Dense and Strange Hadronic Matter

Course with Participations of Group Members

Offers for Theses in the Group

Aufbau eines Triggersdetektors

Höchst sensitive, großflächige Teilchendetektoren sind immer noch ein heißes Thema in der modernen Teilchenphysik. Unsere Arbeitsgruppe hat in den letzten Jahren wesentliche Entwicklungen im Bereich der Gas Electron Multiplier (GEM) für das ALICE Experiment am LHC durchgeführt und die Leitung beim Aufbau des riesigen GEM Detektors für die ALICE TPC, der in diesem Jahr in Betrieb gehen wird. Wir wollen diese Arbeiten aber noch erweitern und GEM Detektoren auch zum Nachweis einzelner Photonen einsetzen. Dazu gilt es die Verstärkerfolien mit einer photosensitiven Schicht auszustatten und dann mit einem Cherenkov-Radiator und kosmischen Myonen als definierte Lichtquelle zu charakterisieren. Ihre Aufgabe ist es in Zusammenarbeit mit unseren Doktoranden einen Testaufbau mit zwei Faserdetektoren zu erstellen, mit dem es gelingt Richtung und Form des Cherenkovkegels zu definieren und damit die GEM Folien zu beleuchten. Sie lernen dabei nicht nur modernste experimentelle Techniken wie Silizium Photomultiplier und GEM Detektoren kennen, sondern gehen auch erste Schritte beim Umgang mit hochintegrierter Datenaufnahme Elektronik auf Basis von Field Programmable Gate Arrays (FPGAs), die eine wesentliche Basis von künstlicher Intelligenz sind.

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 anal-yses 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 mea-surements. 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 specific 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

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Investigating effects of gas humidity on electrical discharge formation in MPGDs

Micropattern gas detectors (MPGD) are a type of particle detectors used in many large high energy physics experiments (Atlas, CMS, Alice) given their easy scalability. MPGDs work by amplifying the primary ionisation signals generated by impeding charged particles as they traverse a gas volume. This amplification of primary electrons is achieved by using structures with micrometer scale patterns that are different for various types of MPGDs, which include Gas Electron Multipliers (GEMs) and Micro-MEsh Gaseous Structure (Micromegas). One of the limiting factors for the long term stable operation of MPGDs is the formation of electrical discharges inside the amplification structures. Due to this, there has been an extensive effort over the years to understand and to develop methods to mitigate these discharges. One of the remaining questions however is how the humidity (the water content) of the used gas mixture affects the formation of discharges in MPDS. The aim of this project is to conduct the first comprehensive studies investigating the correlation between gas humidity and MPGD discharge stability. For this task, a dedicated detector chamber will be used with modifications to the gas system which enables the precise control of the ambient humidity levels. This venture is a great entry point for anyone interested in particle detector hardware research and development. The achieved results of which might end up shaping the next generation of cutting edge high energy physics experiments

suitable as

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Investigating the three-body strong interaction using correlation techniques at the LHC

One of the most compact and dense astrophysical objects in our Universe are the Neutron Stars (NS). The composition of the inner region of the NS is still not known, and several hypotheses have been postulated in the last decades (for a complete review see [1]). Our current knowledge reveals that, beside the neutrons, particles with strange quark content (called hyperons) can be produced. The inner structure and composition of the NS can be modelled by means of Equation of States in which all the fundamental interactions among the constituents are considered. A crucial role to understand the inner structure of the NS is played by the three-body forces among the nucleons and the hyperons. Nevertheless, an accurate microscopic description of the three-body problem is still far to be achieved and precise experimental data to test the existing models are strongly demanded. The two-body strong interaction among hadrons have been recently explored with femtoscopy studies at the LHC with the ALICE detector (see e.g. [2-3]). The femtoscopy technique analyses the correlation in the momentum space between the particles (e.g. hyperons and nucleons) emitted in proton-proton collisions at the center of mass energy of 13 TeV. The theoretical correlation functions are also calculated, given the interaction potentials or the wave functions of the interacting two-body systems (see [4]). Such powerful analysis technique will be extended to the three-body systems. The candidate student will develop this new analysis method in the case of the three-body interaction between produced particles. Given the interaction potential, the student will calculate the analytical wave function by using the perturbation theory in the context of the non-relativistic Quantum Mechanics and will implement an algorithm in the C++ language that will allow to solve the Schroedinger equation for the three interacting particles. The analysis tools developed in this work will be tested by using the ALICE RUN2 data and will be used to analyse the future RUN3 data (the data taking will start in 2022) that will provide the highest statistic ever in number of events to study the three-body correlations. To conclude, the proposed work of thesis will serve to the student in developing both the theoretical and data analysis skills; the student will work in the context of an international collaboration and will contribute to extend the femtoscopy technique to the case of the three-body forces among hadrons which are fundamental to unveil the inner composition and structure of one of the most fascinating objects in our Universe. [1] L. Tolos and L. Fabbietti Prog.Part.Nucl.Phys. 112 (2020) 103770 [2] ALICE Collaboration, Nature, e-Print: 2005.11495 [nucl-ex] [3] ALICE Collaboration, Physics Letters B 805 (2020), 135419 [4] D. L. Mihaylov, V. Mantovani Sarti, O.W. Arnold, L. Fabbietti, B. Hohlweger et al., Eur.Phys.J.C 78 (2018) 5, 394

