A study of measurement precision of the Higgs boson branching ratios at the International Linear Collider

Precise measurement of the Higgs boson couplings is an important task for International Linear Collider (ILC) experiments and will clarify the understanding of the particle mass generation mechanism. In particular, high precision measurement of Higgs branching ratios plays a key role in the search for the origin of the Yukawa and Higgs interactions. In this study, the measurement accuracies of Higgs boson branching ratios to b and c quarks and gluons were evaluated using a full detector simulation based on the International Large Detector, and assuming a Higgs mass of 120 GeV/c(2). We analyze two center-of-mass (CM) energies, 250 and 350 GeV, close to the e(+)e(-) -> ZH and e(+)e(-) -> t (t) over bar production thresholds. At both energies, an integrated luminosity of 250 fb(-1) and an electron (positron) beam polarization of -80 % (+30 %) were assumed. We obtain the following measurement accuracies for the product of the Higgs production cross section and the branching ratio of the Higgs into b (b) over bar, c (c) over bar, and gg: 1.0 %, 6.9 %, and 8.5 % at a CM energy of 250 GeV and 1.0 %, 6.2 %, and 7.3 % at 350 GeV. (After writing our article, Large Hadron Collider experiments reported the observation of a new resonance around the mass of 125 GeV/c(2) (ATLAS Collaboration, arXiv: 1207.7214v1 [hep-ex]; CMS Collaboration, arXiv: 1207.7235v1 [hep-ex]). Considering the small difference in branching ratios of the Higgs at masses of 120 and 125 GeV/c(2), our results are not significantly affected by this mass difference.)