Same-sign charged Higgs boson pair production in bosonic decay channels at the HL-LHC and HE-LHC

The same-sign charged Higgs pair production via vector-boson scattering is a useful probe of the mass spectrum among the heavier scalar, pseudoscalar, and charged Higgs bosons in two-Higgs-doublet models. It has been shown that the production cross section scales as the square of the mass difference $\mathrm{\Delta }m=(m_{H^0}-m_{A^0})$ in the alignment limit $(\cos (\beta -\alpha )=0)$. We study the potential measurement of this same-sign charged Higgs boson pair production at the high-luminosity LHC and the proposed 27 TeV $pp$ collider, with emphasis in the decay channel $H^{\pm }{H}^{\pm }\to (W^{\pm }{A}^0)(W^{\pm }{A}^0)$, which is in general the dominant mode when the charged Higgs mass is above the $W^{\pm }{A}^0$ threshold. We also examine the current allowed parameter space taking into account the theoretical constraints on the model, the electroweak precision test measurements, $B$ decays, and direct searches in the $H^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$ and $H^{\pm }\to W^{\pm }{A}^0\to ({\ell }^{\pm }{\nu }_{\ell })(\mu \mu )$.

Figure 1

The allowed parameter space in the plane of ($\mathrm{\Delta }m\equiv m_{H^0}-m_{A^0}$, $m_{H^{\pm }}$) due to the constraints from the oblique $S$ and $T$ parameters, and all theoretical constraints. The upper panels are for $m_{A^0}=65\mathrm{GeV}$, while the lowers for $m_{A^0}=100\mathrm{GeV}$, in which $\tan \beta =2.6$ (left), 5 (middle), and 10 (right) are shown. The green points are right at the alignment limit $\sin (\beta -\alpha )=1$, while the red points satisfy $0.97<\sin (\beta -\alpha )<1$ (near-alignment limit).

Figure 2

Branching fractions of the charged Higgs boson versus $m_{H^{\pm }}$ for type-I 2HDM with $m_{A^0}=65\mathrm{GeV}$ (upper-left panel), $m_{A^0}=100\mathrm{GeV}$ (upper-right panel), and for type-X 2HDM with $m_{A^0}=65\mathrm{GeV}$ (lower-left panel), $m_{A^0}=100\mathrm{GeV}$ (lower-right panel). The alignment limit $\sin (\beta -\alpha )=1$ is assumed.

Figure 3

Branching fractions of the $CP$-odd Higgs boson $A^0$ versus $\tan \beta$ for $m_{A^0}=65\mathrm{GeV}$ in type-I 2HDM (left panel) and type-X 2HDM (right panel).

Figure 4

Interpretation of CMS exclusion regions [11, 12, 13] in the 2HDM type I (left panel) and type X (right panel) projected on the plane of $(m_{H^{\pm }},\tan \beta )$. The red points stand for the case the $WA$ mode is closed, while the green points are for the case that the $WA$ mode is open, with $m_{A^0}=65\mathrm{GeV}$.

Figure 5

Exclusions in the parameter space of $(m_{H^{\pm }},\tan \beta )$ for type I (left panel) and for type X (right panel) 2HDMs obtained by rescaling the observed limits of the CMS results in Ref. [25] based on $t\to b{H}^{+}\to b{W}^{+}A\to b(l^{+}{\nu }_l)({\mu }^{+}{\mu }^{-})$.

Figure 6

The production cross sections of $pp\to H^{+}{H}^{+}{j}_F{j}_F$ (solid line) and $pp\to H^{-}{H}^{-}{j}_F{j}_F$ (dashed line) versus $m_{H^{\pm }}$ at $\sqrt{s}=14\mathrm{TeV}$ (left panel) and $\sqrt{s}=27\mathrm{TeV}$ (right panel), for $\mathrm{\Delta }m=100\mathrm{GeV}$ (black), 200 GeV (blue), and 300 GeV (red). Notice the VBF cut ${\eta }_{j_1}\times {\eta }_{j_2}<0$ and $|\mathrm{\Delta }{\eta }_{jj}|>2.5$ for the minimum rapidity difference between the forward jet pair are applied.

Figure 7

Invariant mass distributions of $M_{bb{l}^{\pm }}$ (left panel) and $M_{bb}$ (right panel) for the signal with $m_{H^{\pm }}=205\mathrm{GeV}$, $m_{A^0}=65\mathrm{GeV}$, $\mathrm{\Delta }m=200\mathrm{GeV}$, $\tan \beta =5$, and $\sin (\beta -\alpha )=0.97$, and the total background at $\sqrt{s}=14\mathrm{TeV}$. Preselection cuts in Eqs. (16) and (17) are imposed.

Figure 8

The significance $Z$ versus $m_{A^0}$ from 63 to 100 GeV in type-I 2HDM at $\sqrt{s}=27\mathrm{TeV}$ with luminosity $\mathcal{L}=15{\mathrm{ab}}^{-1}$. We have fixed $\sin (\beta -\alpha )=1$ and $\tan \beta =5$ with $\mathrm{\Delta }m\equiv m_{H^0}-m_{A^0}=100\mathrm{GeV}$ (upper-left panel), 200 GeV (upper-right panel), and 250 GeV (lower panel). The dashed lines correspond to additional 5% systematic uncertainties of the SM background events in Eq. (23).

Figure 9

Invariant mass distributions of $M_{l^{\pm }{\tau }^{+}{\tau }^{-}}$ (left panel) and $M_{{\tau }^{+}{\tau }^{-}}$ (right panel) for the signal with $m_{H^{\pm }}=205\mathrm{GeV}$, $m_{A^0}=65\mathrm{GeV}$, $\mathrm{\Delta }m=200\mathrm{GeV}$, $\tan \beta =5$, and $\sin (\beta -\alpha )=0.97$, and the total background at $\sqrt{s}=14\mathrm{TeV}$. Preselection cuts in Eqs. (28)–(30) are imposed.

Figure 10

The same as Fig. 8, but in type-X 2HDM.