Previous events

Previous events at Discovery in 2020

Master thesis defense by Christian Michelsen

17 January 2020 kl. 15:00

Title: A Physicist’s Approach To Machine learning – Understanding The Basic Bricks

PhD defense by Vojtech Pacik

12 February 2020 kl. 11:00

Title: Measurement of anisotropic flow using the ALICE experiment at CERN-LHC


The primary goal of ultra-relativistic heavy-ion physics is the study of the created strongly- interacting quark-gluon plasma (sQGP).Measurements of the azimuthal anisotropy of created particles, quantified by anisotropic flow vn coefficients, compared to hydrodynamic calculations, can be used to investigate this unique state of nuclear matter and its properties.

Due to the absence of the QGP-like medium, small collision systems have been considered as a baseline for the heavy-ion measurements. However, high-multiplicity pp and p-Pb collisions have revealed similar collective behaviour traditionally associated with the expanding medium.The origin of such features is not yet understood and is a focus point of the present work.

This work presents the analysis of azimuthal correlations of inclusive charged hadrons and identified particles in Pb-Pb and p-Pb collisions at centre-of-mass energy of 5.02 TeV recorded by ALICE detector at the Large Hadron Collider. Besides the vn measurement obtained for the first time using the 4-particle cumulants, more advanced observables such as flow fluctuations and non-linear flow response are studied in Pb-Pb collisions. The presented results exhibit an explicit mass ordering consistent with radial expansion with universal velocity, as described by hydrodynamical calculations based on the iEBE-VISHNU model for low pT < 3 GeV/c, and baryon/meson grouping at intermediate pT region.

Non-flow correlations, arising from jet fragmentation and resonance decays, present a challenge as they generally dominate in small collision systems. In order to reduce such contamination, a pseudo-rapidity separation between correlated particles is applied as well as subtraction of remaining non-flow estimate based on a measurement of minimum-bias pp collisions at centre-of-mass energy of 13 TeV. Motivated by Pb-Pb measurements, an initial attempt for extracting v2 using the 4-particle cumulant is made.The mass-related features observed in Pb-Pb collisions are also apparent in non-flow subtracted p-Pb measurement.

Overall, these differential measurements of vn coefficients present challenges for theoretical calculations further constraining the medium properties as well as initial conditions of the collision. In addition to the inclusive particles, the measurements using identified hadrons provide unique insights into particle production mechanisms. The results presented here mark a starting point for potential future development in investigating the obscure origin of the collectivity by analysing high-multiplicity pp collisions.

Seminar by Prof. Torsten Åkesson

20 February 2020 kl. 12:00

Title: Search for Light Dark Matter using a Primary Electron Beam
The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for the origin of dark matter sharpen the focus on a narrower range of masses: the natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the DM mass to lie within about an MeV to 100 TeV. Considerable experimental attention has been given to exploring Weakly Interacting Massive Particles in the upper end ...

Master thesis defense by Loui Nørgaard Wentzel

21 February 2020 kl. 15:00

Using Machine Learning on electron identification and energy regression in the forward region in ATLAS

ONLINE PhD Defense: Freja Thoresen

30 April 2020 kl. 11:00

Title: Pseudorapidity dependence of long-range correlations

Bachelor thesis defense by Frederik Sebastian Kehn Jensen

27 August 2020 kl. 11:00

Title: Statistical stability study of multiparticle cumulants in small collision systems at the LHC
Abstract: For many years, one of the primary phenomena for investigating Quark-Gluon Plasma is by the anisotropic flow. Multi-particle cumulant has provided a valid and stable method for flow analysis in the heavy-ion collision. The statistical dependence and stability have not yet been explored when applied in smaller collisions systems, such as proton-proton collisions. This thesis makes use of a Toy Monte Carlo model to simulate low multiplicity collision (events) with known generated elliptic flow. A...

Master thesis defense by Helle K. Leerberg

28 August 2020 kl. 14:00

Title: Higgs decay to Zγ - A study of efficiency

Abstract: This thesis presents a novel approach to improve the Higgs boson selection from the H → Zγ decay presented in the ATLAS article "Searches for the Zγ decay mode of the Higgs boson and for new high-mass resonances in pp collisions at sqrt{s}=13 TeV with the ATLAS detector". The improvement is performed using Machine Learning (ML) models on Monte Carlo (MC) data from the ATLAS experiment simulating collisions at the Large Hadron Collider at CERN. The H → Z...

