10,487 research outputs found
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.
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
Two-dimensional global manifolds of vector fields
We describe an efficient algorithm for computing two-dimensional stable and unstable manifolds of three-dimensional vector fields. Larger and larger pieces of a manifold are grown until a sufficiently long piece is obtained. This allows one to study manifolds geometrically and obtain important features of dynamical behavior. For illustration, we compute the stable manifold of the origin spiralling into the Lorenz attractor, and an unstable manifold in zeta(3)-model converging to an attracting limit cycle
Verification-guided modelling of salience and cognitive load
Well-designed interfaces use procedural and sensory cues to increase the cognitive salience of appropriate actions. However, empirical studies suggest that cognitive load can influence the strength of those cues. We formalise the relationship between salience and cognitive load revealed by empirical data. We add these rules to our abstract cognitive architecture, based on higher-order logic and developed for the formal verification of usability properties. The interface of a fire engine dispatch task from the empirical studies is then formally modelled and verified. The outcomes of this verification and their comparison with the empirical data provide a way of assessing our salience and load rules. They also guide further iterative refinements of these rules. Furthermore, the juxtaposition of the outcomes of formal analysis and empirical studies suggests new experimental hypotheses, thus providing input to researchers in cognitive science
Bulk Dynamics in Heavy Ion Collisions
The features of heavy ion collisions that suggest the relevance of collective
dynamics, as opposed to mere superpositions of nucleon-nucleon or even
parton-parton collisions, are reviewed. The surprise of these studies is that
bulk observables are far simpler than typical dynamical models of
nucleus-nucleus collisions would imply. These features are shown to have a
natural interpretation in terms of statistical-hydrodynamical models. The
relevance of hydrodynamics to heavy ion collisions, coupled with the various
similarities of the heavy ion data with that of more elementary collisions,
raises very basic questions about its relevance to smaller systems.Comment: 10 Pages, 13 Figures, invited parallel talk at the International
Nuclear Physics Conference (INPC 2004), Goteborg, Sweden, June 27 - July 2,
200
Charge Particle Multiplicity and Transverse Energy Measurements in Au-Au collisions in PHENIX at RHIC
We present results on charged particle and transverse energy densities
measured at mid-rapidity in Au-Au collisions at sqrt(s_{NN})=200 GeV. The mean
transverse energy per charged particle is derived. The results are presented as
a function of centrality, which is defined by the number of participating
nucleons, and compared to results obtained in Au-Au collisions at
sqrt{s_{NN})=130 GeV. A comparison with calculations from various theoretical
models is performed.Comment: 4 pages, 5 figures. Talk presented at Quark Matter 2002, Nantes,
France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A
Energy and centrality dependences of charged multiplicity density in relativistic nuclear collisions
Using a hadron and string cascade model, JPCIAE, the energy and centrality
dependences of charged particle pseudorapidity density in relativistic nuclear
collisions were studied. Within the framework of this model, both the
relativistic experimental data and the PHOBOS and PHENIX
data at =130 GeV could be reproduced fairly well without retuning
the model parameters. The predictions for full RHIC energy collisions
and for collisions at the ALICE energy were given. Participant nucleon
distributions were calculated based on different methods. It was found that the
number of participant nucleons, for distinguishing various theoretical models.Comment: 10 pages, 4 figures, submitted to Phy. Lett.
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