High P_T observables associated with hard pQCD processes are regarded as tomographic probes of the medium created in ultrarelativistic heavy-ion collisions. Unfortunately, tomography is unexpectedly complicated in practice due to model uncertainties and the highly averaged nature of many observables. However, a systematic comparison study demanding a simultaneous description of many observables within the same framework is sufficiently powerful to rule out a large fraction of conjectured models about the physics mechanism of parton-medium interaction. From this study, it can be inferred that the relevant mechanism is likely to be perturbatively tractable medium-induced radiation with a small component of elastic energy transfer into the medium.
The phenomenology of gluon saturation at small parton momentum fraction, Bjorken-x, in the proton and in the nucleus is introduced. The experimentally-accessible kinematic domains at the nucleus-nucleus colliders RHIC and LHC are discussed. Finally, the saturation hints emerging from measurements at RHIC and the perspectives for LHC are described.
Despite a wealth of experimental data for high p_T processes in heavy-ion collisions, discriminating between different models of hard parton-medium interactions has been difficult. One important reason is that the pQCD parton spectrum at RHIC kinematics is so steeply falling that distinguishing even a moderate shift in parton energy from complete parton absorption is almost impossible in observable quantities. In essence, energy loss models are effectively only probed in the vicinity of zero energy loss and as a result, only the pathlength dependence of energy loss offers some discriminating p…
Despite a wealth of experimental data for high-P_T processes in heavy-ion collisions, discriminating between different models of hard parton-medium interactions has been difficult. A key reason is that the pQCD parton spectrum at RHIC is falling so steeply that distinguishing even a moderate shift in parton energy from complete parton absorption is essentially impossible. In essence, energy loss models are effectively only probed in the vicinity of zero energy loss and, as a result, at RHIC energies only the pathlength dependence of energy loss offers some discriminating power. At LHC however,…
We discuss our studies of polarized parton distributions which are related to the RHIC-Spin project. First, the parametrization of unpolarized parton distributions is explained as an introduction to general audience. Second, activities of the RHIC-Spin-J working group are reported. In particular, preliminary results are shown on the parametrization of polarized parton distributions. Third, we discuss numerical solution of the DGLAP Q^2 evolution equations for longitudinally polarized and transversity distributions. An efficient and accurate computer program is important for analyzing future RH…
A very promising spin physics programme will be soon on the way at the BNL Relativistic Heavy Ion Collider (RHIC). By studying the spin asymmetries for various processes (single photon, single-jet and $W^{\pm}$ production), we will compare the different predictions obtained using some sets of polarized parton distributions, available in the recent literature. We will put some emphasize on the analysis of the anticipated errors, given the event rates expected from this high luminosity new machine and the current acceptance for the detector systems at RHIC.
Employing a newly developed pQCD inspired parton cascade we simulate the space time evolution of gluons which are produced initially in a heavy ion collision at RHIC energy. The inelastic $gg \leftrightarrow ggg$ interactions are for the first time implemented obeying full detailed balance. The numerical results show that thermalization of gluons is mainly driven by the inelastic gluonic interactions and reaches equilibrium at $1\sim 2$ fm/c. In simulations for noncentral collisions considerable partonic elliptic flow $v_2$ is generated being comparable with the experimental data.
