Rare Higgs decays and couplings to quarks
PT-CERN Call 2021/2
Sandro Fonseca de Souza
Instituto Superior Técnico (Universidade de Lisboa)
Laboratório de Instrumentação e Física Experimental de Partículas
The very high level of background (light quarks are produced abundantly at the LHC, via QCD) renders the signals of direct Higgs decays to light quarks (H->qq) too tiny to be detectable with current data. But there's a catch (!): the quark-antiquark pairs originating from the Higgs decay may bind together (thus forming a meson state). Experimentally, this gives rise to a striking, clean signature: an energetic photon back-to-back to a dilepton resonance, H->Q+gamma. The thesis project consists in the exploration of such rare Higgs decays. The thesis project involves the following tasks: (i) employ the dataset collected by CMS during LHC Run2, to estimate the sensitivity of a baseline analysis, in the Jpsi plus photon channel, which would probe the couplings to the charm quark; (ii) work on the preparation of real-time selection algorithms (trigger), for gaining sensitivity to novel channels, to be deployed for the upcoming LHC Run3, including the phi+photon channel probing the Higgs couplings to the strange quark; (iii) develop machine learning techniques for optimised selection. These are rare processes in the SM that benefit greatly from the HL-LHC phase, and offer sensitivity to the presence of new physics beyond the SM. The research will be carried in the frame of the activities of one of the outstanding research groups in High-Energy Physics in Portugal. Citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”. The thesis project is developed within a close collaboration between LIP/Lisbon and UERJ/Rio groups in CMS.