Search for a new resonance decaying to a W or Z boson and a Higgs boson in the [Formula: see text] final states with the ATLAS detector

Abstract

A search for a new resonance decaying to a W or Z boson and a Higgs boson in the [Formula: see text] final states is performed using 20.3 fb[Formula: see text] of pp collision data recorded at [Formula: see text] 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH / ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.

Fig. 1

Distributions of the reconstructed, a transverse mass $m_{\mathit{\nu }\mathit{\nu }jj}^{\text{T}}$ for the $\mathit{\nu }\mathit{\nu }b\overline{b}$ final state, b invariant mass $m_{\ell \mathit{\nu }jj}$ for the $\ell \mathit{\nu }b\overline{b}$ final state and c invariant mass $m_{\ell \ell jj}$ for the $\ell \ell b\overline{b}$ final state for the 1-b-tag (upper) and 2-b-tag (lower) channels. The background expectation is shown after the profile likelihood fit to the data. Any overflow is included in the last bin. The signals are shown stacked on top of the background and correspond to the benchmark models MWT with $m_{R1}=700$ GeV and HVT with $m_{V^{\prime }}=1000$ GeV normalized to the expected cross sections

Fig. 2

Combined upper limits at the 95 % CL for a the production cross section of $R_1^0$ ($V^{\prime 0}$) times its branching ratio to ZH and branching ratio of H to $b\overline{b}$ and b the production cross section of $R_1^{\pm }$ ($V^{\prime \pm }$) times its branching ratio to WH and branching ratio of H to $b\overline{b}$ . The experimental limits are obtained using samples with a single resonance $R_1$; however, the theory curve line for MWT includes both $R_1$ and $R_2$. The dip near 500 GeV in this theory curve is due to the interference between $R_1$ and $R_2$ [7]

Fig. 3

Exclusion contours at 95 % CL in the plane of the Minimal Walking Technicolor parameter space defined by the bare axial-vector mass versus the strength of the spin-1 resonance interaction {$m_A$, $\tilde{g}$}. Electroweak precision measurements exclude the (green) area in the bottom left corner. The requirement to stay in the walking regime excludes the (blue) area in the right corner. The large (red) area (black dashed line) shows the observed (expected) exclusion. The blue dashed line shows the observed exclusion from the dilepton resonance search [21]. The upper region is excluded due to non-real axial and axial-vector decay constants. Here both resonances predicted by MWT, $R_1$ and $R_2$, are fitted simultaneously

Fig. 4

Observed 95 % CL exclusion contours in the HVT parameter space {($g^2$/$g_V$)$c_F$, $g_V{c}_H$} for resonances of mass 1 $\mathrm{TeV}$, 1.5 $\mathrm{TeV}$ and 1.8 $\mathrm{TeV}$ . The areas outside the curves are excluded. Also shown are the benchmark model parameters A($g_V$=1), A($g_V$=3) and B($g_V$=3)