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Search for Dark Matter with the ATLAS Detector and Development of a Novel Track Reconstruction Algorithm based on Graph Neural Networks for the ATLAS Inner Tracker
Date: Friday, July 25th
Time: 10:00 am - 12:00 pm
Place:
Speaker: Tuan Minh Pham, Physics PhD Graduate Student
Abstract: This thesis is divided into two main parts. The first part presents a summary of dark matter searches performed by the ATLAS experiment and a statistical combination of the three most sensitive analyses. The results are interpreted within the framework of a Two-Higgs-Doublet Model extended by a pseudoscalar mediator (2HDM+a). These analyses are based on 139 fb-1 of proton-proton collision data collected at a center-of-mass energy of 13 TeV during Run 2 of the LHC. The combined analyses target final states involving large missing transverse energy and a visible signature from the decay of a Standard Model Higgs boson or Z boson, as well as processes involving the production of charged Higgs bosons. This work provides the most comprehensive set of constraints on the 2HDM+a model published by ATLAS to date.

The second part focuses on the reconstruction of charged-particle tracks in the ATLAS Inner Tracker (ITk), which is confronted with the extreme pile-up conditions expected in the High-Luminosity phase of the Large Hadron Collider (HL-LHC). Given the anticipated increase in instantaneous luminosity and associated event complexity—resulting in up to 200 simultaneous interactions per bunch crossing—traditional reconstruction algorithms face significant computational challenges. To address this, a novel track reconstruction algorithm based on Graph Neural Networks (GNNs) has been developed and evaluated. Using full detector simulation data on realistic ITk geometry, we demonstrate competitive physics performance of the GNN-based tracking approach with respect to the current tracking algorithm. The computational efficiency is optimized and measured in detail. This approach shows significant potential for efficient pattern recognition in dense detector environments, leveraging modern hardware accelerators such as GPUs and FPGAs for fast and scalable event reconstruction.
Host: Sau Lan Wu
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