59 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.
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
Contribution of #pi#"o and #eta# Dalitz decays to the dilepton invariant-mass spectrum in 1 A.GeV heavy-ion collisions
The Dalitz-decay contributions of #pi#"0 and #eta# mesons to the di-electron invariant-mass spectrum at 1 A.GeV have been obtained from a systematics of inclusive meson production cross sections measured for the collision systems "1"2C+"n"a"tC and "4"0Ar,"4"0Ca+"n"a"tCa in the bombarding-energy range of 0.8 -2.0 A.GeV. These results are compared with the recently published di-electron mass spectra of the DLS collaboration. Systematic errors and angular-distribution effects are discussed. We conclude that the low-mass part of the DLS data cannot be explained by the Dalitz decays of light neutral mesons only. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
The Thoc1 encoded ribonucleoprotein is required for myeloid progenitor cell homeostasis in the adult mouse.
Co-transcriptionally assembled ribonucleoprotein (RNP) complexes are critical for RNA processing and nuclear export. RNPs have been hypothesized to contribute to the regulation of coordinated gene expression, and defects in RNP biogenesis contribute to genome instability and disease. Despite the large number of RNPs and the importance of the molecular processes they mediate, the requirements for individual RNP complexes in mammalian development and tissue homeostasis are not well characterized. THO is an evolutionarily conserved, nuclear RNP complex that physically links nascent transcripts with the nuclear export apparatus. THO is essential for early mouse embryonic development, limiting characterization of the requirements for THO in adult tissues. To address this shortcoming, a mouse strain has been generated allowing inducible deletion of the Thoc1 gene which encodes an essential protein subunit of THO. Bone marrow reconstitution was used to generate mice in which Thoc1 deletion could be induced specifically in the hematopoietic system. We find that granulocyte macrophage progenitors have a cell autonomous requirement for Thoc1 to maintain cell growth and viability. Lymphoid lineages are not detectably affected by Thoc1 loss under the homeostatic conditions tested. Myeloid lineages may be more sensitive to Thoc1 loss due to their relatively high rate of proliferation and turnover
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