomial characterize the effect of the asymmetry. We show that the rapidity shift may affect observables significantly at RHIC energies.
The hadronization of an expanding partonic fireball is studied within the Parton-Hadron-Strings Dynamics (PHSD) approach which is based on a dynamical quasiparticle model (DQPM) matched to reproduce lattice QCD results in thermodynamic equilibrium. Apart from strong parton interactions the expansion and development of collective flow is found to be driven by strong gradients in the parton mean-fields. An analysis of the elliptic flow $v_2$ demonstrates a linear correlation with the spatial eccentricity $epsilon$ as in case of ideal hydrodynamics. The hadronization occurs by quark-antiquark fusion or 3 quark/3 antiquark recombination which is described by covariant transition rates. Since the dynamical quarks become very massive, the formed resonant pre-hadronic color-dipole states ($qbar{q}$ or $qqq$) are of high invariant mass, too, and sequentially decay to the groundstate meson and baryon octets increasing the total entropy. This solves the entropy problem in hadronization in a natural way. Hadronic particle ratios turn out to be in line with those from a grandcanonical partition function at temperature $T approx 170$ MeV.
Using QCD calculations of the cross section of inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions in the LHC kinematics as pseudo-data, we study the effect of including these data using the Bayesian reweighting technique on nCTEQ15, nCTEQ15np, and EPPS16 nuclear parton distribution functions (nPDFs). We find that, depending on the assumed error of the pseudo-data, it leads to a significant reduction of the nPDF uncertainties at small values of the momentum fraction $x_A$. Taking the error to be 5%, the uncertainty of nCTEQ15 and nCTEQ15np nPDFs reduces approximately by a factor of two at $x_A=10^{-3}$. At the same time, the reweighting effect on EPPS16 nPDFs is much smaller due to the higher value of the tolerance and a more flexible parametrization form.
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