Reconstructing singly produced top partners in decays to $Wb$

Fermionic top partners are a feature of many models of physics beyond the standard model. We propose a search strategy for single production of top partners focusing specifically on the dominant decay to $Wb$. The enormous background can be reduced by exploiting jet substructure to suppress top-pair production and by requiring a forward jet. This simple strategy is shown to produce a sensitive search for single top-partner production, in the context of composite Higgs models, that has competitive mass reach with existing experimental searches for top-partner-pair production at the 8 TeV LHC.

Figure 1

Illustration of the usage of large-radius jet mass to veto $t\overline{t}$ background. For the signal $\tilde{T}\to Wb$, the $b$-quark recoils against the $W$-boson. Thus the hardest large-radius jet in the event typically contains a $b$-hadron plus additional soft and collinear radiation, and tends to have a low mass. For the semileptonic $t\overline{t}$ background, right, a mildly boosted hadronically decaying top quark produces large-radius jets containing a significant fraction of the top decay products. The fraction of top decay products contained, and therefore the jet mass, increases with jet $p_{\mathrm{T}}$. Hence, after requiring a matching between a small-radius $b$-jet and large-radius jet, a cut based on the large-radius jet $p_{\mathrm{T}}$ and mass can be optimized to distinguish between signal and $t\overline{t}$ background, whilst still retaining good signal efficiency.

Figure 2

The distribution of the $\tilde{T}$ candidate mass used in the statistical analysis is shown for $20{\mathrm{fb}}^{-1}$ integrated luminosity at the 8 TeV LHC. The shape of the SM background from $W+\text{jets}$, $t\overline{t}$ and single top production are compared to the shape of the expected signal.

Figure 3

The results of the limit-setting procedure when applied to the search for a 700 GeV $\tilde{T}$ using 8 TeV (top) and 14 TeV (bottom) data. The results without requiring a forward jet (left) can be directly compared to the results with a forward jet requirement (right).