2,756 research outputs found
Hydrodynamic description of spectra at high transverse mass in ultrarelativistic heavy ion collisions
Transverse mass spectra of pions and protons measured in central collisions
of heavy ions at the SPS and at RHIC are compared to a hydrodynamic
parameterization. While the chemical temperature needed at RHIC is
significantly higher compared to SPS, the spectra may be described using
kinetic freeze-out parameters which are similar for both beam energies. At RHIC
either the temperature or the flow velocity is higher, but the data provide no
unambiguous proof for much stronger transverse flow. The contribution of such
hydrodynamic emission at high transverse momenta is investigated in detail. It
is shown that hydrodynamics may be relevant up to relatively high transverse
momenta. The importance of the velocity profile used in this context is
highlighted.Comment: 10 pages, 11 figures, accepted in Eur. Phys. J. C, data from more
experiments used in this versio
Mass generation in coalescence - effects on hadron spectra
Different scenarios for the creation of constituent mass in the hadron
formation process are discussed. Effects of these may be observable in hadron
momentum spectra.Comment: Poster Proceedings of Quark Matter 2005, 4 page
The ridge laboratory
Mechanisms proposed to explain the jet-related correlation of long range in
rapidity (the ridge) observed in high-energy heavy-ion collisions are reviewed.
Limitations of a model using the combined effect of transverse flow and a
direction bias of partons suffering energy loss are discussed. The influence of
the time scale of the correlation mechanism on the rapidity range is
investigated.Comment: Talk presented at 4th International Workshop High-pT physics at LHC
09, Prague, Feb. 4-7, 200
Summary of Results on Hard Probes
Results on observables related to hard scattering processes as presented at
this conference are reviewed. This includes in particular measurements related
to jet quenching, a phenomenon which has been predicted as a signature for the
hot and dense early phase of strongly interacting matter.Comment: Summary talk at Quark Matter 2002, Nantes, Proceedings to be
published in Nucl. Phys. A, 10 pages, 6 figures, (one figure added in this
version
Influence of hydrodynamics on the interpretation of the high hadron suppression at RHIC
A hybrid parameterization including contributions of hydrodynamics and of
expectations from the spectral shape observed in p+p collisions is introduced.
This parameterization can successfully describe identified hadron spectra over
a wide range of in Au+Au reactions at = 200 GeV for all
centralities. The parameters of the hydrodynamic source compare reasonably well
to other attempts to describe the spectra. The description is obtained using
one universal suppression factor of the hard scattering component independent
of and hadron species. For the fit results obtained the observed
nuclear modification factor for the different particles converges to a
universal suppression behavior for .Comment: updated version (only typos), 16 pages, 10 figure
Direct Photons in Nuclear Collisions at FAIR Energies
Using the extrapolation of existing data estimations of prompt photon
production at FAIR energies have been made. At the rapidity
density of prompt photons with 1.5 GeV/c per central Au+Au event at 25
AGeV is estimated as . With the planed beam intensity
per second and 1% interaction probability, for 10% of most central events one
can expect the prompt photon rate photons per second.
Direct photons from the hadron scenario of ion collisions generated by the
Hadron-String-Dynamics (HSD) transport approach with implemented meson
scatterings have been analyzed.
Photons from short-living resonances (e.g. )
decaying during the dense phase of the collision should be considered as direct
photons. They contribute significantly in the direct photon spectrum at
GeV/c. At the FAIR energy 25 AGeV in Au+Au central collisions
the HSD generator predicts, as a lower estimate,
0.5% in the region
GeV/c. At GeV/c 2%.
Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics
(BHD) model. The BHD spectra differ strongly from the HSD predictions. The
direct photon spectrum is very sensitive to the initial temperature parameter
of the model. The 10 MeV increase in the value leads to
2 times higher photon yield.Comment: 9 pages, 5 figures, Talk at the session of Russian Academy of
Sciences, ITEP, Moscow, 26 - 30 November 200
The monitoring system for the aerogel Cherenkov counter of the BELLE detector
We report on a design and performances of a monitoring system developed for
the aerogel Cherenkov counters (ACC) of the BELLE detector. The system consists
of blue LEDs, a diffuser box, and optical distributors which distribute the LED
light to the ACC modules. The employed LED (NSPB series) has been observed to
have high reliability on the long term stability and the temprature dependence.
The diffuser box is employed to reduce the intrinsic non-uniformity of the LED
light intensity. The overall performances of the present monitoring system on
uniformity and intensity of the light output have been found to satisfy all the
requirements for the monitoring.Comment: 24 pages, LaTeX, 13 eps figures, to be published in Nucl. Instrum.
and Meth. A. Postscript file (4.5 MB) is available at
http://www-hep.phys.saga-u.ac.jp/~murakami/paper/xxx_accmon.p
Interplay between soft and hard hadronic components for identified hadrons in relativistic heavy ion collisions
We investigate the transverse dynamics in Au+Au collisions at \sqrt{s_NN}=200
GeV by emphasis upon the interplay between soft and hard components through p_T
dependences of particle spectra, ratios of yields, suppression factors, and
elliptic flow for identified hadrons. From hydrodynamics combined with
traversing minijets which go through jet quenching in the hot medium, we
calculate interactions of hard jets with the soft hydrodynamic components. It
is shown by the explicit dynamical calculations that the hydrodynamic radial
flow and the jet quenching of hard jets are the keys to understand the
differences among the hadron spectra for pions, kaons, and protons. This leads
to the natural interpretation for N_p/N_\pi ~ 1, R_{AA} >~ 1 for protons, and
v_2^p > v_2^\pi recently observed in the intermediate transverse momentum
region at Relativistic Heavy Ion Collider (RHIC).Comment: 11 pages, 9 figures; some references added; title changed, some data
points included in figure
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