PLUSPHOTON · Turn the extra light on: enhancing the discovery potential of Higgs production in association with a photon

The observation of the Higgs boson in 2012 marked a significant milestone in particle physics. Following its discovery, the Large Hadron Collider experiments have focused on an extensive characterisation of this scalar particle. However, key questions remain, such as the origin of the electroweak scale and phase transition in the early Universe. This project seeks to address a crucial gap in our understanding of the Higgs boson: a comprehensive study of the Higgs boson production in association with a photon, focusing on the diphoton decay channel, could potentially point to new physics beyond the Standard Model. This process has not yet been observed due to its low cross-section and the relative softness of the extra photon.For this work, four main research objectives are considered. The first is to develop a novel experimental photon isolation technique, soft-drop isolation, with the aim of improving photon isolation at low-transverse momentum. The second one is to produce a complete characterisation of the background from the strong interaction with differential cross-section measurements that can assess the modelling of state-of-the-art Monte Carlo event generators. The third one is to search for Higgs plus photon production in the diphoton decay channel, establishing a framework in which the rich phenomenology of this process can also be studied in other decays. The final one is to evaluate the results in terms of the Standard Model Effective Field Theory and shed light on the origin of potential new physics effects if any deviations from the current theory are found. The project will unlock deeper insights into the Higgs boson´s interactions with fundamental particles, sharpening our grasp of the electroweak symmetry breaking mechanism. It will lay the groundwork for searches in alternative Higgs decay channels and introduce a novel photon isolation technique that will transform the landscape of photon measurements.