Experimental Particle Physics
Alain Bellerive
Research at the Energy Frontier with the ATLAS Detector
Title: Implementing likelihood-based statistical tests for ATLAS at the LHC
In particle physics experiments one often searches for processes that have been predicted but not yet seen, such as production of a Higgs boson. The statistical significance of an observed signal can be quantified by means of a p-value or its equivalent Gaussian significance. It is useful to characterize the sensitivity of an experiment by reporting the expected (e.g., mean or median) significance that one would obtain for a variety of signal hypotheses. Likelihood-based statistical tests are widely used in ATLAS analyses and are extremely important in testing whether data agrees with a given hypothesis. After obtaining a dataset, there are two (of many) important tests to perform. Calculating the p-value for the null hypothesis, p_0, is one way to test how compatible a dataset is with the background-only hypothesis. If the data is found to be compatible, as found in this experiment (using a generated dataset), then an upper limit can be set on the amount of signal that is present. This is done using the test statistic p_µ and finding the 95% confidence level upper limit on the signal strength, µ. The proposed research is dedicated to implement statistical inference code for testing hypotheses. Finding both the significance for a specific data set and the expected significance will involve Monte Carlo simulations and calculations. The project is particularly interested to test if data agrees with the Standard Model of particle physics or with new physics beyond the Standard Model. The second half of the project will cover some of the basic discrimination techniques used in machine learning to improve the separation between signal and background events, or to improve separation between two types of models, from the Run2 and Run3 ATLAS datasets.
For more information on the ATLAS project at Carleton University, please consult http://physics.carleton.ca/atlas/
Thomas Koffas
In 2025-2028, the Large Hadron Collider and the ATLAS detector will undergo major upgrades to prepare for the High Luminosity LHC (HL-LHC) that will start in about 2029. The HL-LHC will operate at a significantly higher intensity: the instantaneous luminosity of the proton beams will be seven times that of the design criteria. This significantly enhances the overall physics potential, but also makes the experimental conditions harsher and more challenging. The entire inner tracking detector of ATLAS will need to be replaced with a new silicon Inner Tracker detector (ITk) to cope with this situation.
The particle physics group at Carleton University is actively working on this detector upgrade, and is looking for interested students to work on the modelling of the strip sensor including active trap defects measured with the Deep Level Transient Spectroscopy (DLTS) method. This work will include measurement and subsequent analysis of the defect characteristics using specially designed test structures under controlled environmental conditions. The measured defects will then need to be implemented in dedicated TCAD models that model the sensor performance. Finally, the models will have to be appropriately tuned in order to reproduce the lab measurements. As a separate task, the student will work on the electrical evaluation of silicon test structures (IV,CV scans) and collect data that will then inform the TCAD simulations. Both projects will require the operation and potential adaptation of the required experimental setups, including LabView-based readout and control software, as well as C++-based analysis of the measurement data. In both projects, students will acquire extensive experience in working in clean rooms under environmentally controlled conditions, in handling state-of-the-art experimental equipment, in performing extensive data analysis using ROOT and other software packages.
Simon Viel / Mark Boulay
DEAP-3600 is a liquid argon detector located underground at SNOLAB, searching for dark matter and other signals such as solar neutrinos. Physics data collection with liquid argon restarted in 2025, in the upgraded detector configuration. Analysis projects are available using these new data, in addition to the earlier 2016-2020 dataset.
Simon Viel / Razvan Gornea
The EXO-100 cryostat located in Herzberg Laboratories at Carleton is used for research and development in support of the nEXO experiment that is proposed to search for neutrinoless double beta decay in liquid xenon. Our current objective is to test ultraviolet-sensitive silicon photomultiplier tiles in liquid xenon. Depending on the time at which they join this project, students will have the opportunity to participate in simulations, detector construction and operation, data collection and analysis.