1,314 research outputs found
What to learn from dilepton transverse momentum spectra in heavy-ion collisions?
Recently the NA60 collaboration has presented high precision measurements of
dimuon spectra double differential in invariant mass and transverse pair
momentum in In-In collisions at . While the
-dependence is important for an understanding of in-medium changes of light
vector mesons and is integrated insensitive to collective expansion, the
-dependence arises from an interplay between emission temperature and
collective transverse flow. This fact can be exploited to derive constraints on
the evolution model and in particular on the contributions of different phases
of the evolution to dimuon radiation into a given window. We present
arguments that a thermalized evolution phase with leaves
its imprint on the spectra.Comment: Contributed to 19th International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions: Quark Matter 2006 (QM 2006), Shanghai, China, 14-
20 Nov 200
Photonic measurements of the longitudinal expansion dynamics in Heavy-Ion collisions
Due to the smallness of the electromagnetic coupling, photons escape from the
hot and dense matter created in an heavy-ion collision at all times, in
contrast to hadrons which are predominantly emitted in the final freeze-out
phase of the evolving system. Thus, the thermal photon yield carries an imprint
from the early evolution. We suggest how this fact can be used to gain
information about where between the two limiting cases of Bjorken
(boost-invariant expansion) and Landau (complete initial stopping and
re-expansion) hydrodynamics the actual evolution can be found. We argue that
both the rapidity dependence of the photon yield and photonic HBT radii are
capable of answering this question.Comment: 10 pages, 3 figure
An Investigation Into Optimization of Melting Processes Variables to Reduce the Scrap Rate of Aluminum Castings
A comprehensive description of multiple observables in heavy-ion collisions at SPS
Combining and expanding on work from previous publications, a model for the
evolution of ultrarelativistic heavy-ion collisions at the CERN SPS for 158
AGeV beam energy is presented. Based on the assumption of thermalization and a
parametrization of the space-time expansion of the produced matter, this model
is able to describe a large set of observables including hadronic momentum
spectra, correlations and abundancies, the emission of real photons, dilepton
radiation and the suppression pattern of charmonia. Each of these obervables
provides unique capabilities to study the reaction dynamics and taken together
they form a strong and consistent picture of the evolving system. Based on the
emission of hard photons, we argue that a strongly interacting, hot and dense
system with temperatures above 250 MeV has to be created early in the reaction.
Such a system is bound to be different from hadronic matter and likely to be a
quark-gluon plasma, and we find that this assumption is in line with the
subsequent evolution of the system that is reflected in other observables.Comment: 21 pages, 10 figures, submitted to J. Phys.
Thermal photons from fluctuating initial conditions
Event-by-event fluctuations of initial QCD-matter density produced in
heavy-ion collisions at RHIC enhance the production of thermal photons
significantly in the region GeV/ compared to a smooth
initial-state averaged profile in the ideal hydrodynamic calculation. This
enhancement is a an early time effect due to the presence of hotspots or
over-dense regions in the fluctuating initial state. The effect of fluctuations
is found to be stronger in peripheral than in central collisions.Comment: 4 pages, 3 figures. Talk given at Quark Matter 2011, 22-28 May 2011,
Annecy, Franc
Collision centrality and dependence of the emission of thermal photons from fluctuating initial state in ideal hydrodynamic calculation
Fluctuations in the initial QCD matter density distribution are found to
enhance the production of thermal photons significantly in the range 2 \leq pT
\leq 4 GeV/c compared to a smooth initial state averaged profile in ideal
hydrodynamic calculation for 200 AGeV Au+Au collisions at the Relativistic
Heavy Ion Collider (RHIC) and 2.76 ATeV Pb+Pb collisions at the Large Hadron
Collider (LHC). The thermal emission of photons is strongly dependent on the
initial temperature of the system where the presence of 'hotspots' in the
initial state translates into enhanced production of photons compared to a
smooth profile. The effect of fluctuations in the initial state is found to be
stronger for peripheral collisions and for lower beam energies. The pT spectra
are found to be quite sensitive to the value of the initial formation time of
