Non-Gaussian eccentricity fluctuations

We study the fluctuations of the anisotropy of the energy density profile created in a high-energy collision at the LHC. We show that the anisotropy in harmonic $n$ has generic non-Gaussian fluctuations. We argue that these non-Gaussianities have a universal character for small systems such as p+Pb collisions, but not for large systems such as Pb+Pb collisions where they depend on the underlying non-Gaussian statistics of the initial density profile. We generalize expressions for the eccentricity cumulants $\varepsilon_2\{4\}$ and $\varepsilon_3\{4\}$ previously obtained within the independent-source model to a general fluctuating initial density profile.Comment: 14 pages. Minor revisio

Continuous description of fluctuating eccentricities

We consider the initial energy density in the transverse plane of a high energy nucleus-nucleus collision as a random field \rho(\x), whose probability distribution $P[\rho]$, the only ingredient of the present description, encodes all possible sources of fluctuations. We argue that it is a local Gaussian, with a short-range 2-point function, and that the fluctuations relevant for the calculation of the eccentricities that drive the anisotropic flow have small relative amplitudes. In fact, this 2-point function, together with the average density, contains all the information needed to calculate the eccentricities and their variances, and we derive general model independent expressions for these quantities. The short wavelength fluctuations are shown to play no role in these calculations, except for a renormalization of the short range part of the 2-point function. As an illustration, we compare to a commonly used model of independent sources, and recover the known results of this model

Correlations in the Monte Carlo Glauber model

Event-by-event fluctuations of observables are often modeled using the Monte Carlo Glauber model, in which the energy is initially deposited in sources associated with wounded nucleons. In this paper, we analyze in detail the correlations between these sources in proton-nucleus and nucleus-nucleus collisions. There are correlations arising from nucleon-nucleon correlations within each nucleus, and correlations due to the collision mechanism, which we dub twin correlations. We investigate this new phenomenon in detail. At the RHIC and LHC energies, correlations are found to have modest effects on size and eccentricity fluctuations, such that the Glauber model produces to a good approximation a collection of independent sources.Comment: minor improvements, 14 pages, 9 figure

J/Psi suppression in central Pb-Pb collisions

We discuss the recent NA50 J/Psi production data in Pb--Pb collisions, in particular the second drop at high transverse energies which correspond to the most central collisions. Using a model which relates the J/Psi suppression to the local energy density, we show that the data can be explained by taking into account transverse energy fluctuations at a given impact parameter. Predictions of this model for RHIC are briefly discussed.Comment: to appear in the Proceedings of Quark Matter'200

Transverse energy fluctuations and the pattern of J/Psi suppression in Pb-Pb collisions

The NA50 collaboration has recently observed that the J/psi production rate in Pb-Pb collisions decreases more rapidly as a function of the transverse energy for the most central collisions than for less central ones. We show that this phenomenon can be understood as an effect of transverse energy fluctuations in central collisions. A good fit of the data is obtained using a model which relates J/psi suppression to the local energy density. Our results suggest that the J/psi is completely suppressed at the highest densities achieved in Pb-Pb collisions.Comment: v2, 4 pages, LaTeX, 3 eps figures include

Elliptic flow and incomplete equilibration at RHIC

We argue that RHIC data, in particular those on the anisotropic flow coefficients v_2 and v_4, suggest that the matter produced in the early stages of nucleus-nucleus collisions is incompletely thermalized. We interpret the parameter (1/S)(dN/dy), where S is the transverse area of the collision zone and dN/dy the multiplicity density, as an indicator of the number of collisions per particle at the time when elliptic flow is established, and hence as a measure of the degree of equilibration. This number serves as a control parameter which can be varied experimentally by changing the system size, the centrality of the collision, or the beam energy. We provide predictions for Cu-Cu collisions at RHIC as well as for Pb-Pb collisions at the LHC.Comment: 5 pages, 2 figures, minor correction

Detecting a First-Order Transition in the QCD Phase Diagram with Baryon-Baryon Correlations

We suggest baryon-baryon correlations as an experimentally accessible signature for a first-order phase transition between a baryon-rich phase, like quarkyonic, and a baryon-suppressed hadronic phase in the QCD phase diagram. We examine the consequences of baryon-rich bubble formation in an expanding medium and show how the two-particle correlations vary in the transverse and longitudinal direction depending on the strength of the radial flow, the bubble temperature, and the time when the baryons are emitted.Comment: Revised published version, 6 pages in PL

Signals of the quark-gluon plasma in nucleus-nucleus collisions

This talk is a brief overview of the present status of our understanding of nucleus-nucleus collisions at high energy and the search for signals of the quark-gluon plasma.Comment: flatex qm99.tex, 2 files XIV International Conference on `Ultra-Relativistic Nucleon-Nucleon Collisions' Torino, Italie 1999-05-10 1999-05-15 May 10-15, 1999 [SPhT-T99/103

Collective fermionic excitations in systems with a large chemical potential

We study fermionic excitations in a cold ultrarelativistic plasma. We construct explicitly the quantum states associated with the two branches which develop in the excitation spectrum as the chemical potential is raised. The collective nature of the long wavelength excitations is clearly exhibited. Email contact: [email protected]: Saclay-T93/018 Email: [email protected]

Particle dependence of elliptic flow in Au+Au collisions at sNN=\sqrt{s_{NN}}= 200 GeV

The elliptic flow parameter ($v_2$) for $K_S^0$ and $\Lambda+\bar{\Lambda}$ has been measured at mid-rapidity in Au + Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV by the STAR collaboration. The $v_2$ values for both $K_S^{0}$ and $\Lambda+\bar{\Lambda}$ saturate at moderate $p_T$, deviating from the hydrodynamic behavior observed in the lower $p_T$ region. The saturated $v_2$ values and the $p_T$ scales where the deviation begins are particle dependent. The particle-type dependence of $v_2$ shows features expected from the hadronization of a partonic ellipsoid by coalescence of co-moving quarks. These results will be discussed in relation to the nuclear modification factor ($R_{CP}$) which has also been measured for $K_S^0$ and $\Lambda+\bar{\Lambda}$ by the STAR collaboration.Comment: 6 pages, 3 figures, Strange Quark Matter 2003 Conference (SQM 2003): updated with 2 figures from original talk that did not appear in the journa