System size dependence of cluster properties from two-particle angular correlations in Cu+Cu and Au+Au collisions at sNN\sqrt{s_{_{NN}}} = 200 GeV

We present results on two-particle angular correlations in Cu+Cu and Au+Au collisions at a center of mass energy per nucleon pair of 200 GeV over a broad range of pseudorapidity ($\eta$) and azimuthal angle ($\phi$) as a function of collision centrality. The PHOBOS detector at RHIC has a uniquely-large angular coverage for inclusive charged particles, which allows for the study of correlations on both long- and short-range scales. A complex two-dimensional correlation structure in $\Delta \eta$ and $\Delta \phi$ emerges, which is interpreted in the context of a cluster model. The effective cluster size and decay width are extracted from the two-particle pseudorapidity correlation functions. The effective cluster size found in semi-central Cu+Cu and Au+Au collisions is comparable to that found in proton-proton collisions but a non-trivial decrease of the size with increasing centrality is observed. Moreover, a comparison between results from Cu+Cu and Au+Au collisions shows an interesting scaling of the effective cluster size with the measured fraction of total cross section (which is related to the ratio of the impact parameter to the nuclear radius, $b/2R$), suggesting a geometric origin. Further analysis for pairs from restricted azimuthal regions shows that the effective cluster size at $\Delta\phi \sim 180^{\circ}$ drops more rapidly toward central collisions than the size at $\Delta\phi \sim 0^{\circ}$. The effect of limited $\eta$ acceptance on the cluster parameters is also addressed, and a correction is applied to present cluster parameters for full $\eta$ coverage, leading to much larger effective cluster sizes and widths than previously noted in the literature. These results should provide insight into the hot and dense medium created in heavy ion collisions.Comment: 9 pages, 8 figures, Published in Phys. Rev.

Nucleon-Gold Collisions at 200 AGeV Using Tagged d+Au Interactions in PHOBOS

Forward calorimetry in the PHOBOS detector has been used to study charged hadron production in d+Au, p+Au and n+Au collisions at sqrt(s_nn) = 200 GeV. The forward proton calorimeter detectors are described and a procedure for determining collision centrality with these detectors is detailed. The deposition of energy by deuteron spectator nucleons in the forward calorimeters is used to identify p+Au and n+Au collisions in the data. A weighted combination of the yield of p+Au and n+Au is constructed to build a reference for Au+Au collisions that better matches the isospin composition of the gold nucleus. The p_T and centrality dependence of the yield of this improved reference system is found to match that of d+Au. The shape of the charged particle transverse momentum distribution is observed to extrapolate smoothly from pbar+p to central d+Au as a function of the charged particle pseudorapidity density. The asymmetry of positively- and negatively-charged hadron production in p+Au is compared to that of n+Au. No significant asymmetry is observed at mid-rapidity. These studies augment recent results from experiments at the LHC and RHIC facilities to give a more complete description of particle production in p+A and d+A collisions, essential for the understanding the medium produced in high energy nucleus-nucleus collisions.Comment: 17 pages, 18 figure

Participant and spectator scaling of spectator fragments in Au + Au and Cu + Cu collisions at √sNN = 19.6 and 22.4 GeV

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to nitrogen (Z=7), are measured in PHOBOS. These fragments are observed in Au+Au (√sNN =19.6GeV) and Cu+Cu (22.4 GeV) collisions at high pseudorapidity (η). The dominant multiply-charged fragment is the tightly bound helium (α), with lithium, beryllium, and boron all clearly seen as a function of collision centrality and pseudorapidity. We observe that in Cu+Cu collisions, it becomes much more favorable for the α fragments to be released than lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. A detailed comparison of the shapes for α and lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.United States. Department of Energy (Grant DE-AC02-98CH10886)United States. Department of Energy (Grant DE-FG02-93ER40802)United States. Department of Energy (Grant DE-FG02-94ER40818)United States. Department of Energy (Grant DE-FG02-94ER40865)United States. Department of Energy (Grant DE-FG02- 99ER41099)United States. Department of Energy (Grant DE-AC02-06CH11357)National Science Foundation (U.S.) (Grant 9603486)National Science Foundation (U.S.) (Grant 0072204)National Science Foundation (U.S.) (Grant 0245011

