Pictures

Fig. 1: Longitudinal cross section of the top right quadrant of the CLIC_ILD (left) and CLIC_SiD (right) detector concepts.


Feynman diagrams

Fig. 3: Feynman diagrams of the highest cross section Higgs production processes at CLIC; Higgsstrahlung (top left), WW-fusion (top right) and ZZ-fusion (bottom).

Fig. 4: Feynman diagrams of the main processes at CLIC involving the top Yukawa coupling gHtt (top left), the Higgs boson trilinear self-coupling λ (top right) and the quartic coupling gHHWW (bottom).

Fig. 23: Feynman diagrams of leading-order processes that produce two Higgs bosons and missing energy at CLIC at √s = 1.4 TeV and 3 TeV. The top left diagram is sensitive to the trilinear Higgs self-coupling. The top right diagram is sensitive to the quartic coupling gHHWW . All four diagrams are included in the generated e + e − → HH νe νe signal samples.


Event displays

Fig. 13: Event display of a H → τ + τ − event at √s = 1.4 TeV. A 1-prong tau decay is visible in the central part of the detector. The other tau lepton decays to three charged particles and is reconstructed in the forward direction. A few soft particles from beam-induced backgrounds are also visible.

Fig. 17: Event display of a H → Z γ → qq γ event at √s = 1.4 TeV. Both jets are visible in the forward region. The photon creates a cluster in the central part of the electromagnetic calorimeter.

Fig. 21: Event display of a tt H → bb bb qq τ − ντ event at √s = 1.4 TeV. The tau lepton decays hadronically.


Graphs

Fig. 2: Cross section as a function of centre-of-mass energy for the main Higgs production processes at an e + e − collider for mH = 126 GeV. The values shown correspond to unpolarised beams and do not include the effect of beamstrahlung.

Fig. 24: Cross section for the e + e − → HH νe νe process as a function of the ratio λ /λ SM at √s = 1.4 TeV and 3 TeV.


Distributions

Fig. 5: Generated Higgs polar angle distributions for single Higgs events at √s = 350 GeV, 1.4 TeV and 3 TeV, including the effects of the CLIC beamstrahlung spectrum and ISR. Distributions are normalised to unity.

Fig. 6: Reconstructed recoil mass distributions of e + e − -> ZH events at √s = 350 GeV, where ZH -> μ + μ − X (a) and ZH -> e + e − X with Bremstrahlung recovery (b). Distributions are normalised to Lint = 500 fb−1.

Fig. 7: Reconstructed recoil mass distributions of e + e − -> ZH events at √s = 350 GeV, showing the H → invis. signal (for a 100 % BR) and SM backgrounds as stacked histograms. Distributions are normalised to Lint = 500 fb−1.

Fig. 8: BDT classifier distributions for e + e − -> ZH events at √s = 350 GeV, for H → invis. signal and all SM backgrounds. Distributions are normalised to Lint = 500 fb−1.

Fig. 9: Reconstructed di-jet invariant mass versus reconstructed recoil mass distributions for selected ZH -> qq X events at √s = 350 GeV, showing ZH signal (left) and all non-Higgs background (right).

Fig. 10: b-likeness versus c-likeness distributions for e + e − -> ZH events at √s = 350 GeV, for all events ('data') and for the different event classes: H → bb , H → cc, H → gg, background from other Higgs decays and non-Higgs SM background. Distributions are normalised to Lint = 500 fb−1.

Fig. 11: Reconstructed Higgs candidate transverse momentum distributions for selected H νν events at √s = 350 GeV, showing the contributions from Higgsstrahlung, WW-fusion and non-Higgs background as stacked histograms. Distributions are normalised to Lint = 500 fb−1.

Fig. 12: BDT classifier distributions for H → τ + τ − events at √s = 350 GeV, showing the signal and main backgrounds as stacked histograms. Distributions are normalised to Lint = 500 fb−1.

Fig. 14: Reconstructed Higgs invariant mass distributions for preselected H -> WW* events at √s = 1.4 TeV, showing the signal and main backgrounds as stacked histograms. Distributions are normalised to Lint = 1.5 ab−1.

Fig. 15: Reconstructed Higgs invariant mass distributions of H → ZZ ∗ → qq + − events at √s = 1.4 TeV, showing the signal and main backgrounds as stacked histograms a) after preselection, and b) after the full event selection including a cut on the BDT classifier. Distributions are normalised to Lint = 1.5 ab−1.

Fig. 16: Reconstructed di-photon invariant mass distribution of preselected signal H → γ γ events at √s = 1.4 TeV. The statistical uncertainties shown correspond to the uncertainties of the simulated sample and are not scaled to a specific integrated luminosity. The fit indicates the average mass resolution in the signal sample with σ = 3.3 GeV. The backgrounds are flat and exceed the signal peak by more than three orders of magnitude after the preselection. The distribution is normalised to Lint = 1.5 ab−1.

Fig. 18: Reconstructed di-muon invariant mass distribution of selected H → μ + μ − events at √s = 3 TeV. The distribution is normalised to Lint = 2 ab−1, assuming 80% electron polarisation.

Fig. 19: Generated electron pseudorapidity distributions for e + e − → He + e − events at √s = 1.4 TeV and 3 TeV. Distributions are normalised to Lint = 1.5 ab-1 and 2 ab-1 respectively. The vertical arrows show the detector acceptance.

Fig. 20: Likelihood distributions for H → bb events at √s = 1.4 TeV, shown for the signal and main background. Distributions are normalised to Lint = 1.5 ab−1.

Fig. 22: BDT classifier distributions for fully-hadronic ttH events at √s = 1.4 TeV, shown for the tt H signal and main backgrounds. Distributions are normalised to Lint = 1.5 ab−1. The vertical arrow shows the value of the cut, chosen to give the highest significance.


Fit illustrations

Fig. 25: Illustration of the precision of the Higgs couplings of the three-stage CLIC programme determined in a model-independent fit.

Fig. 26: Illustration of the precision of the Higgs couplings of the three-stage CLIC programme determined in a model-dependent fit.

Fig. 27: Illustration of the precision of the model-independent Higgs couplings and of the self-coupling as a function of particle mass.