We present a phenomenological approach (EPOS), based on the parton model, but going much beyond, and try to understand proton-proton and deuteron-gold collisions, in particular the transverse momentum results from all the four RHIC experiments. It turns out that elastic and inelastic parton ladder splitting is the key issue. Elastic splitting is in fact related to screening and saturation, but much more important is the inelastic contribution, being crucial to understand the data. We investigate in detail the rapidity dependence of nuclear effects, which is actually relatively weak in the mode…
Production and elliptic flow of heavy quarks are investigated in nucleus-nucleus collisions at RHIC and LHC within the Boltzmann Approach of MultiParton Scatterings (BAMPS). The initial heavy quark yield is estimated with the leading order mini-jet model and compared to PYTHIA for several parton distribution functions. Secondary production of heavy quarks in the quark-gluon plasma is examined within the full 3+1 dimensional BAMPS simulation of heavy ion collisions. At RHIC this yield is negligible, but for LHC charm production in the QGP plays a significant role. In addition, we study the elli…
Fully dynamic simulations of heavy ion collisions at RHIC and at LHC energies within the perturbative QCD-based partonic transport model BAMPS (Boltzmann Approach to Multi-Parton Scatterings) are presented, focusing on the simultaneous investigation of jet quenching and elliptic flow. The model features inelastic 2 <-> 3 processes based on the Gunion-Bertsch matrix element and has recently been extended to include light quark degrees of freedom, allowing for direct comparison to hadronic data on the nuclear modification factor via a fragmentation scheme for high-pT partons. The nuclear modific…
The hydrodynamic (hydro) model applied to data from the relativistic heavy ion collider (RHIC) suggests that a dense QCD medium opaque to partons is formed in more-central Au-Au collisions. However, two-component spectrum analysis reveals a hard component, consistent with parton fragmentation described by pQCD, which can masquerade as "radial flow." Minimum-bias angular correlations reveal that most scattered partons survive as "minijets" even in central Au-Au collisions. Such alternative methods quantitatively describe spectrum and correlation structure via pQCD calculations. RHIC collisions …
We discuss recent applications of the partonic pQCD based cascade model BAMPS with focus on heavy-ion phenomeneology in hard and soft momentum range. The nuclear modification factor as well as elliptic flow are calculated in BAMPS for RHIC end LHC energies. These observables are also discussed within the same framework for charm and bottom quarks. Contributing to the recent jet-quenching investigations we present first preliminary results on application of jet reconstruction algorithms in BAMPS. Finally, collective effects induced by jets are investigated: we demonstrate the development of Mac…
We demonstrate that strong suppression of the relative production rate (d+Au)/(p+p) of inclusive high-pT hadrons at forward rapidities observed at RHIC is due to parton multiple rescatterings in nuclear matter. The light-cone dipole approach-based calculations are in a good agreement with BRAHMS and STAR data. They also indicate a significant nuclear suppression at midrapidities with a weak onset of the coherence effects. This prediction is supported by the preliminary d+Au data from the PHENIX Collaboration. Moreover, since similar suppression pattern is also expected to show up at lower ener…
The RHIC facility at BNL will be operating soon, part of the year, as a polarized proton-proton collider. This will allow the undertaking of a vast spin physics programme, mainly by the two large detectors PHENIX and STAR. We review some theoretical aspects of this research programme which will allow, firstly to improve our present knowledge on polarized quark, gluon and sea distributions in a nucleon, secondly to perform novel QCD spin tests and finally, perhaps, to uncover some new physics.
The ratio of nuclear modification factors of high-pT heavy-flavored mesons to light-flavored hadrons (``heavy-to-light ratio'') in nucleus-nucleus collisions tests the partonic mechanism expected to underlie jet quenching. Heavy-to-light ratios are mainly sensitive to the mass and color-charge dependences of medium-induced parton energy loss. Here, we assess the potential for identifying these two effects in D and B meson production at RHIC and at the LHC. To this end, we supplement the perturbative QCD factorized formalism for leading hadron production with radiative parton energy loss. For D…
We study the production of $W^{\pm}$ and $Z$ gauge bosons in proton-proton and proton-neutron collisions up to a center-of-mass energy $\sqrt s=0.5\ TeV$, in connection with the realistic possibility of having proton-deuteron collisions at RHIC with a high luminosity. We stress the importance of measuring unpolarized cross sections for a better determination of the flavor asymmetry of the sea quarks. Since polarized proton beams will be available at RHIC, we evaluate several spin-dependent observables like, double helicity asymmetries $A_{LL}$ as a test of the sea quark polarization, double tr…
From Pythia simulations of pp collisions we determine the mean transverse momentum <Pt> of partons producing the leading and associated particles studied in di-hadron correlations. The dependence of <Pt> on the associated particle transverse momentum and expected differences at RHIC and LHC centre of mass energies are discussed.
