The first heavy ion collisions at the LHC - HIC10

I will review the present status of dynamical models for the
evolution of relativistic heavy ion collision fireballs based on viscous
relativistic hydrodynamics coupled to a hadron rescattering cascade, and
discuss the extraction of the quark-gluon plasma viscosity from a
comparison of this approach with experimental data. Further improvements
of the modelling that are presently in the pipeline and will eventually
address remaining open issues will also be discussed.

The estimation of deviations from local equilibrium in heavy-ion 
collisions is essential  in getting  information on the microscopic  
rates/processes in the dense matter. We show that elliptic flow observables
are strongly dominated by dissipative processes at the hadronic stage. On the
other hand, directed flow is an observable sensitive to the  expansion details
at the  first 1-2fm/c. It is the only observable requiring a simultaneous
acceleration from the longitudinal and transverse pressures. We present first
calculation from 3+1D hydrodynamics assuming non-isotropic pressure and show
that directed flow data indicate a fast pressure equilibration (<0.25fm/c).

Relativistic second-order viscous hydrodynamics at finite temperature is discussed. Using the Weyl-covariant formalism the constraints by conformal invariance are derived. The transport coefficients, e.g. shear viscosity etc., as a function of temperature are obtained from the strongly coupled N=4 SUSY theory applying the AdS/CFT correspondence. Recent results from a comparison with RHIC experimental data are quoted.

We  argue that   in the proximity of the  black disc QCD regime   forward partons propagating through the nuclear matter fluctuate to multiparton configurations - post selection phenomenon -  leading to effective fractional energy losses. The effect leads  to the significant suppression of the forward jet production in the central NA collisions at  RHIC  energies with a moderate suppression of recoiling jet at central rapidities. Our expectations  agreement with the  correlation RHIC  deuteron-gold data.  The post-selection phenomenon   should be grossly amplified at the LHC energies in pA/AA collisions. It also leads  to production of  pancakes of valence quarks and gluons of density > 100 GeV/fm^3 in the nuclear fragmentation region in the central heavy ion collisions.

I  will discuss a recently completed calculation of the NNLO calculation of the HTL-reorganized thermodynamics for QCD.  I will review the basic idea of reorganization of finite temperature perturbation theory and motivate why this hard work is necessary.  The final result will be a comparison of the NNLO calculation for the pressure, energy density, and entropy.  I will show that the HTL-reorganized calculation agrees quite well with available lattice data down to temperatures on the order of 2 to 3 times the critical temperature.  Finally, I will present an outlook for the application of the method to real time quantities such as transport coefficients, heavy quark drag/diffusion, etc.

I will present a general fluidity measure which allows to compare fluids a vastly different length scales. Next I will discuss supercritical fluids and make contact to the fluid generated at RHIC and what this could imply for flow measurements at the LHC

We compare string percolation phenomenology to glasma results on particle rapidity densities, transverse size correlations,long range rapidity correlations and behaviour of the width of multiplicity distributions. We also discuss the equation of state in string percolation showing that agrees with lattice results.

A model-independent method of studying the forward-backward correlations in symmetric high-energy  processes is developped. The method allows a systematic study of properties of various particle sources and to uncover asymmetric structures in symmetric hadron-hadron and nucleus-nucleus inelastic reactions.

Thermodynamics and the phase structure of the Polyakov loop-extended chiral quark--meson  model is explored beyond the
mean-field approximation.  The analysis of the  model is based on the functional renormalization group  method at finite temperature and baryon density. We focus on net-quark number  fluctuations as well as  their higher moments and discuss the influence of non-perturbative effects and  the gluon background on their properties near the chiral crossover transition. We relate the model predictions with lattice QCD results and with the first  data on net proton fluctuations in Au-Au collisions obtained at RHIC by the STAR Collaboration.

I will discuss a possible source of P and CP odd fluctuations observed at RHIC. The basic idea is deeply related to topological properties,   the $\theta$ dependence and the resolution of $U(1)_A$ problem in QCD.

Recent lattice thermodynamics results of the Wuppertal-Budapest Collaboration are reviewed. The results are obtained with physical quark masses and extrapolated to the continuum limit. The transition temperature and the equation of state are discussed.

