Experimental Particle Physics
Table of Contents
ATLAS
Muon Reconstruction with the ATLAS New Small Wheel at the LHC
Alain Bellerive
In 2022, the CERN Large Hadron Collider (LHC) beneath the France–Switzerland border near Geneva turned on after a major upgrade that double its delivered instantaneous luminosity. This is an important milestone that follows a very successful two periods of running that saw, among other things, the discovery of the Higgs boson. To cope with the anticipated LHC operating conditions, an extensive overhauling of the detector reconstruction algorithms for ATLAS is underway to reflect the introduction of a new subsystem called the New Small Wheel (NSW). These hardware and software enhancements will allow ATLAS to maintain its capability to perform cutting edge physics studies under the new experimental conditions during 2023/2024 and beyond. The Carleton University ATLAS group was a major contributor to the construction of the recently installed NSW upgrade to the ATLAS endcap muon spectrometer. The small-Strip Thin Gap Chambers (sTGCs) allow for a much better rejection of fake tracks at the trigger level, as well as improved reconstruction of muon candidates. Now that the sTGC has been deployed in the ATLAS experimental cavern and the first data from LHC Run3 has started to come in, the NSW needs to be optimized for data mining and validated for physics analyses.
Interested students will participate in the various aspects of the performance evaluation of the new muon tracking using Monte Carlo simulation and real collision data. The student will be developing advanced patter recognition algorithm for the reconstruction of tracks from hits in the NSW. This will enable the Carleton ATLAS team to be ready for the new 2024 LHC data. While the honours project will be during Fall2023-Winter2024, the student selected for this project will be giving the opportunity to be hired as a summer research assistant and be located at CERN during the May-August 2024 period. Students who work on this project will contribute to the development and validation of the muon reconstruction software. This will require learning the basics of particle physics, particle detector design and operation, and programming skills in ROOT, Python and C++.
Characterization of the electrical properties of silicon sensors for the ATLAS detector upgrade at the LHC
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 characterization and performance evaluation of the ITk detector sensors. This work will include the study of the state-of-the-art thin silicon sensors, as well as specially designed test structures that will be probed by dedicated equipment in order to understand their physics performance under carefully controlled environmental conditions. As a separate task, the evaluation of the performance of silicon test structures under high radiation conditions and the study of radiation-induced effects on semiconductor materials, will also be pursued. Both projects will require the development 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 and in basic database operations.
ATLAS statistical data analysis
Dag Gillberg
Project 1: Jet calibration using the 'forward folding' technique. The most common fundamental particles produced at the Large Hadron Colliders are quarks and gluons. However, as a high energetic quark or gluon emerges from the collision point, it will undergo so-called hadronization and produce a collimated spray of particles known as a jet. Jets are hence extremely common at the Large Hadron Collider and very important for most of the physics analyses. This project is about investigating the potential of using a new technique called ‘forward folding’ to measure the ATLAS detector's response to jets. The two key quantities to be extracted are the mean jet detector response and the associated resolution. The forward folding technique is based on convolution. The aim of the project would be to investigate the use of this technique with ALTAS Z+jets data and simulation, which is something that has not been done before.
Project 2: Visualization and statistical compatibility tests of unbinned data. Most analyses at ATLAS that measure distributions provide and analyse these as histograms. However, new machine learning-based techniques have started to produce unbinned measurements, provided as event-datasets. Presenting such measurements as histograms does not do them justice: it would be better to construct a smooth function based on the unbinned data, which is possible using Gaussian Kernels, and perhaps other similar techniques. This project would be to investigate easy to visualize unbinned measurements, and quantify the uncertainties. In part it would include a literature review - looking if this problem already has been encountered in other fields. The goal would be to find a good way to visualize unbinned data for particle physics applications, and if times permit, investigate how to compare two different spectra to see if they are compatible or not within uncertainty.
The EXO Experiment
Razvan Gornea
Noble liquid time projection chambers (TPC) are excellent detectors for rare event searches in neutrino physics. For example, the EXO-200 detector employs a 200 kg liquid xenon (LXe) with a TPC configuration which allows the collection of the electric charge produced by ionizing particles. When energy is deposited in a noble liquid, pairs of electron/hole are formed and can be collected by applying an external electric field. The amount of electrons collected is proportional to the initial energy of the ionizing particle.
During their drift in the TPC, electrons may encounter impurities with a large electron affinity and, therefore, part of the initial electric charge could be lost. When the noble liquid in a TPC is of low purity a large amount of charge is lost and then accurate event energy reconstruction becomes challenging. The average time for the electron to get captured is called the "electron lifetime". Experimentally, it often occurs that a LXe TPC can easily suffer from a short electron lifetime or, equivalently, a large concentration of impurities. On the other hand, the accurate measurement of a very long electron lifetime is challenging when using a compact device.
In this project, the student will design, optimize and build a compact purity monitoring device able to measure both short and long electron lifetimes using a custom pulsed VUV-LED-based electron source previously developed at Carleton. SIMION simulations will be employed to design and optimize a compact drift volume able to recycle the probing electron cloud. Hardware development, construction and testing will also be part of the project. Elements of front-end electronics, computer control and system programing using LabVIEW complete the program. A full year commitment is better suited for this project.