Collision geometry scaling of Au+Au pseudorapidity density from sqrt(s_NN) = 19.6 to 200 GeV

The centrality dependence of the midrapidity charged particle multiplicity in Au+Au collisions at sqrt(s_NN) = 19.6 and 200 GeV is presented. Within a simple model, the fraction of hard (scaling with number of binary collisions) to soft (scaling with number of participant pairs) interactions is consistent with a value of x = 0.13 +/- 0.01(stat) +/- 0.05(syst) at both energies. The experimental results at both energies, scaled by inelastic p(pbar)+p collision data, agree within systematic errors. The ratio of the data was found not to depend on centrality over the studied range and yields a simple linear scale factor of R_(200/19.6) = 2.03 +/- 0.02(stat) +/- 0.05(syst).Comment: 5 pages, 4 figures, submitted to PRC-R

The uptake of soluble and nanoparticulate imaging isotope in model liver tumours after intra-venous and intra-arterial administration

Delivery of chemotherapeutic drugs to tumours by reformulation as nanoparticles has often been proposed as a means of facilitating increased selective uptake, exploiting the increased permeability of the tumour vasculature. However realisation of this improvement in drug delivery in cancer patients has met with limited success. We have compared tumour uptake of soluble Tc99m-pertechnetate and a colloid of nanoparticles with a Tc99m core, using both intra-venous and intra-arterial routes of administration in a rabbit liver VX2 tumour model. The radiolabelled nanoparticles were tested both in untreated and cationised form. The results from this tumour model in an internal organ show a marked advantage in intra-arterial administration over the intra-venous route, even for the soluble isotope. Tumour accumulation of nanoparticles from arterial administration was augmented by cationisation of the nanoparticle surface with histone proteins, which consistently facilitated selective accumulation within microvessels at the periphery of tumours.Sources of support for this research: Sirtex Medical Ltd, Sydney Australia

Centrality dependence of charged antiparticle to particle ratios near mid-rapidity in d+Au collisions at sqrt(s_NN)=200 GeV

The ratios of the yields of charged antiparticles to particles have been obtained for pions, kaons, and protons near mid-rapidity for d+Au collisions at sqrt(s_NN) = 200 GeV as a function of centrality. The reported values represent the ratio of the yields averaged over the rapidity range of 0.1<y_pi<1.3 and 0<y_(K,p)<0.8, where positive rapidity is in the deuteron direction, and for transverse momenta 0.1<p_(T)^(pi,K)<1.0 GeV/c and 0.3<p_(T)^(p)<1.0 GeV/c. Within the uncertainties, a lack of centrality dependence is observed in all three ratios. The data are compared to results from other systems and model calculations.Comment: 6 pages, 4 figures, submitted to PR

Pseudorapidity Distributions of Charged Particles in d + Au and p + p Collisions at sNN\sqrt{s_{_{NN}}} = 200GeV

The measured pseudorapidity distributions of primary charged particles are presented for d + Au and p + p collisions at ${\sqrt{s_{_{NN}}} =}$ 200 GeV over a wide pseudorapidity range of ${\rm \mid \eta \mid \le}$ 5.4. The results for d + Au collisions are presented for minimum-bias events and as a function of collision centrality. The measurements for p + p collisions are shown for minimum-bias events. The ratio of the charged particle multiplicity in d + Au and p + A collisions relative to that for inelastic p + p collisions is found to depend only on ${}$, and it is remarkably independent of collision energy and system mass. The deuteron and gold fragmentation regions in d + Au collisions are in good agreement with proton nucleus data at lower energies.Comment: 4 pages, 3 figures. To appear in the proceedings of Seventeenth International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004), Oakland, California from January 11-17, 2004. Submitted to Journal of Physics G: Nuclear and Particle Physic

Centrality and pseudorapidity dependence of elliptic flow for charged hadrons in Au+Au collisions at sqrt(sNN) = 200 GeV

This paper describes the measurement of elliptic flow for charged particles in Au+Au collisions at sqrt(sNN)=200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The measured azimuthal anisotropy is presented over a wide range of pseudorapidity for three broad collision centrality classes for the first time at this energy. Two distinct methods of extracting the flow signal were used in order to reduce systematic uncertainties. The elliptic flow falls sharply with increasing eta at 200 GeV for all the centralities studied, as observed for minimum-bias collisions at sqrt(sNN)=130 GeV.Comment: Final published version: the most substantive change to the paper is the inclusion of a complete description of how the errors from the hit-based and track-based analyses are merged to produce the 90% C.L. errors quoted for the combined results shown in Fig.

