3,096 research outputs found
Dileptons in High-Energy Heavy-Ion Collisions
The current status of our understanding of dilepton production in
ultrarelativistic heavy-ion collisions is discussed with special emphasis on
signals from the (approach towards) chirally restored and deconfined phases. In
particular, recent results of the CERN-SPS low-energy runs are compared to
model predictions and interpreted. Prospects for RHIC experiments are given.Comment: Invited talk at ICPAQGP, Jaipur, India, Nov. 26-30, 2001; 1 Latex and
9 eps-/ps-files Reoprt No.: SUNY-NTG-02-0
Probing dense and hot matter with low-mass dileptons and photons
Results on low-mass dileptons, covering the very broad energy range from the
BEVALAC up to SPS are reviewed. The emphasis is on the open questions raised by
the intriguing results obtained so far and the prospects for addressing them in
the near future with the second generation of experiments, in particular HADES,
NA60 and PHENIX.Comment: 6 pages, 8 figures, Proceedings of Hard Probes 2004 Conference,
Ericeira, November 4-10, 2004. Caption of Figure 2 corrected. To be published
in Eur. Phys. J. C. The orginal version is available at www.springerlink.co
-Process simulations with a modified reaction library
We have performed -process simulations with the most recent stellar
cross sections from the "Karlsruhe Astrophysical Database of
Nucleosynthesis in Stars" project (version v0.2,
http://nuclear-astrophysics.fzk.de/kadonis). The simulations were carried out
with a parametrized supernova type II shock front model (`` process'')
of a 25 solar mass star and compared to recently published results. A decrease
in the normalized overproduction factor could be attributed to lower cross
sections of a significant fraction of seed nuclei located in the Bi and Pb
region around the =126 shell closure.Comment: 5 pages, 1 figure Proceedings "Nuclear Physics in Astrophysics
NPA-III", Dresden/Germany (2007
Thermal Dileptons from a Nonperturbative Quark-Gluon Phase
Assuming that gluon condensates are important even above the deconfining
phase transition, we develop a model for the dilepton yield from a quark gluon
plasma. Using a simple fire ball description of a heavy ion collision, and
various estimates of the strengths of the gluon condensates, we compare our
predicted dilepton yields with those observed in the CERES and HELIOS
experiments at CERN. The simple model gives an adequate description of the
data, and in particular it explains the observed considerable enhancement of
the yield in the low mass region.Comment: 7 pages, 6 figures, reference adde
The Vector Probe in Heavy-Ion Reactions
We review essential elements in using the channel as a probe for
hot and dense matter as produced in (ultra-) relativistic collisions of heavy
nuclei. The uniqueness of the vector channel resides in the fact that it
directly couples to photons, both real and virtual (dileptons), enabling the
study of thermal radiation and in-medium effects on both light () and heavy () vector mesons. We emphasize the importance
of interrelations between photons and dileptons, and characterize relevant
energy/mass regimes through connections to Quark-Gluon-Plasma emission and
chiral symmetry restoration. Based on critical analysis of our current
understanding of data from fixed-target energies, we identify open key
questions to be addressed.Comment: Invited Talk at the Hot Quarks 2004 Workshop, July 18-24, 2004 (Taos
Valley, NM, USA), 15 pages latex incl 14 figs and iop style files, to appear
in the proceeding
Low mass dilepton radiation at RHIC
In this work we discuss the emission of low mass dilepton radiation from a
hydrodynamic evolution model of Au-Au collisions and make comparisons with
recent PHENIX measurements. The dilepton emission rates from the hadronic phase
are treated at finite temperature and baryon density and are completely
constrained by broken chiral symmetry in a density expansion. The rates are
expressed in terms of vacuum correlators which are measured in
annihilation, decays and photo-reactions on nucleons and nuclei. We
consider two possibilities for the hadronic phase: A chemical equilibrated an
off equilibrium hadronic gas. We find that while chemical off-equilibrium helps
explain part of the low mass (0.15 M GeV 0.7) enhancement seen in
the data there is still a large discrepancy.Comment: 8 pages, 12 figure
Theoretical mass sensitivity of Love wave and layer guided acoustic plate mode sensors
A model for the mass sensitivity of Love wave and layer guided shear horizontal acoustic plate mode (SH–APM) sensors is developed by considering the propagation of shear horizontally polarized acoustic waves in a three layer system. A dispersion equation is derived for this three layer system and this is shown to contain the dispersion equation for the two layer system of the substrate and the guiding layer plus a term involving the third layer, which is regarded as a perturbing mass layer. This equation is valid for an arbitrary thickness perturbing mass layer. The perturbation, Δν, of the wave speed for the two-layer system by a thin third layer of density, ρp and thickness Δh is shown to be equal to the mass per unit area multiplied by a function dependent only on the properties of the substrate and the guiding layer, and the operating frequency of the sensor. The independence of the function from the properties of the third layer means that the mass sensitivity of the bare, two-layer, sensor operated about any thickness of the guiding layer can be deduced from the slope of the numerically or experimentally determined dispersion curve. Formulas are also derived for a Love wave on an infinite thickness substrate describing the change in mass sensitivity due to a change in frequency. The consequences of the various formulas for mass sensing applications are illustrated using numerical calculations with parameters describing a (rigid) poly(methylmethacrylate) wave-guiding layer on a finite thickness quartz substrate. These calculations demonstrate that a layer-guided SH–APM can have a mass sensitivity comparable to, or higher, than that of Love waves propagating on the same substrate. The increase in mass sensitivity of the layer guided SH–APMs over previously studied SH–APM sensors is of significance, particularly for liquid sensing applications. The relevance of the dispersion curve to experiments using higher frequencies or frequency hopping and to experiments using thick guiding layers is discussed
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Small-scale structures in neutrals and charged aerosol particles as observed during the ECOMA/MASS rocket campaign
We present results of in situ measurements of neutral temperature during the ECOMA/MASS rocket campaign. We present and compare results of turbulence measurements conducted simultaneously by both in situ and doppler radar techniques. We show that the derived values of the turbulence energy dissipation rates are similar on average. We also find a region with a near adiabatic lapse rate with turbulence detected at the upper and lower edge. We note that it is consistent with expectation for a Kelvin-Helmholtz instability.
We also present an estimate of the Schmidt numbers, Sc, for the charged aerosols that utilizes in situ measured small-scale density fluctuations of charged aerosols and both in situ and radar turbulence measurements. The derived Schmidt numbers fall within the range between 100 and 4500. This result agrees with previous estimates based on multi-frequency observations of PMSE (Rapp et al., 2008) and also with estimates of microphysical parameters presented in the companion paper by Rapp et al. (2009)
Small-scale structures in neutrals and charged aerosol particles as observed during the ECOMA/MASS rocket campaign
We present results of in situ measurements of neutral temperature during the ECOMA/MASS rocket campaign. We present and compare results of turbulence measurements conducted simultaneously by both in situ and doppler radar techniques. We show that the derived values of the turbulence energy dissipation rates are similar on average. We also find a region with a near adiabatic lapse rate with turbulence detected at the upper and lower edge. We note that it is consistent with expectation for a Kelvin-Helmholtz instability. <br><br> We also present an estimate of the Schmidt numbers, <I>Sc</I>, for the charged aerosols that utilizes in situ measured small-scale density fluctuations of charged aerosols and both in situ and radar turbulence measurements. The derived Schmidt numbers fall within the range between 100 and 4500. This result agrees with previous estimates based on multi-frequency observations of PMSE (Rapp et al., 2008) and also with estimates of microphysical parameters presented in the companion paper by Rapp et al. (2009)
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