System size, energy and pseudorapidity dependence of directed and elliptic flow at RHIC

PHOBOS measurements of elliptic flow are presented as a function of pseudorapidity, centrality, transverse momentum, energy and nuclear species. The elliptic flow in Cu-Cu is surprisingly large, particularly for the most central events. After scaling out the geometry through the use of an alternative form of eccentricity, called the participant eccentricity, which accounts for nucleon position fluctuations in the colliding nuclei, the relative magnitude of the elliptic flow in the Cu-Cu system is qualitatively similar to that measured in the Au-Au system.Comment: Presented at the 18th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions in Budapest, Hungary, Aug. 4-9, 200

Vertex Reconstruction Using a Single Layer Silicon Detector

Typical vertex finding algorithms use reconstructed tracks, registered in a multi-layer detector, which directly point to the common point of origin. A detector with a single layer of silicon sensors registers the passage of primary particles only in one place. Nevertheless, the information available from these hits can also be used to estimate the vertex position, when the geometrical properties of silicon sensors and the measured ionization energy losses of the particles are fully exploited. In this paper the algorithm used for this purpose in the PHOBOS experiment is described. The vertex reconstruction performance is studied using simulations and compared with results obtained from real data. The very large acceptance of a single-layered multiplicity detector permits vertex reconstruction for low multiplicity events where other methods, using small acceptance subdetectors, fail because of insufficient number of registered primary tracks.Comment: accepted for publication in Nucl. Instr. Meth.

Particle production at very low and intermediate transverse momenta in d+Au and Au+Au collisions

The transverse momentum spectra of identified charged particles have been measured at very low and intermediate transverse momenta in Au+Au collisions at sqrt(s_NN) = 62.4 GeV and d+Au collisions at sqrt(s_NN) = 200 GeV using the PHOBOS detector at RHIC. New results on charged particle production at very low p_T in central Au+Au collisions at sqrt(s_{NN) = 200 GeV in the centrality intervals 0-6% and 6-15% are presented. A comparison of the PHOBOS low-p_T data with predictions of a recent optical model is shown. The shapes of m_T spectra for d+Au and Au+Au collisions are compared.Comment: Presented at the 18th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2005, Budapest, Hungary, Aug. 4-9, 200

Heavy ion collisions in the used nucleon model

It is shown that recently proposed by R.J. Glauber the used nucleon model combined with the assumption that the nucleon consists of two constituents (a quark and a diquark) describes well the PHOBOS data on particle production at midrapidity.Comment: 5 pages, 2 figure

Saving Wildlife around the World

Julia Back ’07 has been nose-to-nose with curious sea lions, beak-clacking albatross and ancient giant tortoises. Now she’s back in Oregon helping protect the wildlife she grew up around

Limiting fragmentation from scale-invariant merging of fast partons

Exploiting the idea that the fast partons of an energetic projectile can be treated as sources of color radiation interpreted as wee partons, it is shown that the recently observed property of extended limiting fragmentation implies a scaling law for the rapidity distribution of fast partons. This leads to a picture of a self-similar process where, for fixed total rapidity Y, the sources merge with probability varying as 1/y.Comment: 10 pages, 1 figure (2 eps files). Final version, also updated w.r.t. the published version in Phys. Lett. B665/1 (2008) pp. 35-3

Charged Particle Multiplicities in Ultra-relativistic Au+Au and Cu+Cu Collisions

The PHOBOS collaboration has carried out a systematic study of charged particle multiplicities in Cu+Cu and Au+Au collisions at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory. A unique feature of the PHOBOS detector is its ability to measure charged particles over a very wide angular range from 0.5 to 179.5 deg. corresponding to |eta|<5.4. The general features of the charged particle multiplicity distributions as a function of pseudo-rapidity, collision energy and centrality, as well as system size, are discussed.Comment: Proceedings of "Lake Louise Winter Institute 2006", Lake Louise, Alberta, Canada, February 17-23, 2006, World Scientific 5 pages, 3 figure