Collider Probes of the MSSM Higgs Sector with Explicit CP Violation

TL;DR

This work analyzes the MSSM with explicit CP violation in the Higgs sector using the CPX benchmark to study collider phenomenology in SM-like search channels. It combines radiative-correction-enhanced Higgs couplings, derived self-couplings, and realistic collider simulations to map coverage at the Tevatron and LHC, revealing small parameter regions where all neutral Higgs bosons evade standard detection due to decays into lighter Higgses or suppressed couplings. The study highlights the importance of complementary channels and the potential need for dedicated analyses (e.g., $H_2\to H_1H_1$ decays) to fully probe CPX scenarios, and it provides analytic tools (CPDECAYCPHDECAY) for Higgs couplings and self-couplings in CP-violating two-Higgs-doublet models. Overall, the results underscore both the robustness of SM-like Higgs searches in many CPV scenarios and the necessity of exploring nonstandard signatures to fully test the MSSM Higgs sector with explicit CP violation.

Abstract

We investigate the hadron collider phenomenology of the Minimal Supersymmetric Standard Model (MSSM) with explicit CP violation for Higgs bosons that can be observed in Standard Model search channels: W/ZH(->b-bbar) at the Tevatron, and gg->H(->gamma-gamma), t-tbar-H(->b-bbar) and WW->H(->tau+tau-) at the LHC. Our numerical analysis is based on a benchmark scenario proposed earlier called CPX, which has been designed to showcase the effects of CP violation in the MSSM, and on several variant benchmarks. In most of the CPX parameter space, these hadron colliders will find one of the neutral MSSM Higgs bosons. However, there are small regions of parameter space in which none of the neutral Higgs bosons can be detected in the standard channels at the Tevatron and the LHC. This occurs because the neutral Higgs boson with the largest coupling to W and Z bosons decays predominantly into either two lighter Higgs bosons or a Higgs boson and a gauge boson, whilst the lighter Higgs boson has only small couplings to the W and Z bosons and the top quark. For other choices of CP-violating parameters, all three neutral Higgs bosons can have significant couplings to W and Z bosons, producing overlapping signatures: these may or may not be distinguishable from backgrounds. The existence of these regions of parameters provides a strong motivation for a detailed experimental simulation of these channels.

Figures (13)

• Figure 1: Approximate LEP exclusion limits in the $M_{H_1}$--$\tan\beta$ plane for various CPX scenarios, using combined LEP results. The light grey covers all the region of parameter space that is consistent with electroweak symmetry breaking, the medium grey shows the exclusion from $e^+ e^- \to Z H_i$, the dark grey shows the region excluded by $Z^*\to H_i H_j \to 4b$ searches, and the black region is excluded by both searches.
• Figure 2: LEP exclusion limits in the CPX benchmark scenario in the $M_{H^+}$--$\tan \beta$ plane for different values of the phases arg$(A)$ and arg$(m_{\tilde{g}})$ of the trilinear couplings $A_{t,b}$ and the gluino mass parameter, respectively. The four panels show the results for (0,0); (90,0); (90,90) and (135,90) degrees, respectively. The light grey region is disallowed theoretically, the medium grey region is excluded by the absence of $Z H_1$, $45^\circ$-hatched region by the absence of $H_1 H_2$, $135^\circ$-hatched region by the absence of $Z H_2$, and the horizontally-hatched region by the absence of $H_1 H_3$.
• Figure 3: Panels (a) and (b) are similar to Fig. \ref{['fig:lep1']}, but for CP-violating phases (60,60) and (140,140) degrees. Panels (c) and (d) show two special scenarios 3HGC1 and 3HGC2, which are particularly challenging for all colliders: 3HGC1: $M_{\rm SUSY}=0.5$ TeV, $\bar{A}=1.95$, $\bar{\mu}=2.4$, arg$(A)=\arg(m_{\tilde{g}})=75^\circ$; 3HGC2: $M_{\rm SUSY}=0.5$ TeV, $\bar{A}=2$, $\bar{\mu}=2$, arg$(A)=\arg(m_{\tilde{g}})=145^\circ$, $M_{\widetilde{g}}=0.5$ TeV. The shadings and hatchings have the same significances as in Fig. \ref{['fig:lep1']}.
• Figure 4: The non-monotonic behavior of $M_{H_1}$, the mass of the lightest neutral Higgs boson, in the CPX scenario with arg($A_t$) = arg($m_{\widetilde{g}}$) = 140$^\circ$ for different values of $M_{H^+}$. The dip for $15 < \tan \beta < 30$ is due to the behavior of the radiative corrections from the sbottom sector, which are screened at large $\tan \beta$, as discussed in the text.
• Figure 5: Approximate Tevatron/LHC discovery and LEP exclusion limits in the $M_{H_1}$--$\tan\beta$ plane for the CPX scenario with both phases set to: (a) $90^\circ$, (b) $60^\circ$, (c) $30^\circ$, and (d) $0^\circ$. The reach of the Tevatron $W/ZH_i(\to b\bar{b})$ search is shown as $45^\circ$ lines and that of the combined LHC search channels as $135^\circ$ lines.The combined LEP exclusion is shown in medium gray, superimposed on the theoretically allowed region in light grey.