Open Thesis Topics

Quarkonia are unstable hadrons made up of identical quark-antiquark pairs, which decay according to the electromagnetic, strong or weak interactions. This project will work on improving the modelling of these decays in the simulation program "Sherpa" by updating branching ratios from measured results and implementing matrix elements for the most relevant decay channels.

Effective field theory (EFT) allows us to make accurate predictions about phenomena beyond the Standard Model (SM) without requiring a complete understanding of the fundamental mechanisms involved. Vector boson scattering (VBS) processes are ideal for precision measurements within the SM. In this project, it will be working on final states consisting of two photons and two jets (yyjj) produced by VBS processes. Using EFT interpretations, it is aimed to make predictions for neutral gauge couplings that do not exist in the SM.

The production of four leptons from photons are a very sensitive probe of the electroweak gauge structure. Data recorded by the ATLAS Experiment in the LHC run-2 are used to quantify the agreement of the theoretical predictions. This is done by constraining higher-dimensional beyond-the-Standard-Model operators that generate purely neutral electroweak interaction vertices between photons and the Z boson.

The production of W boson pairs from photons are a very sensitive probe of the electroweak gauge structure. Data recorded by the ATLAS Experiment in the LHC run-2 are used to quantify the agreement of the theoretical predictions. This is done by constraining higher-dimensional beyond-the-Standard-Model operators that modify the γγWW vertex.

Tbd

Studying specific polarisation configurations in which W or Z bosons can be produced is interesting due to the connection of the longitudinal polarisation of massive vector bosons to the Higgs mechanism and electroweak symmetry breaking. This is often done in the leptonic decay modes of the W/Z boson, but the high rate of the hadronic decay mode makes it an attractive alternative final state. We want to study simulations for polarised hadronically decaying W/Z bosons and identify interesting observables for a future analysis of these with the ATLAS detector.

More information to follow.

The complexity of matrix element calculations for final states with a high multiplicity is so high, that their computational cost often limits theory simulations for the LHC. In this project we want to extend a machine learning based approach to simplify these calculations by approximating the matrix elements. The goal is to study various parameters for the architecture and training of deep neural networks in this approach.

The simulation of different polarisation states allows us to study effects from physics beyond the Standard Model in more detail. In this project we want to study, how effective-field-theory extensions of the Standard Model will affect different polarisations of W bosons in W±W± pair production at the LHC.

The simulation of different polarisation states allows us to study effects from physics beyond the Standard Model in more detail. In this project we want to study, how effective-field-theory extensions of the Standard Model will affect different polarisations of W and Z bosons in WZ pair production at the LHC.

Investigating the polarization of vector bosons (VB) in VB production processes provides tests for the Standard Model's gauge symmetry structure and the concrete mechanism of electroweak symmetry breaking, as well as sensitivity to new physics. The ATLAS VB polarisation analysis is currently trying to measure the contribution of longitudinally-polarised W-bosons in the scattering of two same-charged W-bosons. To enhance the measurement’s sensitivity, artificial neural networks (ANNs) are used to separate the different VB polarisation components. At the moment, the Monte-Carlo simulations used to train the ANNs are based on the matrix element generator MadGraph.

Since recently, the event generator Sherpa is also able to simulate polarized cross sections of VB production processes. In preparation for its application in the ATLAS VB polarisation analysis, a first proof of concept study has been performed to investigate different methods to train ANNs to separate the VB polarisations. However, these investigations are so far based on “truth-level” simulations, i.e. without the inclusion of detector effects. In addition to extending the existing study to more complex training procedures, the goal of this Bachelor thesis is to apply the collected knowledge to “reconstruction-level” samples that include the effects of the detector simulation and object reconstruction. This allows a direct comparison of the expected measurement sensitivity when using ANNs trained on MadGraph vs. Sherpa-samples.

Investigating the polarization of vector bosons (VB) in VB production processes provides tests for the Standard Model's gauge symmetry structure and the concrete mechanism of electroweak symmetry breaking, as well as sensitivity to new physics. As one of the VB production processes with a very clean signature due to four charged leptons in the final state, the ZZ electroweak production process is very interesting for this purpose. Some literature studies on this process already exist. Since recently, the Monte-Carlo-Eventgenerator Sherpa is able to simulate polarized cross section of vector boson production. The goal of this thesis is to test this new feature with this process. Furthermore, aspects of this process not yet studied, such as the contribution of particle showers, can be investigated.

