Natural SUSY Endures

Abstract

The first 1/fb of LHC searches have set impressive limits on new colored particles decaying to missing energy. We address the implication of these searches for naturalness in supersymmetry (SUSY). General bottom-up considerations of natural electroweak symmetry breaking show that higgsinos, stops, and the gluino should not be too far above the weak scale. The rest of the spectrum, including the squarks of the first two generations, can be heavier and beyond the current LHC reach. We have used collider simulations to determine the limits that all of the 1/fb searches pose on higgsinos, stops, and the gluino. We find that stops and the left-handed sbottom are starting to be constrained and must be heavier than about 200-300 GeV when decaying to higgsinos. The gluino must be heavier than about 600-800 GeV when it decays to stops and sbottoms. While these findings point toward scenarios with a lighter third generation split from the other squarks, we do find that moderately-tuned regions remain, where the gluino is just above 1 TeV and all the squarks are degenerate and light. Among all the searches, jets plus missing energy and same-sign dileptons often provide the most powerful probes of natural SUSY. Overall, our results indicate that natural SUSY has survived the first 1/fb of data. The LHC is now on the brink of exploring the most interesting region of SUSY parameter space.

Figures (21)

• Figure 1: Natural electroweak symmetry breaking constrains the superpartners on the left to be light. Meanwhile, the superpartners on the right can be heavy, $M \gg 1$ TeV, without spoiling naturalness. In this paper, we focus on determining how the LHC data constrains the masses of the superpartners on the left.
• Figure 2: Possible decay modes in the simplified model consisting only of a left-handed stop/sbottom, or right-handed stop, decaying to a higgsino LSP. On the left, we show decays of the left-handed stop and left-handed sbottom, whose masses are both determined by $m_{Q_3}$. On the right, we show possible decays of the right-handed stop, whose mass is determined by $m_{u_3}$. At this stage, we neglect left-right stop mixing.
• Figure 3: The LHC limits on the left-handed stop/sbottom ( left) and right-handed stop ( right), with a higgsino LSP. The axes correspond to the stop pole mass and the higgsino mass. We find that the strongest limits on this scenario come from searches for jets plus missing energy. For comparison, we show the $D0$ limit with $5.2\; \mathrm {fb}^{-1}$ (green), which only applies for $m_{\tilde{N}_1} \lesssim 110$ GeV, and has been surpassed by the LHC limits.
• Figure 4: Possible decay modes of the left-handed stop/sbottom ( left), or right-handed stop ( right), to a bino or gravitino LSP. Higher body final states occur when the mass splittings squeeze out the two-body decays of the stops, $m_{\tilde{t}_{L,R}} < m_{\tilde{B}} - m_t$.
• Figure 5: The LHC limits on left-handed stop/sbottom, with a bino LSP. The axes correspond to the stop pole mass and the bino mass. The limit with a gravitino LSP in place of the bino can be inferred from looking at the line with $m_{\tilde{B}} \approx 0\; \mathrm {GeV}.$ We find that searches for jets plus missing energy set the strongest limits, which surpass the $D0$ limit with $5.2\; \mathrm {fb}^{-1}$ (green). We do not show the case with a right-handed stop with bino/gravitino LSP, where we find no limit above $m_{\tilde{t}} \gtrsim 200\; \mathrm {GeV}$. We find that there may be marginal sensitivity for lighter right-handed stops, although this requires further investigation due to the similarity of the stop signal and the irreducible top background.