98 research outputs found
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.
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.
Isospin dependence of relative yields of and mesons at 1.528 AGeV
Results on and meson production in Ru +
Ru and Zr + Zr collisions at a beam kinetic
energy of 1.528 GeV, measured with the FOPI detector at GSI-Darmstadt, are
investigated as a possible probe of isospin effects in high density nuclear
matter. The measured double ratio ()/() is
compared to the predictions of a thermal model and a Relativistic Mean Field
transport model using two different collision scenarios and under different
assumptions on the stiffness of the symmetry energy. We find a good agreement
with the thermal model prediction and the assumption of a soft symmetry energy
for infinite nuclear matter while more realistic transport simulations of the
collisions show a similar agreement with the data but also exhibit a reduced
sensitivity to the symmetry term.Comment: 5 pages, 3 figures. accepted for publication in Phys. Rev.
Directed flow in Au+Au, Xe+CsI and Ni+Ni collisions and the nuclear equation of state
We present new experimental data on directed flow in collisions of Au+Au,
Xe+CsI and Ni+Ni at incident energies from 90 to 400A MeV. We study the
centrality and system dependence of integral and differential directed flow for
particles selected according to charge. All the features of the experimental
data are compared with Isospin Quantum Molecular Dynamics (IQMD) model
calculations in an attempt to extract information about the nuclear matter
equation of state (EoS). We show that the combination of rapidity and
transverse momentum analysis of directed flow allow to disentangle various
parametrizations in the model. At 400A MeV, a soft EoS with momentum dependent
interactions is best suited to explain the experimental data in Au+Au and
Xe+CsI, but in case of Ni+Ni the model underpredicts flow for any EoS. At 90A
MeV incident beam energy, none of the IQMD parametrizations studied here is
able to consistently explain the experimental data.Comment: RevTeX, 20 pages, 30 eps figures, accepted for publication in Phys.
Rev. C. Data files available at http://www.gsi.de/~fopiwww/pub
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
First analysis of anisotropic flow with Lee--Yang zeroes
We report on the first analysis of directed and elliptic flow with the new
method of Lee--Yang zeroes. Experimental data are presented for Ru+Ru reactions
at 1.69 AGeV measured with the FOPI detector at SIS/GSI. The results obtained
with several methods, based on the event-plane reconstruction, on Lee--Yang
zeroes, and on multi-particle cumulants (up to 5th order) applied for the first
time at SIS energies, are compared. They show conclusive evidence that
azimuthal correlations between nucleons and composite particles at this energy
are largely dominated by anisotropic flow.Comment: 5 pages, 3 figures, submitted to Phys. Rev. C Rapid Co
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
First insights into the vertical habitat use of the whitespotted eagle ray Aetobatus narinari revealed by popâup satellite archival tags
The whitespotted eagle ray Aetobatus narinari is a tropical to warmâtemperate benthopelagic batoid that ranges widely throughout the western Atlantic Ocean. Despite conservation concerns for the species, its vertical habitat use and diving behaviour remain unknown. Patterns and drivers in the depth distribution of A. narinari were investigated at two separate locations, the western North Atlantic (Islands of Bermuda) and the eastern Gulf of Mexico (Sarasota, Florida, U.S.A.). Between 2010 and 2014, seven popâup satellite archival tags were attached to A. narinari using three methods: a throughâtail suture, an external tailâband and throughâwing attachment. Retention time ranged from 0 to 180âdays, with tags attached via the throughâtail method retained longest. Tagged rays spent the majority of time (82.85â±â12.17% S.D.) within the upper 10 m of the water column and, with one exception, no rays travelled deeper than ~26âm. One Bermuda ray recorded a maximum depth of 50.5 m, suggesting that these animals make excursions off the foreâreef slope of the Bermuda Platform. Individuals occupied deeper depths (7.42â±â3.99âm S.D.) during the day versus night (4.90â±â2.89âm S.D.), which may be explained by foraging and/or predator avoidance. Each individual experienced a significant difference in depth and temperature distributions over the diel cycle. There was evidence that mean hourly depth was best described by location and individual variation using a generalized additive mixed model approach. This is the first study to compare depth distributions of A. narinari from different locations and describe the thermal habitat for this species. Our study highlights the importance of region in describing A. narinari depth use, which may be relevant when developing management plans, whilst demonstrating that diel patterns appear to hold across individuals
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