Results on the production of the double-strange cascade hyperon \(\mathrm{\Xi^-}\) 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 \(\mathrm{\Xi^-}\) production is observed in proton-nucleus interactions. Assuming a \(\mathrm{\Xi^-}\) phase-space distribution similar to that of \(\mathrm{\Lambda}\) hyperons, the production probability amounts to \(P_{\mathrm{\Xi^-}}=(2.0\,\pm0.4\,\mathrm{(stat)}\,\pm 0.3\,\mathrm{(norm)}\,\pm 0.6\,\mathrm{(syst)})\times10^{-4}\) resulting in a \(\mathrm{\Xi^-/(\Lambda+\Sigma^0)}\) ratio of \(P_{\mathrm{\Xi^-}}/\ P_{\mathrm{\Lambda+\Sigma^0}}=(1.2\pm 0.3\,\mathrm{(stat)}\pm0.4\,\mathrm{(syst)})\times10^{-2}\). Available model predictions are significantly lower than the estimated \(\mathrm{\Xi^-}\) yield.
The tagged quasi-free $np \to np\pi^+\pi^-$ reaction has been studied
experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI
at a deuteron incident beam energy of 1.25 ...GeV/nucleon ($\sqrt s \sim$ 2.42
GeV/c for the quasi-free collision). For the first time, differential
distributions for $\pi^{+}\pi^{-}$ production in $np$ collisions have been
collected in the region corresponding to the large transverse momenta of the
secondary particles. The invariant mass and angular distributions for the
$np\rightarrow np\pi^{+}\pi^{-}$ reaction are compared with different models.
This comparison confirms the dominance of the $t$-channel with $\Delta\Delta$
contribution. It also validates the changes previously introduced in the
Valencia model to describe two-pion production data in other isospin channels,
although some deviations are observed, especially for the $\pi^{+}\pi^{-}$
invariant mass spectrum. The extracted total cross section is also in much
better agreement with this model. Our new measurement puts useful constraints
for the existence of the conjectured dibaryon resonance at mass M$\sim$ 2.38
GeV and with width $\Gamma\sim$ 70 MeV.
Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have
analyzed HADES data of the reaction $p(3.5GeV)+p\to pK^{+}\Lambda$. This
reaction might contain information about the kaonic ...cluster "$ppK^-$" via its
decay into $p\Lambda$. Due to interference effects in our coherent description
of the data, a hypothetical $\overline{K}NN$ (or, specifically "$ppK^-$")
cluster signal must not necessarily show up as a pronounced feature (e.g. a
peak) in an invariant mass spectra like $p\Lambda$. 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 $\overline{K}NN$ cluster. At a
confidence level of CL$_{s}$=95\% such a cluster can not contribute more than
2-12\% to the total cross section with a $pK^{+}\Lambda$ final state, which
translates into a production cross-section between 0.7 $\mu b$ and 4.2 $\mu b$,
respectively. The range of the upper limit depends on the assumed cluster mass,
width and production process.
Phys. Rev. C 90, 054906 (2014) We present the analysis of the inclusive $K^{0}$ production in p+p and p+Nb
collisions measured with the HADES detector at a beam kinetic energy of 3.5
GeV. Data are ...compared to the GiBUU transport model. The data suggest the
presence of a repulsive momentum-dependent kaon potential as predicted by the
Chiral Perturbation Theory (ChPT). For the kaon at rest and at normal nuclear
density, the ChPT potential amounts to $\approx 35$ MeV. A detailed tuning of
the kaon production cross sections implemented in the model has been carried
out to reproduce the experimental data measured in p+p collisions. The
uncertainties in the parameters of the model were examined with respect to the
sensitivity of the experimental results from p+Nb collisions to the in-medium
kaon potential.
The PANDA experiment will be built at the FAIR facility at Darmstadt (Germany) to perform accurate tests of the strong interaction through bar pp and bar pA annihilation's studies. To track charged ...particles, two systems consisting of a set of planar, closed-packed, self-supporting straw tube layers are under construction. The PANDA straw tubes will have also unique characteristics in term of material budget and performance. They consist of very thin mylar-aluminized cathodes which are made self-supporting by means of the operation gas-mixture over-pressure. This solution allows to reduce at maximum the weight of the mechanical support frame and hence the detector material budget. The PANDA straw tube central tracker will not only reconstruct charged particle trajectories, but also will help in low momentum (< 1 GeV) particle identification via dE/dx measurements. This is a quite new approach that PANDA tracking group has first tested with detailed Monte Carlo simulations, and then with experimental tests of detector prototypes. This paper addresses the design issues of the PANDA straw tube trackers and the performance obtained in prototype tests.
Results on \(\Lambda\) 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 \(90\,\)MeV at a rapidity of \(y=1.0\), i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions, \(y_{cm}=1.12\). The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The \(\Lambda\) 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 \(\Lambda\) 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 \(\Lambda\) polarization in the weak decay \(\Lambda\rightarrow p \pi^-\). Finite negative values of the polarization in the order of \(5-20\,\%\) are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for \(p_t>300\,\)MeV/c and increases with decreasing rapidity for \(y < 0.8\).
An exclusive analysis of the 4-body final states \(\mathrm{\Lambda + p + \pi^{+} + K^{0}}\) and \(\mathrm{\Sigma^{0} + p + \pi^{+} + K^{0}}\) measured with HADES for p+p collisions at a beam kinetic ...energy of 3.5 GeV is presented. The analysis uses various phase space variables, such as missing mass and invariant mass distributions, in the four particle event selection (p, \(\pi^+\), \(\pi^+\), \(\pi^-\)) to find cross sections of the different production channels, contributions of the intermediate resonances \(\mathrm{\Delta^{++}}\) and \(\mathrm{\Sigma(1385)^{+}}\) and corresponding angular distributions. A dominant resonant production is seen, where the reaction \(\mathrm{\Lambda + \Delta^{++} + K^{0}}\) has an about ten times higher cross section (\(\mathrm{29.45\pm0.08^{+1.67}_{-1.46}\pm2.06\,\mu b}\)) than the analogous non-resonant reaction (\(\mathrm{2.57\pm0.02^{+0.21}_{-1.98}\pm0.18\,\mu b}\)). A similar result is obtained in the corresponding \(\Sigma^{0}\) channels with \(\mathrm{9.26\pm0.05^{+1.41}_{-0.31}\pm0.65\,\ mu b}\) in the resonant and \(\mathrm{1.35\pm0.02^{+0.10}_{-1.35}\pm0.09\,\mu b}\) in the non-resonant reactions.
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