Dense and Strange Hadronic Matter

Course with Participations of Group Members

Offers for Theses in the Group

Absorption of antinuclei in ALICE Time Projection Chamber using machine learning algorithms

Dark Matter (DM) is believed to account for roughly 27% of the mass-energy of our Universe, and its nature remains one of the most intriguing unsolved questions of modern physics. Multiple balloon- and space-borne experiments are searching for the traces of DM using the idea of possible annihilation or decay of DM particles into ordinary (anti)particles, including light (anti)nuclei. The latter (such as antideuterons and antihelium nuclei) are considered as especially promising probe for such indirect DM searches, as the background stemming from ordinary collisions between cosmic rays and the interstellar medium is expected to be very low with respect to the DM signal. In order to reliably estimate the fluxes of antinuclei near Earth stemming from DM and from background, it is necessary to know the probability for antinuclei to interact inelastically with ordinary matter on their way to the detectors (e.g. with interstellar medium and Earth's atmosphere). This probability is driven by the inelastic cross section of corresponding processes, which for antinuclei are still poorly (or not) known. This fact hinders precise calculations of antinuclei fluxes near Earth and forces existing estimates to rely on extrapolations and modelling. The here advertised master project will deal with the analysis of inelastic interactions of antinuclei inside the gas volume of the Time Projection Chamber of the ALICE detector. Such interactions typically create a bunch of secondary (charged) particles with low momentum with a characteristic topology of secondary vertex inside the TPC volume. The pattern can be recognised by machine learning algorithms trained on simulated events, in which such annihilation processes happen in a controlled environment. After the validation of algorithms with simulated events, one can analyse real experimental data and tag the annihilation events of interest, which in turn can be used to evaluate the effective antinuclei + A inelastic cross section. This project will be structured in the following way: - simulation of the inelastic interactions of antinuclei with the TPC gas using Geant4 toolkit - training and validation of neural networks to reliably recognise antinuclei annihilation events - Analysis of the ALICE experimental data from pp collisions at sqrt(s) = 13 TeV - Evaluation of the effective antinuclei + A inelastic cross sections

suitable as

• Master’s Thesis Nuclear, Particle, and Astrophysics

Supervisor: Laura Fabbietti

Characterizing CsI coated THGEMs for photon detection

Traditional devices for photon detection like the Photomultiplier Tube or more recent technologies such as Silicon Photomultipliers are very cost-intensive. Therefore, especially with large area experiments in mind it is very interesting to investigate new ways of detecting photons. In this project we are taking the approach of combining a photosensitive material with a Thick GEM (THGEM) in a gaseous detector. THGEMs are robust, low-cost devices, which can be used for electron multiplication. The THGEM is coated with a photosensitive material and placed within an electrical field. When a photon releases an electron from the material the photo electron drifts in the THGEM hole and undergoes avalanche amplification due to a high electric field that is preset inside the holes. Below the THGEM an anode is used for electron readout. Depending on the gain of the THGEM this could enable single photon detection. In the scope of the thesis CsI coated THGEMs, which are useful in the UV light range, will be characterized and their quantum efficiency will be studied.

suitable as

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Development of new approach to study particle correlations using femtoscopy

One of the most precise and most powerful approaches to probe the strong interaction between different particle pairs is the femtoscopy method [1] which is based on measuring the correlation in the momentum space between hadrons produced at particle colliders such as the LHC. The correlation function is obtained by using the same and mixed event particle pair distributions as functions of their relative momenta. The former carries the information about the interaction while the latter provides information on the available phase-space of the produced pair. Two particles produced in one collision makes the same event pair while the mixed event pairs are constructed by taking two particles from two di erent collisions. The technique of event mixing is a very well working approximation, however, more sophisticated solutions are of increasing interest as the femtoscopic method is used in more and more complicated studies and is being extended to probe the multi-hadron interactions. In this work, a new approach to account for the particle phase space will be elaborated by using marginalized probability distribution functions. Toy Monte Carlo simulations will be used to test the mathematical basis of the method which will be then applied on the proton-proton collision data collected by the ALICE detector to study its feasibility in real experimental conditions. [1] Hadron-hadron interactions measured by ALICE at the LHC, L. Fabbietti, V. Mantovani Sarti, O. V azquez Doce, arXiv: 2012.09806 (2020)

suitable as

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Entwicklung eines neuen Silizium Detektor mit der CMOS Technologie

