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Many QCD based and phenomenological models predict changes of hadron properties in a strongly interacting environment. The results of these models differ significantly and the experimental determination of hadron properties in nuclear matter is essential. In this paper we present a review of selected physics results obtained at GSI Helmholtzzentrum für Schwerionenforschung GmbH by HADES (High-Acceptance Di-Electron Spectrometer). The e+e− pair emission measured for proton and heavy-ion induced collisions is reported together with results on strangeness production. The future HADES activities at the planned FAIR facility are also discussed.
n this paper we report on the investigation of baryonic resonance production in proton-proton collisions at the kinetic energies of 1.25 GeV and 3.5 GeV, based on data measured with HADES. Exclusive channels npπ+ and ppπ0 as well as ppe+e− were studied simultaneously in the framework of a one-boson exchange model. The resonance cross sections were determined from the one-pion channels for Δ(1232) and N(1440) (1.25 GeV) as well as further Δ and N* resonances up to 2 GeV/c2 for the 3.5 GeV data. The data at 1.25 GeV energy were also analysed within the framework of the partial wave analysis together with the set of several other measurements at lower energies. The obtained solutions provided the evolution of resonance production with the beam energy, showing a sizeable non-resonant contribution but with still dominating contribution of Δ(1232)P33. In the case of 3.5 GeV data, the study of the ppe+e− channel gave the insight on the Dalitz decays of the baryon resonances and, in particular, on the electromagnetic transition form-factors in the time-like region. We show that the assumption of a constant electromagnetic transition form-factors leads to underestimation of the yield in the dielectron invariant mass spectrum below the vector mesons pole. On the other hand, a comparison with various transport models shows the important role of intermediate ρ production, though with a large model dependency. The exclusive channels analysis done by the HADES collaboration provides new stringent restrictions on the parameterizations used in the models.
his contribution aims to give a basic overview of the latest results regarding the production of resonances in different collision systems. The results were extracted from experimental data collected with HADES that is a multipurpose detector located at the GSI Helmholtzzentrum, Darmstadt. The main points discussed here are: the properties of the strange resonances Λ(1405) and Σ(1385), the role of Δ’s as a source of pions in the final state, the production dynamics reflected in form of differential cross sections, and the role of the ϕ meson as a source for K− particles.
We build on previous work on operational performance evaluation of private equity portfolio companies as we are able to at least partially decrypt the black box consisting of restructuring tools these investors use and the corresponding impact on their portfolio companies. Beyond answering whether private equity improves operating efficiency we figure out which of the typical restructuring tools drive operating efficiency. Using a set of over 300 international leveraged buyout transactions in the last thirty years we find that while there is vast improvement in operational efficiency these gains vary considerably. Our top performing transactions are subject to strong equity incentives, frequent asset restructuring and tight control by the investor. Furthermore, investors experience has a positive and financial leverage a negative influence on operational performance.
This study investigates the transition from being a listed company with a dispersed ownership structure to being a privately held company with a concentrated ownership structure. We consider a sample of private equity backed portfolio companies to evaluate the consequences of the corporate governance changes on operational performance. Our analysis shows significant positive abnormal growth in several performance ratios for the private period of our sample companies relative to comparable public companies. These performance differences come from the increase in ownership concentration after the leveraged buyout transaction.
The production of Σ0 baryons in the nuclear reaction p (3.5 GeV) + Nb (corresponding to sNN=3.18 GeV) is studied with the detector set-up HADES at GSI, Darmstadt. Σ0s were identified via the decay Σ0→Λγ with subsequent decays Λ→pπ− in coincidence with a e+e− pair from either external (γ→e+e−) or internal (Dalitz decay γ⁎→e+e−) gamma conversions. The differential Σ0 cross section integrated over the detector acceptance, i.e. the rapidity interval 0.5<y<1.1, has been extracted as ΔσΣ0=2.3±(0.2)stat±(−0.6+0.6)sys±(0.2)norm mb, yielding the inclusive production cross section in full phase space σΣ0total=5.8±(0.5)stat±(−1.4+1.4)sys±(0.6)norm±(1.7)extrapol mb by averaging over different extrapolation methods. The Λall/Σ0 ratio within the HADES acceptance is equal to 2.3±(0.2)stat±(−0.6+0.6)sys. The obtained rapidity and momentum distributions are compared to transport model calculations. The Σ0 yield agrees with the statistical model of particle production in nuclear reactions. Keywords: Hyperons, Strangeness, Proton, Nucleus.