We discuss the recent claim that hadron multiplicities measured at RHIC energies are directly described in terms of gluon degrees of freedom fixed from the initial conditions of central heavy ion collisions. The argument is based on the parton saturation scenario expected to be valid at high parton densities and on the assumption of conserved gluon number. Alternatively we conjecture that "bottom-up" equilibration before hadronization modifies this picture, due to nonconservation of the number of gluons.
We present a systematic study of the dijet suppression at RHIC using the VNI/BMS parton cascade. We examine the modification of the dijet asymmetry A_j and the within-cone transverse energy distribution (jet-shape) along with partonic fragmentation distributions z and j_t in terms of: qhat; the path length of leading and sub-leading jets; cuts on the jet energy distributions; jet cone angle and the jet-medium interaction mechanism. We find that A_j is most sensitive to qhat and relatively insensitive to the nature of the jet-medium interaction mechanism. The jet profile is dominated by qhat an…
In nucleus-nucleus collisions at the Relativistic Heavy Ion Collider (RHIC), one generically observes a strong medium-induced suppression of high-pT hadron production. This suppression is accounted for in models which assume a significant medium-induced radiative energy loss of high-pT parent partons produced in the collision. How can we further test the microscopic dynamics conjectured to underly this abundant high-pT phenomenon? What can we learn about the dynamics of parton fragmentation, and what can we learn about the properties of the medium which modifies it ? Given that inelastic parto…
Employing the perturbative QCD inspired parton cascade, we investigate kinetic and chemical equilibration of the partonic matter created in central heavy ion collisions at RHIC and LHC energies. Two types of initial conditions are chosen. One is generated by the model of wounded nucleons using the PYTHIA event generator and Glauber geometry. Another is considered as a color glass condensate. We show that kinetic equilibration is almost independent on the chosen initial conditions, whereas there is a sensitive dependence for chemical equilibration. The time scale of thermalization lies between …
The attenuation of heavy-flavored particles in nucleus-nucleus collisions tests the microscopic dynamics of medium-induced parton energy loss and, in particular, its expected dependence on the identity (color charge and mass) of the parent parton. We discuss the comparison of theoretical calculations with recent single-electron data from RHIC experiments. Then, we present predictions for the heavy-to-light ratios of D and B mesons at LHC energy.
We consider $W^{\pm}$ gauge bosons production in connection with recent results from BNL-RHIC and FNAL-Tevatron and interesting predictions from the statistical parton distributions. They concern relevant aspects of the structure of the nucleon sea and the high-$x$ region of the valence quark distributions. We also give predictions in view of future proton-neutron collisions experiments at BNL-RHIC.
The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for partons (DQPM) matched to reproduce recent lattice-QCD results -- including the partonic equation of state -- in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark-antiquark pairs or three quarks (antiquarks), respectively, obeying flavor current-conservation, color ne…
Different treatments for the inclusion of higher-order perturbative QCD corrections in parton based transport models of relativistic heavy-ion collisions are studied and their influence on experimental observables is investigated. At RHIC, particle multiplicities may vary by more than 30%, depending on the correction scheme. A detailed analysis of the squared relative momentum transfers to be expected in parton (re)scatterings at RHIC casts doubt on the applicability of pQCD based transport approaches at the SPS and rules out the application of higher-order correction schemes based on a rescal…
The "jet-quenching" interpretation of suppressed high-pT hadron production at RHIC implies that jet multiplicity distributions and jet-like particle correlations in heavy-ion collisions at RHIC and LHC differ strongly from those seen at e+e- or pp colliders. Here, we present an approach for describing the changes induced by the medium, which implements jet quenching as a probabilistic medium-modified parton shower, treating leading and subleading parton splittings on an equal footing. We show that the strong suppression of single inclusive hadron spectra measured in Au-Au collisions at RHIC im…
Inclusive cross sections for pion production in $pp$ collisions are calculated for the first time fully based on unintegrated gluon, quark and antiquark distributions (uPDF). We use recently developed Kwieciński uPDF's and different phenomenological fragmentation functions (FF) from the literature. In addition to the $gg \to g$ diagram we include also $g q \to q$ and $q g \to q$ diagrams for inclusive parton production. The cross section for pions is obtained then by convoluting the inclusive parton distributions and FFs. Applications for SPS and RHIC are shown.
