Extracting Higgs boson couplings from CERN LHC data

Abstract

We show how LHC Higgs boson production and decay data can be used to extract gauge and fermion couplings of Higgs bosons. We show that very mild theoretical assumptions, which are valid in general multi-Higgs doublet models, are sufficient to allow the extraction of absolute values for the couplings rather than just ratios of the couplings. For Higgs masses below 200 GeV we find accuracies of 10 ÿ 40% for the Higgs boson couplings and total width after several years of LHC running. Slightly stronger assumptions on the Higgs gauge couplings even lead to a determination of couplings to fermions at the level of 10 ÿ 20%. We also study the sensitivity to deviations from SM predictions in several supersymmetric benchmark scenarios as a subset of the analysis.

Two-loop electroweak corrections to the Higgs-boson decay

“…In the F 2l W part, the diagrams corresponding to Fig. 3 exhibit a first cut through lines (1,2), (4,5) and (1,3,5) (or (2,3,4)) at q 2 = 4m 2 W because the only massless particle in the purely bosonic contribution is the photon (we work in the Feynman gauge) that in this specific example can only appear in position 3 (see Fig. 2(a) ).…”

“…At hadron colliders, the decay into two photons provides a very clean signature for the discovery in the gluon-gluon fusion production [3], for the measurements of the couplings in the vector-boson fusion channel [4] and, depending on the achievable integrated luminosity, also in the W H, ZH, and ttH associated productions. While none of the above measurements alone can provide information on the partial width (what is measured is σ(pp → H)· Br(H → γγ)), their combination with signals in other decay modes, will allow a determination of the total width of the Higgs and of the couplings with a precision of 10-40% [5]. A much better determination of the Higgs width into two photons could be achieved at a e + e − linear collider, via the fusion process γγ → H, with the photons generated by Compton-back scattering of laser light [6,7].…”

Two-Higgs models for large tan β and heavy second Higgs

“…For example, from Eq. (8), we can deduce the tree-level change in Yukawa in a supersymmetric theory, which is g 2 +g 2 2 v 2 m 2 H , which is about 0.3 for Higgs mass comparable to v. The LHC will measure couplings, even for the tau, to an accuracy of at most about 15 % [10,11,14]. This means that a 2 sigma measurement might just probe this deviation from the Standard Model.…”

“…In this case, the tau rate would increase or decrease when the photon rate does, unlike Type II models where they would change in opposite directions. The ratio of photon and tau partial branching fractions is likely to be measured at the 15-30 % level [6,14] and absolute branching fractions might also be measured at reasonable levels [14]. Of course especially for the photon loop effects from nonstandard model physics might also be significant.…”

The road towards the international linear collider: Higgs, top/quantum chromodynamics, loops

“…If a (SM-like) Higgs mechanism is realized in nature, the LHC will find a Higgs boson and measure it characteristics [12][13][14][15]. To be certain the state observed is indeed the Higgs boson, it is necessary to measure the couplings of this state to the W and Z gauge bosons, and to fermions such as the top and bottom quarks and the tau leptons.…”