Charm quarks and Higgs bosons: Probing their interaction using ATLAS measurements of Higgs boson production rates

Sammanfattning

Since its discovery in 2012, the properties of the Higgs boson (H) and its interactions have been studied in great detail. The Standard Model (SM) predicts particles with mass to interact with the Higgs boson, with heavier particles expected to interact more strongly. The coupling of the heaviest SM particles – the vector bosons and the three heaviest matter particles (top quark, bottom quark and τ-lepton) – have been observed to agree with prediction. The ATLAS and CMS experiments at the Large Hadron Collider (LHC) have attempted to measure the interaction between the Higgs boson and the charm quarks (c), which is the third heaviest quark. To directly probe this interaction requires measuring the H → cc̄ process, which is experimentally challenging. The ATLAS experiment sets an upper limit on the interaction strength at 4.2 times the SM prediction at 95% confidence level. The CMS experiment reports similar results. Measurements of the differential Higgs boson production cross-section in the H → γγ channel are used to probe the interaction between the Higgs boson and charm quarks indirectly by considering its impact on the Higgs boson production rates. With this complementary approach, the study sets an indirect 95% confidence level limit on the interaction strength to a range between -2.2 and 2.1 times the SM prediction following a similar analysis done by the ATLAS experiment. This result is largely model-dependent but can be further generalised. Additionally, with the future High-Luminosity-LHC upgrade, the amount of data is expected to grow by a factor of about 20 compared to the ATLAS dataset recorded between 2015 and 2018 used in this study. The impact of the larger dataset is explored using simulated pseudodatasets to compare expected results with current uncertainties to expected results with uncertainties scaled down by a factor of √10. This yields upper limit on the interaction strength that is reduced by 30% to 50% and the comparison gives an indication that future amounts of data would provide narrower confidence intervals and by extension, stronger indirect constraints on the interaction between charm quarks and Higgs bosons.