This is a personal summary of the meeting "Saturation, the Color Glass Condensate and Glasma: What Have we Learned from RHIC?" that took place at BNL in May 2010. The purpose of the meeting was to discuss the status of high density QCD and parton saturation, and to review the progress that RHIC has allowed in the field.
We present a next-to-leading order QCD calculation of the cross section and longitudinal spin asymmetry in single-inclusive charged-lepton production, pp -> l X, at RHIC, where the lepton is produced in the decay of an electroweak gauge boson. Our calculation is presented in terms of a multi-purpose Monte-Carlo integration program that may be readily used to include experimental spin asymmetry data in a global analysis of helicity parton densities. We perform a toy global analysis, studying the impact of anticipated RHIC data on our knowledge about the polarized anti-quark distributions.
Significant jet quenching in central $Au+Au$ collisions has been discovered at RHIC. This paper provides theoretical arguments and lists experimental evidence that the observed jet quenching at RHIC is due to parton energy loss instead of hadron rescattering or absorption in a hadronic medium. These include: (1) hadron formation time based on the uncertainty principle, (2) $p_T$ dependence and (3) centrality dependence of the observed jet quenching, (4) jet-like leading hadron correlations (5) high-$p_T$ azimuthal anisotropy and (6) experimental data from $Pb+Pb$ collisions at SPS and $e+A$ co…
The production and space-time evolution of charm and bottom quarks in nucleus-nucleus collisions at RHIC and LHC are investigated with the partonic transport model BAMPS (Boltzmann Approach of MultiParton Scatterings). Heavy quarks, produced in primary hard parton scatterings during nucleon-nucleon collisions, are sampled using the Monte Carlo event generator PYTHIA or the leading order mini-jet model in conjunction with the Glauber model, revealing a strong sensitivity on the parton distribution functions, scales, and heavy quark mass. In a comprehensive study exploring different charm masses…
We present a new parton model approach for nuclear collisions at RHIC energies (and beyond). It is a selfconsistent treatment, using the same formalism for calculating cross sections like the total and the inelastic one and, on the other hand, particle production. Actually, the latter one is based on an expression for the total cross section, expanded in terms of cut Feynman diagrams. Dominant diagrams are assumed to be composed of parton ladders between any pair of nucleons, with ordered virtualities from both ends of the ladder.
We present an improved leading-order global DGLAP analysis of nuclear parton distribution functions (nPDFs), supplementing the traditionally used data from deep inelastic lepton-nucleus scattering and Drell-Yan dilepton production in proton-nucleus collisions, with inclusive high-$p_T$ hadron production data measured at RHIC in d+Au collisions. With the help of an extended definition of the $χ^2$ function, we now can more efficiently exploit the constraints the different data sets offer, for gluon shadowing in particular, and account for the overall data normalization uncertainties during the …
The impact parameter and rapidity dependence of the Cronin effect for massless pions in $d+Au$ reactions at $\sqrt{s}_{NN}=200$ GeV at RHIC is computed in the framework of pQCD multiple elastic scattering on a nuclear target. We introduce a formalism to incorporate initial state energy loss in perturbative calculations and take into account the elastic energy loss in addition to the transverse momentum broadening of partons.We argue that the centrality dependence of the Cronin effect can distinguish between different hadron production scenarios at RHIC. Its magnitude and rapidity dependence ar…
We evaluate the Cronin effect in pA collisions at the CERN LHC and at RHIC in the framework of Glauber-Eikonal model of initial state multiparton interactions. Taking carefully into account all kinematical constraints of each multi-parton interaction process we obtain a softening of the spectrum of produced partons, improving in this way the agreement of the model with the recent measurements of pi0 production in d+Au collisions at sqrt{s}=200 AGeV.
