HIPARCOS Emmy Noether Independent Junior Research Group

The Higgs boson as a bridge between Particle Physics and Cosmology

Below you can find information for:

     * Topics for Bachelor and Master theses

     * HiWis (internships for BSc, MSc students)

     * Internships for international students (EU)

     * BOGY internships for high-school students

Master and Bachelor projects

Topics are available for BSc and MSc thesis projects (typically lasting about 3 months and 1 year respectively).

The students acquire hands-on research experience, working on ongoing research projects carried out by our group in collaboration with international research teams in the context of the ATLAS collaboration at CERN, where students can also present the outcome of their thesis project.

The students learn:

     - how to develop algorithms for the analysis of the LHC data (C++/python/shell scripting)

     - how to use machine learning techniques

     - how Monte-Carlo event generators are used in the simulation of hadronic collisions

     - how we search for new physics at the Large Hadron Collider

A good knowledge of particle physics (preferentially also with some knowledge about detectors) and at least one programming language (C++ preferred) is required.

Below is a list of detailed topics that we offer.To obtain more information about the open positions and available projects, contact Tetiana Moskalets and Spyros Argyropoulos.

A. Monte-Carlo event generators


    1. Modelling dark matter signals (Bachelor thesis - for a Master thesis this can be combined with topics C1-C3 below)

          The first step in the development of a search for new physics is the preparation of simulated samples of the signal process. The simulation of such signals is made with general purpose event generators like MadGraph_aMC@NLO. Simulated samples can then be analysed with simplified analysis tools like Rivet, and compared against background to identify selection criteria (cuts) that can be used to enhance the signal-to-background ratio.

          The simluation of such signals is not always straightforward, since care has to be taken to identify all possible Feynman diagrams (s- and t-channel, resonant and non-resonant diagrams etc) and include them in the simulation. A potential thesis could revolve around the following topics:

          - production of signals for dark matter produced in association with heavy Higgs bosons

          - production of signals with Type-I 2HDM models

          - improving the simulation of 4-top signals in dark matter searches

Competences acquired

- understanding how to search for new physics at the LHC

- usage of MadGraph_aMC@NLO and Pythia event generators

- usage of Rivet simplified analysis tool

- usage of C++, python, bash

B. Machine learning and improvement of ATLAS performance and existing analyses

              1. Improvement of b-jet identification techniques with Machine Learning algorithms (Master thesis - exceptionally for Bachelor thesis)


          The identification of jets originating from B-hadrons is of paramount importance for an array of measurements and searches carried out at the LHC, and in particular for the understanding of the properties of the Higgs boson, which decays predominantly to b-quarks. When the momentum of the B-hadrons is high, they are expected to decay far from the interaction point, reducing the ability to reconstruct the B-hadron track and thereby lowering the performance of the b-jet identification algorithms. Studies are under way to develop b-jet identification algorithms based on the recognition of the B-hadron hit pattern in the silicon tracker.

          The aim of the thesis will be to further improve these algorithms, in particular including more information of the hit properties and building more sophisticated machine learning architectures (GNN). Time permitting, the performance of the hit-based algorithms will be compared to the current b-jet identification algorithms.

          2. Improving the sensitivity of Higgs measurements or new physics searches with b-jet triggers (Master thesis - exceptionally for Bachelor thesis)

           Searches for models of new physics that can explain the generation of the matter-antimatter asymmetry and dark matter rely so far on the existence of a large amount of missing energy. Several models however, predict signals that have moderate missing energy, which consequently fail to be recorded, thereby limiting the sensitivity reach. Newly implemented triggers exploiting the presence of jets from b-quarks instead of missing energy, can be exploited to expand the sensitivity of new physics searches to such signals.

          The goal of the thesis will be to estimate the impact of the existing b-jet triggers on new physics searches or Higgs measurements, particularly the search for two heavy Higgs bosons in the A→ZH→vvbb final state or the Higgsstrahlung measurement, and identify the trigger(s) which maximise the signal acceptance. Time permitting the student will also design a new search region that can be implemented in future analyses and estimate the associated increase in the sensitivity. For a Master project, the topic will be extended in the direction of either providing a full background estimate for the low missing-energy region and/or a study of the impact of b-jet triggers on other similar analyses.

C. Development of searches for new physics in uncovered final states

          1. Search for Dark Matter in final states with heavy Higgs bosons (Bachelor or Master thesis)


          Several theory models suggest that Dark Matter (DM) might be intimately connected to the Higgs sector. Searches for DM have already been carried out in final states containing the Standard Model Higgs boson, however no such search has been performed so far in final states containing heavier Higgs bosons, that are predicted in theories beyond the Standard Model.

