133 research outputs found

    The HADES alignment strategy

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    The Λp\bf{\Lambda p} interaction studied via femtoscopy in p + Nb reactions at sNN=3.18 GeV\mathbf{\sqrt{s_{NN}}=3.18} ~\mathrm{\bf{GeV}}

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    We report on the first measurement of pΛp\Lambda and pppp correlations via the femtoscopy method in p+Nb reactions at sNN=3.18 GeV\mathrm{\sqrt{s_{NN}}=3.18} ~\mathrm{GeV}, studied with the High Acceptance Di-Electron Spectrometer (HADES). By comparing the experimental correlation function to model calculations, a source size for pppp pairs of r0,pp=2.02±0.01(stat)0.12+0.11(sys) fmr_{0,pp}=2.02 \pm 0.01(\mathrm{stat})^{+0.11}_{-0.12} (\mathrm{sys}) ~\mathrm{fm} and a slightly smaller value for pΛp\Lambda of r0,Λp=1.62±0.02(stat)0.08+0.19(sys) fmr_{0,\Lambda p}=1.62 \pm 0.02(\mathrm{stat})^{+0.19}_{-0.08}(\mathrm{sys}) ~\mathrm{fm} is extracted. Using the geometrical extent of the particle emitting region, determined experimentally with pppp correlations as reference together with a source function from a transport model, it is possible to study different sets of scattering parameters. The pΛp\Lambda correlation is proven sensitive to predicted scattering length values from chiral effective field theory. We demonstrate that the femtoscopy technique can be used as valid alternative to the analysis of scattering data to study the hyperon-nucleon interaction.Comment: 12 pages, 11 figure

    Medium effects in proton-induced K0K^{0} production at 3.5 GeV

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    We present the analysis of the inclusive K0K^{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 35\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.Comment: 13 pages, 14 figure

    Partial Wave Analysis of the Reaction p(3.5GeV)+ppK+Λp(3.5 GeV)+p \to pK^+\Lambda to Search for the "ppKppK^-" Bound State

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    Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction p(3.5GeV)+ppK+Λp(3.5GeV)+p\to pK^{+}\Lambda. This reaction might contain information about the kaonic cluster "ppKppK^-" via its decay into pΛp\Lambda. Due to interference effects in our coherent description of the data, a hypothetical KNN\overline{K}NN (or, specifically "ppKppK^-") cluster signal must not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectra like pΛp\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 KNN\overline{K}NN cluster. At a confidence level of CLs_{s}=95\% such a cluster can not contribute more than 2-12\% to the total cross section with a pK+ΛpK^{+}\Lambda final state, which translates into a production cross-section between 0.7 μb\mu b and 4.2 μb\mu b, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.Comment: 7 Pages, 5 Figure

    Lambda hyperon production and polarization in collisions of p(3.5 GeV) + Nb

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    Results on Λ\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 9090\,MeV at a rapidity of y=1.0y=1.0, i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions, ycm=1.12y_{cm}=1.12. The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The Λ\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 Λ\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 Λ\Lambda polarization in the weak decay Λpπ\Lambda\rightarrow p \pi^-. Finite negative values of the polarization in the order of 520%5-20\,\% are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for pt>300p_t>300\,MeV/c and increases with decreasing rapidity for y<0.8y < 0.8.Comment: accepted by Eur. Phys. J.

    Subthreshold Xi- Production in Collisions of p(3.5 GeV)+Nb

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    Results on the production of the double-strange cascade hyperon Ξ\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 Ξ\mathrm{\Xi^-} production is observed in proton-nucleus interactions. Assuming a Ξ\mathrm{\Xi^-} phase-space distribution similar to that of Λ\mathrm{\Lambda} hyperons, the production probability amounts to PΞ=(2.0±0.4(stat)±0.3(norm)±0.6(syst))×104P_{\mathrm{\Xi^-}}=(2.0\,\pm0.4\,\mathrm{(stat)}\,\pm 0.3\,\mathrm{(norm)}\,\pm 0.6\,\mathrm{(syst)})\times10^{-4} resulting in a Ξ/(Λ+Σ0)\mathrm{\Xi^-/(\Lambda+\Sigma^0)} ratio of $P_{\mathrm{\Xi^-}}/\ P_{\mathrm{\Lambda+\Sigma^0}}=(1.2\pm 0.3\,\mathrm{(stat)}\pm0.4\,\mathrm{(syst)})\times10^{-2}.Availablemodelpredictionsaresignificantlylowerthantheestimated. Available model predictions are significantly lower than the estimated \mathrm{\Xi^-}$ yield.Comment: 6 pages, 3 figure

    Inclusive pion and eta production in p+Nb collisions at 3.5 GeV beam energy

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    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

    Production of Sigma{\pm}pi?pK+ in p+p reactions at 3.5 GeV beam energy

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    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
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