The onset of classical QCD dynamics in relativistic heavy ion collisions

The experimental results on hadron production obtained recently at RHIC offer a new prospective on the energy dependence of the nuclear collision dynamics. In particular, it is possible that parton saturation -- the phenomenon likely providing initial conditions for the multi--particle production at RHIC energies -- may have started to set in central heavy ion collisions already around the highest SPS energy. We examine this scenario, and make predictions based on high density QCD for the forthcoming 22 GeV run at RHIC.Comment: 4 pages, 2 figures, revte

GDR in Superdeformed Nuclei

A search for the gamma decay of the Giant Dipole Resonance built on superdeformed nuclear configurations was made. The superdeformed states of the Eu-143 nucleus were populated using the reaction Pd-110(Cl-37, 4n)Eu-143 at a beam energy of 165 MeV. High energy gamma-rays were detected in 8 large BaF2 scintillators in coincidence with discrete transitions measured with part of the NORDBALL array (17 HPGe detectors and a 2 pi multiplicity filter). Spectra of high-energy gamma-rays gated by low-energy transitions from states fed by the superdeformed bands show an excess yield in the 7-10 MeV region with respect to those gated by transitions from states not populated by the superdeformed bands. Because the dipole oscillation along the superdeformed axis of the nucleus is expected to have a frequency corresponding to approximate to 8 MeV (low energy component of the GDR strength function), the present result gives the first experimental indication of gamma-ray emission of the GDR built on a superdeformed states

Evidence for Thermal Equilibration in Multifragmentation Reactions probed with Bremsstrahlung Photons

The production of nuclear bremsstrahlung photons (E$_{\gamma}>$ 30 MeV) has been studied in inclusive and exclusive measurements in four heavy-ion reactions at 60{\it A} MeV. The measured photon spectra, angular distributions and multiplicities indicate that a significant part of the hard-photons are emitted in secondary nucleon-nucleon collisions from a thermally equilibrated system. The observation of the thermal component in multi-fragment $^{36}$Ar+$^{197}$Au reactions suggests that the breakup of the thermalized source produced in this system occurs on a rather long time-scale.Comment: Revised version, accepted for publication in Physical Review Letters. 4 pages, 4 fig

Anatomy of nuclear shape transition in the relativistic mean field theory

A detailed microscopic study of the temperature dependence of the shapes of some rare-earth nuclei is made in the relativistic mean field theory. Analyses of the thermal evolution of the single-particle orbitals and their occupancies leading to the collapse of the deformation are presented. The role of the non-linear $\sigma-$field on the shape transition in different nuclei is also investigated; in its absence the shape transition is found to be sharper.Comment: REVTEX file (13pages), 12 figures, Phys. Rev. C(in press), \documentstyle[aps,preprint]{revtex

Centrality dependence of charged-particle pseudorapidity distributions from d+Au collisions at sqrt(s_{NN})=200 GeV

Charged-particle pseudorapidity densities are presented for the d+Au reaction at sqrt{s_{NN}}=200 GeV with -4.2 <= eta <= 4.2$. The results, from the BRAHMS experiment at RHIC, are shown for minimum-bias events and 0-30%, 30-60%, and 60-80% centrality classes. Models incorporating both soft physics and hard, perturbative QCD-based scattering physics agree well with the experimental results. The data do not support predictions based on strong-coupling, semi-classical QCD. In the deuteron-fragmentation region the central 200 GeV data show behavior similar to full-overlap d+Au results at sqrt{s_{NN}}=19.4 GeV.Comment: 4 pages, 3figures; expanded discussion of uncertainties; added 60-80% centrality range; added additional discussion on centrality selection bia

High Pt Hadron Spectra at High Rapidity

We report the measurement of charged hadron production at different pseudo-rapidity values in deuteron+gold as well as proton+proton collisions at $sqrt{s_{NN}}$ = 200GeV at RHIC. The nuclear modification factors $R_{dAu}$ and $R_{cp}$ are used to investigate new behaviors in the deuteron+gold system as function of rapidity and the centrality of the collisions respectively.Comment: Nine pages 4 figures to be published in the QM2004 Proceedings, typos corrected and one reference adde

Large Nuclear shape transition at finite temperature in a relativistic mean field approach

The relativistic Hartree-BCS theory is applied to study the temperature dependence of nuclear shape and pairing gap for $^{166}Er$ and $^{170}Er$. For both the nuclei, we find that as temperature increases the pairing gap vanishes leading to phase transition from superfluid to normal phase as is observed in nonrelativistic calculation. The deformation evolves from prolate shapes to spherical shapes at $T\sim 2.7$ MeV. Comparison of our results for heat capacity with the ones obtained in the non-relativistic mean field framework indicates that in the relativistic mean field theory the shape transition occurs at a temperature about 0.9 MeV higher and is relatively weaker. The effect of thermal shape fluctuations on the temperature dependence of deformation is also studied. Relevant results for the level density parameter are further presented. PACS numbers: 21.10.Ma, 21.60.-n, 27.70.+qComment: ReVtex file of 17 pages, 11 ps files for figures, To be appear in Phys. ReV.

CGC, QCD Saturation and RHIC data (Kharzeev-Levin-McLerran-Nardi point of view)

This is the talk given at the Workshop:"Focus on Multiplicitioes", Bari, Italy, 17-19 June,2004.. In this talk, we are going to discuss ion-ion and deuteron - nucleus RHIC data and show that they support, if not more, the idea of the new QCD phase: colour glass condensate with saturated parton density. .Comment: 26 pages with 33 figure