arXiv subjects

J. Adamczewski-Musch

Publications and source records attributed to J. Adamczewski-Musch.

28 records · Page 2Linked to original sources

arXiv2019

Identical pion intensity interferometry in central Au+Au collisions at 1.23A GeV

We investigate identical pion HBT intensity interferometry for central Au+Au collisions at 1.23A GeV. High-statistics $π^-π^-$ and $π^+π^+$ data are measured with HADES at SIS18/GSI. The radius parameters, derived from the correlation function depending on relative momenta in the longitudinal-comoving system and parametrized as three-dimensional Gaussian distribution, are studied as function of transverse momentum. A substantial charge-sign difference of the source radii is found, particularly pronounced at low transverse momentum. The extracted Coulomb-corrected source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy. Our data would thus rather disfavour any strong energy dependence of the radius parameters in the low energy region.

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arXiv2018

Sub-threshold production of K^{0}_{s} mesons and Λ hyperons in Au(1.23A GeV)+Au

We present first data on sub-threshold production of K0 s mesons and Λ hyperons in Au+Au collisions at $\sqrt{s_{NN}}$ = 2.4 GeV. We observe an universal scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of the latter can simultaneously describe all observables with reasonable \c{hi}2 values.

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arXiv2018

Strong absorption of hadrons with hidden and open strangeness in nuclear matter

We present the first observation of K- and ϕabsorption within nuclear matter by means of π- -induced reactions on C and W targets at an incident beam momentum of 1.7 GeV/c studied with HADES at SIS18/GSI. The double ratio (K-/K+)W / (K-/K+)C is found to be 0.319 \pm 0.009(stat)+0.014-0.012 (syst) indicating a larger absorption of K- in heavier targets as compared to lighter ones. The measured ϕ/K- ratios in π-+C and π^- +W reactions within the HADES acceptance are found to be equal to $0.55 \pm 0.03(stat)+0.06-0.07$ (syst) and to $0.63 \pm 0.05(stat)-0.11+0.11$ (syst), respectively. The similar ratios measured in the two different reactions demonstrate for the first time experimentally that the dynamics of the ϕmeson in nuclear medium is strongly coupled to the K- dynamics. The large difference in the ϕproduction off C and W nuclei is discussed in terms of a strong \phiN in-medium coupling.

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arXiv2018

Centrality determination of Au+Au collisions at 1.23A GeV with HADES

The centrality determination for Au+Au collisions at 1.23A GeV, as measured with HADES at the GSI-SIS18, is described. In order to extract collision geometry related quantities, such as the average impact parameter or number of participating nucleons, a Glauber Monte Carlo approach is employed. For the application of this model to collisions at this relatively low centre-of-mass energy of $\sqrt{s_{\mathrm{NN}}} = 2.42$ GeV special investigations were performed. As a result a well defined procedure to determine centrality classes for ongoing analyses of heavy-ion data is established.

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arXiv2017

Deep sub-threshold ϕ production and implications for the K+/K- freeze-out in Au+Au collisions

We present data on charged kaons (K+-) and ϕ mesons in Au(1.23A GeV)+Au collisions. It is the first simultaneous measurement of K and ϕ mesons in central heavy-ion collisions below a kinetic beam energy of 10A GeV. The ϕ/K- multiplicity ratio is found to be surprisingly high with a value of 0.52 +- 0.16 and shows no dependence on the centrality of the collision. Consequently, the different slopes of the K+ and K- transverse-mass spectra can be explained solely by feed- down, which substantially softens the spectra of K- mesons. Hence, in contrast to the commonly adapted argumentation in literature, the different slopes do not necessarily imply diverging freeze- out temperatures of K+ and K- mesons caused by different couplings to baryons.