We present the results of two-pion production in tagged quasi-free np collisions at a deutron incident beam energy of 1.25 GeV/c measured with the High-Acceptance Di-Electron Spectrometer (HADES) installed at GSI. The specific acceptance of HADES allowed for the first time to obtain high-precision data on π+π− and π−π0 production in np collisions in a region corresponding to large transverse momenta of the secondary particles. The obtained differential cross section data provide strong constraints on the production mechanisms and on the various baryon resonance contributions (∆∆, N(1440), N(1520), ∆(1600)). The invariant mass and angular distributions from the np → npπ+π −and np → ppπ−π0 reactions are compared with different theoretical model predictions.
Sondierungsstudie im Auftrag des Bundesministeriums für Bildung und Forschung: Die jüngste Finanzkrise und die darauf folgende Staatsschuldenkrise hat sowohl wirtschaftlich als auch gesellschaftlich tiefgreifende Spuren hinterlassen. Dabei wurden auch sehr deutliche Lücken in der Forschung offenbar. Ziel dieser Studie ist es, aufbauend auf dem aktuellen Forschungsstand weiteren Forschungsbedarf in den wesentlich mit Finanzkrisen verbundenen Bereichen aufzuzeigen. Es werden fünf Forschungsbereiche mit jeweiligen Unterthemen vorgeschlagen. Diese fünf Forschungsbereiche gehen unmittelbar aus der Struktur und den Mechanismen der Finanz- und Staatsschuldenkrise hervor. Dabei wird besonderes Augenmerk auf die wirtschafts- und regulierungspolitische Relevanz der Themen sowie dem Umstand getragen, dass die Beantwortung vieler der Fragen interdisziplinäre Zusammenarbeit erfordert.
Finanzkrisen sind inherent mit dem Bankenmodell verbunden. Aufgrund von Verbindungen der Banken untereinander können Probleme einzelner Institute auf andere Institute übertragen werden. Diese systemischen Risiken können das gesamte Finanzsystem destabilisieren. Das Finanzsystem nimmt durch die Kreditvergabe und Bereitstellung von Transaktionssystemen eine herausragende Stellung in einer Volkswirtschaft ein, wodurch stabilisierende Eingriffe der Politik notwendig werden können. Eingriffe zur Wiederherstellung von Stabilität können sehr kostspielig sein und, wie aktuell eindrucksvoll belegt, die stabilisierenden Staaten selbst destabilisieren. Die alternativen Eingriffe vorab betreffen neben der Geldpolitik vor allem regulatorische Eingriffe. Im besonderen sind die Corporate Governance von Finanzinstituten und die Informationsbereitstellung bzw. Transparenz innerhalb des Finanzsektors von Bedeutung. In den vergangen Jahren wuchs vor dem Hintergrund von Regulierung zudem ein paralleles Schattenbankensystems heran, das in seiner Bedeutung dem traditionellen Bankensystem nur unwesentlich nachsteht.
Zwar sind die groben Zusammenhänge und Auswirkungen in den einzelnen Bereichen bekannt, jedoch ist für ein tiefgreifendes Verständnis als Grundlage zur Vermeidung bzw. Eindämmung zukünftiger Krisen sowie zur Folgenabschätzung von Regulierung weitere Forschung unabdingbar.
We investigate the decisions of listed firms to go private once again. We start by revealing that while a significant number of firms which go public is VC-backed, an overproportional share of these VC-backed firms go private later on (they stay on the exchange for an average of 8.5 years). We interpret this very robust pattern such that IPOs of VC-backed firms are to a large extent a temporary rather than a permanent feature of the corporate governance of these firms. We investigate various potential hypotheses why VCs actually seem to be able to bring marginal firms to the exchange by relating the going-private decisions to various characteristics of the IPO market as well as to VC characteristics. We find strong support for the certification ability of VCs: more experienced and reputable VCs are more able to bring marginal firms to public exchanges via an IPOs. These marginal firms backed-by more reputable and experienced VCs are more likely to go private later on. Hence, our analysis suggests that IPOs backed by experienced VCs are most likely to be a temporary rather than the final stage in the life of the portfolio firm. We find no support that reputable VCs underprice their IPO-exits more implying that they have no need to leave more money on the table to take the marginal firms public.
