Higgs boson coupling measurements and direct searches as complementary probes of the phenomenological MSSM

The parameter space of the minimal supersymmetric standard model (MSSM) can be probed via many avenues, such as by precision measurements of the couplings of the $\sim 126\mathrm{GeV}$ Higgs boson, as well as the direct searches for supersymmetry (SUSY) partners. We examine the connection between these two collider observables at the LHC and International Linear Collider (ILC) in the $19/20$-parameter phenomenological MSSM (pMSSM). Within this scenario, we address two questions: (i) How will potentially null direct searches for SUSY at the LHC influence the predicted properties of the lightest SUSY Higgs boson? (ii) What can be learned about the properties of the superpartners from precision measurements of the Higgs boson couplings? In this paper, we examine these questions by employing three different large sets of pMSSM models with either the neutralino or gravitino being the lightest supersymmetric particle. We make use of the ATLAS direct SUSY searches at the $7/8\mathrm{TeV}$ LHC as well as expected results from 14 TeV operations, and the anticipated precision measurements of the Higgs boson couplings at the 14 TeV LHC and at the ILC. We demonstrate that the future Higgs coupling determinations can deeply probe the pMSSM parameter space and, in particular, can observe the effects of models that are projected to evade the direct searches at the 14 TeV LHC with $3{\mathrm{ab}}^{-1}$ of integrated luminosity. In addition, we compare the reach of the Higgs coupling determinations to the direct heavy Higgs searches in the $M_A-\tan \beta$ plane and show that they cover orthogonal regions. This analysis demonstrates the complementarity of the direct and indirect approaches in searching for supersymmetry, and the importance of precision studies of the properties of the Higgs boson.

Figure 1

Histograms of signal strengths for $h\to \gamma \gamma$ in the $gg$-fusion (top left) and vector boson fusion (top right) production channels for the subset of neutralino models that predict $m_h=126\pm 3\mathrm{GeV}$. The blue (red) histogram represents models before any ATLAS searches (after the 7 and 8 TeV SUSY searches) are applied, while the green (purple) histograms show models that are expected to survive the zero-lepton jets plus MET plus the $0,1\text{−}\ell$ stop searches at 14 TeV, assuming a luminosity of 300 $(3000){\mathrm{fb}}^{-1}$. The ratio $r_{\text{total}}$ for the total width of the Higgs is analogously shown in the bottom panel.

Figure 2

Histograms of the ratio of partial widths for $h\to \gamma \gamma$ for the subset of neutralino (top), gravitino (lower left) and low-FT models (lower right) that predict $m_h=126\pm 3\mathrm{GeV}$. The blue (red) histogram represents models before any ATLAS searches (after the 7 and 8 TeV SUSY searches) are applied while the green (purple) histograms show models that are expected to survive both the zero-lepton jets plus MET and the $0,1\text{−}\ell$ stop searches at 14 TeV, assuming an integrated luminosity of 300 $(3000){\mathrm{fb}}^{-1}$. The vertical lines show the expected future limits on $r_{\gamma \gamma }$, and are discussed in the text.

Figure 3

Same as the previous figure but now for $h\to gg$.

Figure 4

Same as in Fig. 2 but now for $h\to b\overline{b}$.

Figure 5

Same as in Fig. 2 but now for $h\to {\tau }^{+}{\tau }^{-}$.

Figure 6

Values of the ratio $r_{bb}$ as a function of the lightest sbottom mass for the neutralino model set incorporating the influence of the ATLAS direct SUSY searches. The lower panel shows those models probed by the searches at 14 TeV.

Figure 7

Same as the previous figure but now for the gravitino model set.

Figure 8

Same as the previous figure but now for the low-FT model set.

Figure 9

Branching fraction of the invisible Higgs decay $h\to {\tilde{\chi }}_1^0{\widetilde{{\chi }_1}}^0$ for neutralino LSP models (top) with the observed Higgs mass. The points are color coded according to their coverage by the LHC direct SUSY searches. The analogous results for the gravitino (bottom left) in the case of a neutralino NLSP, and for the low-FT (bottom right) model sets are also shown.

Figure 10

Histograms of the predicted values of the ratio $r_{tt}$, defined in the text, for the various pMSSM model sets: neutralino (red, upper), gravitino (green, middle), and low FT (blue, lower).

Figure 11

Coverage of the pMSSM parameter space for the neutralino model set in the $M_A-\tan \beta$ plane, showing the fraction of models probed in each bin by the anticipated sensitivity to the combined $\gamma \gamma$, $\tau \tau$, and $b\overline{b}$ Higgs couplings at various colliders as indicated. The white curves correspond to the present limits from the direct searches for $H/A\to \tau \tau$.