          The aim of the thesis will be to assess the potential of the LHC to discover DM produced in association with a heavy Higgs boson. The student will learn how to use Monte-Carlo event generators to simulate the signal process (consisting of a heavy Higgs decaying to a bottom quark pair and a pseudoscalar mediator decaying into two DM particles) and then exploit the existing search for heavy Higgs bosons (in the vvbb final state) to evaluate the DM discovery potential. Time permitting, the student can also work on the optimisation of the search strategy.

          2. Search for heavy Higgs bosons decaying to top quarks in the b-associated production channel (Bachelor or Master thesis)

          Searches for heavy Higgs bosons in the A→ZH final state are key to constraining electroweak baryogenesis models. Our group has pioneered the search for  A→ZH in the final state where the Z-boson decays to leptons and the H boson decays to top quarks. This has so far only been performed in the gluon-gluon fusion production mode. In Type-II 2-Higgs Doublet Models, the b-associated production is expected to provide enhanced sensitivity in the high tanβ region and open up a parameter space that has not been explored so far. This scenario would lead to a final state with 3 leptons, 4 b-jets and missing energy, which is challenging to model.

          The aim of the thesis would be to explore the feasibility of probing the b-associated A→ZH→lltt process. The student will start from generating the signal process (thus familiarising themselves with Monte-Carlo event generators) and will then peform truth-level studies to estimate the expected signal yield and the sensitivity of the process. Time permitting (/for a Master thesis), optimisation studies aiming at increasing the expected significance will also be performed.

          3. Search for heavy Higgs bosons with final states containing leptonically decaying top quarks for constraining Electroweak baryogenesis (Master thesis)

          Baryogenesis is one of the biggest open questions in particle physics and cosmology. Some extensions of the Standard Model of particle physics allow to explain the matter-antimatter asymmetry by introducing additional heavy Higgs bosons, whose existence can be probed at the LHC. Several searches for heavy Higgs bosons are ongoing in different Higgs boson decay channels, in particular when one of the Higgs bosons decays into a top-antitop pair.

          The aim of this thesis is to extend the latter search to the dileptonic decay channel of the top-antitop pair. The student will get acquainted with the data analysis framework, learn to optimise the selection cuts and caclulate the exclusion potential for different regions of the heavy Higgs boson masses. Time permitting the student can also get acquanted with the generation of signal events with Monte-Carlo event generators and/or the usage of likelihood fits.

HiWi (internships for Bachelor/Master students at Uni Freiburg)

For Bachelor and Master students we offer the possibility of short paid internships (HiWi). These offer the possibility for interested students to get hands-on experience with the research that we do and can also be done indepenedently of a Bachelor/Master thesis.

If you are interested contact Tetiana Moskalets and Spyros Argyropoulos to discuss the possibilities.

Internships for international students (EU)

Students enrolled in a university of an EU country can do short-term studentships at the University of Freiburg under the Freemover programme. The conditions for participation and details about the administrative procedure can be found at this webpage.

Students that are interested to perform a short (~2 month) internship with our group are advised to contact  Spyros Argyropoulos at least 2 months prior to the date that they wish to start to discuss about the possible topics and the procedures.

BOGY internships

The university of Freiburg offers the opportunity for a short internship for high-school students. Normally students spend a week at the university, interating with different research groups. Information on how to apply and contacts can be found here. If you are particularly interested in working with our group please contact Spyros Argyropoulos to discuss about the opportunities.

The topics that are discussed during a BOGY internship include:

   - Discussion on particle physics (what are the elementary

     particles and their interactions, how we detect them,

     radiation and cosmic rays and open questions)

   - Building a DIY cloud chamber which can be used to

     detect cosmic rays

   - Hands-on computing exercise on the discovery of the

     W or Z bosons based on the nternational masterclasses

     for particle physics (understand the function of the different

     detector parts, learn to identify particles based

     on ATLAS event displays)

   - Virtual workshop on PET scan and how we can detect

      tumours based on the principles of particle physics

      (CERN's S'cool lab)

   - Visit of the clean room where the part of the ATLAS detectors

      are built with potential hands-on exercise

   - Hands-on computing exercise on the calibration of the ATLAS

     calorimeter and the discovery of the Z boson (learn how we do

     actual data analyses in ATLAS using python)

Building a DIY cloud chamber