I study the impact of recent measurements performed at the Relativistic Heavy Ion Collider on the determination of helicity-dependent parton distribution functions of the proton. Specifically, I consider: preliminary data on longitudinally single-spin asymmetries for $W$-boson production recorded by the STAR experiment during the 2013 run at a center-of-mass energy $\sqrt{s}=510$ GeV; data on longitudinally double-spin asymmetries for di-jet production recorded by the STAR experiment during the 2009 run at $\sqrt{s}=200$ GeV; and data on longitudinally double-spin asymmetries for neutral pion …
Heavy quarks are a unique probe to study the medium produced in ultra-relativistic heavy ion collisions. Within the partonic transport model Boltzmann approach to multi-parton scatterings (BAMPS) the production, energy loss and elliptic flow of heavy quarks are investigated in 3+1 dimensional simulations of the quark gluon plasma evolution. With only binary interactions between heavy quarks and particles from the medium calculated within perturbative QCD, the results on elliptic flow and the nuclear modification factor are not compatible with experimental data from RHIC and LHC. However, if th…
The explanation of the suppression of high-pT hadron yields at RHIC in terms of jet-quenching implies that the multiplicity distributions of particles inside a jet and jet-like particle correlations differ strongly in nucleus-nucleus collisions at RHIC or at the LHC from those observed at e+e- or hadron colliders. We present a framework for describing the medium-induced modification, which has a direct interpretation in terms of a probabilistic medium-modified parton cascade, and which treats leading and subleading partons on an equal footing. We show that our approach can account for the stro…
Production and space-time evolution of heavy quarks in central and non-central heavy-ion collisions at RHIC and LHC are studied with the partonic transport model Boltzmann Approach of MultiParton Scatterings (BAMPS). In addition to the initially created heavy quarks in hard parton scatterings during nucleon-nucleon collisions, secondary heavy quark production in the quark-gluon plasma is investigated and the sensitivity on various parameters is estimated. In BAMPS heavy quarks scatter with particles of the medium via elastic collisions, whose cross section is calculated with the running coupli…
We calculate the yields of a variety of hadrons for RHIC and LHC energies assuming thermodynamical equilibration of the produced minijets, and using as input results from pQCD for the energy densities at midrapidity. In the calculation of the production of partons and of transverse energy one has to account for nuclear shadowing. By using two parametrizations for the gluon shadowing one derives energy densities differing strongly in magnitude. In this publication we link those perturbatively calculated energy densities of partons via entropy conservation in an ideal fluid to the hadron multipl…
We compare results of $2 \to 1$ $k_t$-factorization approach with Kwieciński unintegrated parton distributions and the standard collinear factorization approach at RHIC and slightly smaller energies. Our approach contains only one free parameter responsible for internal parton motion in nucleons. In contrast to recent works in the literature our $k_t$-factorization approach includes also quark degrees of freedom in addition to purely gluonic terms. Both mid and forward rapidity regions are considered. We discuss uncertainties due to fragmentation functions. In general, the $k_t$-factorization …
We introduce a transport approach which combines partonic and hadronic degrees of freedom on an equal footing and discuss the resulting reaction dynamics. The initial parton dynamics is modeled in the framework of the parton cascade model, hadronization is performed via a cluster hadronization model and configuration space coalescence, and the hadronic phase is described by a microscopic hadronic transport approach. The resulting reaction dynamics indicates a strong influence of hadronic rescattering on the space-time pattern of hadronic freeze-out and on the shape of transverse mass spectra. …
The observed suppression of high-$p_\perp$ hadrons allows different explanations. We discuss two possible scenarios: In scenario 1, parton energy loss from scattering in the hot medium is complemented by final state interactions in the resonance matter. Scenario 2 has an enhanced transport parameter $\hat q$ which is fitted to RHIC data. For LHC, the two scenarios lead to very different predictions for the nuclear modification factor of hadrons. In addition, jet reconstruction allows more specific tests of the mechanisms responsible for jet quenching. We calculate the distribution of partons i…
We calculate the yields of pions, kaons, and $ϕ$-mesons for RHIC and LHC energies assuming thermodynamical equilibration of the produced minijets, and using as input results from pQCD for the energy densities at midrapidity. In the calculation of the production of partons and of transverse energy one has to account for nuclear shadowing. By using two parametrizations for the gluon shadowing one derives energy densities differing strongly in magnitude. In this publication we link those perturbatively calculated energy densities of partons via entropy conservation in an ideal fluid to the hadron…
New results on $ϕ$-meson production and elliptic flow $v_{2}$ measurements from RHIC 2004 run (Run-IV) have been reviewed. In addition, the di-hadron correlation function between the trigged $ϕ$ and $Ω$ and the associated soft particles was simulated. Knowledge about these results are discussed.
