Inelastic Diffraction at Heavy Ion Colliders

The heavy ion physics approach to global event characterization has led us to instrument the forward region in the PHENIX experiment at RHIC. In heavy ion collisions this coverage yields a measurement of the "spectator" energy and its distribution about the beam direction. This energy flow is the basis of event-by-event determination of the centrality and reaction plane which are key to analyzing particle production in heavy ion collisions. These same tools have also enabled a unique set of measurements on inelastic diffraction with proton, deuteron and gold ion beams in the PHENIX experiment. We present first new results on this topic and discuss briefly the opportunity for diffractive physics with Heavy Ion beams at the LHC.Comment: RHIC overview talk presented at "Diffraction 2004" in Dorgali, Sardegna, Ital

Source Parameters from Identified Hadron Spectra and HBT Radii for Au-Au Collisions at sqrt(s_NN)=200 GeV in PHENIX

The characteristics of the particle emitting source are deduced from low transverse momentum identified hadron spectra (transverse mass less than 1 GeV) and HBT radii using a hydrodynamic interpretation. From the most peripheral to the most central data, the single particle spectra are fit simultaneously for all pions, kaons, and (anti-)protons using the parameterization in [1] and assuming a linear transverse flow profile. Within the systematic uncertainties, the expansion parameters called the freeze-out temperature and flow velocity, respectively decrease and increase with the number of participants, saturating for both at mid-centrality. The expansion using analytic calculations of the kT dependence of HBT radii in [2] is fit to the data but no chi-squared minimum is found.Comment: 4 pages, 4 figures, Contribution to Quark Matter 2002, Nantes, France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A

Transport model analysis of particle correlations in relativistic heavy ion collisions at femtometer scales

The pion source as seen through HBT correlations at RHIC energies is investigated within the UrQMD approach. We find that the calculated transverse momentum, centrality, and system size dependence of the Pratt-HBT radii $R_L$ and $R_S$ are reasonably well in line with experimental data. The predicted $R_O$ values in central heavy ion collisions are larger as compared to experimental data. The corresponding quantity $\sqrt{R_O^{2}-R_S^{2}}$ of the pion emission source is somewhat larger than experimental estimates.Comment: 12 pages, 5 figures, to be published in PR

Traces of Thermalization from Transverse Momentum Fluctuations in Nuclear Collisions

Scattering of particles produced in Au+Au collisions at RHIC can wrestle the system into a state near local thermal equilibrium. I illustrate how measurements of the centrality dependence of the mean transverse momentum and its fluctuations can exhibit this thermalization.Comment: 4 pages, 2 eps figures, final version to appear in PR

Heavy ion collisions: Correlations and Fluctuations in particle production

Correlations and fluctuations (the latter are directly related to the 2-particle correlations) is one of the important directions in analysis of heavy ion collisions. At the current stage of RHIC exploration, when the details matter, basically any physics question is addressed with help of correlation techniques. In this talk I start with a general introduction to the correlation and fluctuation formalism and discuss weak and strong sides of different type of observables. In more detail, I discuss the two-particle $p_t$ correlations/\mpt fluctuations. In spite of not observing any dramatic changes in the event-by-event fluctuations with energy, which would indicate a possible phase transition, such correlations measurements remain an interesting and important subject, bringing valuable information. Lastly, I show how radial flow can generate characteristic azimuthal, transverse momentum and rapidity correlations, which could qualitatively explain many of recently observed phenomena in nuclear collisions.Comment: 8 pages, 8 figures. Invited talk at 5th International Conference on Physics and Astrophysics of Quark Gluon Plasma, February 8-12, 2005, Salt Lake City, Kolkata, Indi

Is Anomalous Production of Omega and anti-Omega Evidence for Disoriented Chiral Condensates?

No conventional picture of nucleus-nucleus collisions has yet been able to explain the abundance of Omega and anti-Omega hyperons in central collisions between Pb nuclei at 158 A GeV at the CERN SPS. We argue that this is evidence that they are produced as topological defects arising from the formation of disoriented chiral condensates (DCC) with an average domain size of about 2 fm.Comment: version 2 containing formulas, accepted by PR

Transport model analysis of the transverse momentum and rapidity dependence of pion interferometry at SPS energies

Based on the UrQMD transport model, the transverse momentum and the rapidity dependence of the Hanbury-Brown-Twiss (HBT) radii $R_L$, $R_O$, $R_S$ as well as the cross term $R_{OL}$ at SPS energies are investigated and compared with the experimental NA49 and CERES data. The rapidity dependence of the $R_L$, $R_O$, $R_S$ is weak while the $R_{OL}$ is significantly increased at large rapidities and small transverse momenta. The HBT "life-time" issue (the phenomenon that the calculated $\sqrt{R_O^{2}-R_S^{2}}$ value is larger than the correspondingly extracted experimental data) is also present at SPS energies.Comment: 17 pages, 11 figure

A Unified Approach towards Describing Rapidity and Transverse Momentum Distributions in Thermal Freeze-Out Model

We have attempted to describe the rapidity and transverse momentum spectra, simultaneously, of the hadrons produced in the Ultra-relativistic Nuclear Collisions. This we have tried to achieve in a single statistical thermal freeze-out model using single set of parameters. We assume the formation of a hadronic gas in thermo-chemical equilibrium at the freeze-out. The model incorporates a longitudinal as well as a transverse hydrodynamic flow. We have also found that the role of heavier hadronic resonance decay is important in explaining the particle spectra.Comment: 22 pages, 11 figure

Chemical equilibration of quarks and gluons at RHIC and LHC energies

We study chemical equilibration of quarks and gluons in central nuclear collisions at RHIC and LHC energies. The initial quark and gluon densities are taken from earlier studies as well as from recent perturbative QCD estimates and are then evolved via rate equations coupled to longitudinally boost-invariant fluid dynamics. We find that, for RHIC initial conditions, the lifetime of quark-gluon matter is too short in order for the quark and gluon number densities to chemically equilibrate prior to hadronization. In contrast, at LHC energies chemical equilibration is complete before the system hadronizes. Entropy production due to chemical equilibration can be as large as 30%.Comment: 30 pages (latex2e), 13 postscript figures, corrected one figure, further analysis performed, to be published in NP

Does HBT Measure the Freeze-out Source Distribution?

It is generally assumed that as a result of multiple scattering, the source distribution measured in HBT interferometry corresponds to a chaotic source at freeze-out. This assumption is subject to question as effects of multiple scattering in HBT measurements must be investigated within a quantum-mechanical framework. Applying the Glauber multiple scattering theory at high energies and the optical model at lower energies, we find that multiple scattering leads to an effective HBT density distribution that depends on the initial chaotic source distribution with an absorption.Comment: 4 pages, talk presented at QM2004 Conference, January 11-17, 2004, Oakland, California, USA, to be published in the Proceeding