Search

At PANDA (FAIR) proton time-like form factors measurements are foreseen. In this work, following detailed simulations, we study the sensitivity to possible two photon exchange contribution in the annihilation process $\bar p+p\to e^++e^-$, through the induced asymmetry in the angular distribution. Asymmetries related to systematic errors are also investigated.

The search for a modification of hadron properties inside nuclear matter at normal and/or high temperature and density is one of the more interesting issues of modern nuclear physics. Dilepton experiments, by providing interesting results, give insight into the properties of strong interaction and the nature of hadron mass generation. One of these research tools is the HADES spectrometer. HADES is a high acceptance dilepton spectrometer installed at the heavy-ion synchrotron (SIS) at GSI, Darmstadt. The main physics motivation of HADES is the measurement of e+e- pairs in the invariant-mass range up to 1 GeV/c2 in pion- and proton-induced reactions, as well as in heavy-ion collisions. The goal is to investigate the properties of the vector mesons rho, omega and of other hadrons reconstructed from e+e- decay pairs. Dileptons are penetrating probes allowing to study the in-medium properties of hadrons. However, the measurement of such dilepton pairs is difficult because of a very large background from other processes in which leptons are created. This thesis presents the analysis of the data provided by the first physic run done with the HADES spectrometer. For the first time e+e- pairs produced in C+C collisions at an incident energy of 2 GeV per nucleon have been collected with sufficient statistics. This experiment is of particular importance since it allows to address the puzzling pair excess measured by the former DLS experiment at 1.04 AGeV. The thesis consists of five chapters. The first chapter presents the physics case which is addressed in the work. In the second chapter the HADES spectrometer is introduced with the characteristic of specific detectors which are part of the spectrometer. Chapter three focusses on the issue of charged-particle identification. The fourth chapter discusses the reconstruction of the di-electron spectra in C+C collisions. In this part of the thesis a comparison with theoretical models is included as well. The conclusion and final remarks are given in chapter five. Eines der Hauptziele der modernen Kernphysik ist die Untersuchung der Modifikation von Eigenschaften von Hadronen bei normaler und hoher Temperatur und Dichte. Dileptonen-Experimente liefern interessante Ergebnisse und geben einen Einblick in die Eigenschaften der starken Wechselwirkung und in die Natur der Massenerzeugung von Hadronen. Eines dieser Forschungswerkzeuge ist das HADES Spektrometer. HADES ist ein Dileptonen Spektrometer mit hoher Akzeptanz am Schwerionensynchroton der GSI in Darmstadt. Die wesentliche physikalische Motivation des Experiments ist, e+e- -Paare im invarianten Massenbereich bis GeV/c2, sowohl in pion- und protoninduzierten Reaktionen, als auch in Schwerionenkollisionen zu messen. Das Ziel ist die Untersuchung der Eigenschaften der Vektormesonen rho, omega und anderer Hadronen, welche aus e+e- -Paare rekonstruiert werden. Da Dileptonen nicht durch die starke Wechselwirkung beeinflusst werden, machen sie das Studium der Eigenschaften von Hadronen in Kernmaterie möglich. Allerdings ist die Messung dieser Dileptonenpaare schwierig, da Leptonen, die in anderen Prozessen erzeugt werden, einen grossen Untergrund erzeugen. In dieser Arbeit werden die Analyse von Daten, die mit dem HADES Spektrometer aufgenommen wurden, so wie Resultate derselben, diskutiert. Zum ersten Mal wurden mit ausreichender Statistik e+e- -Paare aufgezeichnet, die in der Kollision C+C bei einer Projektilenergie von 2 GeV per Nukleon erzeugt wurden. Dieses erste Experiment der HADES Kollaboration, da es ermöglicht, den von der DLS Kollaboration bei 1.04 AGeV gemessenen Paar-Überschuss zu verifizieren. Diese Arbeit besteht aus fünf Kapiteln. Das erste Kapitel beschreibt die dieser Arbeit zugrunde liegende Physik. Im zweiten Kapitel wird das HADES Spektrometer mit den typischen Eigenschaften der einzelnen Komponenten vorgestellt. Kapitel 3 fokussiert das Thema der Identifikation von geladenen Teilchen. Das 4. Kapitel präsentiert die Rekonstruktion von Dielektronen-Spektren in C+C Kollisionen. In diesem Teil der Arbeit wird auch der Vergleich mit theoretischen Modellen berücksichtigt. Die Schlussfolgerungen befinden sich im Kapitel 5.

Time-like electromagnetic form factors can be obtained from unpolarized measurements of the differential cross section in proton antiproton annihilation in a pair of leptons, as $\overline{p}$ + p ↔ e+ + e− , with the PANDA detector at FAIR. We study the sensitivity of such measurements and focus on observables such as the angular asymmetry and the ratio of electric to magnetic form factors. We also collect useful formulas and references for future simulations and studies.

Biomolecular condensates (BMCs) play important roles in cellular structures including transcription factories, splicing speckles, and nucleoli. BMCs bring together proteins and other macromolecules, selectively concentrating them so that specific reactions can occur without interference from the surrounding environment. BMCs are often made up of proteins that contain intrinsically disordered regions (IDRs), form phase-separated spherical puncta, form liquid-like droplets that undergo fusion and fission, contain molecules that are mobile, and are disrupted with phase-dissolving drugs such as 1,6-hexanediol. In addition to cellular proteins, many viruses, including influenza A, SARS-CoV-2, and human immunodeficiency virus type 1 (HIV-1) encode proteins that undergo phase separation and rely on BMC formation for replication. In prior studies of the retrovirus Rous sarcoma virus (RSV), we observed that the Gag protein forms discrete spherical puncta in the nucleus, cytoplasm, and at the plasma membrane that co-localize with viral RNA and host factors, raising the possibility that RSV Gag forms BMCs that participate in the virion intracellular assembly pathway. In our current studies, we found that Gag contains IDRs in the N-terminal (MAp2p10) and C-terminal (NC) regions of the protein and fulfills many criteria of BMCs. Although the role of BMC formation in RSV assembly requires further study, our results suggest the biophysical properties of condensates are required for the formation of Gag complexes in the nucleus and the cohesion of these complexes as they traffic through the nuclear pore, into the cytoplasm, and to the plasma membrane, where the final assembly and release of virus particles occurs.