Proposed Post-LEP Benchmarks for Supersymmetry

Abstract

We propose a new set of supersymmetric benchmark scenarios, taking into account the constraints from LEP, b to s gamma, g_mu - 2 and cosmology. We work in the context of the constrained MSSM (CMSSM) with universal soft supersymetry-breaking masses and assume that R parity is conserved. We propose benchmark points that exemplify the different generic possibilities, including focus-point models, points where coannihilation effects on the relic density are important, and points with rapid relic annihilation via direct-channel Higgs poles. We discuss the principal decays and signatures of the different classes of benchmark scenarios, and make initial estimates of the physics reaches of different accelerators, including the Tevatron collider, the LHC, and e+ e- colliders in the sub- and multi-TeV ranges. We stress the complementarity of hadron and lepton colliders, with the latter favoured for non-strongly-interacting particles and precision measurements. We mention features that could usefully be included in future versions of supersymmetric event generators.

Figures (9)

• Figure 1: Qualitative overview of the locations of our proposed benchmark points in a generic $(m_{1/2}, m_0)$ plane. The light (turquoise) shaded area is the cosmologically preferred region with $0.1\leq\Omega_{\chi} h^2\leq 0.3$, whose exact shape depends on the value of $\tan\beta$, and to some extent on the Standard Model inputs $m_t$, $m_b$ and $\alpha_s$. In the dark (brick red) shaded region at bottom right, the LSP is the charged ${\tilde{\tau}}_1$, so this region is excluded. Electroweak symmetry breaking is not possible in the dark (pink) shaded region at top left. The LEP experimental constraints, in particular that on $m_h$, and measurements of $b \rightarrow s \gamma$ exert pressure from the left side. The BNL E821 measurement of $g_\mu - 2$ favours relatively low values of $m_0$ and $m_{1/2}$ for $\mu > 0$. The CMSSM benchmark points we propose are indicated roughly by the (blue) crosses. We propose points in the 'bulk' region at bottom left, along the coannihilation 'tail' extending to larger $m_{1/2}$, in the 'focus-point' region at large $m_0$, and in the rapid-annilation 'funnel' that may appear at intermediate $m_0 / m_{1/2}$ for large $\tan \beta$.
• Figure 2: The $(m_{1/2}, m_0)$ planes for $\tan \beta =$ (a) 5 ($\mu > 0$), (b) 10 ($\mu > 0$), (c) 10 ($\mu < 0$), all for $m_t = 175$ GeV, and (d) 10 ($\mu > 0$) with $m_t = 171$ GeV. In each case we have assumed $A_0 = 0$ and $m_b(m_b)^{\overline {MS}}_{SM} = 4.25$ GeV, and used the SSARD code. The near-vertical (red) dot-dashed lines are the contours $m_h = 113$ GeV, as evaluated using the FeynHiggs code. The medium (dark green) shaded regions are excluded by $b \to s \gamma$. The light (turquoise) shaded areas are the cosmologically preferred regions with $0.1\leq\Omega_{\chi} h^2\leq 0.3$. In the dark (brick red) shaded regions, the LSP is the charged ${\tilde{\tau}}_1$, so this region is excluded. The regions allowed by the E821 measurement of $a_\mu$ at the 2-$\sigma$ level are shaded (pink) and bounded by solid black lines, with dashed lines indicating the 1-$\sigma$ ranges. Electroweak symmetry breaking is not possible in the dark (pink) shaded region at the top left of panel (d). The (blue) crosses denote the proposed benchmark points A to F.
• Figure 3: The $(m_{1/2}, m_0)$ planes for $\tan \beta =$ (a) 20 ($\mu > 0$), (b) 35 ($\mu > 0$), (c) 35 ($\mu < 0$), and (d) 50 ($\mu > 0$), found using SSARD and assuming $A_0 = 0, m_t = 175$ GeV and $m_b(m_b)^{\overline {MS}}_{SM} = 4.25$ GeV. The notations are the same as in Fig. \ref{['fig:locations1']}. The (blue) crosses denote the proposed benchmark points G to M. At larger $\tan\beta$, the size as well as the exact shape of the cosmologically preferred region obtained is subject to considerable uncertainty, and different programs yield different answers for the same fixed values of the input parameters. The differences arise due to different calculational algorithms, and to neglecting different sets of higher-order terms. We elaborate more on these issues in Section \ref{['uncertainties']}.
• Figure 4: Left: the cosmologically preferred region obtained with Neutdriverneut and mass spectra from the BMPZ code Pierce:1997zz, for the same parameters as in Fig. \ref{['fig:locations2']}d. Right: the corresponding result from SSARD, but for $\tan\beta=52$ and $m_t=170.3$ GeV.
• Figure 5: Characteristic features of the spectra and principal decay modes in the two classes of benchmark points.