Abstract
We studied the possibility of constraining production of new scalar particles at CLIC running at 380 GeV and 1.5 TeV, assuming the associated production of Higgs-like neutral scalar with mathrm{Z}{}{} boson and its invisible decays. The analysis is based on the Whizard event generation and fast simulation of the CLIC detector response with Delphes. We considered {mathrm{e}{}{}}^{+} {mathrm{e}{}{}}^{-} background processes but also relevant upgamma {}{} upgamma {}{} and upgamma {}{} mathrm{e}{}{} ^{pm } interactions. The approach consisting of a two-step analysis was used to optimise separation between signal and background processes. First, a set of preselection cuts was applied; then, multivariate analysis methods were employed to optimise the significance of observations. We first estimated the expected limits on the invisible decays of the 125 GeV Higgs boson, which were then extended to the cross section limits for production of an additional neutral scalar, assuming its invisible decays, as a function of its mass. Extracted model-independent branching ratio and cross section limits were then interpreted in the framework of the Higgs-portal models to set limits on the mixing angle between the SM-like Higgs boson and the new scalar of the “dark sector”.
Highlights
All available experimental results seem to confirm that the new particle discovered in 2012 by the ATLAS and CMS experiments at LHC [1,2] is the last missing constituent of the Standard Model (SM), the Higgs boson
The results indicate that the experiment at CLIC will be able to exclude new scalar production with rate of about 1% of the SM production cross section for masses up to about 200 GeV, assuming 4000 fb−1 of data collected at 380 GeV
We studied the sensitivity to invisible Higgs boson decays and the possibility of constraining production of new scalar particles at CLIC running at 380 GeV and 1.5 TeV
Summary
All available experimental results seem to confirm that the new particle discovered in 2012 by the ATLAS and CMS experiments at LHC [1,2] is the last missing constituent of the Standard Model (SM), the Higgs boson. Some extensions of the Standard Model predict additional channels for invisible Higgs boson decays—into new, unobservable particles. Stronger constraints are expected from direct searches at e+e− Higgs factories, where the Higgs-strahlung process, e+e− → ZH, allows for decay-mode independent tagging of Higgs boson production events. Both leptonic and hadronic decay modes of the Z boson can be considered. In the so-called Higgs-portal models, existence of additional fundamental scalars of the “hidden sector” is assumed [15,16,17] These new particles could mix with the SM Higgs, and open new decay channels of the SM-like 125 GeV state into DM particles. Similar study, based on the leptonic Z boson decays, has been recently presented for ILC [24]
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