Removing Gaps in the Exclusion of Top Squark Parameter Space

Light stops are a hallmark of the most natural realizations of weak-scale supersymmetry. While stops have been extensively searched for, there remain open gaps around and below the top mass, due to similarities of stop and top signals with current statistics. We propose a new fast-track avenue to improve light stop searches for $R$-parity-conserving supersymmetry by comparing top cross section measurements to the theoretical prediction. Stop masses below $\sim 180\mathrm{GeV}$ can now be ruled out for a light neutralino. The possibility of a stop signal contaminating the top mass measurement is also briefly addressed.

Figure 1

Efficiencies and acceptances for stop pair production (a) and top pair production with one or two tops decaying to stop and neutralino (b) in the CMS top cross section measurement considered [70]. The efficiencies are normalized to the SM top efficiency of 0.12, which includes decays to hadronic and leptonic taus. Solid lines refer to a right-polarized stop (blue or upper solid line for the case of bino LSP, purple or lower solid line for the gravitino LSP), while dashed lines refer to a left-polarized stop (red or upper dashed for bino LSP and orange or lower dashed for gravitino LSP). We use pythia for $2(t\to \tilde{t})$ (dotted magenta), neglecting polarization and off-shell effects.

Figure 2

Exclusion limits for stop decaying into a massless LSP, for bino (left) and gravitino (right). Left and right stop polarizations are shown with (red, blue) and (orange, purple) lines, respectively. Solid lines correspond to the observed limits while dashed lines correspond to the expected limits. LEP exclusions from ALEPH [88] are shown as shaded gray (the case for minimal and maximal stop coupling to the $Z$ boson are shown).

Figure 3

(a) Two-dimensional 95% C.L. exclusion limits in the neutralino-stop mass plane. Our derived limits are shown in red (with expected limits shown as a dashed line), with LEP limits [88] in gray, and the CMS direct stop search in the light stop region [30] shown in blue. (b) Excluded regions for massless neutralino in the stop-top mass plane. Excluded region from our analysis derived using the top cross section alone (i.e., without assuming prior knowledge of the top mass) are shaded in red, while the LEP limits are shown in gray. The effect of combining the ${\sigma }_{t\overline{t}}$ measurement with current $m_t$ measurements (assuming no stop contamination) is shown as a blue line. Expected limits are shown as dashed lines. For both plots we assume right-handed stop ${\tilde{t}}_R$.