Study of Higgs self-coupling at the ILC based on the full detector simulation at √ s = 500 GeV and √ s = 1 TeV

In this analysis we investigated the feasibilities of the measurement of Higgs self-coupling at the International Linear Collider (ILC) during its two phases of operation with centre-of-mass energy of 500 GeV and 1 TeV. Three combinations of the decay modes of double Higgs strahlung process e+e− → ZHH , where Z → l+l−, Z → νν̄ and Z → qq̄ accompanying with both Higgs decay into bb̄, were analyzed together at 500 GeV. The decay mode of WW fusion process e+e− → νν̄HH , where both Higgs decay into bb̄ was analyzed at 1 TeV. Both the signal and background event samples are generated by a full detector simulation based on the International Large Detector (ILD). At 500 GeV, assuming an integrated luminosity of 2 ab−1 and the Higgs mass of 120 GeV, an excess of the e+e− → ZHH events with a statistical significance of 5.0σ is expected to be observed in case of the polarized electron and positron beams, P (e−, e) = (−0.8,+0.3). The cross section of e+e− → ZHH can be measured to the precision of 27%, corresponding to the precision of 44% on the Higgs trilinear self-coupling. At 1 TeV, in case of P (e−, e) = (−0.8,+0.2), we can expect the precision of self-coupling to be 18%.