LHC research program

Nodes involved: UoA, UoM

Chief Investigators: E. Barberio, P. Jackson, G. Taylor, P. Urquijo, M. White

Postdocs: H. Potti, J. Webb

RHD students: M. Amerl, I. Carr, M. Fewell, E. Filmer, J. Gallagher, C. Grant, M. Green, A. Kong, J. Kull, H. Pandya, J. Pham, T. Ruggeri, E. Ting, S. Williams

Partner Investigator: K. Jakobs

Collider Searches for dark matter: Large Hadron Collider - ATLAS experiment

The Centre for dark matter Particle Physics provides an opportunity to search for dark matter direct production at a unique facility in the world, namely the experimental environment provided by the world’s highest energy particle collider - Large Hadron Collider at CERN in Geneva, Switzerland. At this laboratory members of the Centre work on the ATLAS experiment, one of two multi-purpose detectors well equipped to search for evidence of dark matter production in proton-proton collisions. Throughout 2022, the ATLAS experiment was recording data at a new world-record collision energy of 13.6 Tera Electron Volts (TeV). Centre researchers focus their attention on several aspects of the search for dark matter with ATLAS, understanding the reconstruction and calibration of hadronic jets of particles and missing transverse momentum (MET). The aim is to find direct evidence of Standard Model particles produced in conjunction with a signature of MET, which it is postulated would be carried away by the dark matter candidate(s).

Centre researchers have led analyses searching for evidence of hadronic jets that have been tagged as originating from charmquarks. This signature has resulted in increased sensitivity to models of Supersymmetry or other beyond Standard Model theories that propose pair production of new particles that subsequently decay to massive particles that interact weakly with our detectors and leave a significant signal by their absence. This analysis work is close to completion with results to be published in 2023.

In models where the Higgs boson decays to dark matter, we infer its presence by studying signals of invisible decays of the Higgs boson. Centre researchers have combined various production and decay mechanisms to increase the sensitivity to invisible decays of the Higgs boson.

DM searches with ATLAS data are underpinned by performance work and require a thorough understanding the objects that manifest in the detector environments. Centre researchers are working to strengthen our understanding of hadronic jets by deploying advanced machine learning techniques and algorithms based on particle flow to extract greater precision. Efforts on calibration and tagging of jets is also prominent.

Beyond performance and physics analysis the next big transition in fundamental physics will come with the upgrade to the HighLuminosity LHC era (2026 and beyond) this will require a near complete refurbishment of the ATLAS detector. Centre researchers are focused on the construction, testing and deployment of modules for the inner tracker upgrade (ITK). Having passed review milestones at each site, module production will occur in Melbourne with modules then sent to Adelaide to perform a thermal cycling and rigorous testing procedure prior to them being shipped to CERN for assembly and ultimately deployment into the experiment.

Dark matter searches in the context of pair produced objects and using initial-state-radiation signatures have benefitted from the application of Recursive Jigsaw Reconstruction which Centre researchers pioneered. Within the Centre we continue to lead all aspects of deploying this method within the ATLAS experiment.

In models where the Higgs boson decays to dark matter, we would be sensitive to inferring its presence by studying invisible decays of the Higgs boson. Combining various production and decay mechanisms increases the sensitivity to this and within the Centre we are heavily involved in these combinations to extract the greatest sensitivity to invisible decays of the Higgs boson.

All these searches, and others like them, are undergirded by performance work in understanding the objects that manifest in the detector environments. Most prominently for dark matter searches this involves hadronic jets and missing momentum. Centre researchers are working to strengthen our understanding of hadronic jets by deploying advanced machine learning techniques and algorithms based on particle flow to extract greater precision.

Beyond performance and physics analysis, the long-term health and productivity of the detector is important. In the upcoming High-Luminosity LHC era this will require new subdetectors as ATLAS is completely revamped. Centre researchers are focused on the construction, testing and deployment of modules for the inner tracker upgrade, known as ITK. In the Centre we leverage the symbiotic relationship between the Adelaide and Melbourne groups to drive this work forward. We anticipate first modules to be produced in Melbourne in the coming year and then sent to Adelaide for testing and quality assurance steps.