Multichannel assault on natural supersymmetry at the high luminosity LHC

Recent clarifications of naturalness in supersymmetry robustly require the presence of four light Higgsinos with mass $\sim 100–300\mathrm{GeV}$ while gluinos and (top) squarks may lie in the multi-TeV range, possibly out of LHC reach. We project the high-luminosity ($300–3000{\mathrm{fb}}^{-1}$) reach of LHC14 via gluino cascade decays and via same-sign diboson production. We compare these to the reach for neutralino pair production ${\tilde{Z}}_1{\tilde{Z}}_2$ followed by ${\tilde{Z}}_2\to {\tilde{Z}}_1{\ell }^{+}{\ell }^{-}$ decay to soft dileptons which recoil against a hard jet. It appears that $3000{\mathrm{fb}}^{-1}$ is just about enough integrated luminosity to probe naturalness with up to 3% fine-tuning at the $5\sigma$ level, thus either discovering natural supersymmetry or else ruling it out.

Figure 1

High-luminosity reach of CERN LHC for natural SUSY in the $m_0$ vs $m_{1/2}$ plane for $\mu =150\mathrm{GeV}$, $m_A=1\mathrm{TeV}$, $\tan \beta =15$ and $A_0=-1.6m_0$ in the NUHM2 model. To aid the reader, we note that $m_{\tilde{g}}\sim 2.5m_{1/2}$.

Figure 2

Feynman diagram for $pp\to {\tilde{Z}}_1{\tilde{Z}}_2$ production followed by ${\tilde{Z}}_2\to {\ell }^{+}{\ell }^{-}{\tilde{Z}}_1$ plus radiation of a gluon jet from the initial state.

Figure 3

$S/\sqrt{B}$ from HL-LHC for $pp\to {\tilde{Z}}_1{\tilde{Z}}_{2}j$ followed by ${\tilde{Z}}_2\to {\tilde{Z}}_1{\ell }^{+}{\ell }^{-}$ decay versus $\mu$, scaled for the luminosity from Ref. [50]. The blue lines are for $m_{1/2}=1000\mathrm{GeV}$ while red lines are for $m_{1/2}=800\mathrm{GeV}$.

Figure 4

Plot of ${\mathrm{\Delta }}_{\mathrm{EW}}$ contours (red) in the $m_{1/2}$ vs $\mu$ plane of the NUHM2 model for $A_0=-1.6m_0$, $m_0=5\mathrm{TeV}$ and $\tan \beta =15$. We also show the region excluded by LHC8 gluino pair searches (left of the solid blue contour), and the projected region accessible to LHC14 searches via the SSdB channel with $300/3000{\mathrm{fb}}^{-1}$ of integrated luminosity (dashed/dot-dashed contours). The LHC14 reach via the ${\tilde{Z}}_1{\tilde{Z}}_{2}j$ channel is also shown, assuming it is insensitive to the choice of $m_{1/2}$ in the low-${\mathrm{\Delta }}_{\mathrm{EW}}$ region of interest. We also show the reach of various ILC machines for Higgsino pair production (black contours). The blue (gray) shaded region is excluded by LEP2 (LEP1) searches for chargino pair production. To aid the reader, we note that $m_{\tilde{g}}\simeq 2.5m_{1/2}$.