High energy nucleus-nucleus collisions

Experimental results on high energy nucleus-nucleus interactions are presented. The data are discussed within the framework of standard super-position models and from the point-of-view of the possible formation of new states of matter in heavy ion collisions

Intermittency and QCD jets

Multiplicity distributions in rapidity bins are studied in the Marchesini–Webber model for e$^{+}$e$^{-}$ annihilation. The intermittent, power-like growth of the scaled factorial moments for small rapidity bins is found. Corrections accounting for the rapidity dependence of the single particle density are analyzed and shown to lead to the universal behaviour for various choices of the studied rapidity range

Latest results from the PHOBOS experiment

Over the past years PHOBOS has continued to analyze the large datasets obtained from the first five runs of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The two main analysis streams have been pursued. The first one aims to obtain a broad and systematic survey of global properties of particle production in heavy ion collisions. The second class includes the study of fluctuations and correlations in particle production. Both type of studies have been performed for a variety of the collision systems, covering a wide range in collision energy and centrality. The uniquely large angular coverage of the PHOBOS detector and its ability to measure charged particles down to very low transverse momentum is exploited. The latest physics results from PHOBOS, as presented at Quark Matter 2008 Conference, are contained in this report.Comment: 9 pages, 9 figures, presented at the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur, India, Feb.4-10, 200

Heavy Ion Physics with the ATLAS Detector

This talk reports on the studies of the ATLAS experiment capability for heavy-ion physics. These studies show a very good potential of the ATLAS detector for measurements of global properties of nucleus-nucleus collisions such as charged particle multiplicities and azimuthal anisotropies as well as heavy quark and quarkonia production and jet quenching. The results from the first round of studies obtained with the full-simulation of the detector response are presented and on going activities are briefly summarized

Direct Calculations of the Odderon Intercept in the Perturbative QCD

The odderon intercept is calculated directly, from its expression via an average energy of the odderon Hamiltonian, using both trial wave functions in the variational approach and the wave function recently constructed by R.A.Janik and J.Wosiek. The results confirm their reported value for the energy. The odderon intercept is calculated directly, from its expression via an average energy of the odderon Hamiltonian, using both trial wave functions in the variational approach and the wave function recently constructed by R.A.Janik and J.Wosiek.The results confirm their reported value for the energy. Variational calculations give energies some 30% higher. However they also predict the odderon intercept to be quite close to unity. In fact, for realistic values of $\alpha_s$, the intercept calculated variationally is at most 2% lower than the exact one: 0.94 instead of 0.96. It is also found that the solution for $q_3=0$ does not belong to the odderon spectrum. The diffusion parameter is found to be of the order 0.6.Comment: 20 page

Direct solution of the hard pomeron problem for arbitrary conformal weight

A new method is applied to solve the Baxter equation for the one dimensional system of noncompact spins. Dynamics of such an ensemble is equivalent to that of a set of reggeized gluons exchanged in the high energy limit of QCD amplitudes. The technique offers more insight into the old calculation of the intercept of hard Pomeron, and provides new results in the odderon channel.Comment: Contribution to the ICHEP96 Conference, July 1996, Warsaw, Poland. LaTeX, 4 pages, 3 epsf figures, includes modified stwol.sty file. Some references were revise

The Bose-Einstein effect in Monte-Carlo generators: weight methods

We present a method which incorporates the Bose-Einstein effect into Monte Carlo generators for multiple production by weighting the events. Various aspects of weight calculations are discussed in detail. We show that our method allows to describe reasonably well a sample of data and we outline the future tests and applications.Comment: Latex, 10 pages including 4 .eps figure

The Importance of Correlations and Fluctuations on the Initial Source Eccentricity in High-Energy Nucleus-Nucleus Collisions

In this paper, we investigate various ways of defining the initial source eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we examine the participant eccentricity, which quantifies the eccentricity of the initial source shape by the major axes of the ellipse formed by the interaction points of the participating nucleons. We show that reasonable variation of the density parameters in the Glauber calculation, as well as variations in how matter production is modeled, do not significantly modify the already established behavior of the participant eccentricity as a function of collision centrality. Focusing on event-by-event fluctuations and correlations of the distributions of participating nucleons we demonstrate that, depending on the achieved event-plane resolution, fluctuations in the elliptic flow magnitude $v_2$ lead to most measurements being sensitive to the root-mean-square, rather than the mean of the $v_2$ distribution. Neglecting correlations among participants, we derive analytical expressions for the participant eccentricity cumulants as a function of the number of participating nucleons, \Npart,keeping non-negligible contributions up to \ordof{1/\Npart^3}. We find that the derived expressions yield the same results as obtained from mixed-event MCG calculations which remove the correlations stemming from the nuclear collision process. Most importantly, we conclude from the comparison with MCG calculations that the fourth order participant eccentricity cumulant does not approach the spatial anisotropy obtained assuming a smooth nuclear matter distribution. In particular, for the Cu+Cu system, these quantities deviate from each other by almost a factor of two over a wide range in centrality.Comment: 18 pages, 10 figures, submitted to PR

Intermittency in Branching Processes

We study the intermittency properties of two branching processes, one with a uniform and another with a singular splitting kernel. The asymptotic intermittency indices, as well as the leading corrections to the asymptotic linear regime are explicitly computed in an analytic framework. Both models are found to possess a monofractal spectrum with $\varphi_{q}=q-1$. Relations with previous results are discussed.Comment: 20 pages, UCLA93/TEP/2

Automated track recognition and event reconstruction in nuclear emulsion

The major advantages of nuclear emulsion for detecting charged particles are its submicron position resolution and sensitivity to minimum ionizing particles. These must be balanced, however, against the difficult manual microscope measurement by skilled observers required for the analysis. We have developed an automated system to acquire and analyze the microscope images from emulsion chambers. Each emulsion plate is analyzed independently, allowing coincidence techniques to be used in order to reject background and estimate error rates. The system has been used to analyze a sample of high-multiplicity Pb-Pb interactions (charged particle multiplicities ∼1100) produced by the 158 GeV/c per nucleon 208Pb beam at CERN. Automatically measured events agree with our best manual measurements on 97% of all the tracks. We describe the image analysis and track reconstruction techniques, and discuss the measurement and reconstruction uncertainties