Light at the LHC
The Light@LHC project is funded by the ERC within a Consolidator Grant and aims to search for axion-like particles with long live-times at the ATLAS Experiment. The underlying theoretical models could explain the discrepancy between the observed and measured discrepancy of the muonic (g-2) value and predict challenging signatures at the LHC, in particular anomalous decays of the Higgs boson into two axions. Within this project, we combined on innovative searches for displaced photon signatures in proton-proton collisions, searches for axions in ultra peripheral heavy ion collisions and searches at the FASER Experiment. We have developed new methods to estimate systematic uncertainties for displaced photon signatures, innovative reconstruction algorithms for collinear photons as well as contributed to the setup of the FASER experiment and its upgrade. The project was established at the Johannes Gutenberg University of Mainz in 2019 and will end in 2024. More than six full time researchers have been contributing to the success of the Light@LHC project.
Detector Developments
Within Light@LHC we designed and constructed a pre-shower detector system for FASER, that allows in principle an identification of single and collinear photon signatures based on Micromegas Technology. An alternative approach is based on silicon detectors, which are developed and constructed by the University of Geneva with whom we are cooperating also on this methodology.
Search for Axions in Light-by-Light Scattering
Highly relativistic ions are surrounded by a large electromagnetic field that can be interpreted as a flux of high photons. When two heavy ions do not collide but rather pass by very closely to each other, those surrounding photons can interaction. The Standard Model process here is light-by-light scattering, originally predicted by Heisenberg and Euler. However, those photons could in principle also form an axion-like-particle which decays afterwards again into two photons. We have been looking for such signatures with the ATLAS Experiment
Search for anomalous H->aa decays
While the mass of axion like particles has not to be generated by the Higgs mechanism, it is plausible that the Higgs couples also to ALPs. Given the potentially weak coupling constants to ALPs to photons, the expected experimental signature of Higgs decays into two axions and further into four photons are up to four displaced or collinear photon signatures. We performed the first search for such signatures yielding the most stringent limits on ALPs in the mass between 100 MeV to 62 GeV.
Identification of merged photons signatures using neural networks
Low mass axions tend to decay into two collinear photons, which can hardly be distinguished from single photon signatures. Moreover, neutral pion decays yield similar signatures, so that the standard reconstruction algorithms are not optimized for collinear photon signatures. Within Light@LHC we developed specific neural network based classifiers based on convolutional networks that allow for a highly efficient signal selection.
Systematic uncertainties on displaced photons
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