Observability of 2HDM neutral Higgs bosons with different masses at future e+e− linear colliders

Assuming two-Higgs-doublet model (2HDM) at SM-like scenario as the theoretical framework, this study addresses the question of possibility of observation of neutral CP-even and CP-odd Higgs bosons H and A at a linear collider operating at center-of-mass energies of 500 and 1000 GeV. The signal production channel is e−e+→AH→ZHH with subsequent leptonic decay of the Z boson and Higgs bosons decays into b quark pairs. To be specific, Type-I 2HDM is used to allow dominant Higgs boson decay to b-quark pairs below the top quark pair production threshold. The ISR+beamstrahlung effects are taken into account and the detector simulation is carried out based on the SiD detector at ILC. Several benchmark scenarios are defined and studied. Results indicate that in all scenarios, both Higgs bosons are observable with signals exceeding 5σ and with possibility of mass measurement. These results are beyond the current reach of LHC at 30 fb−1 and extend the exclusion contour of LHC in (mH,mA) plane.