236 research outputs found
A Global Classification of Astronomical Tide Asymmetry and Periodicity Using Statistical and Cluster Analysis
ABSTRACT: Tidal asymmetry plays a key role in the behavior of estuaries. Positive and negative asymmetries are associated with flood- and ebb-dominated estuaries, respectively. Asymmetry arises from both the interaction among the main tidal constituents and the harmonics generated when tide propagates in shallow waters. Most previous research focuses on the deformation of the tide within estuaries; however, ocean tide may show asymmetry at the estuary entrance, which implies that the boundary condition is already deformed. This fact has important implications for tide propagation, estuarine transport processes, and flow exchanges between estuaries and open oceans. In this study, the global astronomical tide is classified according to its asymmetry and periodicity. The objective is to provide a guiding framework of representative astronomical tide types (ATtypes) on a worldwide scale to be used as a reference for further research on the transport of substances in estuaries. The applied methodology is based on the use of the TPXO9-atlas global barotropic tidal solution and detailed statistical analysis. Probability density functions of the tidal elevation time derivative and the tidal form factor were extracted from TPXO9-atlas with a spatial resolution ranging from 1/6° to 1/30°. The K-means algorithm was applied to these parameters, and 25 representative ATtypes were identified. The classification was validated with 757 worldwide tide gauge records. The results show that 11.3% of coastal areas show negative asymmetries, 11.3% positive asymmetries, while symmetric tides dominate 77.4% of coastal areas. In these areas, estuaries can show asymmetries exclusively dependent on overtides and compound tides generated during inland propagation without being externally conditione
Search for short-lived axions in a nuclear isoscalar transition
Axions, if existing, can cause a strong signal of positron-electron pairs in isoscalar M1 transitions in competition with gamma-ray emission. We searched for such a signal in the 3.59 MeV transition in 10B with a fourfold Mini-Orange spectrometer. No axion events were found within two percent of the prediction for the standard axion- to γ-ray branching ratio
Partial Wave Analysis of the Reaction to Search for the "" Bound State
Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have
analyzed HADES data of the reaction . This
reaction might contain information about the kaonic cluster "" via its
decay into . Due to interference effects in our coherent description
of the data, a hypothetical (or, specifically "")
cluster signal must not necessarily show up as a pronounced feature (e.g. a
peak) in an invariant mass spectra like . Our PWA analysis includes a
variety of resonant and non-resonant intermediate states and delivers a good
description of our data (various angular distributions and two-hadron invariant
mass spectra) without a contribution of a cluster. At a
confidence level of CL=95\% such a cluster can not contribute more than
2-12\% to the total cross section with a final state, which
translates into a production cross-section between 0.7 and 4.2 ,
respectively. The range of the upper limit depends on the assumed cluster mass,
width and production process.Comment: 7 Pages, 5 Figure
Production of Sigma{\pm}pi?pK+ in p+p reactions at 3.5 GeV beam energy
We study the production of Sigma^+-pi^+-pK^+ particle quartets in p+p
reactions at 3.5 GeV kinetic beam energy. The data were taken with the HADES
experiment at GSI. This report evaluates the contribution of resonances like
Lambda(1405$, Sigma(1385)^0, Lambda(1520), Delta(1232), N^* and K^*0 to the
Sigma^+- pi^-+ p K+ final state. The resulting simulation model is compared to
the experimental data in several angular distributions and it shows itself as
suitable to evaluate the acceptance corrections properly.Comment: 15 pages, 5 figure
Inclusive pion and eta production in p+Nb collisions at 3.5 GeV beam energy
Data on inclusive pion and eta production measured with the dielectron
spectrometer HADES in the reaction p+93Nb at a kinetic beam energy of 3.5 GeV
are presented. Our results, obtained with the photon conversion method,
supplement the rather sparse information on neutral meson production in
proton-nucleus reactions existing for this bombarding energy regime. The
reconstructed e+e-e+e- transverse-momentum and rapidity distributions are
confronted with transport model calculations, which account fairly well for
both pi0 and eta production.Comment: 12 pages, 9 figures, submitted to Physical Review
Inclusive dielectron production in proton-proton collisions at 2.2 GeV beam energy
Data on inclusive dielectron production are presented for the reaction p+p at
2.2 GeV measured with the High Acceptance DiElectron Spectrometer (HADES). Our
results supplement data obtained earlier in this bombarding energy regime by
DLS and HADES. The comparison with the 2.09 GeV DLS data is discussed. The
reconstructed e+e- distributions are confronted with simulated pair cocktails,
revealing an excess yield at invariant masses around 0.5 GeV/c2. Inclusive
cross sections of neutral pion and eta production are obtained
Searching a Dark Photon with HADES
We present a search for the e+e- decay of a hypothetical dark photon, also
names U vector boson, in inclusive dielectron spectra measured by HADES in the
p (3.5 GeV) + p, Nb reactions, as well as the Ar (1.756 GeV/u) + KCl reaction.
An upper limit on the kinetic mixing parameter squared epsilon^{2} at 90% CL
has been obtained for the mass range M(U) = 0.02 - 0.55 GeV/c2 and is compared
with the present world data set. For masses 0.03 - 0.1 GeV/c^2, the limit has
been lowered with respect to previous results, allowing now to exclude a large
part of the parameter region favoured by the muon g-2 anomaly. Furthermore, an
improved upper limit on the branching ratio of 2.3 * 10^{-6} has been set on
the helicity-suppressed direct decay of the eta meson, eta-> e+e-, at 90% CL
Subthreshold Xi- Production in Collisions of p(3.5 GeV)+Nb
Results on the production of the double-strange cascade hyperon
are reported for collisions of p\,(3.5~GeV)\,+\,Nb, studied
with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI
Helmholtzzentrum for Heavy-Ion Research, Darmstadt. For the first time,
subthreshold production is observed in proton-nucleus
interactions. Assuming a phase-space distribution similar to
that of hyperons, the production probability amounts to
resulting in a
ratio of $P_{\mathrm{\Xi^-}}/\
P_{\mathrm{\Lambda+\Sigma^0}}=(1.2\pm
0.3\,\mathrm{(stat)}\pm0.4\,\mathrm{(syst)})\times10^{-2}\mathrm{\Xi^-}$ yield.Comment: 6 pages, 3 figure
Lambda hyperon production and polarization in collisions of p(3.5 GeV) + Nb
Results on hyperon production are reported for collisions of p(3.5
GeV) + Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at
SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. The transverse
mass distributions in rapidity bins are well described by Boltzmann shapes with
a maximum inverse slope parameter of about MeV at a rapidity of ,
i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions,
. The rapidity density decreases monotonically with increasing
rapidity within a rapidity window ranging from 0.3 to 1.3. The
phase-space distribution is compared with results of other experiments and with
predictions of two transport approaches which are available publicly. None of
the present versions of the employed models is able to fully reproduce the
experimental distributions, i.e. in absolute yield and in shape. Presumably,
this finding results from an insufficient modelling in the transport models of
the elementary processes being relevant for production, rescattering
and absorption. The present high-statistics data allow for a genuine
two-dimensional investigation as a function of phase space of the
self-analyzing polarization in the weak decay . Finite negative values of the polarization in the order of
are observed over the entire phase space studied. The absolute value of the
polarization increases almost linearly with increasing transverse momentum for
MeV/c and increases with decreasing rapidity for .Comment: accepted by Eur. Phys. J.
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