Charged antiparticle to particle ratios near midrapidity in p+p collisions at sqrt(s_NN)=200 GeV

The ratios of the yields of primary charged antiparticles to particles have been obtained for pions, kaons, and protons near midrapidity for p+p collisions at sqrt(s_NN) = 200 GeV. Ratios of =1.000 +/- 0.012 (stat.) +/- 0.019 (syst.), =0.93 +/- 0.05 (stat.) +/- 0.03 (syst.), and =0.85 +/- 0.04 (stat.) +/- 0.03 (syst.) have been measured. The reported values represent the ratio of the yields averaged over the rapidity range of 0.1<y_{pi}<1.3 and 0<y_{K,p}<0.8, and for transverse momenta of 0.1<p_T^{pi,K}<1.0 GeV/c and 0.3<p_T^{p}<1.0 GeV/c. Within the uncertainties, all three ratios are consistent with the values measured in d+Au collisions at the same energy. The data are compared to results from other collision systems and energies.Comment: 3 pages, 2 figures, 1 table, submitted to Phys. Rev.

Phobos results on charged particle multiplicity and pseudorapidity distributions in Au+Au, Cu+Cu, d+Au, and p+p collisions at ultra-relativistic energies

Pseudorapidity distributions of charged particles emitted in $Au+Au$, $Cu+Cu$, $d+Au$, and $p+p$ collisions over a wide energy range have been measured using the PHOBOS detector at RHIC. The centrality dependence of both the charged particle distributions and the multiplicity at midrapidity were measured. Pseudorapidity distributions of charged particles emitted with $|\eta|<5.4$, which account for between 95% and 99% of the total charged-particle emission associated with collision participants, are presented for different collision centralities. Both the midrapidity density, $dN_{ch}/d\eta$, and the total charged-particle multiplicity, $N_{ch}$, are found to factorize into a product of independent functions of collision energy, $\sqrt{s_{_{NN}}}$, and centrality given in terms of the number of nucleons participating in the collision, $N_{part}$. The total charged particle multiplicity, observed in these experiments and those at lower energies, assumes a linear dependence of $(\ln s_{_{NN}})^2$ over the full range of collision energy of $\sqrt{s_{_{NN}}}$=2.7-200 GeV.Comment: 25 pages, 29 figures, 8 table

Elliptic Flow in Au+Au Collisions at RHIC

Elliptic flow is an interesting probe of the dynamical evolution of the dense system formed in the ultrarelativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). The elliptic flow dependences on transverse momentum, centrality, and pseudorapidity were measured using data collected by the PHOBOS detector, which offers a unique opportunity to study the azimuthal anisotropies of charged particles over a wide range of pseudorapidity. These measurements are presented, together with an overview of the analysis methods and a discussion of the results.Comment: Presented at Hot Quarks 2004; 7 pages, 6 figure

Energy dependence of elliptic flow over a large pseudorapidity range in Au+Au collisions at RHIC

This paper describes the measurement of the energy dependence of elliptic flow for charged particles in Au+Au collisions using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). Data taken at collision energies of $\sqrt{s_{_{NN}}} =$ 19.6, 62.4, 130 and 200 GeV are shown over a wide range in pseudorapidity. These results, when plotted as a function of $\eta'=|\eta|-y_{beam}$, scale with approximate linearity throughout $\eta'$, implying no sharp changes in the dynamics of particle production as a function of pseudorapidity or increasing beam energy.Comment: 5 pages, 4 figure

Event-by-event fluctuations of azimuthal particle anisotropy in Au+Au collisions at sqrt(s_NN) = 200 GeV

This paper presents the first measurement of event-by-event fluctuations of the elliptic flow parameter v_2 in Au+Au collisions at sqrt(s_NN) = 200GeV as a function of collision centrality. The relative non-statistical fluctuations of the v_2 parameter are found to be approximately 40%. The results, including contributions from event-by-event elliptic flow fluctuations and from azimuthal correlations that are unrelated to the reaction plane (non-flow correlations), establish an upper limit on the magnitude of underlying elliptic flow fluctuations. This limit is consistent with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. These results provide important constraints on models of the initial state and hydrodynamic evolution of relativistic heavy ion collisions.Comment: 5 pages, 2 figures, Published in Phys. Rev. Lett