In this talk, we show the crucial role played by quantum fluctuations in order to reach the equation of state in a system of quantum fields.

In high density QCD the hadron production stems from decay of mini-jets that have the transverse momenta of the order of the saturation scale. I will show that this idea is able to describe in a unique fashion the first data from the LHC for the inclusive charged-hadron production in pp collisions, the deep inelastic scattering at HERA at small Bjorken-x, and the hadron multiplicities in AA collisions at RHIC. Recently reported data from ALICE, CMS and ATLAS including inclusive charged-hadron transverse-momentum and multiplicity distribution in pp collisions are well described in our approach. I provide quantitative predictions for the rapidity, centrality and energy dependencies of inclusive charged-hadron productions for the LHC in AA collisions based on the idea of gluon saturation in the color-glass condensate framework. I also provide predictions for the nuclear modification factor for pions and direct-photon production in pA collisions at LHC energy.

The factorization of long-range phenomena into process-independent parton distributions, which underlies global PDF extractions for the proton, is assumed to extend to nuclear effects in the extraction of nuclear PDFs. As a consequence, assessing the reliability of nPDFs for benchmark calculations goes beyond testing the numerical accuracy of their extraction and requires phenomenological tests of the factorization assumption. We argue that a proton-nucleus collision program at the LHC would provide a set of measurements allowing for unprecedented tests of the factorization assumption underlying global nPDF fits.

Bulk and shear viscosity coefficients of deconfined strongly interacting
matter are studied by means of an effective Boltzmann kinetic theory
assuming the quark-gluon plasma to be describable in terms of
quasiparticle excitations with medium-dependent dispersion relations.
At large temperatures, the results resemble parametric dependencies
on temperature and coupling known from perturbative QCD. This allows
for an extrapolation of the latter into the non-perturbative region finding
fairly nice agreement with available lattice QCD results. Correspondingly,
a small specific shear viscosity for energy densities reachable under
LHC conditions is predicted.

We consider the radiation of photons from quarks scattering on
color-magnetic monopoles in the Quark-Gluon Plasma. The calculation is performed in the classical, non-relativistic approximation and results are compared to photon emission from Coulomb scattering of quarks, known to provide a significant contribution to the photon emission rates from the QGP. The present study is a first step towards understanding whether this scattering process can give a sizable contribution to dilepton
production in heavy-ion collisions.

I will describe two recent results in the string description of strongly coupled gauge theory plasmas. The first one is a new mechanism whereby a quark loses energy by Cherenkov-radiating mesons in the plasma. The second is a gravity solution dual to the N=4 SYM plasma in an anisotropic state. I will discuss implications of these results for heavy-ion collision experiments.

We present our new results on the QCD transition temperature and equation of state with 2+1 flavors of dynamical quarks. All these results are confronted with the predictions of the Hadron Resonance Gas model and Chiral Perturbation Theory for temperatures below the transition region.

We investigate the behavior of the order parameters at finite temperature and imaginary chemical potential by making use of PNJL model. We discuss results from different Polyakov loop potentials and their implication to the dual order parameters.

In ultrarelativistic heavy-ion collisions, the Fourier decomposition of the relative azimuthal angle, $\Delta\phi$,
 distribution of particle pairs yields a large $\cos (3\Delta\phi)$ component, extending out to large rapidity separations $\Delta \eta>1$.  This component captures a significant portion of the ridge and shoulder structures in the $\Delta\phi$ distribution, which have been observed after contributions from elliptic flow are subtracted.  An average finite triangularity due to event-by-event fluctuations in the initial matter distribution, followed by collective flow, naturally produces a $\cos (3\Delta\phi)$ correlation.  Using ideal and viscous hydrodynamics, and transport theory, we study the physics of triangular ($v_3$) flow in comparison to elliptic ($v_2$), quadrangular ($v_4$) and pentagonal ($v_5$) flow.  We make quantitative predictions for $v_3$ at RHIC and LHC as a function of centrality and transverse momentum.  Our results for the centrality dependence of $v_3$ show a quantitative agreement with data extracted from previous correlation measurements by the STAR collaboration. This study supports previous results on the importance of triangular flow in the understanding of ridge and shoulder structures. Triangular flow is found to be a sensitive probe of initial geometry fluctuations and viscosity.

