Probing dense and hot nuclear matter via di-electron spectroscopy
Dr. Vlassis Petousis
Technical University of Cyprus
Abstract: Over the last decades a lot of effort has been devoted to the study of nuclear matter far from its ground state. With high quality beams provided by High Acceptance Di-Electron Spectrometer (HADES), the investigation of nuclear matter at densities several times higher than nuclear ground state density using so-called rare and penetrating probes is possible. These penetrating probes are electromagnetic decays of hadrons inside the dense medium into pairs of leptons. Such purely leptonic final states, carry important information of the decaying objects to the detectors without being affected by strong final state interaction while traversing the medium. In this talk we will explore some of the latest results from HADES experiments, focusing on electron-positron pair (di-electrons) production in elementary collisions and also the strategy which has been developed to reconstruct the di-electron signal.
More specific, we will focus on the investigation of baryonic resonance production in proton-proton collisions at the kinetic energies of 1.25 GeV/u and 3.5 GeV/u. Exclusive channels npπ+ and ppπ0 as well as ppe+e− will be presented in the framework of a one-boson exchange model. Furthermore, analysis of Δ(1232) production at 1.25 GeV/u in the ppe+e−γ decay channel will be presented in a comparison with the partialwave analysis of the hadronic ppπ0 channel. This allow to access both Δ+ → pπ0(e+e−γ) and Δ+ → pe+e− Dalitz decay channels and the perfect reconstruction of the well-known π0 Dalitz decay, serves as a proof of the consistency of the analysis. The Δ(1232) Dalitz decay identified for the first time and the sensitivity to N- Δ transition form factors have been tested, also the decay branching ratio determined for the first time (4.19±0.62 syst. ± 0.34 stat.)x10−5.
Continuing, we will follow on the very latest investigation of dielectron production in tagged quasi-free neutron-proton collisions, by using a deuteron beam of kinetic energy 1.25 GeV/u impinging on a liquid hydrogen target. We will see a confirmation of a significant excess of e+e− pairs above the π0 mass in the exclusive channel dp→npe+e− (pspect) as compared to the exclusive channel ppe+e− measured in proton-proton collisions at the same energy. Follows a presentation of two models, which were evaluated for the role of the charged pion exchange between nucleons and double-Δ excitation combined with intermediate ρ-meson production. Closing, we will see that 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 sides.
Seminar takes place on Tuesday, December 19th 2017 at 2:00 PM
in the IEAP meeting room, Praha 2 ‐ Albertov, Horská 3a/22.
| doc. Dr. André Sopczak seminar organizer |
doc. Ing. Ivan Štekl, CSc. headmaster |
doc. Dr. André Sopczak IEEE CS - NPSS chair |
NUCLEAR & PLASMA SCIENCES SOCIETY CHAPTER
IEEE Czechoslovakia section
http://www.ieee.cz/en/nps