9,648 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.
Geoneutrinos in Borexino
This paper describes the Borexino detector and the high-radiopurity studies
and tests that are integral part of the Borexino technology and development.
The application of Borexino to the detection and studies of geoneutrinos is
discussed.Comment: Conference: Neutrino Geophysics Honolulu, Hawaii December 14-16, 200
Rapidity equilibration in d + Au and Au + Au systems
In a Relativistic Diffusion Model (RDM), the evolution of net-proton rapidity
spectra with sqrt(s_NN) in heavy systems is proposed as an indicator for local
equilibration and longitudinal expansion. The broad midrapidity valley recently
discovered at RHIC in central Au + Au collisions at sqrt(s_NN)= 200 GeV
suggests rapid local equilibration which is most likely due to deconfinement,
and fast longitudinal expansion. Rapidity spectra of produced charged hadrons
in d + Au and Au + Au systems at RHIC energies and their centrality dependence
are well described in a three-sources RDM. In central collisions, about 19 % of
the produced particles are in the equilibrated midrapidity region for d + Au.Comment: 10 pages, 4 figures; QGPTH05 Vienna; references update
Energy and precious fuels requirements of fuel alcohol production. Volume 4: Appendices G and H, methanol from coal
Coal mine location, mining technology, energy consumption in mining, coal transport, and potential availability of coal are discussed. Methanol from coal is also discussed
Explosive propulsion applications
The feasibility and application of an explosive propulsion concept capable of supporting future unmanned missions in the post-1980 era were examined and recommendations made for advanced technology development tasks. The Venus large lander mission was selected as the first in which the explosive propulsion concept can find application. A conceptual design was generated and its performance, weight, costs, and interaction effects determined. Comparisons were made with conventional propulsion alternatives. The feasibility of the explosive propulsion system was verified for planetology experiments within the dense atmosphere of Venus as well as the outer planets. Additionally, it was determined that the Venus large lander mission could be augmented ballistically with a significant delivery margin
Non-linear spin-wave excitation at low bias fields
Non-linear magnetization dynamics is essential for the operation of many
spintronics devices. For microwave assisted switching of magnetic elements the
low field regime is of particular interest. In addition a large number of
experiments uses high amplitude FMR in order to generate d.c. currents via spin
pumping mechanism. Here we use time resolved X-ray magnetic circular dichroism
experiments to determine the number density of excited magnons in magnetically
soft Ni_80Fe_20 thin films at small bias fields and large rf-excitation
amplitudes. Our data shows that the common model of non-linear ferromagnetic
resonance is not suitable to describe the low bias field limit. Here we derive
a new model of parametric spin-wave excitation which correctly predicts
threshold amplitudes and decay rates also at low bias fields. In fact a new
series of critical modes with amplitude phase oscillations is found,
generalizing the theory of parametric spin-wave excitation
Damping by slow relaxing rare earth impurities in Ni80Fe20
Doping NiFe by heavy rare earth atoms alters the magnetic relaxation
properties of this material drastically. We show that this effect can be well
explained by the slow relaxing impurity mechanism. This process is a
consequence of the anisotropy of the on site exchange interaction between the
4f magnetic moments and the conduction band. As expected from this model the
magnitude of the damping effect scales with the anisotropy of the exchange
interaction and increases by an order of magnitude at low temperatures. In
addition our measurements allow us to determine the relaxation time of the 4f
electrons as a function of temperature
Anisotropy effects on the magnetic excitations of a ferromagnetic monolayer below and above the Curie temperature
The field-driven reorientation transition of an anisotropic ferromagnetic
monolayer is studied within the context of a finite-temperature Green's
function theory. The equilibrium state and the field dependence of the magnon
energy gap are calculated for static magnetic field applied in plane
along an easy or a hard axis. In the latter case, the in-plane reorientation of
the magnetization is shown to be continuous at T=0, in agreement with free spin
wave theory, and discontinuous at finite temperature , in contrast with
the prediction of mean field theory. The discontinuity in the orientation angle
creates a jump in the magnon energy gap, and it is the reason why, for ,
the energy does not go to zero at the reorientation field. Above the Curie
temperature , the magnon energy gap vanishes for H=0 both in the
easy and in the hard case. As is increased, the gap is found to increase
almost linearly with , but with different slopes depending on the field
orientation. In particular, the slope is smaller when is along the hard
axis. Such a magnetic anisotropy of the spin-wave energies is shown to persist
well above ().Comment: Final version accepted for publication in Physical Review B (with
three figures
Studies of multiplicity in relativistic heavy-ion collisions
In this talk I'll review the present status of charged particle multiplicity
measurements from heavy-ion collisions. The characteristic features of
multiplicity distributions obtained in Au+Au collisions will be discussed in
terms of collision centrality and energy and compared to those of p+p
collisions. Multiplicity measurements of d+Au collisions at 200 GeV
nucleon-nucleon center-of-mass energy will also be discussed. The results will
be compared to various theoretical models and simple scaling properties of the
data will be identified.Comment: "Focus on Multiplicity" Internationsl Workshop on Particle
Multiplicity in Relativistic Heavy Ion Collisions, Bari, Italy, June 17-19,
2003, 16 pages, 15 figure
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