622 research outputs found
Liquid-Gas Phase Transition in Nuclear Equation of State
A canonical ensemble model is used to describe a caloric curve of nuclear
liquid-gas phase transition. Allowing a discontinuity in the freeze out density
from one spinodal density to another for a given initial temperature, the
nuclear liquid-gas phase transition can be described as first order. Averaging
over various freeze out densities of all the possible initial temperatures for
a given total reaction energy, the first order characteristics of liquid-gas
phase transition is smeared out to a smooth transition. Two experiments, one at
low beam energy and one at high beam energy show different caloric behaviors
and are discussed.Comment: 12 pages in Revtex including two Postscript figure
Time-Dependent Hartree-Fock simulation of the expansion of abraded nuclei
A recent interpretation of the caloric curve based on the expansion of the
abraded spectator nucleus is re-analysed in the framework of the Time-Dependent
Hartree-Fock (TDHF) evolution. It is shown that the TDHF dynamics is more
complex than a single monopolar collective motion at moderate energy. The
inclusion of other important collective degrees of freedom may lead to the
dynamical creation of hollow structure. Then, low density regions could be
locally reached after a long time by the creation of these exotic density
profiles. In particular the systematic of the minimum density reached during
the expansion (the so-called turning points) appears to be different.Comment: 30 Latex pages including 9 figure
Characterisation and calibration of a scintillating fibre detector with > 4000 multi-anode photomultiplier channels
In the Kaos spectrometer at the Mainz Microtron a high-resolution coordinate
detector for high-energy particles is operated. It consists of scintillating
fibres with diameters of 4000 multi-anode
photomultiplier channels. It is one of the most modern focal-plane detectors
for magnetic spectrometers world-wide. To correct variations in the detection
efficiency, caused by the different gains and the different optical
transmittances, a fully automated off-line calibration procedure has been
developed. The process includes the positioning of a radioisotope source
alongside the detector plane and the automated acquisition and analysis of the
detector signals. It was possible to characterise and calibrate each individual
fibre channel with a low degree of human interaction.Comment: Nucl. Instrum. Meth. A (2012
Antihyperon potentials in nuclei via exclusive antiproton-nucleus reactions
The exclusive production of hyperon-antihyperon pairs close to their
production threshold in antiproton - nucleus collisions offers a unique and
hitherto unexplored opportunity to elucidate the behaviour of antihyperons in
nuclei. For the first time we analyse these reactions in a microscopic
transport model using the the Gie\ss en Boltzmann-Uehling-Uhlenbeck transport
model. The calculation take the delicate interplay between the strong
absorption of antihyperons, their rescattering and refraction at the nuclear
surface as well as the Fermi motion of the struck nucleon into account. We find
a substantial sensitivity of transverse momentum correlations of coincident
-pairs to the assumed depth of the
-potential. Because of the high cross section for this
process and the simplicity of the experimental method our results are highly
relevant for future activities at the international Facility for Antiproton and
Ion Research (FAIR)
Exotic hadrons from dynamical clustering of quarks in ultrarelativistic heavy ion collisions
Results from a model study on the formation of exotic quark clusters at the
hadronization stage of a heavy ion collision are presented. The dynamical quark
molecular dynamics (qMD) model which is used is sketched, and results for
exotica made of up to six (anti-)quarks are shown. The second part focuses on
pentaquarks. The rapidity distribution are shown, and the distribution of
strangeness is found to yield an indicator of thermalization and homogenisation
of the deconfined quark system. Relative Theta^+ yields are found to be lower
than thermal model estimates.Comment: 4 pages, 5 figures, to appear in the proceedings of Strangeness in
Quark Matter 2004 (SQM2004), Cape Town, South Africa, 15-20 September 200
Formation of hypermatter and hypernuclei within transport models in relativistic ion collisions
Within a combined approach we investigate the main features of the production
of hyper-fragments in relativistic heavy-ion collisions. The formation of
hyperons is modelled within the UrQMD and HSD transport codes. To describe the
hyperon capture by nucleons and nuclear residues a coalescence of baryons (CB)
model was developed. We demonstrate that the origin of hypernuclei of various
masses can be explained by typical baryon interactions, and that it is similar
to processes leading to the production of conventional nuclei. At high beam
energies we predict a saturation of the yields of all hyper-fragments,
therefore, this kind of reactions can be studied with high yields even at the
accelerators of moderate relativistic energies.Comment: 9 pages, 9 figures, submitted to Phys. Lett.
Experimental Indications for the Response of the Spectators to the Participant Blast
Precise momentum distributions of identified projectile fragments, formed in
the reactions 238U + Pb and 238U + Ti at 1 A GeV, are measured with a
high-resolution magnetic spectrometer. With increasing mass loss, the
velocities first decrease as expected from previously established systematics,
then level off, and finally increase again. Light fragments are on the average
even faster than the projectiles. This finding is interpreted as the response
of the spectators to the participant blast. The re-acceleration of projectile
spectators is sensitive to the nuclear mean field and provides a new tool for
investigating the equation of state of nuclear matter.Comment: 7 pages, 3 figures, background information on
http://www-wnt.gsi.de/kschmidt
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