The property of  extended longitudinal scaling of rapidity distributions was noticed recently over a broad  range of beam energies. It is shown here that this property is consistent with predictions of the statistical thermal model up to the highest RHIC beam energies. We expect,however, that at LHC energies the rapidity distribution of produced particles will violate extended longitudinal scaling.

We develop a framework for event-by-event ideal hydrodynamics to study the differential elliptic flow which is measured at different centralities in Au+Au collisions at Relativistic Heavy Ion Collider (RHIC). Fluctuating initial energy density profiles, which here are the event-by-event analogues of the eWN profiles, are created using a Monte Carlo Glauber model. Using the same event plane method for obtaining $v_2$ as in the data analysis, we can reproduce both the measured centrality dependence and the $p_T$ shape of charged-particle elliptic flow up to $p_T\sim2$~GeV. We also consider the relation of elliptic flow to the initial state eccentricity using different reference planes, and discuss the correlation between the physical event plane and the initial participant plane. Our results demonstrate that event-by-event hydrodynamics with initial state fluctuations must be accounted for before a meaningful lower limit for viscosity can be obtained from elliptic flow data.

based on: Hannu Holopainen, Harri Niemi, Kari J. Eskola,
e-Print: arXiv:1007.0368 [hep-ph]

Spontaneous chiral symmetry breaking and trace anomaly are intrinsically tied via the emergence of a scale in QCD. I discuss thermodynamics and chiral properties of baryons in a parity doublet model.

We employ a conformal mapping of the chemical potential $\mu$ to explore the thermodynamics of strongly interacting matter at finite values of the baryon chemical potential $\mu$.  This method allows us to identify the singularity corresponding to the critical point of a second-order phase transition at finite $\mu$ given information only at $\mu=0$. This scheme is potentially useful for computing thermodynamic properties of strongly interacting hot and dense matter in lattice QCD. The usefulness of this technique is illustrated by an application to a chiral effective model.

or the collisions of heavy ions, the crucial question is whether results at the LHC will be similar, or dramatically different, from those at RHIC.  I discuss how they might be very different, based upon an ansatz for the transition region to deconfinement, the "semi" QGP.  I discuss various processes change markedly, including the shear viscosity and energy loss, although surprising, not dilepton production.

I will discuss the inclusion of medium-modified splitting functions, according to the BDMPS approximation, in parton shower generators. Particular care will be taken about the implementation in the HERWIG algorithm, which satisfies the angular ordering prescription. I will present results on transverse momentum, angle and energy distributions, which exhibit remarkable medium effects.

Effects of decoherence and resulting destruction of angular ordering on the properties of the in-medium QCD cascades is discussed

We demonstrate that a formalism where one assumes a hard jet to be weakly coupled to a medium, which may itself be strongly or weakly coupled, can be used to explain high $p_T$ leading particle suppression and azimuthal anisotropy. In this calculation the scattering and multiple emissions of partons within a jet is computed entirely within perturbation theory. The scattering matrix elements are assumed to be factorized into a hard partonic part and a soft non-perturbative part. The soft part may be expressed as the expectation of certain operator products in the medium. There exist a set of related operators which encode the usual transport coefficients which describe transverse broadening, elastic energy loss and longitudinal diffusion. Relating these operators to each other such that there exists only one undetermined constant, which is scaled with temperature according to its energy dimensions, we successfully describe both heavy and light flavor jet modification. Imposing additional constraints on the coefficients such as requiring that they be computed within Leading Order HTL tends to worsen the fit. This indicates that jet quenching coefficients cannot be calculated at Leading Order in HTL theory.  

We propose a hybrid model for medium-induced parton energy loss, in which the hard scales in the process are treated perturbatively, while the soft scales which involve strong coupling dynamics are modeled by AdS/CFT calculations. After fitting a single parameter on R_AA for central Au+Au collisions, we are able to predict different observables like R_AA and I_AA as a function of centrality and reaction plane. We obtain a consistent picture of how jet quenching is modified if the quark-gluon plasma is strongly interacting, and we provide quantitative predictions.

