Higgs Boson-charm Quark Coupling Prospects

Student: Sky Merlin Goddard

Faculty Mentor: Alexandra Miller

Physics & Astronomy

College of Science, Technology, and Business

 In 2012, the Higgs boson’s discovery completed the Standard Model (SM). We continue to measure Higgs properties and interactions in various SM precision measurements. According to the SM, the interaction strength between the Higgs boson and fermions scales with fermion masses. Currently, the predicted coupling constants from the Yukawa sector of the SM have not been experimentally verified for lighter fermions, including the charm quark. This research builds upon a search for the production of a Higgs boson and a charm quark in proton-proton collision data from Run 2 of the LHC, with an integrated luminosity of 140 fb⁻¹ collected by the ATLAS experiment. The signal was an inclusive H + c and includes a process sensitive to the charm coupling constant (yc). In this work, the signal is redefined to target only the yc-sensitive process to obtain an expected upper limit on κc, the charm Yukawa coupling modifier, which relates the Yukawa coupling constant’s observed value to the theoretical value. A projection of the yc sensitivity to the High-Luminosity LHC (HL-LHC) is performed assuming an expected total dataset of 3000 fb⁻¹. The statistics-only 95% CLs upper limit on κc for the Run 2 dataset is presented, along with the expected 95% CLs upper limit on κc for the HL-LHC projection. This upper limit assesses the expected sensitivity to the charm Yukawa coupling constant that may be obtained with the full expected dataset of the HL-LHC.