HADES Collaboration

University of Milan, Milano, Lombardy, Italy

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Publications (14)

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    HADES Collaboration · G. Agakishiev · O. Arnold · [...] · Y. Zanevsky
    [Show abstract] [Hide abstract] ABSTRACT: We present results on the K*(892)+ production in proton-proton collisions at a beam energy of E = 3.5 GeV, which is hitherto the lowest energy at which this mesonic resonance has been observed in nucleon-nucleon reactions. The data are interpreted within a two-channel model that includes the 3-body production of K*(892)+ associated with the Lambda- or Sigma-hyperon. The relative contributions of both channels are estimated. Besides the total cross section sigma(p+p -> K*(892)+ + X) = 9.5 +- 0.9 +1.1 -0.9 +- 0.7 mub, that adds a new data point to the excitation function of the K*(892)+ production in the region of low excess energy, transverse momenta and angular spectra are extracted and compared with the predictions of the two-channel model. The spin characteristics of K*(892)+ are discussed as well in terms of the spin-alignment.
    Full-text Article · May 2015 · Physical Review C
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    HADES Collaboration · G. Agakishiev · A. Balanda · [...] · Y. Zanevsky
    [Show abstract] [Hide abstract] ABSTRACT: 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.
    Full-text Article · Nov 2013 · Physics Letters B
  • HADES Collaboration · G. Agakishiev · D. Belver · [...] · Y. Zanevsky
    [Show abstract] [Hide abstract] ABSTRACT: A high-statistic data sample of Ar(1.76 AGeV)+KCl events recorded with HADES is used to search for a hypertriton signal. An upper production limit per centrality-triggered event of 1.04 x $10^{-3}$ on the $3\sigma$ level is derived. Comparing this value with the number of successfully reconstructed $\Lambda$ hyperons allows to determine an upper limit on the ratio $N_{_{\Lambda}^3H}/N_{\Lambda}$, which is confronted with statistical and coalescence-type model calculations.
    Article · Oct 2013 · European Physical Journal A
  • K. Lapidus · G. Agakishiev · A Balanda · [...] · HADES Collaboration
    [Show abstract] [Hide abstract] ABSTRACT: After the completion of the experimental program at SIS18 the HADES setup will migrate to FAIR, where it will deliver high-quality data for heavy-ion collisions in an unexplored energy range of up to 8 A GeV. In this contribution, we briefly present the physics case, relevant detector characteristics and discuss the recently completed upgrade of HADES.
    Article · May 2012 · Physics of Atomic Nuclei
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    HADES Collaboration · G. Agakishiev · H. Alvarez-Pol · [...] · P. Zumbruch
    [Show abstract] [Hide abstract] ABSTRACT: We present measurements of exclusive \(\ensuremath \pi^{+,0}\) and \( \eta\) production in pp reactions at 1.25GeV and 2.2GeV beam kinetic energy in hadron and dielectron channels. In the case of \( \pi^{+}_{}\) and \( \pi^{0}_{}\) , high-statistics invariant-mass and angular distributions are obtained within the HADES acceptance as well as acceptance-corrected distributions, which are compared to a resonance model. The sensitivity of the data to the yield and production angular distribution of \( \Delta\)(1232) and higher-lying baryon resonances is shown, and an improved parameterization is proposed. The extracted cross-sections are of special interest in the case of pp \( \rightarrow\) pp \( \eta\) , since controversial data exist at 2.0GeV; we find \(\ensuremath \sigma=0.142\pm0.022\) mb. Using the dielectron channels, the \( \pi^{0}_{}\) and \( \eta\) Dalitz decay signals are reconstructed with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance-corrected helicity angle distributions are found in good agreement with model predictions.
    Full-text Article · Mar 2012 · European Physical Journal A
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    HADES Collaboration · P. K. Kurilkin · G. Agakishiev · [...] · Y. Zanevsky
    [Show abstract] [Hide abstract] ABSTRACT: First results of the differential cross section in dp elastic scattering at 1.25 GeV/u measured with the HADES over a large angular range are reported. The obtained data corresponds to large transverse momenta, where a high sensitivity to the two-nucleon and three-nucleon short-range correlations is expected.
    Full-text Conference Paper · Jan 2011
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    G. Agakishiev · A. Balanda · B. Bannier · [...] · HADES Collaboration
    [Show abstract] [Hide abstract] ABSTRACT: We present transverse momentum spectra, rapidity distribution and multiplicity of Lambda-hyperons measured with the HADES spectrometer in the reaction Ar(1.76A GeV)+KCl. The yield of Xi- is calculated from our previously reported Xi-/(Lambda+Sigma0) ratio and compared to other strange particle multiplicities. Employing a strangeness balance equation the multiplicities of the yet unmeasured charged Sigma hyperons can be estimated. Finally a statistical hadronization model is used to fit the yields of pi-, K+, K0s, K-, phi, Lambda and Xi-. The resulting chemical freeze-out temperature of T=(76+-2) MeV is compared to the measured slope parameters obtained from fits to the transverse mass distributions of the particles.
    Full-text Article · Oct 2010 · European Physical Journal A
  • K. O. Lapidus · HADES collaboration
