Implications of the Higgs Discovery in the MSSM Golden Region

TL;DR

The paper analyzes how a lightest MSSM Higgs in the golden region could reveal stop-sector parameters by combining measurements of the Higgs mass $m_h$ and the gluon-fusion production rate into two photons, $B\sigma(gg\to h\to \gamma\gamma)$. It shows that while the production and the $h\to \gamma\gamma$ amplitude are dominated by stop loops, the total width—and thus the branching ratio to $\gamma\gamma$—depends strongly on $m_A$ and $\mu$ through $h\to b\bar b$, making $R(B\sigma)$ sensitive to these parameters. In the golden region, with large stop mixing ($|X_t|/m_{\tilde t}\sim 2$) and relatively light stops, the contours of constant $R(B\sigma)$ and $m_h$ become nearly orthogonal in the $(m_{\tilde t}, X_t/m_{\tilde t})$ plane when $m_A$ is known, permitting estimates of $m_{\tilde t}$ and $X_t$ even if $\mu$ is not precisely known. The study underscores the importance of $m_A$ in interpreting Higgs signals and provides a pathway to probing naturalness-driven stop structure at the LHC, potentially complementing indirect methods like those proposed by Dermisek et al.

Abstract

If the lightest CP-even Higgs boson in the MSSM is discovered at the LHC, two measurements could be made simultaneously: the Higgs mass m_h and the event rate Bs(gg -> h -> gamma gamma). We study to what extent the combination of these two measurements would allow us to extract parameters in the stop mass matrix, including the off-diagonal mixing term, with a focus on the MSSM golden region where the stops are light and the mixing is large. Even though both the production cross-section and the decay amplitude are not sensitive to supersymmetric parameters outside of the stop sector, the branching ratio depends on the total decay width, which is dominated by the Higgs decay to b quarks and sensitive to both the pseudo-scalar mass m_A and the supersymmetric Higgs mass μ. In the end we find m_A is an important input in extracting the stop mass parameters, while a fair estimate of the off-diagonal mixing term could be obtained without prior knowledge of μ.

Figures (6)

• Figure 1: Plot of $R(B\sigma)= B\sigma({\rm MSSM})/B\sigma({\rm SM})$ as a function of $r$ for $m_{\tilde{t}}=500$ GeV, $m_A=400$ GeV, $\mu=200$ GeV,and $M_{\rm SUSY}=1$ TeV. The (dark) solid and (red) dashed lines are for $\tan\beta=10$ and $40$, respectively. The three sets of curves from top to bottom are for $X_t/m_{\tilde{t}}=0, -1,$ and $-2$ respectively.
• Figure 2: Contour plot of $m_{\chi_1}$ and $R(B\sigma)$ in the $\mu-M_2$ plane. In this plot $\tan\beta=30$, $M_{SUSY}=1000$ GeV, $m_{\tilde{t}_L}=m_{\tilde{t}_R}= 500$ GeV, and $X_t=-700$ GeV. The (dark) solid lines correspond to the $R(B\sigma)$ contours, whereas the (red) dashed lines are for the $m_{\chi_1}$ contours. This set of parameters would result in a Higgs mass slightly above the LEP bound of 114 GeV.
• Figure 3: Dependence on $\mu$ in the event rate $R(B\sigma)$. In these plots $\tan\beta=30$, $M_{SUSY}=500$ (solid lines) and $1000$ (dashed lines) GeV, $m_{\tilde{t}_L}=m_{\tilde{t}_R}= 300$ GeV, and $X_t=\pm 500$ and $\pm 600$ GeV. The two choices of $X_t$ correspond a Higgs mass of 116 and 119 GeV, respectively. The left plot is for $m_A=$ 400 GeV and the right for $m_A=$ 1000 GeV. In the plots we have also set the gaugino mass parameter $M_2=M_{SUSY}$.
• Figure 4: Dependence of $R(B\sigma)$ on $m_A$. In this plot $\tan\beta=30$, $M_{SUSY}=1000$ GeV, $m_{\tilde{t}_L}=m_{\tilde{t}_R}= 300$ GeV, and $X_t=\pm 500$ and $\pm 600$ GeV. These two choices of $X_t$ correspond a Higgs mass of 116 and 119 GeV, respectively. In the plot we have set $\mu=M_2=M_{SUSY}$.
• Figure 5: Contours of $R(B\sigma)$ and $m_h$ in the $m_{\tilde{t}}-X_t/m_{\tilde{t}}$ plane. This plot is for $\tan\beta=30$, $M_{SUSY}=1000$ GeV, and $m_A$=1000 GeV. The shaded regions correspond to the variation in $R(B\sigma)$ when changing $\mu$ from 200 to 1000 GeV.