Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Department of Physics

Experimental High Energy Physics (HEP)

The Experimental High Energy Physics Group at Humboldt University of Berlin is led by Cigdem Issever. The group focusses on

  • Searches and measurements with the ATLAS experiment at CERN, Geneva,
  • Development of advanced methods for particle identification with neural network algorithms and quantum computing,
  • R&D on digital calorimeters.


The group is part of the international ATLAS collaboration at the Large Hadron Collider (LHC) at CERN.

The primary purpose of the experiments at the Large Hadron Collider at CERN is the discovery of physics beyond our current understanding of nature and the measurements of the properties of the Standard Model particles, including the newly discovered Higgs boson.

One of the most prominent signatures at the LHC to do these studies are final states with hadrons which produce complex particle showers initiated by them and by interactions with the detector material. These particle showers are reconstructed in the detectors as so called “jets”.




Origin of Mass - Higgs Pair Production at the LHC

The group will be working on searches for new physics in di-Higgs final states where at least one of the Higgs bosons decays into a b-quark pair.  It will actively work on the calibration and performance studies of jets and b-quark jets in the ATLAS detector. We will work on developing b-quark triggers with very low trigger thresholds and exploit novel algorithms to reconstruct final state particles and perform large scale data analysis. In this context we are also exploring the possibility to use quantum computing algorithms for the reconstruction and identification of Higgs bosons that decay into b-quark pairs.

In addition to searching for new physics beyond the Standard Model, the groups' long term goal is to measure the Higgs self-coupling at the LHC using di-Higgs final states. The Higgs self-coupling is an important parameter and its value influences the shape of the Higgs potential that is important for the mass generation in nature. This research area of the EHEP group is supported by an ERC grant from the Horizon 2020 program.

LHC Forward Cross Section Measurements and Cosmic air shower physics


Strong interactions in a regime of low momentum transfer (so-called soft interactions) cannot be treated perturbatively, which makes the modelling of such processes strongly dependent on experimental input from hadron colliders. In hadron-hadron collisions, e.g. at the LHC, such soft hadronic interactions manifest themselves by the creation of particles in the very forward regions (which means at large rapidities).

These can be measured either by calorimeters in the ultra-forward region of ATLAS, ZDC, or the LHCf detector which can detect neutral particles or by tracking devices located close to the beam like ATLAS AFP and ALFA detectors, which are used for the detection of scattered protons. The measured particle spectra and cross sections will help to tune the currently available phenomenological models for soft hadronic interactions. The improved accuracy of such models would benefit the simulation of air showers induced by cosmic particles as well as the understanding of strong interaction background in proton-proton collisions at the LHC (so-called pile-up). Part of the group is working on the preparations of such measurements with the aforementioned detectors for Run 3 at the LHC for proton-proton collisions as well as for the foreseen proton-Oxygen collisions. Furthermore, we are cooperating with the DESY Zeuthen gamma ray group to exploit synergies in that topic.


Digital Calorimeter R&D


We are also working in collaboration with DESY on the development of digital calorimeters. We have two test stands where we are measuring the charecteristics of sensors.


Thesis Topics


In all the areas above we can offer Master and Bachelor thesis topics. Please get in touch with Prof. Issever. We have for example: 


Master Thesis Topics

  • Phenomenology studies for diHiggs to 4b sensitivity studies

    In the context of the ERC HiggsSelfCoupling project we have this phenomenology study that aims to improve the sensitivity of our searches for diHiggs to 4b events and also the measurement of the Higgs self-coupling paramemters. In this study you would work with neural network algorithms and simulated collision events.

  • Development of novel flavour tagging techniques using neural network algorithms

    This project would involve working with Prof. Todd Huffman at Oxford University and Dr. Spyros Argyropoulos at Freiburg University on novel flavour tagging techniques by modifying or developing an existing Neural network that is used to “tag” high energy Jets generated at the Large Hadron Collider in the ATLAS experiment at CERN.

    Starting from a framework that contains the information of hit multiplicities in jets, the student would study the impact of additional hit variables (e.g. the probability of the hit to originate from more than one charged particles) on the performance of the ATLAS Deep Learning algorithms for b-tagging. The existing framework needs to be retrained with more simulations, but in addition we would like the student to study expanding these “hit-based” additions to the Neural Network to include clusters that appear in new regions of the detector that have not been previously considered. Specifically the outer SCT strip tracker and also the pixel disk detectors. We would also like to explore the possibility of using a Graphical Neural Network where the pixel position, but also the energy and angle of the highest energy track in the jet provide a kind of “picture” that GNN systems seem particularly suited to recognizing patterns. This last depends upon whether the appropriate framework can be established and how quickly the first parts of the project progress. Since this project will be in collaboration with colleagues in the UK the student should be fluent in English. Experience in programming is also desireable.  

Bachelor Thesis Topics

  • Preparatory studies on proton-Oxygen collisions at the LHC

    One of the most important sources of uncertainties in studying cosmic rays with Cherenkov telescopes is the modelling of hadronic interactions of an incoming cosmic particle and an atomic nucleus in Earth's atmosphere. In the upcoming Run 3 of the LHC a unique opportunity presents itself to explore exactly those interactions under laboratory conditions by studying collisions of protons and Oxygen nuclei with the help of the ATLAS detector and other detectors in the forward region of ATLAS. The goal of this Bachelor project will be to study adequate observables with which individual hadronic processes can be separated and also isolated from background processes. This should enable us to measure the cross sections of those processes and the energy spectra of the created particles, as soon as the p-O collision data will have been taken at the end of run 3. Moreover, the detectors' positions in the forward region and the beam optics of the LHC should be optimized for such a measurement.


Prof. Dr. Cigdem Issever