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The effects of fluctuating initial conditions are studied in the context of relativistic heavy ion collisions where a rapidly evolving system is formed. Two-particle correlation analysis is applied to events generated with the NEXSPHERIO hydrodynamic code, starting with fluctuating nonsmooth initial conditions (IC). The results show that the nonsmoothness in the IC survives the hydroevolution and can be seen as topological features of the angular correlation function of the particles emerging from the evolving system. A long range correlation is observed in the longitudinal direction and in the azimuthal direction a double peak structure is observed in the opposite direction to the trigger particle. This analysis provides clear evidence that these are signatures of the combined effect of tubular structures present in the IC and the proceeding collective dynamics of the hot and dense medium.

On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and trans- verse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η| < 0.5, we obtain dN ch /dη = 3.10 ± 0.13(stat.) ± 0.22(syst.) for all inelastic interactions, and dN ch /dη = 3.51 ± 0.15(stat.) ± 0.25(syst.) for nonsingle diffractive interactions. These results are consistent with previous measurements in proton-antiproton interactions at the same centre-of-mass energy at the CERN SppS collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase.

In this communication, we report results of three-dimensional hydrodynamic computations, by using equations of state with a critical end point as suggested by the lattice QCD. Some of the results are an increase of the multiplicity in the mid-rapidity region and a larger elliptic-flow parameter v 2 . We discuss also the effcts of the initial-condition fluctuations and the continuous emission.

In this work we present a study of the influence of nucleus initializations on the event-by-event elliptic flow coefficient, v 2 . In most Monte-Carlo models, the initial positions of the nucleons in a nucleus are completely uncorrelated, which can lead to very high density regions. In a simple, yet more realistic model where overlapping of the nucleons is avoided, fluctuations in the initial conditions are reduced. However, v 2 distributions are not very sensitive to the initialization choice.

Elliptic flow at RHIC is computed event-by-event with NeXSPhe-RIO. Reasonable agreement with experimental results on v 2 (η) is obtained. Various effects are studied as well: reconstruction of impact parameter direction, freeze out temperature, equation of state (with or without crossover), emission mecanism.

After five years of running at RHIC, and on the eve of the LHC heavy-ion program, we highlight the status of femtoscopic measurements. We emphasize the role interferometry plays in addressing fundamental questions about the state of matter created in such collisions, and present an enumerated list of measurements, analyses and calculations that are needed to advance the field in the coming years.Keywords: Theoretical and experimental identical-particle correlations; Theoretical and experimental femtoscopy; Particleantiparticle correlationsThe first two-pion interferometric measurements of the collider era emerged within a year of RHIC becoming operational. To the surprise of many in the field, the measurements were remarkably similar to those recorded at the AGS and the SPS. The analyses were inconsistent, both qualitatively and quantitatively, with dynamic models incorporating first-order phase transitions in general. In fact, parametric explanations of the data, the forms of which are often motivated by solutions to dynamical equations, suggest that the matter explodes violently, growing from a radius of 6 fm to 13 fm in only 10 fm/c. The surprisingly strong acceleration required for such behavior and the associated failure of many of the field's most sophisticated models became known as the "HBT Puzzle".Five years later, the field has made steady progress on a variety of fronts. Theoretically, sophisticated dynamic models have more successfully reproduced experimental results (though the very sophistication of these models has made it difficult to ascertain which aspects of the models are being validated by the comparison). New techniques have been applied to the analysis of experimental correlation functions, revealing greater detail about the size and shape of the emission region. During our discussions at the workshop, it was clear that a remarkable consensus had developed among the practitioners of the field. Although this agreement by no means represented a final conclusion, we found numerous points that could be stated without dissent. In this white paper we will first list the points concerning the current status of the field, then further below, enumerate points where participants agreed were important for further progress. Achievements:• Remarkable agreement has been observed between the RHIC experiments, PHENIX, PHOBOS and STAR. All three have produced high-statistics high-quality pion correlations, whose apparent source sizes are consistent to a few tenths of a fm. A similar consistency was observed among measurements performed at the top SPS energy; at lower SPS energies the maximum deviations are on the level of 20%.• Femtoscopic studies are highly multi-dimensional. Even the simplest and most common case of twoidentical pion correlations depend on six independent variables, which have only been fully explored within the past few years. This includes extracting characteristic source sizes as function of transverse momentum, rapidity and the angle with respect to the reaction plane for off-axis co...

Effects of lattice-QCD-inspired equations of state and continuous emission on some observables are discussed, by solving a 3D hydrodynamics. The particle multiplicity as well as v 2 are found to increase in the mid-rapidity. We also discuss the effects of the initial-condition fluctuations.Keywords: LatticeQCD equations of state, hydrodynamic model PACS: 24.10.Nz, 25.75.Ld FIGURE 1. The initial energy density at η = 0 is plotted in units of GeV/fm 3 . One random event is shown vs. average over 30 random events (≃ smooth initial conditions in the usual hydro approach). FIGURE 7. k T dependence of HBT radii R s and R o for pions in the most central Au+Au at 200A GeV, computed with event-by-event fluctuating IC. The data are from PHENIX Collab.[14].