During the Light@LHC project, the primary goal was to search for axion-like particles (ALPs) within a mass range of 10 MeV to 1 TeV, particularly focusing on extremely low axion-photon couplings. The research aimed to probe parameter spaces relevant to models addressing the discrepancy between theoretical and experimental values of the muonic (g-2). Over the course of the project, three distinct phases were completed, each contributing significantly to the scientific objectives.
In Phase 1, the team developed advanced trigger and photon reconstruction algorithms using modern machine learning techniques. These innovations enabled, for the first time, the identification of merged photon signatures and established a method to handle photons reconstructed with significant displacement from the original collision point in the detector. Additionally, the Light@LHC team in Mainz played a crucial role in constructing the FASER experiment, including designing and building a novel pre-shower detector scheme. The attached image shows members of the ERC Light@LHC Team during the installation of the FASER experiment during the Covid-19 pandemic.
Phase 2 focused on searching for ALPs at the ATLAS experiment through ultraperipheral proton-proton and lead-lead collisions. The results from this phase, published in peer-reviewed journals, set the most stringent limits to date, excluding the relevant parameter space between 5 GeV and 1 TeV. A significant component of this phase involved analyzing anomalous Higgs boson decays, where decays into two ALPs led to final states with four photons. By leveraging the tools developed in Phase 1, the team achieved world-leading limits on ALP masses between 1 and 60 GeV and uniquely probed extended ALP lifetimes down to 10E-7 1/TeV. Complementing the ATLAS analyses, the team examined FASER data, establishing additional unprecedented constraints on ALP interactions. The cumulative results were widely disseminated through publications, presentations, and media coverage, maximizing the project's impact on the scientific community and beyond.The results are illustrated on the attached images from the ATLAS and FASER collaborations.
In summary, the Light@LHC project successfully achieved all objectives, providing the most precise limits on ALP interactions within the explored parameter space. While no direct evidence for ALPs was found, the project advanced the field by developing innovative technologies and methodologies that will support future particle physics experiments. Additionally, the project fostered scientific growth and career development for team members, highlighting the far-reaching benefits of ERC funding in enabling high-impact research.
