Detectors and Physics at a Future Linear Collider

An electron-positron linear collider is an option for future large particle accelerator projects. Such a collider would focus on precision tests of the Higgs boson properties. This thesis describes three studies related to the optimisation of highly granular calorimeters and one study on the sensitivity of Higgs couplings at CLIC. Photon reconstruction algorithms were developed for highly granular calorimeters of a future linear collider detector. A sophisticated pattern recognition algorithm was implemented, which uses the topological properties of electromagnetic showers to identify photon candidates and separate them from nearby particles. It performs clustering of the energy deposits in the detector, followed by topological characterisation of the clusters, with the results being considered by a multivariate likelihood analysis. This algorithm leads to a significant improvement in the reconstruction of both single photons and multiple photons in high energy jets compared to previous reconstruction software. The reconstruction and classification of tau lepton decay products was studied. Utilising highly granular calorimeters, the high resolution of energy and invariant mass of the tau decay products enabled a high classification rate. A hypothesis test was performed for expected decay final states. A multivariate analysis was trained to classify decay final states with a machine learning method. The performance of tau decay classification is used for the electromagnetic calorimeter optimisation at the ILC or CLIC. A proof-of-principle analysis using the correlation between the polarisations of the tau pair from a boson decay as a signature to differentiate the Higgs boson from the Z boson is presented. Sensitivity of Higgs couplings at CLIC was studied using the double Higgs production process. Algorithms were developed for signal event selection. The event selection relies on the jet reconstruction and the flavour tagging. A multivariate analysis is performed to select signal events. An attempt at extracting Higgs trilinear self-coupling and quartic coupling was conducted

Double Higgs boson production and Higgs self-coupling extraction at CLIC

AbstractThe Compact Linear Collider (CLIC) is a future electron–positron collider that will allow measurements of the trilinear Higgs self-coupling in double Higgs boson events produced at its high-energy stages with collision energies from $$\sqrt{s}$$ s  = 1.4 to 3 TeV. The sensitivity to the Higgs self-coupling is driven by the measurements of the cross section and the invariant mass distribution of the Higgs-boson pair in the W-boson fusion process, $$\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$$ e + e - → HH ν ν ¯ . It is enhanced by including the cross-section measurement of ZHH production at 1.4 TeV. The expected sensitivity of CLIC for Higgs pair production through W-boson fusion is studied for the decay channels $$\mathrm{b}\bar{\mathrm{b}}\mathrm{b}\bar{\mathrm{b}}$$ b b ¯ b b ¯   and $$\mathrm{b}\bar{\mathrm{b}}\mathrm{W}\mathrm{W}^{*}$$ b b ¯ W W ∗   using full detector simulation including all relevant backgrounds at $$\sqrt{s}$$ s = 1.4 TeV with an integrated luminosity of $$\mathcal {L}$$ L  = 2.5 ab$$^{-1}$$ - 1 and at $$\sqrt{s}$$ s = 3 TeV with $$\mathcal {L}$$ L  = 5 ab$$^{-1}$$ - 1 . Combining $$\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$$ e + e - → HH ν ν ¯ and ZHH  cross-section measurements at 1.4 TeV with differential measurements in $$\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$$ e + e - → HH ν ν ¯ events at 3 TeV, CLIC will be able to measure the trilinear Higgs self-coupling with a relative uncertainty of $$-8\%$$ - 8 % and $$+11\%$$ + 11 % at 68% C.L., assuming the Standard Model. In addition, prospects for simultaneous constraints on the trilinear Higgs self-coupling and the Higgs-gauge coupling HHWW are derived based on the $${\text {H}\text {H}\nu \bar{\nu }}$$ HH ν ν ¯ measurement.</jats:p

Double Higgs boson production and Higgs self-coupling extraction at CLIC

The Compact Linear Collider (CLIC) is a future electron–positron collider that will allow measurements of the trilinear Higgs self-coupling in double Higgs boson events produced at its high-energy stages with collision energies from $\sqrt{s}$ = 1.4 to 3 TeV. The sensitivity to the Higgs self-coupling is driven by the measurements of the cross section and the invariant mass distribution of the Higgs-boson pair in the W-boson fusion process, $\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$. It is enhanced by including the cross-section measurement of ZHH production at 1.4 TeV. The expected sensitivity of CLIC for Higgs pair production through W-boson fusion is studied for the decay channels $\mathrm{b}\bar{\mathrm{b}}\mathrm{b}\bar{\mathrm{b}}$  and $\mathrm{b}\bar{\mathrm{b}}\mathrm{W}\mathrm{W}^{*}$  using full detector simulation including all relevant backgrounds at $\sqrt{s}$ = 1.4 TeV with an integrated luminosity of $\mathcal {L}$ = 2.5 ab$^{-1}$ and at $\sqrt{s}$ = 3 TeV with $\mathcal {L}$ = 5 ab$^{-1}$. Combining $\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$ and ZHH  cross-section measurements at 1.4 TeV with differential measurements in $\text {e}^{+}\text {e}^{-}\rightarrow {\text {H}\text {H}\nu \bar{\nu }}$ events at 3 TeV, CLIC will be able to measure the trilinear Higgs self-coupling with a relative uncertainty of $-8\%$ and $+11\%$ at 68% C.L., assuming the Standard Model. In addition, prospects for simultaneous constraints on the trilinear Higgs self-coupling and the Higgs-gauge coupling HHWW are derived based on the ${\text {H}\text {H}\nu \bar{\nu }}$ measurement.The Compact Linear Collider (CLIC) is a future electron-positron collider that will allow measurement of the trilinear Higgs self-coupling in double Higgs boson events produced at its high-energy stages with collision energies of $\sqrt{s}$ = 1.5 and 3 TeV. The sensitivity to the Higgs self-coupling is driven by the measurements of the cross section and the invariant mass distribution of the Higgs-boson pair in the W-boson fusion process, e$^+$e$^-\to$HH$\nu_e \bar{\nu}_e$. It is enhanced by including the cross-section measurement of ZHH production at 1.5 TeV. The expected sensitivity of CLIC for Higgs pair production through W-boson fusion is studied for the decay channels bbbb and bbWW using full detector simulation including all relevant backgrounds. With an integrated luminosity of $\mathcal{L}$ = 5 ab$^{-1}$ at $\sqrt{s}$ = 3 TeV, CLIC will be able to measure the trilinear Higgs self-coupling with a relative uncertainty of $-8\,\%$ and $+11\,\%$ at $68\,\%$ C.L., assuming the Standard Model

A detector for CLIC: main parameters and performance

Together with the recent CLIC detector model CLICdet a new software suite was introduced for the simulation and reconstruction of events in this detector. This note gives a brief introduction to CLICdet and describes the CLIC experimental conditions at 380 GeV and 3 TeV, including beam-induced backgrounds. The simulation and reconstruction tools are introduced, and the physics performance obtained is described in terms of single particles, particles in jets, jet energy resolution and flavour tagging. The performance of the very forward electromagnetic calorimeters is also discussed

A detector for CLIC: main parameters and performance

Together with the recent CLIC detector model CLICdet a new software suite was introduced for the simulation and reconstruction of events in this detector. This note gives a brief introduction to CLICdet and describes the CLIC experimental conditions at 380 GeV and 3 TeV, including beam-induced backgrounds. The simulation and reconstruction tools are introduced, and the physics performance obtained is described in terms of single particles, particles in jets, jet energy resolution and flavour tagging. The performance of the very forward electromagnetic calorimeters is also discussed