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Register a new userImproving Higgs coupling measurements through ZZ Fusion at the ILC
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We evaluate the $e^- e^+ to e^- e^+ +h$ process through the $ZZ$ fusion channel at the International Linear Collider (ILC) operating at $500$ GeV and $1$ TeV center of mass energies. We perform realistic simulations on the signal process and background processes. With judicious kinematic cuts, we find that the inclusive cross section can be measured to $2.9%$ after combining the $500$ GeV at $500 text{fb}^{-1}$ and $1$ TeV at $1~ text{ab}^{-1}$ runs. A multivariate log-likelihood analysis further improves the precision of the cross section measurement to $2.3%$. We discuss the overall improvement to model-independent Higgs width and coupling determinations and demonstrate the use of different channels in distinguishing new physics effects in Higgs physics. Our study demonstrates the importance of the $ZZ$ fusion channel to Higgs precision physics, which has often been neglected in the literature.
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Measurement of the cross-section of ee->ZHH offers the information of the trilinear Higgs self-coupling, which is important to confirm the mechanism of the electro-weak symmetry breaking. Since there is huge background in the signal region, background rejection is key point to identify ZHH events. In this paper, we study the possibility to observe the $ZHH$ events at ILC by using ZHH->vvHH/qqHH events.
Now that the Higgs particle has been observed by the ATLAS and CMS experiments at the LHC, the next endeavour would be to probe its fundamental properties and to measure its couplings to fermions and gauge bosons with the highest possible accuracy. However, the measurements will be limited by significant theoretical uncertainties that affect the production cross section in the main production channels as well as by experimental systematical errors. Following earlier work, we propose in this paper to consider ratios of Higgs production cross sections times decay branching ratios in which most of the theoretical uncertainties and some systematical errors, such as the ones due to the luminosity measurement and the Higgs decay branching fractions, cancel out. The couplings of the Higgs particle could be then probed in a way that will be mostly limited by the statistical accuracy achievable at the LHC and accuracies at the percent level are foreseen for some of the ratios at the end of the LHC run. At the theoretical level, these ratios are also interesting as they do not involve the ambiguities that affect the Higgs total decay width in new physics scenarios. To illustrate how these ratios can be used to determine the Higgs couplings, we perform a rough analysis of the recent ATLAS and CMS data which shows that there is presently no significant deviation from the Standard Model expectation.
The anomalous $WWgamma$ coupling is probed through $egammarightarrow u W$ at the ILC. With a spectacular single lepton final state, this process is well suited to study the above coupling. Cross section measurements can probe $delta kappa_gamma$ to about $pm 0.004$ for a luminosity of 100 fb$^{-1}$ at $500$ GeV center-of-mass energy with unpolarized electron beam. The limits derivable on $lambda_gamma$ from the total cross section are comparatively more relaxed. Exploiting the energy-angle double distribution of the secondary muons, kinematic regions sensitive to these couplings are identified. The derivable limit on $lambda_gamma < 0$ could be improved to a few per-mil, focusing on such regions. More importantly, the angular distributions at fixed energy values, and energy distribution at fixed angles present very interesting possibility of distinguishing the case of $lambda_gamma <0$ and $lambda_gamma ge 0$.
Deviations from the standard Higgs sector generated by some new physics at an energy scale $Lambda$ could be described by an effective $SU(3)_c times SU(2)_L times U(1)$ invariant non-renormalizable Lagrangian terms of dimension six. A systematic study of various Higgs boson production channels ($gamma gamma$, $ZZ$, $WW$, $b bar b$, $tau bar tau$) at the International Linear Collider (ILC) in the SM extension by effective operators is carried out. Statistical methods are used to establish a degree of consistency for the standard Higgs sector with the forthcoming data, using the expected ILC accuracies of the Higgs boson production channels. Global fits in the two-parametric anomalous coupling space indicating to possible deviations from the standard Higgs-fermion and Higgs-gauge boson couplings are performed.
An important physics goal of a possible next-generation high-energy hadron collider will be precision characterisation of the Higgs sector and electroweak symmetry breaking. A crucial part of understanding the nature of electroweak symmetry breaking is measuring the Higgs self-interactions. We study dihiggs production in proton-proton collisions at 100 TeV centre of mass energy in order to estimate the sensitivity such a machine would have to variations in the trilinear Higgs coupling around the Standard Model expectation. We focus on the two b-jets plus diphotons final state, including possible enhancements in sensitivity by exploiting dihiggs recoils against a hard jet. We find that it should be possible to measure the trilinear self-coupling with 40% accuracy given 3/ab and 12% with 30/ab of data.
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