Monojetlike Searches for Top Squarks with a $b$ Tag

The LHC searches for light compressed top squarks have resulted in considerable bounds in the case where the top squark decays to a neutralino and a charm quark. However, in the case where the top squark decays to a neutralino, a bottom quark, and two fermions via an off-shell $W$ boson, there is currently a significant unconstrained region in the top-squark–neutralino mass plane, still allowing for top squark masses in the range 90–140 GeV. In this Letter we propose a new monojetlike search for light top squarks, optimized for the four-body decay mode, in which at least one $b$-tagged jet is required. We show that, by using the existing 8 TeV LHC data set, such a search would cover the entire unconstrained region. Moreover, in the process of validating our tools against an ATLAS monojet search, we show that the existing limit can be extended to exclude also top squark masses below 100 GeV.

Figure 1

(Left panel) Summary of the existing limits in the top-squark–neutralino mass plane, as well as our exclusion curve for the M1 signal region of the ATLAS search [42], in which we also extend the range of excluded top squark masses below 100 GeV. (Right panel) Exclusion arising from our proposed search $\mathrm{M}1+b$ tag, indicated by the red solid curve. The red dashed curve denotes the change caused by a 20% increase of the total background error.