Hydrodynamic Models for Heavy Ion Collisions

Application of hydrodynamics for modeling of heavy-ion collisions is reviewed. We consider several physical observables that can be calculated in this approach and compare them to the experimental measurements.Comment: 42 pages, 15 figures, An invited review for Nov. 2006 edition of Annual Review of Nuclear and Particle Physic

Photon HBT interferometry for non-central heavy-ion collisions

Currently, the only known way to obtain experimental information about the space-time structure of a heavy-ion collision is through 2-particle momentum correlations. Azimuthally sensitive HBT interferometry (Hanbury Brown-Twiss intensity interferometry) can complement elliptic flow measurements by constraining the spatial deformation of the source and its time evolution. Performing these measurements on photons allows us to access the fireball evolution at earlier times than with hadrons. Using ideal hydrodynamics to model the space-time evolution of the collision fireball, we explore theoretically various aspects of 2-photon intensity interferometry with transverse momenta up to 2 GeV, in particular the azimuthal angle dependence of the HBT radii in non-central collisions. We highlight the dual nature of thermal photon emission, in both central and non-central collisions, resulting from the superposition of QGP and hadron resonance gas photon production. This signature is present in both the thermal photon source function and the HBT radii extracted from Gaussian fits of the 2-photon correlation function.Comment: 18 pages, 12 figure

Hadron multiplicities, pT-spectra and net-baryon number in central Pb+Pb collisions at the LHC

We compute the initial energy density and net baryon number density in 5% most central Pb+Pb collisions at $\sqrt s=5.5$ TeV from pQCD + (final state) saturation, and describe the evolution of the produced system with boost-invariant transversely expanding hydrodynamics. In addition to the total multiplicity at midrapidity, we give predictions for the multiplicity of charged hadrons, pions, kaons and (anti)protons, for the total transverse energy and net-baryon number, as well as for the $p_T$-spectrum of charged hadrons, pions and kaons. We also predict the region of applicability of hydrodynamics by comparing these results with high-$p_T$ hadron spectra computed from pQCD and energy losses.Comment: 2 pages, 2 figures, to be presented at the workshop "Heavy Ion Collisions at the LHC: Last Call for Predictions" at CERN 29 May - 2 Jun

Transverse Spectra of Hadrons in Central AAAA Collisions at RHIC and LHC from pQCD+Saturation+Hydrodynamics and from pQCD+Energy Losses

We study the transverse spectra of hadrons in nearly central $AA$ collisions at RHIC and LHC in a broad transverse momentum range Low-$p_T$ spectra are calculated by using boost-invariant hydrodynamics with initial energy and net-baryon densities from the EKRT pQCD+saturation model. High-$p_T$ spectra are obtained from pQCD jet calculation including the energy loss of the parton in the matter prior to its fragmentation to final hadrons.Comment: 4 pages, 2 figures, proceedings for Quark Matter 200

RHIC-tested predictions for low-pTp_T and high-pTp_T hadron spectra in nearly central Pb+Pb collisions at the LHC

We study the hadron spectra in nearly central $A$+$A$ collisions at RHIC and LHC in a broad transverse momentum range. We cover the low-$p_T$ spectra using longitudinally boost-invariant hydrodynamics with initial energy and net-baryon number densities from the perturbative QCD (pQCD)+saturation model. Build-up of the transverse flow and sensitivity of the spectra to a single decoupling temperature \Tdec are studied. Comparison with RHIC data at \ssNN=130 and 200 GeV suggests a rather high value \Tdec=150 MeV. The high-$p_T$ spectra are computed using factorized pQCD cross sections, nuclear parton distributions, fragmentation functions, and describing partonic energy loss in the quark-gluon plasma by quenching weights. Overall normalization is fixed on the basis of p+$\bar{\rm p}$(p) data and the strength of energy loss is determined from RHIC Au+Au data. Uncertainties are discussed. With constraints from RHIC data, we predict the $p_T$ spectra of hadrons in 5 % most central Pb+Pb collisions at the LHC energy \ssNN=5500 GeV. Due to the closed framework for primary production, we can also predict the net-baryon number at midrapidity, as well as the strength of partonic energy losses at the LHC. Both at the LHC and RHIC, we recognize a rather narrow crossover region in the $p_T$ spectra, where the hydrodynamic and pQCD fragmentation components become of equal size. We argue that in this crossover region the two contributions are to a good approximation mutually independent. In particular, our results suggest a wider $p_T$-region of applicability for hydrodynamical models at the LHC than at RHIC.Comment: 45 pages, 16 eps-figure