In dieser Arbeit wollen wir einen Prototyp für einen ultradünnen Siliziumdetektor der nächsten Generation für die Hochenergie-Teilchenphysik entwickeln, der die CMOS-Technologie nutzt. Ziel ist es, einen echten 3-D-Tracker zu bauen, der aus ultradünnen und biegbaren Detektoren besteht, und ein Experiment an einem kleinen Beschleuniger durchzuführen, um die Auflösung des Aufbaus mit Hilfe von elastischen pp-Kollisionen zu bestimmen. Die Arbeit umfasst die Arbeit im Labor, den Entwurf der mechanischen Struktur der Detektoren, die Prüfung der Sensoren und die Teilnahme an Tests.

suitable as

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Exploring the properties of Quark-Gluon Plasma with anisotropic flow measurements at the Large Hadron Collider

The matter produced in ultra-relativistic heavy-ion collisions resembles the Quark-Gluon Plasma (QGP), which is an extreme state of nuclear matter consisting of deconfined quarks and gluons. Such a state existed in the early Universe, just a few microseconds after the Big Bang. Its properties can be experimentally accessed by measuring the azimuthal anisotropies in the momentum distribution of produced particles in heavy-ion collisions, for instance, in lead-lead collisions reconstructed with the ALICE experiment at CERN's Large Hadron Collider (LHC). Of particular interest in this context is the anisotropic flow phenomenon, which is an observable directly sensitive to the properties of QGP. In this project, we introduce the basics of anisotropic flow and corresponding analyses techniques, and we guide a student throughout all steps needed for its final measurement, in the large-scale LHC datasets distributed on Grid. We start a project by briefly introducing a theoretical framework within which an anisotropic flow phenomenon can be defined and quantified. Next, we introduce sophisticated multi-particle correlation techniques, which were developed recently by experimentalists particularly for anisotropic flow measurements. We go in detail through the practical implementation of multi- particle correlations, students are expected at this point to perform some simple analytic calculations, and to learn and perform programming tasks both in ROOT and AliROOT. ROOT is the object-oriented analysis frame- work written in C++ programming language, and it is used at the moment as a default software in high-energy physics by all major collaborations world- wide, while AliROOT is the more speci c analysis framework developed by ALICE experiment, and which is based on ROOT. We wind up the project by letting the student do an independent ani- sotropic flow analysis with his/her own newly developed code in AliROOT, utilizing multi-particle correlation techniques, over real heavy-ion collisions collected by ALICE at LHC, and stored on Grid.

suitable as

• Master’s Thesis Nuclear, Particle, and Astrophysics

Supervisor: Laura Fabbietti

Half-life measurement of medium mass proton emitters at R3B

Protonenradioaktivität ist ein, seit einigen Dekaden experimentell verifiziertes Phänomen, das unter anderem auch an der TU-München entdeckt wurde. Trotzdem sind die Lebensdauern für die meisten Protonemitter noch nicht, oder nur sehr ungenau vermessen. Wir wollen im Rahmen eines BMBF geförderten Projektes eine neuartige Methode für diese Messungen etablieren und damit ein umfangreiches Messprogramm zusammen mit der R3B Kollaboration bei FAIR in Darmstadt beginnen. Das R3B – Experiment (Reactions with Relativistic Radioactive Beams) spielt eine herausragende Rolle bei der Untersuchung exotischer Kerne mit extremem Proton zu Neutron Verhältnis. Ein zentraler Detektor in diesem Projekt ist das, aus mehreren tausend Einzelkristallen bestehende, CALIFA Kalorimeter, das einen hochselektiven Trigger für die quasifreie Streuung liefert. Wir wollen damit und einem gerade im Aufbau befindlichen, hochauflösenden Silizium Tracking-Array durch Vertex-Rekonstruktion die Lebensdauer kurzlebiger Kerne vermessen. Im Rahmen einer Masterarbeit sollen dafür zum einen erste Simulationsrechnungen gemacht werden, die den Parameterbereich der Methode eingrenzen, zum andern soll das Detektorsystem in einem ersten Experiment bereits im kommenden Frühjahr untersucht und charakterisiert werden. ADVISOR: Prof. L. Fabbietti / Dr. R. Gernhäuser

suitable as

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Current and Finished Theses in the Group