612 research outputs found
Silicon Pad Detectors for the PHOBOS Experiment at RHIC
The PHOBOS experiment is well positioned to obtain crucial information about
relativistic heavy ion collisions at RHIC, combining a multiplicity counter
with a multi-particle spectrometer. The multiplicity arrays will measure the
charged particle multiplicity over the full solid angle. The spectrometer will
be able to identify particles at mid-rapidity. The experiment is constructed
almost exclusively of silicon pad detectors. Detectors of nine different types
are configured in the multiplicity and vertex detector (22,000 channels) and
two multi-particle spectrometers (120,000 channels). The overall layout of the
experiment, testing of the silicon sensors and the performance of the detectors
during the engineering run at RHIC in 1999 are discussed.Comment: 7 pages, 7 figures, 1 table, Late
Longitudinal broadening of near side jets due to parton cascade
Longitudinal broadening along direction on near side in
two-dimensional () di-hadron correlation
distribution has been studied for central Au+Au collisions at =
200 GeV, within a dynamical multi-phase transport model. It was found that the
longitudinal broadening is generated by a longitudinal flow induced by strong
parton cascade in central Au+Au collisions, in comparison with p+p collisions
at = 200 GeV. The longitudinal broadening may shed light on the
information about strongly interacting partonic matter at RHIC.Comment: 5 pages, 4 figures; accepted by Eur. Phys. J.
quasiharmonic equations of state for dynamically-stabilized soft-mode materials
We introduce a method for treating soft modes within the analytical framework
of the quasiharmonic equation of state. The corresponding double-well
energy-displacement relation is fitted to a functional form that is harmonic in
both the low- and high-energy limits. Using density-functional calculations and
statistical physics, we apply the quasiharmonic methodology to solid periclase.
We predict the existence of a B1--B2 phase transition at high pressures and
temperatures
Wave scattering from self-affine surfaces
Electromagnetic wave scattering from a perfectly reflecting self-affine
surface is considered. Within the framework of the Kirchhoff approximation, we
show that the scattering cross section can be exactly written as a function of
the scattering angle via a centered symmetric Levy distribution for general
roughness amplitude, Hurst exponent and wavelength of the incident wave. The
amplitude of the specular peak, its width and its position are discussed as
well as the power law decrease (with scattering angle) of the scattering cross
section.Comment: RevTeX, 4 pages including 2 figures. Submitted Phys. Rev. Let
Effect of Finite Granularity of Detectors on Anisotropy Coefficients
The coefficients that describe the anisotropy in the azimuthal distribution
of particles are lower when the particles are recorded in a detector with
finite granularity and measures only hits. This arises due to loss of
information because of multiple hits in any channel. The magnitude of this loss
of signal depends both on the occupancy and on the value of the coefficient.
These correction factors are obtained for analysis methods differing in detail,
and are found to be different.Comment: 11 pages including 2 figure
Transverse flow and hadro-chemistry in Au+Au collisions at \sqrt{s_{NN}}=200 GeV
We present a hydrodynamic assessment of preliminary particle spectra observed
in Au+Au collisions at \sqrt{s_{NN}}=200 GeV. The hadronic part of the
underlying equation of state is based on explicit conservation of (measured)
particle ratios throughout the resonance gas stage after chemical freezeout by
employing chemical potentials for stable mesons, nucleons and anti-nucleons. We
find that under these conditions the data (in particular the proton spectra)
favor a low freeze-out temperature of around 100 MeV. Furthermore we show that
through inclusion of a moderate pre-hydrodynamic transverse flow field the
shape of the spectra improves with respect to the data. The effect of the
initial transverse boost on elliptic flow and the freeze-out geometry of the
system is also elucidated.Comment: as published: more data included in Fig. 1, discussions throughout
the text improved, 6 pages, 4 figure
Isolation of Bartonella species from rodents in Taiwan including a strain closely related to 'Bartonella rochalimae' from Rattus norvegicus
An increasing number of Bartonella species originally isolated from small mammals have been identified as emerging human pathogens. During an investigation of Bartonella infection in rodent populations carried out in Taiwan in 2006, a total of 58 rodents were tested. It was determined that 10.3% (6/58) of the animals were Bartonella bacteraemic. After PCR/RFLP analysis, four isolates were identified as Bartonella elizabethae and one isolate as Bartonella tribocorum. However, there was one specific isolate with an unrecognized PCR/RFLP pattern. After further sequence and phylogenetic analyses of the gltA, ftsZ and rpoB genes, and the 16S-23S rRNA intergenic spacer region, the results indicated that this specific isolate from Rattus norvegicus was closely related to human pathogenic 'Bartonella rochalimae'. Further studies need to be conducted to evaluate whether this rodent species could be a reservoir for 'B. rochalimae'
Quarkonia Measurements with STAR
We report results on quarkonium production from the STAR experiment at the
Relativistic Heavy-Ion Collider (RHIC). J/psi spectra in p+p and Cu+Cu
collisions at sqrt(s) = 200 GeV with transverse momenta in the range of 0.5-14
GeV/c and 5-8 GeV/c, respectively, are presented. We find that for p_T > 5
GeV/c yields in p+p collisions are consistent with those in minimum-bias Cu+Cu
collisions scaled with the respective number of binary nucleon-nucleon
collisions. In this range the nuclear modification factor, R_AA, is measured to
be 0.9+-0.2(stat). For the first time at RHIC, high-p_T J/psi-hadron
correlations were studied in p+p collisions. Implications from our measurements
on J/psi production mechanisms, constraints on open bottom yields, and J/psi
dissociation mechanisms at high-p_T are discussed. In addition, we give a brief
status of measurements of Upsilon production in p+p and Au+Au collisions and
present projections of future quarkonia measurements based on an upgrades to
the STAR detector and increased luminosity achieved through stochastic cooling
of RHIC.Comment: 5 pages, 5 figures. Prepared for 3rd International Conference on Hard
and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes
2008), A Toxa, Spain, June 8-14, 200
Calculating the jet-quenching parameter in STU background
In this paper we use the AdS/CFT correspondence to compute the jet-quenching
parameter in a N=2 thermal plasma. We consider the general three-charge black
hole and discuss some special cases. We add a constant electric field to the
background and find the effect of the electric field on the jet-quenching
parameter. Also we include higher derivative terms and obtain the first-order
correction for the jet-quenching parameter.Comment: 17 pages, 3 figures, revised versio
The price of rapid exit in venture capital-backed IPOs
This paper proposes an explanation for two empirical puzzles surrounding initial public offerings (IPOs). Firstly, it is well documented that IPO underpricing increases during “hot issue” periods. Secondly, venture capital (VC) backed IPOs are less underpriced than non-venture capital backed IPOs during normal periods of activity, but the reverse is true during hot issue periods: VC backed IPOs are more underpriced than non-VC backed ones. This paper shows that when IPOs are driven by the initial investor’s desire to exit from an existing investment in order to finance a new venture, both the value of the new venture and the value of the existing firm to be sold in the IPO drive the investor’s choice of price and fraction of shares sold in the IPO. When this is the case, the availability of attractive new ventures increases equilibrium underpricing, which is what we observe during hot issue periods. Moreover, I show that underpricing is affected by the severity of the moral hazard problem between an investor and the firm’s manager. In the presence of a moral hazard problem the degree of equilibrium underpricing is more sensitive to changes in the value of the new venture. This can explain why venture capitalists, who often finance firms with more severe moral hazard problems, underprice IPOs less in normal periods, but underprice more strongly during hot issue periods. Further empirical implications relating the fraction of shares sold and the degree of underpricing are presented
- …