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arXiv2017

$Σ^0$ production in proton nucleus collisions near threshold

The production of $Σ^{0}$ baryons in the nuclear reaction p (3.5 GeV) + Nb (corresponding to $\sqrt{s_{NN}}=3.18$ GeV) is studied with the detector set-up HADES at GSI, Darmstadt. $Σ^{0}$s were identified via the decay $Σ^{0} \rightarrow Λγ$ with subsequent decays $Λ\rightarrow p π^{-}$ in coincidence with a $e^{+}e^{-}$ pair from either external ($γ\rightarrow e^{+} e^{-}$) or internal (Dalitz decay $γ^{*}\rightarrow e^{+} e^{-}$) gamma conversions. The differential $Σ^0$ cross section integrated over the detector acceptance, i.e. the rapidity interval $0.5 < y < 1.1$, has been extracted as $Δσ_{Σ^{0}} = 2.3 \pm (0.2)^{stat} \pm \left(^{+0.6}_{-0.6}\right)^{sys} \pm (0.2)^{norm}$ mb, yielding the inclusive production cross section in full phase space $σ^{total}_{Σ^{0}} = 5.8 \pm (0.5)^{stat} \pm \left(^{+1.4}_{-1.4}\right)^{sys} \pm (0.6)^{norm} \pm (1.7)^{extrapol}$ mb by averaging over different extrapolation methods. The $Λ_{all}$/$Σ^{0}$ ratio within the HADES acceptance is equal to 2.3 $\pm$ $(0.2)^{stat}$ $\pm$ $(^{+0.6}_{-0.6})^{sys}$. The obtained rapidity and momentum distributions are compared to transport model calculations. The $Σ^{0}$ yield agrees with the statistical model of particle production in nuclear reactions.

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arXiv2017

$Δ$(1232) Dalitz decay in proton-proton collisions at T=1.25 GeV measured with HADES

We report on the investigation of $Δ$(1232) production and decay in proton-proton collisions at a kinetic energy of 1.25 GeV measured with HADES. Exclusive dilepton decay channels $ppe^{+}e^{-}$ and $ppe^{+}e^{-}γ$ have been studied and compared with the partial wave analysis of the hadronic $ppπ^{0}$ channel. They allow to access both $Δ^+ \to pπ^0(e^+e^-γ)$ and $Δ^+ \to pe^+e^-$ Dalitz decay channels. The perfect reconstruction of the well known $π^0$ Dalitz decay serves as a proof of the consistency of the analysis. The $Δ$ Dalitz decay is identified for the first time and the sensitivity to N-$Δ$ transition form factors is tested. The $Δ$(1232) Dalitz decay branching ratio is also determined for the first time; our result is (4.19 $\pm$ 0.62 syst. $\pm$ 0.34 stat.) $\times $ 10$^{-5}$, albeit with some model dependence.

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arXiv2017

Analysis of the exclusive final state npe$^+$e$^-$ in quasi-free np reaction

We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25 GeV/u inpinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of $e^+e^-$ pairs above the $π^{0}$ mass in the exclusive channel $dp \to npe^{+}e^{-}(p_{spect})$ as compared to the exclusive channel $ppe^{+}e^{-}$ measured in proton-proton collisions at the same energy. That excess points to different bremsstrahlung production mechanisms. Two models were evaluated for the role of the charged pion exchange between nucleons and double-$Δ$ excitation combined with intermediate $ρ$-meson production. Differential cross sections as a function of the $e^+e^-$ invariant mass and of the angles of the virtual photon, proton and electrons provide valuable constraints and encourage further investigations on both experimental and theoretical side.

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arXiv2016

Inclusive Λ production in proton-proton collisions at 3.5 GeV

The inclusive production of Λ hyperons in proton-proton collisions at $\sqrt{s}$ = 3.18 GeV was measured with HADES at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. The experimental data are compared to a data-based model for individual exclusive Λ production channels in the same reaction. The contributions of intermediate resonances such as Σ(1385), Δ++ or N* are considered in detail. In particular, the result of a partial wave analysis is accounted for the abundant pK$^+$Λ final state. Model and data show a reasonable agreement at mid rapidities, while a difference is found for larger rapidities. A total Λ production cross section in p+p collisions at $\sqrt{s}$ = 3.18 GeV of σ(pp $\to$ Λ + X) = 207.3 $\pm$ 1.3 +6.0 -7.3 (stat.) $\pm$ 8.4 (syst.) +0.4 -0.5 (model) μb is found.

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arXiv2016

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

We report on the first measurement of $pΛ$ and $pp$ correlations via the femtoscopy method in p+Nb reactions at $\mathrm{\sqrt{s_{NN}}=3.18} ~\mathrm{GeV}$, studied with the High Acceptance Di-Electron Spectrometer (HADES). By comparing the experimental correlation function to model calculations, a source size for $pp$ pairs of $r_{0,pp}=2.02 \pm 0.01(\mathrm{stat})^{+0.11}_{-0.12} (\mathrm{sys}) ~\mathrm{fm}$ and a slightly smaller value for $pΛ$ of $r_{0,Λp}=1.62 \pm 0.02(\mathrm{stat})^{+0.19}_{-0.08}(\mathrm{sys}) ~\mathrm{fm}$ is extracted. Using the geometrical extent of the particle emitting region, determined experimentally with $pp$ correlations as reference together with a source function from a transport model, it is possible to study different sets of scattering parameters. The $pΛ$ 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.

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