Multiplicities and Transverse Energies in Central AA Collisions at RHIC and LHC from pQCD, Saturation and Hydrodynamics

We compute the particle multiplicities and transverse energies at central and nearly central AA collisions at RHIC and LHC. The initial state is computed from perturbative QCD supplemented by the conjecture of saturation of produced partons. The expansion stage is described in terms of hydrodynamics assuming longitudinal boost invariance and azimuthal symmetry. Transverse flow effects, a realistic list of hadrons and resonance decays are included. Comparison with the data of the multiplicities at $\sqrt s=56$ AGeV and 130 AGeV from RHIC is done and predictions for the full RHIC energy and LHC energy are made for the multiplicities and transverse energies. The reduction from the initially released minijet transverse energy to the $E_T$ in the final state is less than in the one-dimensional case but still dramatic: a factor of 2.7 at RHIC, and 3.6 at the LHC.Comment: The results for LHC have been correcte

Multiplicities for LHC Nuclear Collisions Using HERA Structure Functions

We compute in QCD perturbation theory the transverse energy carried by gluons, quarks and antiquarks with $p_T\ge p_0\approx 2$ GeV in Pb+Pb collisions at $\sqrt{s}=5500$ $A$GeV by using structure functions compatible with the small-$x$ increase observed at HERA. This gives a perturbative estimate for the energy and entropy density of the bulk system at times $\tau\sim 0.1$ fm. The predicted initial gluon entropy density gives a lower limit of about 2200...3400 for the final charged multiplicity. Sources of further entropy increase are discussed.Comment: HU-TFT-94-6, 7 pages, 3 PostScript figures included in the end of the tex-fil

Transverse spectra of hadrons at RHIC

We present results on spectra of pions, kaons and (anti)protons from a study of heavy ion collisions using the perturbative QCD + saturation model to calculate the production of initial (transverse) energy and baryon number followed by a hydrodynamic description of the expansion of produced matter. In particular, we study how the hadron spectra and multiplicities depend on the decoupling temperature \Tdec when the low temperature phase contains all hadrons and and hadron resonances with mass below 2 GeV. We show that the spectra and multiplicities of pions, kaons and (anti)protons measured at RHIC in central Au+Au collisions with $\sqrt s=130$ GeV can be obtained with a single decoupling temperature 150$...$160 MeV, common for both the chemical and the kinetic freeze-out.Comment: 4 pages, 2 eps-figures, talk at Quark Matter '02, Nantes, France, July 200

EPS09 - Nuclear PDFs and Their Uncertainties at NLO

In this talk, we present our recent next-to-leading order (NLO) nuclear parton distribution functions (nPDFs), which we call EPS09. As an extension to earlier NLO analyses, we supplement the deep inelastic scattering and Drell-Yan dilepton data by inclusive midrapidity pion measurements from RHIC in order to reduce the otherwize large freedom in the nuclear gluon densities. Our Hessian-type error analysis leading to a collection of nPDF error sets, is the first of its kind among the nPDF analyses.Comment: 4 pages, 4 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

Scaling of transverse energies and multiplicities with atomic number and energy in ultrarelativistic nuclear collisions

We compute how the initial energy density and produced gluon, quark and antiquark numbers scale with atomic number and beam energy in ultrarelativistic heavy ion collisions. The computation is based on the argument that the effect of all momentum scales can be estimated by performing the computation at one transverse momentum scale, the saturation momentum. The initial numbers are converted to final ones by assuming kinetic thermalisation and adiabatic expansion. The main emphasis of the study is at LHC and RHIC energies but it is observed that even at SPS energies this approach leads to results which are not unreasonable: what is usually described as a completely soft nonperturbative process can also be described in terms of gluons and quarks. The key element is the use of the saturation scale.Comment: 13 pages, includes 7 eps-figure

Centrality dependence of multiplicity, transverse energy, and elliptic flow from hydrodynamics

The centrality dependence of the charged multiplicity, transverse energy, and elliptic flow coefficient is studied in a hydrodynamic model, using a variety of different initializations which model the initial energy or entropy production process as a hard or soft process, respectively. While the charged multiplicity depends strongly on the chosen initialization, the p_t-integrated elliptic flow for charged particles as a function of charged particle multiplicity and the p_t-differential elliptic flow for charged particles in minimum bias events turn out to be almost independent of the initial energy density profile.Comment: 11 pages RevTex, including 10 postscript figures. Slightly modified discussion of Figs. 5 and 6, updated references. This version to appear in Nuclear Physics

Structure functions and parton distributions

In this talk, I review the status of theoretical understanding of nuclear structure functions and parton distributions and discuss the constraints on nuclear parton distributions from existing data and the global QCD analysis.Comment: Latex, 10 pages, to appear in the proceedings of QM200

High Energy Nuclear Collisions

Highlights of the results from ultrarelativistic heavy ion collisions at CERN-SPS are reviewed. In particular, I discuss how the experimental results indicate that a collective strongly interacting system has been produced, and what are the implications towards the Quark Gluon Plasma. The physical ideas behind measuring certain observables are introduced. The future program of high energy nuclear collisions at BNL-RHIC and CERN-LHC/ALICE is also briefly discussed.Comment: Plenary talk at the International Europhysics Conference on High Energy Physics, EPS-HEP99, Tampere, Finland, July 1999; 21 page

Minijets in ultrarelativistic heavy ion collisions at future colliders

The role of minijet production as initial conditions for QGP production at $\tau\sim 0.1 fm/c$ in nuclear collisions at the LHC and RHIC energies is discussed.Comment: 15 pages, including 2 figures, an invited article to Comments on Nuclear and Particle Physic

On predictions of the first results from RHIC

In this talk, I will discuss the predictions of the first results from RHIC: the charged particle multiplicity $dN_{\rm ch}/d\eta$, its centrality dependence and the elliptic flow $v_2$.Comment: A plenary review talk at Quark Matter 2001, Stony Brook, USA, January 2001, 10 page