Searching for vector dark matter via Higgs portal at the LHC

A Higgs portal dark matter model for explaining the gamma ray excess from the galactic center can be realized with the extension of local $SU(2{)}_X$ gauge symmetry with one quadruplet. Due to the residual $Z_3$ discrete symmetry of $SU(2{)}_X$, the new gauge bosons are the stable dark matter candidates. Due to the mixture of the standard model Higgs doublet and the introduced quadruplet, dark matter could annihilate into the standard model particles through the Higgs portal and new scalar portal. We study the discovery significance of the vector dark matter at the Large Hadron Collider. The involved parameters are consistent with the constraints from relic density and direct detection and with the data of the galactic center gamma ray excess. With $\sqrt{s}=14\mathrm{TeV}$ and luminosities of 100 and $300{\mathrm{fb}}^{-1}$, we find that a discovery significance of $S/\sqrt{B}=5$ can be easily reached if the production of dark matter is through the invisible decays of the Higgs boson and a new scalar boson.

Figure 1

Contours for invisible decay of SM Higgs $h$ (left) and of new scalar boson $H^0$ (right) as a function of $g_X\tan \theta (g_X\cot \theta )$ and $m_{\chi }$, where $m_h=125\mathrm{GeV}$ [30, 31], ${\mathrm{\Gamma }}_{h\to \mathrm{SM}}=4.21\mathrm{MeV}$ [47], and the measurement of $\mathrm{BR}(h\to \chi \chi )<0.29$ [48] is used. In $H^0\to \chi \chi$, we assume $m_{H^0}=2m_{\chi }+1$.

Figure 2

Bounds of $g_X\sin \theta$ and $m_{\chi }$ from DM scattering off nucleons, where the red solid and black dashed (dotted) lines stand for the limits from the invisible SM Higgs decay and LUX experiment [2] with $m_{H^0}=m_{\chi }(2m_{\chi })$, respectively.

Figure 3

Cross section of each signal channel for on-shell $H^0$ (left) and off-shell $h$ and $H^0$ (right) as a function of $m_{H^0}$, where $\sqrt{s}=14\mathrm{TeV}$ is used, and for each panel, we scaled the cross section by factors of $1/{\sin }^2\theta$ and $1/(g_X^2{\sin }^2\theta {\cos }^2\theta )$, respectively.

Figure 4

Event histogram for $pp\to h(\chi \overline{\chi })qq$ and related background as a function of (a) missing $E_T$, (b) $\mathrm{\Delta }{\eta }_{jj}$, (c) $M_{jj}$, and (d) $\mathrm{\Delta }{\varphi }_{jj}$, where the event selection criteria of Eq. (17) are adopted.

Figure 5

The legend is the same as that in Fig. 4, but both basic and advanced cuts of Eqs. (17) and (18) are applied simultaneously.

Figure 6

Discovery significance as a function of $g_X\sin \theta$, where we set $m_{\chi }=50\mathrm{GeV}$ for ${\mathrm{I}}_{\mathrm{A},\mathrm{B}}$ and $m_{\chi }=70\mathrm{GeV}$ for ${\mathrm{II}}_{\mathrm{A},\mathrm{B}}$, and the luminosities of 100 and $300{\mathrm{fb}}^{-1}$ are used.

Figure 7

The upper left (right) plot shows the correlation between $g_X\sin \theta$ and $m_{\chi }$ for $S=2(5)$ in scheme ${\mathrm{I}}_{\mathrm{A}}$. The lower plot shows the correlation between $\sin \theta$ and $m_H$ in scheme ${\mathrm{II}}_{\mathrm{A}}$. The upper limit of the mixing angle $\sin \theta$ is given from the analysis of the Higgs boson search at the LHC in Fig. 4 of Ref. [46]. The region with thick black lines for the scheme ${\mathrm{I}}_{\mathrm{A}}$ is excluded by the constraint on $\sin \theta$.

Figure 8

Correlation between $g_X\sin \theta$ and $m_{\chi }$ for $S=2$ and $S=5$, where DM direct detection measured by the LUX Collaboration [2] is included, and the upper limit of invisible Higgs decay measured by ATLAS [48] at $\sqrt{s}=8\mathrm{TeV}$ is shown in schemes ${\mathrm{I}}_{\mathrm{A},\mathrm{B}}$.