Abstract
Abstract The first 1 fb−1 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−1 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−1 of data. The LHC is now on the brink of exploring the most interesting region of SUSY parameter space.
Highlights
If the superpartners are too heavy, the contributions to the right-hand side must be tuned against each other to achieve electroweak symmetry breaking at the observed energy scale
By many of the simplest scenarios of SUSY breaking, such as gauge mediation), and to check how strong the limits really are. This is the subject of the left side of figure 16, where we show the LHC limit coming from the scenario where all squarks are flavor degenerate at the electroweak scale, and the gluino mass is fixed to 1.2 TeV, which is heavy enough to deplete the rate of associated gluino-squark production
We have investigated the current LHC limits on Natural SUSY, i.e. on supersymmetric scenarios where the higgsinos, the top squarks, the left-handed bottom squark, and the gluino are bound to be light from the requirement of natural electroweak symmetry breaking
Summary
We review the basic arguments that determine the minimal set of requirements for natural ElectroWeak Symmetry Breaking (EWSB) in a supersymmetric theory. Since the soft parameters m2Q3, m2u3 and At control the stop spectrum, as it is well-known, the requirement of a natural Higgs potential sets an upper bound on the stop masses. For a fixed Higgs boson mass, a hierarchical stop spectrum induced by a large offdiagonal term At tend to worsen the fine-tuning due to the direct presence of At in the r.h.s. of eq (2.4). Before the start of the LHC this was the strongest, though indirect, lower bound on the stop masses and the main source of fine-tuning for the MSSM. The relevant task is to determine the lower bounds on the masses of third generation squarks, the gluino, and higgsinos, coming from direct collider searches, such as the searches. In flavor-blind SUSY mediation models, large splittings between squarks in the IR increases the fine-tuning in the Higgs potential.
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