suitable as

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Measurement of the ΛΦ interaction with femtoscopy studies in pp collisions at ALICE

In low-energy hadronic physics the modeling of the strong interactions among baryons (particles composed of three quarks) is obtained through effective lagrangians in which the mediator of the strong forces are typically mesons (particles composed of two quarks). The interaction amongst strange baryons (so-called hyperons), as Lambdas (Λ), is currently not well constrained experimentally since these particles are unstable and performing scattering experiments is extremely challenging. Hyperon-hyperon interactions though are one of the key ingredients in the physics of Neutron Stars (NS) in order to understand if these strange particles can be one of the ingredients present in the core of these dense astrophysical objects. At the moment, theoretical predictions based on meson-exchange models consider the Φ meson as the mediator of the strong interaction between two Λs, producing a repulsive interaction. However, the coupling between a Λ and Φ is still not measured, hence theoretical predictions currently rely on symmetry relations to establish the strength. Recently in the ALICE experiment we used a technique called femtoscopy, which measures the correlation in the momentum space between two particles, has been used to infer on the strong interaction of the particle pair. At LHC a lot of hyperons and mesons, including Λs and Φs, are produced in the collision of protons at center of mass energy of 13 TeV. The project will include the identification of Lambdas and Phi particles in the RUN2 data measured by the ALICE detector in pp collisions through experimental techiques and the following construction of the main observable: the correlation function. The study of the obtained ΛΦ correlation function will allow to determine the nature and strength of the interaction and the comparison with the current theoretical understanding will allow to shed light on the hyperon-hyperon interaction role inside NS.

suitable as

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Study the absorption of antihelium-4 in ALICE experiment at CERN LHC

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. This massive hole in our knowledge drives multiple experimental searches for DM, and one of the indirect ways to search for DM is to look for the annihilation or decay of DM particles into ordinary (anti)particles such as light (anti)nuclei as employed by several balloon- and space-borne experiments. Low-energy light antinuclei (e.g. antihelium-4) are particularly promising signals for these indirect DM searches, since the background stemming from ordinary collisions between cosmic rays and the interstellar medium is expected to be low with respect to the DM signal. In order to reliably estimate the detection probability of interesting events such as DM -> helium-4 + antihelium-4 + ..., the interaction probability of antihelium-4 with ordinary matter (like interstellar medium, Earth's atmosphere) must be measured, since it defines the amount of antihelium-4 particles lost on the way to detector. However, nuclear inelastic cross sections of antihelium-4 + A processes are completely unknown, forcing current estimates of expected antihelium fluxes near Earth to rely on extrapolations and modelling. The topic of the here advertised master project deals with the measurement of these interactions using the ALICE detector. In heavy-ion collisions at LHC energies (anti)helium-4 nuclei are produced in significant amounts, and unique tracking and PID capabilities of the ALICE experiment make it possible to reliably detect the (anti)helium-4 nuclei in different sub-detector systems. This allows us to quantify the inelastic interaction probability of (anti)helium-4 with the ALICE detector material. This project will be structured in the following way: Analysis of the inclusive spectra of helium-4 and antihelium-4 nuclei in PbPb collisions at TeV Evaluation of the effective antihelium-4 + A inelastic cross sections Estimation of the antihelium-4 rates expected for different DM models in current and future satellite experiments

suitable as

• Bachelor’s Thesis Physics

Supervisor: Laura Fabbietti

Current and Finished Theses in the Group