Design of the 2k Naming Service

.html, March 1997. [15] P. J. Leach, P. H. Levine, B. P. Douros, D. L. Nelson J. A. Hamilton, and B. L. Stumpf. The Architecture of an Integrated Local Network. IEEE Journal on Selected Areas in Communication, pages 842-857, 1983. [16] M. T. Lin, D. P. Tsoy, and R. C. Lian. Design of a Network Operating System for the Distributed Double-Loop Computer Network. Local Computer Networks, 1982. North Holland Company, IFIP. [17] P. V. Mockapetris and K. J. Dunlap. Developement of the Domain Name System. In Proceedings of the SIGCOMM '88 Symposium on Communications Architectures and Protocols, pages 123-133, 1988. References [1] Steven Bernstein. Inferno Namespaces. Available from: http://www.lucentinferno. com/Pages/Developers/Documentation/WhitePapers/namespace.html, 1997. [2] D. R. Boggs. Internet Broadcasting. PhD thesis, Stanford University, 1983. [3] Christian J. Callsen. Open Heterogeneous Distributed Computing. PhD thesis, Aalborg University, August 1994. Available at: http://www-o..

Non-flow correlations and elliptic flow fluctuations in Au+Au collisions at √sNN=200 GeV

This article presents results on event-by-event elliptic flow fluctuations in Au+Au collisions at [sqrt]sNN= 200 GeV, where the contribution from non-flow correlations has been subtracted. An analysis method is introduced to measure non-flow correlations, relying on the assumption that non-flow correlations are most prominent at short ranges (|Δeta|2), relative elliptic flow fluctuations of approximately 30–40% are observed. These results are consistent with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. It is found that the long-range non-flow correlations in Au+Au collisions would have to be more than an order of magnitude strongercompared to the p+p data to lead to the observed azimuthal anisotropy fluctuations with no intrinsic elliptic flow fluctuations.United States. Department of Energy (Grants DE-AC02-98CH10886, DE-FG02-93ER40802, DE-FG02- 94ER40818, DE-FG02-94ER40865, DE-FG02-99ER41099, and DE-AC02-06CH11357)National Science Foundation (Grants 9603486, 0072204, and 0245011)Polish Ministry of Science and Higher Education (Grant N N202 282234 (2008-2010))National Science Council of Taiwan (Contract NSC 89-2112-M-008-024)Hungarian Scientific Research Foundation (grant F 049823

High transverse momentum triggered correlations over a large pseudorapidity acceptance in Au+Au collisions at sqrt(s_NN)=200 GeV

A measurement of two-particle correlations with a high transverse momentum trigger particle (p[subscript T][superscript trig]>2.5  GeV/c) is presented for Au+Au collisions at √sNN=200   GeV over the uniquely broad longitudinal acceptance of the PHOBOS detector (-4<Δη<2). A broadening of the away-side azimuthal correlation compared to elementary collisions is observed at all Δη. As in p+p collisions, the near side is characterized by a peak of correlated partners at small angle relative to the trigger particle. However, in central Au+Au collisions an additional correlation extended in Δη and known as the “ridge” is found to reach at least |Δη|≈4. The ridge yield is largely independent of Δη over the measured range, and it decreases towards more peripheral collisions. For the chosen p[subscript T][superscript trig] cut, the ridge yield is consistent with zero for events with less than roughly 100 participating nucleons.United States. Dept. of Energy (Grants No. DE-AC02-98CH10886, No. DE-FG02-93ER40802, No. DE-FG02-94ER40818, No. DE-FG02-94ER40865, No. DE-FG02-99ER41099, and No. DE-AC02-06CH11357)National Science Foundation (Grants No. 9603486, No. 0072204, and No. 0245011)Polish MNiSW (Grant No. N202 282234 (2008–2010)NSC of Taiwan (Contract No. NSC 89-2112-M-008-024)Hungarian OTKA (Grant No. F 049823