We present a phenomenological analysis of available data on single spin asymmetries for pion and $D$ meson production in proton-proton collisions at RHIC within the color gauge invariant generalized parton model (CGI-GPM), which includes initial (ISIs) and final (FSIs) state interactions in a transverse momentum dependent formalism. This study allows us, for the first time, to put preliminary constraints on the two independent gluon Sivers functions entering the model. We also present a comparison with the simpler generalized parton model (without ISIs and FSIs).
The hydrodynamic (hydro) model applied to heavy ion data from the relativistic heavy ion collider (RHIC) in the form of single-particle spectra and correlations seems to indicate that a dense QCD medium nearly opaque to partons, a strongly-coupled quark-gluon plasma (sQGP), is formed in more-central Au-Au collisions, and that the sQGP may have a very small viscosity ("perfect liquid"). Measurements of radial and elliptic flows, with possible coalescence of "constituent quarks" to form hadrons, seem to support the conclusion. However, other measurements provide contradictory evidence. Unbiased …
The measured data on the nuclear modification factor for pions and reconstructed jets as well as on the high-pT elliptic flow at RHIC and LHC energies are compared to results from a linear pQCD and a highly non-linear hybrid AdS holographic model of jet-energy loss. We find that the high-pT ellitic flow requires to include realistic medium transverse flow fields and a jet-medium coupling including the effects of the energy of the jet, the temperature of the bulk medium, and non-equilibrium effects close to the phase transition. We extend our jet-energy loss model that is coupled to state-of-th…
We discuss the saturation of the parton density in heavy ion collisions at RHIC energiesusing a Pomeron approach. Our predictions for the particle density in ion-ion collisions at RHIC energies can be utilized as the background for the observation of possible quark-gluon plasma production.
High $p_T$ single and dihadron production is studied within a NLO pQCD parton model with jet quenching in high energy $A+A$ collisions at the RHIC/LHC energy. A simultaneous $χ^2$-fit to both single and dihadron spectra can be achieved within a narrow range of energy loss parameter. Punch-through jets are found to result in the dihadron suppression factor slightly more sensitive to medium than the single hadron suppression factor at RHIC. Such jets at LHC are found to dominate high $p_T$ dihadron production and the resulting dihadron spectra are more sensitive to the initial parton distributio…
Heavy quark and charmonium production as well as their space-time evolution are studied in transport simulations of heavy-ion collisions at RHIC and LHC. In the partonic transport model Boltzmann Approach of MultiParton Scatterings (BAMPS) heavy quarks can be produced in initial hard parton scatterings or during the evolution of the quark-gluon plasma. Subsequently, they interact with the medium via binary scatterings with a running coupling and a more precise Debye screening which is derived from hard thermal loop calculations, participate in the flow and lose energy. We present results of th…
An important ingredient for the non-equilibrium evolution of partons at RHIC and LHC is to have some physically reasonable initial conditions for the single particle phase space distribution functions for the partons. We consider several plausible parametrizations of initial conditions for the single particle distribution function f_i(x,p) and fix the parameters by matching \int f(x,p)p^μd σ_μto the invariant momentum space semi-hard parton distributions obtained using perturbative QCD (pQCD), as well as fitting low order moments of the distribution function. We consider parametrizations of f_…
We argue that the suppression of high p_t hadrons discovered recently in heavy ion collisions at RHIC may be a consequence of saturation in the Color Glass Condensate. We qualitatively and semi-quantitatively describe the data, in particular, the dependence upon the number of nucleon participants. We show that if parton saturation sets in at sufficiently small energy, then in nucleus-nucleus collisions at RHIC and LHC energies the cross sections of semi-hard processes should scale approximately with the number of participants, N_{part}. Our results provide a possible explanation of both the ab…
