Impact of the Coulomb field on charged-pion spectra in few-GeV heavy-ion collisions

In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged-pion transverse-mass and rapidity spectra, as well as on pion–pion momentum correlations is investigated in Au + Au collisions at $\sqrt{^{S}NN}$ = 2.4 GeV. We show that the low-m$_{t}$ region (m$_{t}$ < 0.2 GeV / c$^{2}$) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential energy deviates strongly from a $A_{part}^{2/3}$ scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields

Production and decays of hyperons in p+p reactions measured with HADES

Abstract. Preliminary results of inclusive σ+(1385) production in p + p reactions at Ebeam = 4.5 GeV and Λ(1520) in p + p and p + Nb at Ebeam = 3.5 GeV are presented. Both measurements were performed by the HADES ("High Acceptance Di-Electron Spectrometer") experiment at FAIR/GSI. The analysis consisted of multiple steps including track reconstruction, particle identification and the reconstruction of the hyperon signal from their hadronic decays Λ(1520) → Λπ+π− and σ+(1385) → Λπ+. The main part of the analysis, which is signal/background classification, was performed utilizing Machine Learning methods. The employed method relied on a data-driven approach called “Classification Without Labels" and the Multilayer Perceptron style Artificial Neural Networks. The analysis resulted in reconstruction of the resonance distributions for both σ+(1385) and Λ(1520), and allowed for the extraction of parameters of the relativistic Breit-Wigner distributions

Quantum detection with the usage of the NV‾ centre in diamond

W niniejszej pracy przedstawione zostało zagadnienie centrów barwnych w kryształach czyli defektów absorbujących światło. Defekty te oddziałują ze światłem w sposób podobny do atomów, posiadając charakterystyczne widma absorpcyjne i emisyjne. Na szczególna uwagę zasługują centra azot - wakancja w diamentach (centra NV) z uwagi na ich właściwości magnetyczne. Głównym problemem rozważanym w tej pracy jest analiza metod pomiaru pól magnetycznych przy pomocy centrów NV oraz efektów wpływających na ich dokładność.W pierwszej części pracy opisana została struktura kryształu diamentu oraz rodzaje defektów występujących w tej strukturze ze szczególnym uwzględnieniem centrów NV. Następnie opisano metody produkcji diamentów syntetycznych oraz metody wytwarzania defektów NV. Kolejny rozdział poświęcony jest opisowi własności fizycznych centrów NV, a w szczególności ich oddziaływaniu z polem magnetycznym i światłem laserowym. W drugiej części pracy przeanalizowane zostały dwie podstawowe metody pomiaru pola magnetycznego przy użyciu centrów NV, tzw.: metoda pomiaru widma elektronowego rezonansu spinowego (Electron Spin Resonance, ESR) i metoda sekwencji Ramsaya oraz dokładność pomiaru jaką można tymi metodami uzyskać. W trzeciej części pracy poddany został analizie prosty układ do pomiaru pola magnetycznego z wykorzystaniem centrów NV i wyprowadzone zostały wartości czułości takiego aparatu. Z przeprowadzonej analizy uzyskano zaskakująco wysoką dokładność pomiaru pola magnetycznego jak na tak prosty układ. W końcowej części pracy rozważone zostały także sposoby na poprawę parametrów układu pomiarowego i dalsze zwiększenie jego czułości.This work presents the issue of colour centres in crystals, i.e. defects that absorb light. Those defects interact with light in a similar manner as atoms, possessing characteristic absorption and emission spectra. The nitrogen - vacancy centres in diamonds (NV centres) deserve special attention due to their magnetic properties. The main problem discussed in this work is the analysis of magnetic field measurement methods utilising NV centres and effects influencing their accuracy.The first part of the thesis describes the crystal structure of diamond and different types of defects occurring in this structure with particular focus on NV centres. Next, the methods for the production of synthetic diamonds and the method of producing NV defects are described. The next chapter is devoted to the description of the physical properties of NV centres, in particular their interaction with the magnetic field and laser light.In the second part of the thesis, two basic methods of measuring the magnetic field using the NV centres were analysed, the so-called: electron spin resonance (ESR) method and the Ramsay sequence method, as well as measurement precision that can be obtained by these methods.In the third part of the thesis, a simple system for measuring the magnetic field using the NV centres was analysed and the sensitivity values of such a device were derived. The analysis performed gave a surprisingly high accuracy of the magnetic field measurement for such a simple system.In the final part of the thesis, methods for improving the parameters of the measurement system and further increasing its sensitivity were also considered

Development of new data analysis techniques and testing of new detector models for the HADES experiment

Niniejsza praca magisterska została wykonana w ramach projektu naukowego, będącego częścią eksperymentu HADES ("High-Acceptance DiElectron Spectrometer") w ośrodku GSI Helmholtzzentrum für Schwerionenforschung w Darmstadt w Niemczech. Przedstawiona praca składa się z dwóch części. Przedmiotem pierwszej części pracy była analiza wyników pomiarów testowych przeprowadzonych na prototypowych detektorach typu Ultra Fast Silicon Detectors (UFSD), określenie ich parametrów i ewaluacja ich potencjału do zastąpienia aktualnie stosowanych detektorów na bazie diamentów typu scCVD w roli systemu pomiaru czasu zerowego reakcji T0 oraz śledzenia cząstek wiązki w eksperymentach wykorzystujących wiązki protonów i pionów. W części drugiej pracy, przedstawiona została analiza danych z pomiarów elastycznego rozpraszania pionów na tarczach z polietylenu i węgla. Celem tej analizy było wykorzystanie metod Uczenia Maszynowego, w tym wypadku typu sieci neuronowej tzw. Perceptronu Wielowarstwowego oraz metody Klasyfikacji bez Etykiet, w celu odseparowania zdarzeń z rozpraszania na protonach od rozpraszania na węglu.The presented thesis was written as a part of a scientific project which was a section of HADES ("High-Acceptance DiElectron Spectrometer") experiment implemented in GSI Helmholtzzentrum für Schwerionenforschung facility in Darmstadt, Germany. This work consists of two parts. The subject of the first part covers the analysis of results from the testing of prototype particle detectors based on Ultra Fast Silicon Detector technology, determining their parameters, and evaluating their potential for replacing currently utilised scCVD diamond based detectors as T0 measurement and beam tracking system in experiments with proton and pion beams.In the second part of the thesis, the analysis of elastic scattering of pions on poliethylene and carbon targets was presented. The goal of this analysis was to utilise the Machine Learning methods, in this case a specific type of neural networks called Multi Layer Perceptron and the Classification Without Labels method, to separate events of scattering on protons from scattering on carbon

Measurement of global polarization of Λ\Lambda hyperons in few-GeV heavy-ion collisions

The global polarization of Λ hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au collisions at $\sqrt{^{s}NN}$ = 2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon's transverse momentum (p_{T}) and rapidity (y_{CM}) for the range of centrality 0–40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20 – 40%) collisions the polarization magnitudes are \left (%) = 6.8 $\pm$ 1.3 (stat.) $\pm$ 2.1 (syst.) for Au+Au and \left (%) = 6.2 $\pm$ 0.4 (stat.) $\pm$ 0.6 (syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D-fluid-dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model

New results on light nuclei, hyperons and hypernuclei from HADES (HADES collaboration)

International audienceIn March 2019 the HADES experiment recorded 14 billion Ag+Ag collisions at √sNN = 2.55 GeV as a part of the FAIR phase-0 physics program. In this contribution, we present and investigate our capabilities to reconstruct and analyze weakly decaying strange hadrons and hypernuclei emerging from these collisions. The focus is put on measuring the mean lifetimes of these particles