88 research outputs found
On the exact conservation laws in thermal models and the analysis of AGS and SIS experimental results
The production of hadrons in relativistic heavy ion collisions is studied
using a statistical ensemble with thermal and chemical equilibrium. Special
attention is given to exact conservation laws, i.e. certain charges are treated
canonically instead of using the usual grand canonical approach. For small
systems, the exact conservation of baryon number, strangeness and electric
charge is to be taken into account. We have derived compact, analytical
expressions for particle abundances in such ensemble. As an application, the
change in ratios in AGS experiments with different interaction system
sizes is well reproduced. The canonical treatment of three charges becomes
impractical very quickly with increasing system size. Thus, we draw our
attention to exact conservation of strangeness, and treat baryon number and
electric charge grand canonically. We present expressions for particle
abundances in such ensemble as well, and apply them to reproduce the large
variety of particle ratios in GSI SIS 2 A GeV Ni-Ni experiments. At the
energies considered here, the exact strangeness conservation fully accounts for
strange particle suppression, and no extra chemical factor is needed.Comment: Talk given at Strangeness in Quark Matter '98, Padova, Italy (1998).
Submitted to J.Phys. G. 5 pages, 2 figure
Light-Front Analysis of pi^{-} Mesons Produced in Mg - Mg Collisions at 4.3 a Gev/c
Light-front analysis of pi^{-} mesons in Mg-Mg collisions is carried out. The
phase space of secondary pions is naturally divided into two parts in one of
which the thermal equilibration assumption seems to be in a good agreement with
data. Corresponding temperatures are extracted and compared to the results of
other experiments. The experimental results have been compared with the
predictions of the Quark Gluon String Model (QGSM) and satisfactory agreement
between the experimental data and the model has been found.Comment: 14 pages with 7 postscript figures. accepted for publication in Nucl.
Phys.
Dilepton production and -scaling at BEVALAC/SIS energies
We present a dynamical study of production in C + C and Ca + Ca
collisions at BEVALAC/SIS energies on the basis of the covariant transport
approach HSD employing momentum-dependent -meson spectral functions that
include the pion modifications in the nuclear medium as well as the
polarization of the -meson due to resonant scattering. We find
that the experimental data from the DLS collaboration cannot be described
within the -meson spectral function approach. A dropping -mass
scenario leads to a good reproduction of the DLS dilepton data, however,
violates the -scaling of and spectra as observed by the
TAPS collaboration as well as photoproduction on nuclei.Comment: 35 pages, ReVTeX, including 11 postscript figures, UGI-97-06, Nucl.
Phys. A, in pres
K^+ production in the reaction at incident energies from 1 to 2 AGeV
Semi-inclusive triple differential multiplicity distributions of positively
charged kaons have been measured over a wide range in rapidity and transverse
mass for central collisions of Ni with Ni nuclei. The transverse
mass () spectra have been studied as a function of rapidity at a beam
energy 1.93 AGeV. The distributions of K^+ mesons are well described by a
single Boltzmann-type function. The spectral slopes are similar to that of the
protons indicating that rescattering plays a significant role in the
propagation of the kaon. Multiplicity densities have been obtained as a
function of rapidity by extrapolating the Boltzmann-type fits to the measured
distributions over the remaining phase space. The total K^+ meson yield has
been determined at beam energies of 1.06, 1.45, and 1.93 AGeV, and is presented
in comparison to existing data. The low total yield indicates that the K^+
meson can not be explained within a hadro-chemical equilibrium scenario,
therefore indicating that the yield does remain sensitive to effects related to
its production processes such as the equation of state of nuclear matter and/or
modifications to the K^+ dispersion relation.Comment: 24 pages Latex (elsart) 7 PS figures to be submitted to Nucl. Phys
Photon Production in Heavy-ion Collisions Close to the Pion Threshold
We report on a measurement of hard photons (Eg>30 MeV) in the reaction Ar+Ca
at 180A MeV at an energy in which photons from the decay of pi0 mesons are
dominating. Simultaneous measurement with the TAPS spectrometer of the photon
spectrum and photon-photon coincidences used for the identification of pi0
enabled the subtraction of pi0 contribution. The resulting photon spectrum
exhibits an exponential shape with an inverse slope of
E0=(53+-0.03(stat)-5+8(syst)) MeV. The photon multiplicity, equal to
(1.21+-0.03(stat)+0.3-0.2(syst))10E0-2, is roughly one order of magnitude
larger than the value extrapolated from existing systematics. This enhancement
of the hard photon production is attributed to a strong increase in the
contribution of secondary np collisions to the total photon yield. We conclude
that, on average, the number of np collisions which contribute to the hard
photon production is 7 times larger than the number of first chance np
collisions in the reaction Ar+Ca at 180A MeV.Comment: 15 pages, 4 figures, references adde
Modern languages in Germany and Sweden : A Comparison of Subject Requirements for Modern Languages between Schleswig-Holstein and Sweden
Foreign languages are an important part of today's school system. At the beginning of the 2000s, the Common European Framework of Reference for Languages was introduced, which aims to create cross-country comparability of language qualifications.In order to find out whether the teaching content in the two countries has similarities, which ultimately lead to a similar level within the foreign language, I deal with the following ques- tions. On the one hand, What similarities and differences can be observed in the competence area of oral communication in the lower secondary level of foreign languages between Ger- many and Sweden? and on the other hand, What similarities and differences can be observed in the subject areas in the lower secondary level of foreign languages between Germany and Sweden? For this purpose, I conduct a comparative curriculum study and a curriculum analysis, examining the Swedish and Schleswig-Holstein curricula. It could be noted that there were several similarities and differences between the curricula of the two countries. Within the sub- ject areas, many overlapping topics could be identified, such as how to be able to introduce oneself in the target language and to be able to talk about the family. In terms of writing skills, there were similarities in terms of topics, but also in terms of the type of teaching, such as presentations and stories. The biggest differences could be found in the subject areas and in the competence of writing within the structure and scope. Thus, the Schleswig-Holstein curriculum is much more extensive and detailed than the Swedish curriculum
Lichen planus runs along cutaneous superficial veins on the forearms: supravenous lichen planus?
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