P.V. Ruuskanen

Radial and elliptic flow at RHIC: Further predictions

Using a hydrodynamic model, we predict the transverse momentum dependence of the spectra and the elliptic flow for different hadrons in Au+Au collisions at sqrt(s)=130 AGeV. The dependence of the differential and p{_}t-integrated elliptic flow on the hadron mass, equation of state and freeze-out temperature is studied both numerically and analytically.

Scale evolution of nuclear parton distributions

Using the NMC and E665 nuclear structure function ratios F2A/F2D and F2A/F2C from deep inelastic lepton-nucleus collisions, and the E772 Drell-Yan dilepton cross sections from proton-nucleus collisions, and incorporating baryon number and momentum sum rules, we determine nuclear parton distributions at an initial scale Q02. With these distributions, we study QCD scale evolution of nuclear parton densities. The emphasis is on small values of x, especially on scale dependence of nuclear shadowing. As the main result, we show that a consistent picture can be obtained within the leading twist DGLAP evolution, and in particular, that the calculated Q2 dependence of F2Sn/F2C agrees very well with the recent NMC data.

Photon physics in heavy ion collisions at the LHC

Various pion and photon production mechanisms in high-energy nuclear collisions at RHIC and LHC are discussed. Comparison with RHIC data is done whenever possible. The prospect of using electromagnetic probes to characterize quark-gluon plasma formation is assessed...

Photon emission in heavy ion collisions at the CERN SPS

Abstract We compute the thermal photon spectrum in the Pb+Pb collisions at the CERN SPS energy using thermal emission rates and a hydrodynamic description for the evolution of produced hot matter and compare our results with the measurements of the excess photons by the WA98 Collaboration. Our results show that the measured photon spectrum can be reproduced with realistic initial conditions which take properly into account also the finite longitudinal size of the initial collision zone and which simultaneously describe well both the transverse and longitudinal hadron spectra. In the scenario with initial formation of QGP the recently calculated emission rate, complete to order α s , reproduces the measured spectrum. However, the experimental spectrum can also be reproduced in a purely hadronic scenario without transition to QGP state, but a high initial temperature, much over the values predicted for the phase transition temperature T c , is required.

Lepton production from charm decay in nuclear collisions at √ s =200 GeV and 5.5 TeV per nucleon

Measurements of dilepton production from charm decay and Drell-Yan processes respectively probe the gluon and sea quark distributions in hadronic collisions. In nucleus-nucleus collisions, these hard scattering processes constitute a ‘background’ to thermal contributions from the hot matter produced by the collision. To determine the magnitude and behavior of this background, we calculate the hard scattering contribution to dilepton production in nuclear collisions at RHIC and LHC at next to leading order in perturbative QCD. Invariant mass, rapidity and transverse momentum distributions are presented. We compare these results to optimistic hydrodynamic estimates of the thermal dilepton production. We find that charm production from hard scattering is by far the dominant contribution. Experiments therefore can measure the gluon distribution in the nuclear target and projectile and, consequently, can provide new information on gluon shadowing. We then illustrate how experimental cuts on the rapidity gap between the leptons can aid in reducing the charm background, thereby enhancing thermal information. PACS: 12.38.Mh,25.75.+r This manuscript has been authored under contract number DE-AC02-76CH00016 with the U. S. Department of Energy. Accordingly, the U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes. This work was supported in part by the Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U. S. Department of Energy under Contract Number DE-AC03-76SF0098.

Rapidity distributions of dileptons from a hadronizing quark-gluon plasma

It has been predicted that dilepton production may be used as a quark-gluon plasma probe. We calculate the rapidity distributions of thermal dileptons produced by an evolving quark-gluon plasma assuming a longitudinal scaling expansion with initial conditions locally determined from the hadronic rapidity density. These distributions are compared with Drell-Yan production and semileptonic charm decays at invariant mass [ital M]=2, 4, and 6 GeV.

Sensitivity of electromagnetic spectra to equation of state and initial energy density in the Pb + Pb collisions at SPS

Abstract We study Pb + Pb collisions at 158 A GeV/ c using hydrodynamical approach. We test different equations of state (EoSs) and different initial conditions and show that there are more than one initial state for each EoS which reproduce the observed hadronic spectra. We also find that different equations of state favor different freeze-out temperature. Simultaneously we calculate the thermal dilepton and photon spectra for each EoS and initial state. We compare the dilepton mass spectrum to data measured by the CERES collaboration and find that the differences in spectra obtained using different EoSs and initial states are not resolvable within the current experimental resolution. However, at invariant masses over 2 GeV the difference in the yield due to various initial states is close to an order of magnitude. We also study the rapidity distribution of lepton pairs and find that for masses around 800 MeV the shape of the distribution depends strongly on the EoS.

Hydrodynamic simulation of elliptic flow

Abstract We use a hydrodynamic model to study the space-time evolution transverse to the beam direction in ultrarelativistic heavy-ion collisions with nonzero impact parameters. We focus on the influence of early pressure on the development of radial and elliptic flow. We show that at high energies elliptic flow is generated only during the initial stages of the expansion while radial flow continues to grow until freeze-out. Quantitative comparisons with SPS data from semiperipheral Pb+Pb collisions suggest the applicability of hydrodynamical concepts already ≈ 1 fm/c after impact.

Elliptic flow in nuclear collisions at ultrarelativistic energies available at the CERN Large Hadron Collider

We use perfect-fluid hydrodynamical model to predict the elliptic flow coefficients in Pb + Pb collisions at the Large Hadron Collider (LHC). The initial state for the hydrodynamical calculation for central A + A collisions is obtained from the perturbative QCD + saturation (EKRT) model. The centrality dependence of the initial state is modeled by the optical Glauber model. We show that the baseline results obtained from the framework are in good agreement with the data from the Relativistic Heavy Ion Collider (RHIC), and show predictions for the pT spectra and elliptic flow of pions in Pb + Pb collisions at the LHC. Also mass and multiplicity effects are discussed.

Photon production from non-equilibrium QGP in heavy ion collisions

We present a calculation of thermal photon production, i.e. photons from secondary interactions among particles produced in heavy ion collisions at collider energies. This is done within the framework of hydrodynamics. We take into account the lack of chemical equilibrium in QGP. It turns out that the main effects from the chemical non-equilibrium composition of QGP, reduction of particle number and increase in temperature, nearly cancel in the photon spectrum.As is well known, the exact evolution equation of the curvature perturbation plays a very important role in investigation of the inflation power spectrum of the flat universe. However, its corresponding exact extension for the non-flat universes has not yet been given out clearly. The interest in the non-flat, specially closed, universes is being aroused recently. The need of this extension is pressing. We start with most elementary physical consideration and obtain finally this exact evolution equation of the curvature perturbation for the non-flat universes, as well as the evolutionary controlling parameter and the exact expression of the variable mass in this equation. We approximately do a primitive and immature analysis on the power spectrum of non-flat universes. This analysis shows that this exact evolution equation of the curvature perturbation for the non-flat universes is very complicated, and we need to do a lot of numerical and analytic work for this new equation in future in order to judge whether the universe is flat or closed by comparison between theories and observations.