222 research outputs found
Characterisation of solid particles emitted from diesel and petrol engines as a contribution to the determination of the origin of carbonaceous particles in urban aerosol
Solid particles emitted from diesel and petrol engines were studied using a scanning electron microscope fitted with an energy dispersive spectrometer. The soot emitted from different engines under different operating conditions differed in particle size, and the form and size of aggregates. Identification of the soot particles emitted from diesel or petrol engines in urban aerosol based on their size and morphology was found to be impossible
Two-proton small-angle correlations in central heavy-ion collisions: a beam-energy and system-size dependent study
Small-angle correlations of pairs of protons emitted in central collisions of
Ca + Ca, Ru + Ru and Au + Au at beam energies from 400 to 1500 MeV per nucleon
are investigated with the FOPI detector system at SIS/GSI Darmstadt.
Dependences on system size and beam energy are presented which extend the
experimental data basis of pp correlations in the SIS energy range
substantially. The size of the proton-emitting source is estimated by comparing
the experimental data with the output of a final-state interaction model which
utilizes either static Gaussian sources or the one-body phase-space
distribution of protons provided by the BUU transport approach. The trends in
the experimental data, i.e. system-size and beam energy dependences, are well
reproduced by this hybrid model. However, the pp correlation function is found
rather insensitive to the stiffness of the equation of state entering the
transport model calculations.Comment: 9 pages, 8 figures, accepted at Eur. Phys. Journ.
Projected Quasi-particle Perturbation theory
The BCS and/or HFB theories are extended by treating the effect of four
quasi-particle states perturbatively. The approach is tested on the pairing
hamiltonian, showing that it combines the advantage of standard perturbation
theory valid at low pairing strength and of non-perturbative approaches
breaking particle number valid at higher pairing strength. Including the
restoration of particle number, further improves the description of pairing
correlation. In the presented test, the agreement between the exact solution
and the combined perturbative + projection is almost perfect. The proposed
method scales friendly when the number of particles increases and provides a
simple alternative to other more complicated approaches
Charged pion production in Ru+Ru collisions at 400A and 1528A MeV
We present transverse momentum and rapidity spectra of charged pions in
central Ru + Ru collisions at 400 and 1528 MeV. The data exhibit enhanced
production at low transverse momenta compared to the expectations from the
thermal model that includes the decay of -resonances and thermal
pions. Modification of the -spectral function and the Coulomb
interaction are necessary to describe the detailed shape of the transverse
momentum spectra. Within the framework of the thermal model, the freeze-out
radii of pions are similar at both beam energies. The IQMD model reproduces the
shapes of the transverse momentum and rapidity spectra of pions, but the
predicted absolute yields are larger than in the measurements, especially at
lower beam energy.Comment: 12 pages, 11 figure
Direct comparison of phase-space distributions of K- and K+ mesons in heavy-ion collisions at SIS energies - evidence for in-medium modifications of kaons ?
The ratio of K- to K+ meson yields has been measured in the systems RuRu at
1.69 A GeV, Ru+Zr at 1.69 A GeV, and Ni+Ni at 1.93 A GeV incident beam kinetic
energy. The yield ratio is observed to vary across the measured phase space.
Relativistic transport-model calculations indicate that the data are best
understood if in-medium modifications of the kaons are taken into account.Comment: 14 pages including 3 figure
Stopping and Radial Flow in Central 58Ni + 58Ni Collisions between 1 and 2 AGeV
The production of charged pions, protons and deuterons has been studied in
central collisions of 58Ni on 58Ni at incident beam energies of 1.06, 1.45 and
1.93 AGeV. The dependence of transverse-momentum and rapidity spectra on the
beam energy and on the centrality of the collison is presented. It is shown
that the scaling of the mean rapidity shift of protons established for AGS and
SPS energies is valid down to 1 AGeV. The degree of nuclear stopping is
discussed; the IQMD transport model reproduces the measured proton rapidity
spectra for the most central events reasonably well, but does not show any
sensitivity between the soft and the hard equation of state (EoS). A radial
flow analysis, using the midrapidity transverse-momentum spectra, delivers
freeze-out temperatures T and radial flow velocities beta_r which increase with
beam energy up to 2 AGeV; in comparison to existing data of Au on Au over a
large range of energies only beta_r shows a system size dependence
Measurement of and mesons in Al+Al collisions at 1.9 GeV
New measurement of sub-threshold and production is
presented. The experimental data complete the measurement of strange particles
produced in Al+Al collisions at 1.9 GeV measured with the FOPI detector at
SIS/GSI. The / yield ratio is found to be and is in good agreement with the
UrQMD model prediction. These measurements provide information on in-medium
cross section of - fusion which is the dominant process on
sub-threshold production.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev.
Differential directed flow in Au+Au collisions
We present experimental data on directed flow in semi-central Au+Au
collisions at incident energies from 90 to 400 A MeV. For the first time for
this energy domain, the data are presented in a transverse momentum
differential way. We study the first order Fourier coefficient v1 for different
particle species and establish a gradual change of its patterns as a function
of incident energy and for different regions in rapidity.Comment: 5 pages, Latex, 5 eps figures, accepted for publication in Phys. Rev.
C (Rapid Communications). Data files available at
http://www-linux.gsi.de/~andronic/fopi/v1.htm
Excitation function of elliptic flow in Au+Au collisions and the nuclear matter equation of state
We present measurements of the excitation function of elliptic flow at
midrapidity in Au+Au collisions at beam energies from 0.09 to 1.49 GeV per
nucleon. For the integral flow, we discuss the interplay between collective
expansion and spectator shadowing for three centrality classes. A complete
excitation function of transverse momentum dependence of elliptic flow is
presented for the first time in this energy range, revealing a rapid change
with incident energy below 0.4 AGeV, followed by an almost perfect scaling at
the higher energies. The equation of state of compressed nuclear matter is
addressed through comparisons to microscopic transport model calculations.Comment: 10 pages, 4 eps figures, submitted for publication. Data files will
be available at http://www.gsi.de/~fopiwww/pub
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