LHC searches for the $CP$-odd Higgs boson with a jet substructure analysis

The LHC searches for the $CP$-odd Higgs boson $A$ are studied (with masses from 300 GeV to 1 TeV) in the context of the general two-Higgs-doublet model. With the discovery of the 125 GeV Higgs boson at the LHC, we highlight one promising discovery channel of $A\to hZ$. This channel can become significant for a heavy $CP$-odd Higgs boson after the global signal fitting to the 125 GeV Higgs boson in the general two-Higgs-doublet model. It is particularly interesting in the scenario where two $CP$-even Higgs bosons in the two-Higgs-doublet model have the common mass of 125 GeV. Since the final states involve a standard-model-like Higgs boson, we apply the jet substructure analysis of tagging the fat Higgs jet in order to eliminate the standard-model background sufficiently. After performing the kinematic cuts, we present the LHC search sensitivities for the $CP$-odd Higgs boson with mass up to 1 TeV via this channel.

Figure 1

The Feynman diagrams for the production channels of the $CP$-odd Higgs boson $A$.

Figure 2

The inclusive production cross section $\sigma [pp\to AX]$ for $M_A\in (300\mathrm{GeV},1\mathrm{TeV})$ at the LHC 14 TeV runs. Left: 2HDM-I, with inputs of $t_{\beta }=1$ (blue), $t_{\beta }=5$ (green), and $t_{\beta }=10$ (red). Right: 2HDM-II, with inputs of $t_{\beta }=1$ (blue), $t_{\beta }=5$ (green), and $t_{\beta }=20$ (red).

Figure 3

The decay branching ratios of the $CP$-odd Higgs boson $\mathrm{BR}[A]$ for the 2HDM-I case. (a) $M_h=125\mathrm{GeV}$ with $t_{\beta }=1$. (b) $M_h=125\mathrm{GeV}$ with $t_{\beta }=10$. (c) $M_h=M_H=125\mathrm{GeV}$ with $t_{\beta }=1$. (d) $M_h=M_H=125\mathrm{GeV}$ with $t_{\beta }=10$. The decay channels with branching ratios below $10^{-4}$ are not shown.

Figure 4

The decay branching ratios of the $CP$-odd Higgs boson $\mathrm{BR}[A]$ for the 2HDM-II case. (a) $M_h=125\mathrm{GeV}$ with $t_{\beta }=1$. (b) $M_h=125\mathrm{GeV}$ with $t_{\beta }=20$. (c) $M_h=M_H=125\mathrm{GeV}$ with $t_{\beta }=1$. (d) $M_h=M_H=125\mathrm{GeV}$ with $t_{\beta }=20$. The decay channels with branching ratios below $10^{-4}$ are not shown.

Figure 5

The $\sigma [pp\to AX]\times \mathrm{BR}[A\to hZ]$ for $M_A\in (300\mathrm{GeV},1\mathrm{TeV})$ at the LHC 14 TeV runs. (a) $M_h=125\mathrm{GeV}$ for 2HDM-I. (b) $M_h=125\mathrm{GeV}$ for 2HDM-II. (c) $M_h=M_H=125\mathrm{GeV}$ for 2HDM-I. (d) $M_h=M_H=125\mathrm{GeV}$ for 2HDM-II.

Figure 6

The fat Higgs jet tagging rates ${\delta }_H(S/B)$ with the varying jet cone sizes $R$ in the CA jet algorithm. For comparison, we take a common cross section of $\sigma [pp\to AX\to hZ]=100\mathrm{fb}$ for all signal processes. Plots (a)–(h) correspond to the fat Higgs jet tagging rates for the $M_A=(300,400,500,600,700,800,900,1000)\mathrm{GeV}$ cases.

Figure 7

The most optimal cuts to the $p_T$ of the tagged SM-like Higgs boson for different $M_A$ inputs.

Figure 8

The $M_{h,ll}$ distributions of the $pp\to AX\to hZ$ signal process (for the $M_A=600\mathrm{GeV}$ case) and all SM background processes after the kinematic cuts. A nominal cross section of $\sigma [pp\to AX]\times \mathrm{BR}[A\to hZ]=500\mathrm{fb}$ is assumed for the signal. The plot is for the LHC 14 TeV run with integrated luminosity of $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$.

Figure 9

The number of events for the $pp\to AX\to hZ$ signal in the 2HDM-I and the corresponding SM background processes after the jet substructure analysis. (a) $M_h=125\mathrm{GeV}$ for $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$. (b) $M_h=125\mathrm{GeV}$ for $\int \mathcal{L}dt=3000{\mathrm{fb}}^{-1}$. (c) $M_h=M_H=125\mathrm{GeV}$ for $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$. (d) $M_h=M_H=125\mathrm{GeV}$ for $\int \mathcal{L}dt=3000{\mathrm{fb}}^{-1}$. We show samples with $t_{\beta }=1$ (blue), $t_{\beta }=5$ (green), and $t_{\beta }=10$ (red) for each plot. The discovery limit (dashed black curve) of max$\{5\sqrt{B},10\}$ is demonstrated for each plot.

Figure 10

The number of events for the $pp\to AX\to hZ$ signal in the 2HDM-II and the corresponding SM background processes after the jet substructure analysis. (a) $M_h=125\mathrm{GeV}$ for $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$. (b) $M_h=125\mathrm{GeV}$ for $\int \mathcal{L}dt=3000{\mathrm{fb}}^{-1}$. (c) $M_h=M_H=125\mathrm{GeV}$ for $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$. (d) $M_h=M_H=125\mathrm{GeV}$ for $\int \mathcal{L}dt=3000{\mathrm{fb}}^{-1}$. We show samples with $t_{\beta }=1$ (blue), $t_{\beta }=5$ (green), and $t_{\beta }=20$ (red) for each plot. The discovery limit (dashed black curve) of max$\{5\sqrt{B},10\}$ is demonstrated for each plot.

Figure 11

The signal reaches for the $A\to hZ$ on the $(M_A,t_{\beta })$ plane for the 2HDM-I case. Upper left: $M_h=125\mathrm{GeV}$ for $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$. Upper right: $M_h=125\mathrm{GeV}$ for $\int \mathcal{L}dt=3000{\mathrm{fb}}^{-1}$. Lower left: $M_h=M_H=125\mathrm{GeV}$ for $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$. Lower right: $M_h=M_H=125\mathrm{GeV}$ for $\int \mathcal{L}dt=3000{\mathrm{fb}}^{-1}$. Parameter regions of $(M_A,t_{\beta })$ in blue are within the reach for each case.

Figure 12

The signal reaches for the $A\to hZ$ on the $(M_A,t_{\beta })$ plane for the 2HDM-II case. Upper left: $M_h=125\mathrm{GeV}$ for $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$. Upper right: $M_h=125\mathrm{GeV}$ for $\int \mathcal{L}dt=3000{\mathrm{fb}}^{-1}$. Lower left: $M_h=M_H=125\mathrm{GeV}$ for $\int \mathcal{L}dt=100{\mathrm{fb}}^{-1}$. Lower right: $M_h=M_H=125\mathrm{GeV}$ for $\int \mathcal{L}dt=3000{\mathrm{fb}}^{-1}$. Parameter regions of $(M_A,t_{\beta })$ in blue are within the reach for each case.