Heavy Ion Physics at the LHC with the ATLAS Detector

The ATLAS detector at CERN will provide a high-resolution longitudinally-segmented calorimeter and precision tracking for the upcoming study of heavy ion collisions at the LHC (sqrt(s_NN)=5520 GeV). The calorimeter covers |eta|<5 with both electromagnetic and hadronic sections, while the inner detector spectrometer covers |eta|<2.5. ATLAS will study a full range of observables necessary to characterize the hot and dense matter formed at the LHC. Global measurements (particle multiplicities, collective flow) will provide access into its thermodynamic and hydrodynamic properties. Measuring complete jets out to 100's of GeV will allow detailed studies of energy loss and its effect on jets. Quarkonia will provide a handle on deconfinement mechanisms. ATLAS will also study the structure of the nucleon and nucleus using forward physics probes and ultraperipheral collisions, both enabled by segmented Zero Degree Calorimeters.Comment: 9 pages, 8 figures, submitted to the Proceedings of Quark Matter 2006, Shanghai, China, November 14-20, 200

PRODUCTION OF DRELL--YAN PAIRS IN HIGH ENERGY NUCLEON--NUCLEON COLLISIONS

We compute cross sections for the Drell-Yan process in N--N collisions at next-to-leading order in $\alpha_s$. The mass, rapidity, transverse momentum, and angular dependence of these cross sections are presented. An estimate of higher order corrections is obtained from next-to-next-to-leading order calculation of the mass distribution. We compare the results with some of the existing data to show the quality of the agreement between calculations and data. We present predictions for energies which will become available at the RHIC and LHC colliders. Uncertainties in these predictions due to choices of scale, scheme and parton distribution are discussed.Comment: 27 pages (latex) plus 28 postscript figure

Elliptic Flow from a Transversally Thermalized Fireball

The agreement of elliptic flow data at RHIC at central rapidity with the hydrodynamic model has led to the conclusion of very rapid thermalization. This conclusion is based on the intuitive argument that hydrodynamics, which assumes instantaneous local thermalization, produces the largest possible elliptic flow values and that the data seem to saturate this limit. We here investigate the question whether incompletely thermalized viscous systems may actually produce more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast primordial longitudinal expansion of the reaction zone, we investigate a toy model which exhibits thermalization only in the transverse directions but undergoes collisionless free-streaming expansion in the longitudinal direction. For collisions at RHIC energies, elliptic flow results from the model are compared with those from hydrodynamics. With the final particle yield and \kt-distribution fixed, the transversally thermalized model is shown not to be able to produce the measured amount of elliptic flow. This investigation provides further support for very rapid local kinetic equilibration at RHIC. It also yields interesting novel results for the elliptic flow of massless particles such as direct photons.Comment: revtex4, 15 pages + 10 embedded EPS figure

Changes in Magnetization and in Dislocation Arrangements in Cyclically Deformed Iron and Nickel

There are a lot of experimental results concerning the effect of stress, elastic and plastic deformation and dislocation structure on the magnetic properties of ferromagnetic material. Atherton et al. measured stress induced changes in the magnetization of steel pipesl. Schroeder et al. studied domain arrangement in plastically deformed iron single crystals2. Hayashi et al. found that the application of an oscillating magnetic field during tensile testing reduced the flow stress of nickel3. Jiles and Atherton4,5D reported changes in magnetization during one stress cycle as a function of an external magnetic field. They have also reported a theory that describes ferromagnetic hysteresis and the effect of stress on magnetization. This theory is based on the Langevins theory of paramagnetism. Jiles and Atherton4 have experimentally shown that the modified Langevins equation gives the change in magnetization as a function of the applied magnetic field