The dependence of the radiative energy loss of fast partons on the initial thermodynamic parameters is studied for deconfined matter to be expected at RHIC. We demonstrate that the specific QCD radiation pattern with a quadratic dependence of the energy loss on the propagated distance leads to a strong increase of the energy loss with increasing initial entropy of deconfined matter supposed its life-time is less than the average time to pass through the medium. This is in contrast to a parameterization with constant energy loss per unit length of propagation. For a sufficiently high initial te…
We present our recent results on jet tomography of AA-collisions at RHIC and LHC. We focus on flavor dependence of the nuclear modification factor. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant.
We argue that if the growing part of hadron-hadron cross section (described phenomenologically by the supercritical soft Pomeron) is due to instanton/sphaleron mechanism, one should find certain qualitative features of the produced cluster which differ from the usual string fragmentation. Furthermore, we suggest that this mechanism should be even more important for heavy ion collisions in the RHIC energy domain. Large number of parton-parton collisions should result in hundreds of produced sphaleron-like gluomagnetic clusters per unit rapidity. Unlike perturbative gluons (or mini-jets), these …
Within a dynamical quark recombination model we explore various proposed event-by-event observables sensitive to the microscopic structure of the QCD-matter created at RHIC energies. Charge fluctuations, charge transfer fluctuations and baryon-strangeness correlations are computed from a sample of central Au+Au events at the highest RHIC energy available ($\sqrt{s_{NN}}$=200 GeV). We find that for all explored observables, the calculations yield the values predicted for a quark-gluon plasma only at early times of the evolution, whereas the final state approaches the values expected for a hadro…
A number of promising results of a new 3+1 dimensional Monte Carlo parton cascade including inelastic multiplication processes (gg <--> ggg) are elaborated: (1) thermalization and chemical saturation; (2) the onset of longitudinal hydrodynamical expansion; (3) the build up of elliptic flow. We first briefly outline the basic idea of the algorithm. Full simulations are done with initial conditions for the kinetic partons via minijets or with ones stemming from a color glass condensate. The inclusion of the inelastic channels leads to a very fast kinetic equilibration and also to an early creati…
This talk is an attempt to summarize some of the first results obtained at RHIC. I discuss the significance of these measurements for establishing the properties of hot and dense QCD matter and for understanding the dynamics of the theory at the high parton density, strong color field frontier.
The initial conditions in the chemical non-equilibrated medium and Bjorken expanding medium at RHIC are determined. With a set of rate equations describing the chemical equilibration of quarks and gluons based on perturbative QCD, we investigate the consequence for parton evolution at RHIC. With considering parton evolution, it is shown that the Debye screening mass and the inverse mean free-path of gluons reduce with increasing proper time in the QGP medium. The parton evolution affects the parton energy loss with detailed balance, both parton energy loss from stimulated emission in the chemi…
High transverse momentum (P_T) processes are considered to be an important tool to probe and understand the medium produced in ultrarelativistic heavy-ion collisions via the interaction of hard, perturbatively produced partons with the medium. In this context, triggered hard dihadron correlations constitute a class of observables set between hard single inclusive hadrons (dominated by the leading jet fragments) and fully reconstructed jets - while they probe some features of the perturbative QCD evolution of a parton shower in the medium, they do not suffer from the problem of finding a suitab…
