Statistical and Dynamical Fluctuations in Heavy Ion Collisions: Role of Conservation Laws in Event-by-Event Analysis

The analysis of the statistical and dynamical fluctuations in nucleus-nucleus collisions on an event-by-event basis strongly relies on a comparison with specially constructed artificial events where statistical fluctuations and kinematical correlations are under control. In this paper, we present a novel, analytical method of constructing reference events based on independent emission, modified by the energy/momentum constraint, which can lead to a better understanding of the nature of the observed final-state fluctuations. This approach can be easily used in the analysis of other topics in the heavy ion field (e.g. flow, HBT etc.) allowing more precise measurements.Comment: 6 pages, no figure

Xi(Omega) production in Pb + Pb collisions at 158 GeV c exp -1

Using the NA49 main TPC, the central production of hyperons has been measured in CERN SPS Pb - Pb collisions at 158 GeV c-1. The preliminary ratio, studied at 2.0 < y < 2.6 and 1 < pT < 3 GeV c-1, equals ~ (13 ± 4)% (systematic error only). It is compatible, within errors, with the previously obtained ratios for central S + S [1], S + W [2], and S + Au [3] collisions. The fit to the transverse momentum distribution resulted in an inverse slope parameter T of 297 MeV. At this level of statistics we do not see any noticeable enhancement of hyperon production with the increased volume (and, possibly, degree of equilibration) of the system from S + S to Pb + Pb. This result is unexpected and counterintuitive, and should be further investigated. If confirmed, it will have a significant impact on our understanding of mechanisms leading to the enhanced strangeness production in heavy-ion collisions

Quark Gluon Plasma - Recent Advances

While heavy ion collisions at the SPS have produced excited strongly interacting matter near the conditions for quark deconfinement, the RHIC may be the first machine capable of creating quark-antiquark plasmas sufficiently long-lived to allow deep penetration into the new phase. A comprehensive experimental program addressing this exciting physics has been put into place. Presented here are preliminary results from Au+Au at $\sqrt{S}$ = 130 GeV obtained during the first RHIC run and some CERN SPS results from Pb+Pb at $\sqrt{S}$ = 17 GeV (particularly relevant to QGP search).Comment: 15 pages, 19 figure

Prospects for quarkonia production studies in U+U collisions

Collisions of deformed uranium nuclei provide a unique opportunity to study the spatial dependence of charmonium in-medium effects. By selecting the orientations of the colliding nuclei, different path lengths through the nuclear medium could be selected within the same experimental environment. In addition, higher energy densities can be achieved in U+U collisions relative to Au+Au collisions. In this paper, we investigate the prospects for charmonium studies with U+U collisions. We discuss the effects of shadowing and nuclear absorption on the J/\psi\ yield. We introduce a new observable which could help distinguish between different types of J/\psi\ interactions in hot and dense matter.Comment: 13 pages, 10 figure

We Are Family? Examining Parental Leave and Non-Normative Parents in the United States

This article will examine parental leave and the non-normative parent. Parental leave in the United States is currently a hot-button issue. With so much focus on the “Opt-Out” Generation, “Leaning In,” and whether women can in fact “have it all,” the issues faced by parents who are not educated, upper class, and in a heterosexual marriage relationship with the biological father are often ignored in the discussion of how the law is lacking. Instead, the discussion has focused on women at the top echelon of employment. In doing this, a large segment of the population is being completely left out of the efforts to make comprehensive change in parental leave laws. Parental leave, as it currently stands in the United States, is a privilege rather than a right; this must change to account fully for the most comprehensive parental leave possible. In order for the entire nation to progress in this area, the needs of all must be considered in the creation and application of parental leave laws and policies. This paper will examine how laws in the United States are currently structured and applied for all parents. Specifically, it will examine how the Family and Medical Leave Act is insufficient to meet the needs of homosexual parents, single parents, and low-income parents. It will then suggest how the laws can be changed to account for the current gaps

A percolation transition in Yang-Mills matter at finite number of colours

We examine baryonic matter at quark chemical potential of the order of the confinement scale, \mu_q\sim \lqcd. In this regime, quarks are supposed to be confined but baryons are close to the ``tightly packed limit'' where they nearly overlap in configuration space. We show that this system will exhibit a percolation phase transition {\em when varied in the number of colours} $N_c$: at high $N_c$, large distance correlations at quark level are possible even if the quarks are essentially confined. At low $N_c$, this does not happen. We discuss the relevance of this for dense nuclear matter, and argue that our results suggest a new ``phase transition'', varying $N_c$ at constant $\mu_q$.Comment: Accepted for publication, Physical Review Letters. Title changed from original, "Quarkyonic percolation at finite number of colors", at the request of the edito

Stopping in central Pb + Pb collisions at SPS energies and beyond

We investigate stopping and baryon transport in central relativistic Pb + Pb and Au + Au collisions. At energies reached at the CERN Super Proton Synchrotron [sqrt(s_NN) = 6.3-17.3 GeV] and at RHIC (62.4 GeV), we determine the fragmentation-peak positions from the data. The resulting linear growth of the peak positions with beam rapidity is in agreement with our results from a QCD-based approach that accounts for gluon saturation. No discontinuities in the net-proton fragmentation peak positions occur in the expected transition region from partons to hadrons at 6-10 GeV.Comment: 5 pages, 3 figures, 1 table. Figures updated, table shortened, 1 reference adde

Rise of azimuthal anisotropies as a signature of the Quark-Gluon-Plasma in relativistic heavy-ion collisions

The azimuthal anisotropies of the collective transverse flow of hadrons are investigated in a large range of heavy-ion collision energy within the Parton-Hadron-String Dynamics (PHSD) microscopic transport approach which incorporates explicit partonic degrees of freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as dynamical hadronization and hadronic dynamics in the final reaction phase. The experimentally observed increase of the elliptic flow $v_2$ with bombarding energy is successfully described in terms of the PHSD approach in contrast to a variety of other kinetic models based on hadronic interactions. The analysis of higher-order harmonics $v_3$ and $v_4$ shows a similar tendency of growing deviations between partonic and purely hadronic models with increasing bombarding energy. This signals that the excitation functions of azimuthal anisotropies provide a sensitive probe for the underling degrees of freedom excited in heavy-ion collisions.Comment: 4 pages, 3 figures, title change

Signs of Thermalization from RHIC Experiments

Selected results from the first five years of RHIC data taking are reviewed with emphasis on evidence for thermalization in central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.Comment: 10 pages, 6 figure

Chemical fluctuations in high-energy nuclear collisions

Fluctuations of the chemical composition of the hadronic system produced in nuclear collisions are discussed using the $\Phi-$measure which has been earlier applied to study the transverse momentum fluctuations. The measure is expressed through the moments of the multiplicity distribution and then the properties of $\Phi$ are discussed within a few models of multiparticle production. A special attention is paid to the fluctuations in the equilibrium ideal quantum gas. The system of kaons and pions, which is particularly interesting from the experimental point of view, is discussed in detail.Comment: 8 pages, 4 figures, revised version to appear in Phys. Lett.