Measuring the Higgs self-coupling at the International Linear Collider

In this thesis, the experimental prospects of measuring the Standard Model (SM) Higgs self-coupling λ_SM at the International Linear Collider (ILC) are investigated. The observation of double Higgs production is necessary to directly establish a non-zero Higgs self-coupling. Information on λ_SM can be extracted from a measurement of the cross section for this process. At a centre-of-mass energy of √(s)=500 GeV double Higgs-strahlung is the dominant Higgs-pair production process. This measurement is extremely challenging due to very small production cross sections and multi-jet final states which pose large challenges to detector technologies and event reconstruction techniques. A detailed full detector simulation of the International Large Detector is performed for a Higgs boson with a mass of 125 GeV. The analysis is based on ILC beam parameters according to the Technical Design Report and investigates several improvements compared to earlier studies. These include an isolated lepton selection strategy and the application of kinematic fits to final states with heavy-flavoured jets. Depending on the decay mode of the Z boson, relative improvements of up to 25% are obtained in the selection of ZHH (HH → bbbb) events. This results in a relative improvement of 10% in the measurement of σ_ZHH when combining all channels. For the SM scenario, an evidence of 3.5σ for the observation of double Higgs-strahlung and a measurement precision of 30% on σ_ZHH is reached with an integrated luminosity of L=2ab^-1 and a beam polarisation of P(e⁺e^-)=(0.3,-0.8). The result extrapolates to an achievable precision of 21% on σ_ZHH after the full ILC running scenario, which corresponds to a 5.9σ discovery for the observation of double Higgs-strahlung. Combined with the channel HH→bbWW, σ_ZHH can even be measured to a precision of 16%, which corresponds to a precision of 26% on λ_SM. Additionally, the impact of γγ→low-p_T hadrons background is investigated, which proves the need of advanced removal strategies, which include a detailed modelling of the background and exploit the full power of high-granularity detectors.