Discovering extra Higgs boson via pair production of the SM-like Higgs bosons

TL;DR

This work investigates the resonant production of an extra scalar $S$ that decays to two SM-like Higgs bosons $H$, using an effective model with couplings to gluons and a portal to $HH$. By setting $f_1=f_2=1$ and $m_S=400$ GeV, the authors obtain $pp\to S\to HH$ cross-sections around $10$ pb and explore 15 final-state combinations of $HH$ decays at LHC14 with $\sqrt{s}=14$ TeV and $\mathcal{L}=1000\ \mathrm{fb}^{-1}$. They perform cut-based selections and mass-window requirements to estimate signal and background for each channel, finding that many channels achieve high $S/B$ ratios (often exceeding 100) and sizable signal statistics, with the most promising channels including $HH\to (bb)(\ WW^*,ZZ^*,\gamma\gamma,\tau\tau)$ and mixed channels involving photons or leptons. The analysis shows that resonant $S\to HH$ can provide a robust discovery pathway for an extra Higgs in a broad set of final states, though the $b\bar b b\bar b$ channel remains QCD-dominated and requires improved jet-tagging control. Overall, the results highlight a diverse, channel-dependent discovery potential for $S$ at the HL-LHC, guiding experimental prioritization of Higgs-pair final states.

Abstract

In the standard model (SM), pair production rate of Higgs boson at the Large Hadron Collider (LHC) is quite low. One usually think that it is extremely important for the measurement of triple Higgs coupling at the high luminosity LHC. In this paper, we propose to search for the extra Higgs boson (denoted as $S$) utilizing pair production of the SM-like Higgs boson ($H$) which was discovered in July, 2012.The pair production of $H$ can be huge due to the resonant production of heavy scalar $S$, namely $PP \rightarrow S \rightarrow HH$. The couplings of $H$ with weak gauge boson are similar to ones in the SM and it implies that the couplings between $S$ and gauge bosons are likely suppressed. Provided that $S$ is heavy enough, the decay into weak gauge bosons may not be the dominant modes. Instead $S$ can decay into a pair of $H$ and offer the promising channel to discover it. In this paper, we studied the 5 promising decay modes of $H$, i.e. $b\bar{b}$, $WW^*$, $ZZ^*$, $γγ$ and $τ^+τ^-$, and simulated the signals and backgrounds for the 15 combination modes for $HH$ at the LHC with $\sqrt{s}= 14$ TeV and integrated luminosity $\mathcal{L}=1000fb^{-1}$. We found that with the help of suitable selection rules, very good signal to background ratio $S/B$ can be archived in many decay channels, for example $b\bar b+ (WW^*, ZZ^*, γγ, τ^+τ^-)$, $WW^*+(WW^*, ZZ^*, γγ, τ^+τ^-)$ and $τ^+τ^- +(γγ, τ^+τ^-)$. For the detailed results please refer to Table \ref{tab:discovery} in the text. On the contrary, $b\bar b b\bar b$ mode is less important due to the huge QCD background. However if one has excellent control on light jet mis-tagging, the $b\bar b b\bar b$ mode can be promising to discover the extra Higgs boson due to its the largest branching ratio compared to other modes.

Figures (16)

• Figure 1: The resonant cross-section for $S$.
• Figure 2: The $p_T$ and $H_T$ distribution of signal and background for the $S \rightarrow hh \rightarrow b \bar{b} b \bar{b}$. The dashed red line is SM background and the solid black line is signal.
• Figure 3: The $p_T$ and $H_T$ distribution of signal and background for the $b\bar{b}+\gamma\gamma$ final state. The dashed red line is background and the solid black line is signal.
• Figure 4: The jet $p_T$ and the $H_T$ distribution of signal and background for final state $b\bar{b} + ZZ^{*}$. The dashed red line is background, while the solid black line is signal.
• Figure 5: The jet $p_T$ and $H_T$ distribution of signal and background for $b\bar{b} + WW^{*}$ final state. The dashed red line is background and the solid black line is signal.