Master thesis defense by Joachim Carlo Kristian Hansen

28 August 2020 kl. 14:00

Title: Flow fluctuations and flow correlations with Event Shape Engineering at the Large Hadron Collider

Abstract: This thesis aims to summarize the exploration of the properties of Quark-Gluon Plasma (QGP) using anisotropic flow at the CERN Large Hadron Collider. The QGP properties are investigated in Pb-Pb collisions at 5.02 TeV and Xe-Xe collisions at 5.44 TeV. In particular, the fluctuations of elliptic flow subject to the popular technique Event Shape Engineering (ESE) is investigated. The measurements show that ESE might not select only in the initial eccentricity, but also receive contributions from e...

Master thesis defense by Molly Hjort Jensen

18 September 2020 kl. 10:00

Title: Performance study of the dual-readout calorimeter in a multi-particle environment 
Abstract: The Future Circular Collider (FCC) study has proposed a new highest-luminosity high-energy electron-position (FCC-ee) collider. This would allow for unprecedented precision measurements running at among other the Z pole (91.2 GeV). For this collider, the IDEA detector concept including a dual-readout (DR) calorimeter was developed. This fibre-based sampling calorimeter measures scintillation and Cerenkov radiation simultaneously, such that the degree of non-compensation on an event-by-event basi...

Master thesis defense by Kunal Gautam

18 September 2020 kl. 13:00

Title: Flavour Identification Techniques

Development of algorithms for tagging of b- and c- quark for precise measurement of branching fractions of Higgs boson produced in electron-positron collisions

Abstract: The thesis reports on the study and implementation of flavour identification algorithms to distinguish the hadronic decay channels of the Higgs boson. The study has been performed in an environment compatible with proposed future e+e− circular colliders like the Future Circular Collider (FCC).

The first algorithms presented is the Impact Parameter Algorithm. The other algorithm, inspired by the techniques presented in the LCFIPlus framework, developed for future e+e− linear colliders like the International Linear Collider (ILC), classifies events into four categories through secondary vertex reconstruction, with each category representing the majority of decay events to a certain hadronic flavour.

Master thesis defense by Emil Gorm Nielsen

9 October 2020 kl. 10:00

Abstract: One of the main goals of ultra-relativistic nuclear collisions at the LHC is to create a new state of matter called quark-gluon plasma (QGP) and study its properties under controlled conditions. One of the experimental observables is the anisotropic flow $v_n$, defined as correlation of azimuthal angle of each particle with respect to a common symmetry plane $\Psi_n$. The $v_n$ and $\Psi_n$ represent the magnitude and the phase of a complex flow vector $V_n$, respectively. Azimuthal anisotropie...

Master thesis defense by Bjørn Mølvig

30 October 2020 kl. 14:15

Title: Low-Energy Neutrino Reconstructions using Recurrent Neural Networks
Abstract: The IceCube Neutrino Observatory is a physics experiment located at Antarctica. The experiment is capable of detecting neutrinos using light-detecting digital optical modules (DOMs) sitting in an array deep below the surface in the South Pole ice sheet. This thesis presents a versatile Deep Learning-based approach to low-energy neutrino reconstruction and -identification at the IceCube Experiment. The algorithms developed in this work attempt to alleviate some of the weaknesses of the current m...

Master thesis defense by Kassiani Tsemperlidi

9 November 2020 kl. 10:00

Title: Image Guided & Adaptive Radiotherapy in Esophageal Cancer
Abstract: The purpose of this study is to examine the current clinical workflow in radiotherapy in oesophageal cancer and suggest new approaches if needed. The thesis is divided into two parts, in the first one we compared different image registration strategies for image-guided radiotherapy, whereas in the second we investigated the efficiency and coverage of the dose planning through the whole treatment period. We included 20 consecutive patients, treated for oesophageal cancer at Rigshospitalet in 2017...

Master thesis defense by Emmanouil Terzidis

9 November 2020 kl. Approx. at 11:15

Title: Individual anisotropic planning target volumes (PTV) for lung cancer radiotherapy in deep-inspiration breath hold
Abstract: Deep inspiration breath-hold (DIBH) is a cost-efficient technique that can potentially increase the overall quality of a treatment plan, provided that the position of the target is reproducible, within and throughout the course of treatment.
In this dissertation work, four lung cancer p...

PhD defense by Daniel S. Nielsen

17 December 2020 kl. 14:00

Title: In search of new Higgs bosons
The abundance of matter to antimatter in the universe is not explained by the Standard Model (SM). Two Higgs Doublet Models (2HDMs), which introduce additional Higgs particles, and in particular the A→ZH channel may partly explain the origin of the matter asymmetry.

A search for the A→ZH signature is done using data recorded by ATLAS during 2015–2018 proton–proton collisions. The heavy A boson is produced by gluon–gluon fusion. The heavy H boson decays to WW that further decay to qqqq. Z decays to a pair of electrons or muons. No excess above the SM predictions is found. The upper limits at the 95 % confidence level for the production cross-section times branching ratios for A→ZH and H→WW are set to 0.023–8.9 pb,, d...