    [Show abstract] [Hide abstract] ABSTRACT: The inclusive production of electron-positron pairs in proton-proton and deuteron-proton collisions at a beam kinetic energy of 1.25 GeV per nucleon was studied with the HADES (High Acceptance Dielectron Spectrometer) detector. The main objective of the deuteron-proton experiment was to investigate pair production in quasifree neutron-proton collisions. In the invariant-mass region M > 140 MeV/c 2, the invariant-mass spectrum determined in this channel shows a significant enhancement of the pair yield in relation to that in the case of proton-proton collisions.
    Article · Jun 2010 · Physics of Atomic Nuclei
  • Romain Holzmann · A Balanda · D. Belver · [...] · HADES Collaboration
    [Show abstract] [Hide abstract] ABSTRACT: One of the main goals of the HADES experiment is to achieve a detailed understanding of dielectron emission from hadronic systems at moderate bombarding energies. Results obtained on electron pair production in elementary N+N collisions pave the way to a better understanding of the origin of the pair excess seen in heavy-ion collisions. This puzzling excess, reported first by the former DLS experiment, is now being investigated systematically by HADES.
    Article · Mar 2010 · Nuclear Physics A
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    G. Agakishiev · A Balanda · B. Bannier · [...] · HADES Collaboration
    [Show abstract] [Hide abstract] ABSTRACT: We present phase space distributions and multiplicities of K+, K-, and phi mesons produced in Ar+KCl reactions at a kinetic beam energy of 1.756 GeV/nucleon and measured with the HADES spectrometer. The inverse slope parameters and yields of kaons supplement the systematics of previous measurements. The percentage of K- mesons coming from phi decay is found to be 18 +/- 7%.
    Full-text Article · Aug 2009 · Physical Review C
  • H. Ströbele · HADES Collaboration
    [Show abstract] [Hide abstract] ABSTRACT: In-medium effects on K and ω mesons, which have been reported in the past, confirm the importance of experiments which study hadron properties in excited and normal nuclear matter with penetrating probes. The HADES experiment at GSI uses proton and nuclear beams to record experimental data on elementary and nuclear collisions. This second generation high acceptance detector system allows to detect and separate electron–positron pairs in a high multiplicity environment with a hadron suppression factor of 10-9. Preliminary results on dilepton production in C+C collisions at 2 GeV per nucleon are presented. The comparison with UrQMD calculation shows agreement at the 20% level except at invariant masses below 100 MeV where deviations of up to 50% have been traced to shortcomings in the analysis.
    Article · Jan 2006 · Acta Physica Hungarica
  • J Otwinowski · G Agakichiev · C Agodi · [...] · HADES Collaboration
    [Show abstract] [Hide abstract] ABSTRACT: The identification of the light mesons in the HADES spectrometer is based on an invariant mass reconstruction of their decay into e(+)e(-) pairs. In the dilepton (e(+)e(-)) signal reconstruction, particularly important is the reduction of a huge combinatorial background arising from wrong combinations of e(+) and e(-) to unlike sign pairs. Methods of the dilepton signal and combinatorial background reconstruction in the HADES spectrometer will be presented.
    Article · Jan 2005 · International Journal of Modern Physics A
  • P Salabura · HADES Collaboration
    [Show abstract] [Hide abstract] ABSTRACT: HADES is a second generation experiment designed to study dielectron production in proton, pion, and heavy ion induced reactions at the GSI accelerator facility in Darmstadt. The physics programme of HADES is focused on in-medium properties of the light vector mesons. In this contribution we discuss relevance of dielectron spectroscopy to the problem of hadron mass origin. We present status of the HADES experiment, demonstrate its capability to identify rare dielectron signal and show first experimental results obtained from C+C reactions at 2 AGeV.
    Article · Mar 2004 · Acta Physica Polonica Series B
  • Andrej Kugler · HADES collaboration
    [Show abstract] [Hide abstract] ABSTRACT: Theoretical models predict modification of basic properties of hadrons inside nuclear medium in comparison with their vacuum properties. Restoration of chiral symmetry with increasing baryon density and temperature results in corresponding decrease of the constituent quark masses [1, 2]. As a consequence, one expects more or less pronounced changes in mass and resonance width of vector mesons like when embedded in the nuclear medium [3, 4, 5]. Decay branch of them into electron positron pair is known and as leptons do not undergo strong final state interaction, these mesons seem to be ideally suited to probe mass changes of hadrons inside the nuclear medium. Particularly, relatively long lifetime (T ≈ 23.4 fm/c) of w-meson in principle allows to study changes of invariant mass distributions corresponding to di-lepton decay of these ntesons produced inside ordinary nucleus as a function of their momentum. Comparable numbers of fast and slow mesons will decay out of nucleus or inside nucleus, respectively. Essential experimental condition to observe predicted shift and/or broadening of narrow peak (T ≈ 8.4 MeV/c2, M≈. 782 MeV/c2) in invariant mass distribution is very high inass resolution of corresponding apparatus, e.g. better than 1%,.
    Article · Feb 2000 · Czechoslovak Journal of Physics