the plasma which is not known unambiguously and which may vary with collision
centralities at a particular beam energy. Increase in the value of the
formation time lowers the production of thermal photons compared to the results
from a shorter formation time. However, the relative enhancement from
fluctuating initial tates (compared to a smooth initial state) is found to be
stronger for the larger values of formation time. The pT spectra alone are
found to be insufficient to quantify the fluctuations in the initial density
distribution due to the uncertainties in the initial conditions. A suitably
normalized ratio of central-to-peripheral yield as a function of collision
centrality and pT can be a useful measure of the fluctuation size scale.Comment: 10 pages, 10 figure
Comparing different freeze-out scenarios in azimuthal hadron correlations induced by fast partons
I review the linearized hydrodynamical treatment of a fast parton traversing
a perturbative quark-gluon plasma. Using numerical solutions for the medium's
response to the fast parton, I obtain the medium's distribution function which
is then used in a Cooper-Frye freeze-out prescription to obtain an azimuthal
particle spectrum. Two different freeze-out scenarios are considered which
yield significantly different results. I conclude that any meaningful
comparison of azimuthal hadron correlation functions to RHIC data requires
implementing a realistic freeze-out scenario in an expanding medium.Comment: Contribution to the Proceedings for 2008 Hot Quarks in Estes Park,
CO, as accepted for publication in EPJ-
Emission of thermal photons and the equilibration time in Heavy-Ion collisions
The emission of hard real photons from thermalized expanding hadronic matter
is dominated by the initial high-temperature expansion phase. Therefore, a
measurement of photon emission in ultrarelativistic heavy-ion collisions
provides valuable insights into the early conditions realized in such a
collision. In particular, the initial temperature of the expanding fireball or
equivalently the equilibration time of the strongly interacting matter are of
great interest. An accurate determination of these quantities could help to
answer the question whether or not partonic matter (the quark gluon plasma) is
created in such collisions. In this work, we investigate the emission of real
photons using a model which is based on the thermodynamics of QCD matter and
which has been shown to reproduce a large variety of other observables. With
the fireball evolution fixed beforehand, we are able to extract limits for the
equilibration time by a comparison with photon emission data measured by WA98.Comment: 12 pages, 5 figures, accepted for publication at Phys. Rev.
A global description of heavy-ion collisions
A model for the evolution of ultrarelativistic heavy-ion collisions at both
CERN SPS and RHIC top energies is presented. Based on the assumption of
thermalization and a parametrization of the space-time expansion of the
produced matter, this model is able to describe a large set of observables
including hadronic momentum spectra, correlations and abundancies, the emission
of real photons, dilepton radiation and the suppression pattern of charmonia.
Each of these obervables provides unique capabilities to study the reaction
dynamics and taken together they form a strong and consistent picture of the
evolving system. Based on the emission of hard photons measured at SPS, we
argue that a strongly interacting, hot and dense system with temperatures above
250 MeV has to be created early in the reaction. Such a system is bound to be
different from hadronic matter and likely to be a quark-gluon plasma, and we
find that this assumption is in line with the subsequent evolution of the
system that is reflected in other observables.Comment: 7 pages, 5 figures, Talk given at the Hot Quarks 2004 Workshop,
Taos,NM, July 18-24 200
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Liquid Titanium Solute Diffusion Measured by Pulsed Ion-Beam Melting
The diffusivities of Sri, Mo, Zr, and Hf in liquid Ti were determined by pulsed ion-beam melting of thin liquid layers. Time-resolved optical reflectance and one-dimensional heat-flow simulations were employed to determine the melt duration. The broadening of nearly Gaussian solute concentration-depth profiles was determined ex situ using Rutherford backscattering spectrometry. Solute diffusivities in the range of 5 to 9 X 10-5 cm2/s were determined at temperatures in the range of 2200 to 2500 K. Calculations of buoyancy and Marangoni convection indicate that convective contamination is unlikely.Engineering and Applied Science
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