Same-sign tetralepton signature in type-Ⅱ seesaw at lepton colliders

作者：白旭红; 韩志龙; 金毅; 李洪蕾; 孟召霞

来源：Chinese Physics C, 2022, 46(01): 25-34.

The same-sign tetralepton signature via the mixing of neutral Higgs bosons and their cascade decays to charged Higgs bosons is a unique signal in the type-Ⅱ seesaw model with the mass spectrum MA0■MH0> MH±>MH±±.In this study,we investigate this signature at future lepton colliders,such as the ILC,CLIC,and MuC.Direct searches for doubly charged scalar H±± at the LHC have excluded MH±±<350(870) GeV in the H±±→W±W±(l±l±) decay mode.Therefore,we choose MA0=400,600,1000,1500 GeV as our benchmark scenarios.Constrained by direct search,H±±→W±W± is the only viable decay mode for MA0=400 GeV at the s1/2=1 TeV ILC.With an integrated luminosity L=8 ab-1,the promising region,with approximately 150 signal events,corresponds to a narrow band in the range of 10-4 GeV■vΔ■10-2 GeV.Meanwhile,for MA0=600 GeV at the s1/2=1.5 TeV CLIC,approximately 10 signal events can be produced with L=2.5 ab-1.For heavier triplet scalars MA0■870 GeV,although the H±±→l±l±decay mode is allowed,the cascade decays are suppressed.A maximum event number～16 can be obtained at approximately vΔ～4× 10-4 GeV and λ4～0.26 for MA0=1000 GeV with L=5 ab-1 at the s1/2=3 TeV CLIC.Finally,we find that this signature is not promising for MA0= 1500 GeV at the s1/2=6 TeV MuC.Based on the benchmark scenarios,we also study the observability of this signature.In the H±±→W±W±(l±l±) mode,one can probe MAo■800(1160) GeV at future lepton colliders.