Triboson production V(->ll)V(->ll)V(->qq) is a component of the signal definition in vector boson scattering, but is sometimes ignored or generated as a separate process. This thesis should study the impact of the triboson component. In particular the effect of dim-8 EFT operators in the quartic vertex should be studied to quantify the effect of ignoring the triboson production in an EFT study.

In parallel to our analysis of WZ final states at high transverse momentum we want to search for deviations from the Standard Model from new heavy particles decaying into a WZ boson pair.

TODO

The simulation program Sherpa can currently only simulate decay cascades with up to 3 final state particles in each step. For decays of the Higgs boson into 4 fermions via WW or ZZ diagrams it becomes important to simulate the full 1->4 decay. This thesis is about implementing such decays and make phenomenological comparisons to existing calculations.

Tbd

The production of leptons from photons proceeds through purely electromagnetic interactions. The photons are radiated from protons colliding at the LHC. The key experimental signatures for the production of four leptons from photons uses the fact that the protons stay intact and no particles other than the leptons are produced in the interaction. The analysis is based on an earlier measurement of the production of W boson pairs from photons, published in https://arxiv.org/abs/2010.04019.

Es soll ein angeleitetes Rollenspiel für Jugendliche entwickelt und erprobt werden, in welchem die Lernenden Aspekte des wissenschaftlichen Erkenntnisprozesses nachvollziehen und reflektieren können. Der wissenschaftliche Kontext sowie die inhaltliche Schwerpunksetzung kann frei gewählt werden. Es kommen u. a. folgende Schwerpunkte in Frage:

• Kreislauf des wissenschaftlichen Arbeitens – Von der Fragestellung bis zur Veröffentlichung
• Unsicherheiten in der Wissenschaft
• Wissenschaftliche Streitkultur
• Der Prozess des Peer Review

Diese Arbeit soll in Kooperation mit der Didaktik der Physik erstellt werden. Der
Kontext des Rollenspiels muss jedoch nicht ausschließlich die Forschung in der Kern- und Teilchenphysik sein.

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Ziel ist es, die Forschung zum Klimawandel mit der Teilchenphysik durch die Auseinandersetzung mit dem CLOUD-Experiment am CERN (siehe 1 und 2) in einer Unterrichtseinheit zu verknüpfen. Dies hat das Potenzial, die Kreativität, das kritische Denken und das Verständnis für die Natur der Wissenschaft bei den Schüler:innen zu fördern und ihr Verständnis der Teilchenphysik durch deren Anwendung in einem realen Kontext zu vertiefen. Die Unterrichtseinheit soll mit einer kleinen Gruppe von Schüler:innen erprobt werden. Die Arbeit soll in Kooperation mit der Didaktik der Physik erstellt werden.

(1) https://www.home.cern/science/experiments/cloud
(2) https://cerncourier.com/a/cloud-experiment-sharpens-climate-predictions/

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© Martin Kaßner

wissenschaftliche Mitarbeiterin

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Dr. Farahnaz Sadidi

Betreuung Praktikumsveranstaltungen, Seminar kritisches Denken

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Professur für Didaktik der Physik

Professur für Didaktik der Physik

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Im Netzwerk Teilchenwelt wurde umfangreiches Unterrichtsmaterial zur Teilchenphysik erstellt. Die Erkenntnisse des Standardmodells werden darin mithilfe des Konzepts von Ladungen und Wechselwirkungen beschrieben. Dieser Ansatz, der sich in der populärwissenschaftlichen Literatur und in Schulbüchern bislang kaum widerspiegelt, soll durch geeignete Arbeitsblätter ergänzt werden.

Diese Arbeit soll in Kooperation mit der Didaktik der Physik erstellt werden.

Kontakt:

Mitgestaltung und Weiterentwicklung des ATLAS Open Data Portal am CERN (http://opendata.cern.ch/) mit folgenden Aufgaben zur Auswahl:

• Mitarbeit und Aufbereitung der Dokumentation zum ATLAS Datensatz
• Implementierung neuer Inhalte im Open data Portal (nur für Programmier-Profis)
• Entwicklung neuer Ideen für die Darstellung von Lerninhalten auf dem Open Data Portal

Die Arbeit soll in Kooperation mit der Didaktik der Physik erstellt werden.

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