The effects induced by the polarization of the quark-gluon
medium due to penetrating it partons are considered in 
the framework of the macroscopic QCD. Among them are 
Cherenkov gluons, the wake effect and the transition radiation.
Corresponding experimental data are discussed.

I discuss novel theoretical approaches towards understanding the strongly coupled QGP produced in heavy ion collisions. In particular, I shall emphasize the role that dualities play in these approaches. 

Recent developments in the computation of the NLO improvement for non-linear QCD evolution equations has allowed, for the first time, for the consistent description of experimental data using a first principle approach including non-linearities. In particular, the Balitsky-Kovchegov equation including running coupling effects (rcBK) has been shown to provide an excellent global description of inclusive DIS data.
I will present the results of global fits to proton data (with and without heavy quarks), and discuss the ongoing effort to extend to the nuclear case,  performed in a numerical implementation of rcBK. The resulting parametrizations allow for the reliable computation of physical observables in a kinematical region (relevant for both p-p and A-A programmes at the LHC) where the standard DGLAP based techniques are expected to fail.

Since the year 2000, the Relativistic Heavy Ion Collider has explored 
the properties of hot QCD matter in an energy regime where hard QCD probes 
and ab-initio calculations are available. The results from RHIC have led to a
dramatic revision of our notion of the quark-gluon plasma as a strongly coupled,
nearly inviscid liquid highly opaque to probes carrying open color, i.e. quarks and
gluons).However, many details of this new picture remain fuzzy. My lecture will 
give a preview of the opportunities opened up by the LHC, the RHIC upgrades, 
and theoretical advances during the next decade to answer some of the many 
remaining questions about the physics of hot QCD matter.

In this talk, I will present recent results of spectral functions of
charmonia at finite temperature and momentum obtained
from lattice correlators. We used large lattices with large volume
in order to fully include thermal effects. The calculation was
carried out by M. Kitazawa, Y. Kouno, C. Nonaka, and myself.

After surveying the distinguishing features of quarkonia, I discuss their behavior in a quark-gluon plasma, as given by effective field theory and potential models as well as by lattice QCD. This is then
used to discuss sequential quarkonium suppression in nuclear collisions. Finally I consider the possibility of statistical formation of charmonia at hadronization, together with predictions for LHC measurements as resulting from the two scenarios.  

The stochastic dynamics of heavy quarks in the fireball produced in heavy-ion collisions is followed through numerical simulations based on the Langevin equation. The R_AA and v_2 of c and b quarks, hadrons and single-electrons is studied. The transport coefficients are evaluated treating separately the contribution of soft and hard collisions. The initial heavy-quark spectra are generated according to NLO-pQCD, accounting for nuclear effects through recent nPDFs. The evolution of the medium is obtained from the output of two hydro-codes (ideal and viscous). The heavy-quark fragmentation into hadrons and their final semileptonic decays are implemented according to up to date experimental data. A comparison with RHIC data for non-photonic electron spectra is given. Some scenarios of interest for LHC are also explored.

After a short introduction to modern observations of compact stars, which concern different astrophysical objects such as pulsars, double neutron stars, accreting low-mass X-ray binaries etc., we explain how to extract from mass and radius measurements the cold dense equation of state (EoS). In the near future the NASA International X-ray Observatory (IXO) project shall deliver such data with 5% accuracy and thus provide a benchmark for the T=0 EoS which will play a similar role as the zero-density EoS from Lattice QCD.
 
In the main body of the talk, we will outline a quantum field theoretical approach to the EoS of dense quark matter with special emphasis on color superconducting quark matter phases and their importance for understanding the phenomenology of compact stars.

An outlook is given to the problem of generalizing the EoS to a wide enough range of densities, temperatures and isospin asymmetries in order to apply it for both, supernova collapse simulations and heavy-ion collisions from FAIR-CBM and JINR-NICA to BNL-RHIC and CERN-LHC. This is one of the tasks attacked within the research networking programme "The New Physics of Compact Stars - CompStar" (2008-2013) of the European Science Foundation.