Natural SUSY in Plain Sight

TL;DR

The paper investigates whether natural SUSY can be realized with light stops near the electroweak scale to account for anomalies in the $W^+W^-$ cross section observed at the LHC. It introduces four stop-based scenarios (A–D) where WW final states arise from stop decays or associated electroweakinos, and shows that these spectra can improve agreement with WW differential distributions while evading current direct searches. The work also discusses how light sbottoms can enable thermal Bino dark matter and how sleptons could address the $(g-2)_m$ anomaly, along with potential Higgs coupling deviations, highlighting the broader phenomenological implications and testable predictions for Run 2. Overall, the results argue that fully natural SUSY spectra could be hiding in WW measurements and motivate targeted searches for light stops, sbottoms, and associated particles at the LHC.

Abstract

The basic principle of naturalness has driven the majority of the LHC program, but so far all searches for new physics beyond the SM have come up empty. On the other hand, existing measurements of SM processes contain interesting anomalies, which allow for the possibility of new physics with mass scales very close to the Electroweak Scale. In this paper we show that SUSY could have stops with masses ~ O(200) GeV based on an anomaly in the WW cross section, measured by both ATLAS and CMS at 7 and 8 TeV. In particular we show that there are several different classes of stop driven scenarios that not only evade all direct searches, but improve the agreement with the data in the SM measurement of the WW cross section.

Figures (4)

• Figure 1: The four types of stop spectra which could account for the $W^+W^-$ excess via stop pair production, labelled Scenarios A - D. The top and bottom of the spectrum are at $\sim 200 \, {\rm GeV}$ and $\sim 100 \, {\rm GeV}$, with $W$'s (green) being produced when decaying across the big gap in the spectrum. Small gaps are $\lesssim 10 \, {\rm GeV}$. The 2-body decays of each state are shown as blue vertical arrows, with SM decay products on the right of each spectrum. The red color for $Z$ and $b$ indicates that these are not produced from stop pair production but from a different processes (direct $\tilde{\chi}^0_2 \tilde{\chi}^\pm_1$ and $\tilde{b}_1 \tilde{b}_1^*$ production). The soft $b$'s (orange) should be practically undetectable.
• Figure 2: Regions of the stop-neutralino mass-plane excluded and preferred by the different $W^+W^-$ cross section measurements in Scenario A ("One Light Stop, $W$ from EWino"). We fix $\Delta m = \tilde{t}_1 - \chi^\pm_1 \approx 10\, {\rm GeV}$ to avoid hard b-jets. Solid (dashed) orange line: $95\%$ exclusion from the $W^+W^-$ measurement with fixed (floating) normalization of SM contribution. Thin blue contours show values of $\chi^2_\mathrm{SM+stops}/\chi^2_\mathrm{SM}$, with the thick contour indicating the region most preferred by the $W^+W^-$ measurement. Exclusions from ATLAS stop searches shown in red ATLAS8stop1 and green ATLAS7stop1. Observed (expected) exclusion from ATLAS trilepton $\chi^0_2 \chi^\pm_1$ search atlastrilepton shown as solid (dot-dashed) brown line: note how an excess compatible with the $W^+W^-$ preferred region pushes the observed bounds down in Bino mass.
• Figure 3: Bounds on a single sbottom decaying via $\tilde{b}_1 \to b + \tilde{\chi}^0_1$. Black: LEP $\sqrt{s}=208\, {\rm GeV}$LEPsb. Purple: low-MET ATLAS 8TeV 12.8 $\mathrm{fb}^{-1}$ search ATLASsb2. Green: D0 5.2 $\mathrm{fb}^{-1}$D0sb. Orange: CMS 4.7 $\mathrm{fb}^{-1}$ mono-jet recast by Yangbai. Gray: $m_{\tilde{b}_1} = m_{\tilde{\chi}^0_1}$ kinematic limit.
• Figure 4: Regions of the stop-neutralino mass-plane excluded and preferred by the different $W^+W^-$ cross section measurements in Scenario C ("Two Light Stops, $W$ from EWino"). We fix $\Delta m = \tilde{t}_1 - \chi^\pm_1 \approx 10\, {\rm GeV}$ to avoid hard b-jets, and make the two stops degenerate $m_{\tilde{t}_1} \approx m_{\tilde{t}_2}$. There is no large sbottom mixing, so $m_{\tilde{b}_1}$ is given by Eq. (\ref{['e.msbottom']}). Solid (dashed) orange line: $95\%$ exclusion from the $W^+W^-$ measurement with fixed (floating) normalization of SM contribution. Thin blue contours show values of $\chi^2_\mathrm{SM+stops}/\chi^2_\mathrm{SM}$, with the thick contour indicating the region most preferred by the $W^+W^-$ measurement. Exclusions from the ATLAS stop search shown in red ATLAS8stop1. Observed (expected) exclusion from ATLAS trilepton $\chi^0_2 \chi^\pm_1$ search atlastrilepton shown as solid (dot-dashed) brown line. The purple line is the ATLAS sbottom search ATLASsb2, but this constraint can be removed by increasing sbottom mixing.