Searches for long-lived axion-like particles at the ATLAS experiment 

Supervisors: Monica D’Onofrio (UoL), Nikos Rompotis (UoL) 
Institution: University of Liverpool

The Large Hadron Collider (LHC) at CERN (Geneva) is the highest energy proton-proton collider ever built and produces as well heavy ions collisions. The ATLAS and CMS experiments at the LHC discovered the Higgs boson in 2012 and produced a plethora of precision measurements of the Standard Model (SM) parameters and hundreds of searches for new physics. Large datasets have been collected at different centre-of-mass energies since LHC start of operation, and data-taking is continuing in the Run 3 of the LHC until mid-2026. The dataset collected by then will have reached almost 300 fb-1, and will provide excellent opportunities for discovery.  

Theories predicting new, hidden (dark) sectors weakly connected with the SM have gained considerable interest within the community.  Axion-like particles (ALPs, a) are among the most credited particles that could arise in dark sectors. At ATLAS, ALPs could be produced as the decay product of the Higgs boson. They decay in a pair of photons, or an electron-positron pair if sufficiently massive, either promptly or displaced (long-lived), i.e. their decay being slow enough to be displaced from the primary vertex of the proton-proton interactions. 

In this project, you will work on the search for long-lived ALPs decaying into displaced photons or electron-positron pairs within the ATLAS calorimeter volume. The main challenge for these signatures lies in the reconstruction of displaced electromagnetic objects, since standard ATLAS reconstruction procedures are highly inefficient. You will work with a team of local and international experts to develop neural network procedures to distinguish background processes from signal and you will carry out the analysis within the international collaboration using the full ATLAS dataset. As such, you will have the possibility of either discover ALPs, or constrain significantly new physics models, learning cutting-edge technologies for data analysis.    

Throughout the project you will have targeted training in data science provided by the University of Liverpool with the Centre for Doctoral Training LIV.INNO. You will also be given the opportunity to carry out an industry placement of six months to broaden your wider research and career skills. 

This project will be carried out over 48 months based at the University of Liverpool but you have the opportunity to spend up to year in CERN. Whilst in the UK, a standard RKUK PhD stipend will be paid, during the time at CERN. A mandatory 6-months industry placement forms part of the project. 

https://www.liverpool.ac.uk/study/postgraduate-research/how-to-apply/

The delivery of this project is subject to funding approval. Information on how to apply will follow shortly.