[Paper Review] Observability of MSSM Higgs bosons via sparticle decay modes in CMS

F. Moortgat, S. Abdullin+1 more|ArXiv.org|Dec 4, 2001

Particle physics theoretical and experimental studies18 citations

TL;DR

This paper investigates the observability of heavy MSSM Higgs bosons ($A^0$, $H^0$) decaying into pairs of next-to-lightest neutralinos ($\chi^0_2$), followed by $\chi^0_2 \to l^+l^-\chi^0_1$, resulting in a clean four-lepton + missing transverse energy signature at the LHC. Using CMS detector simulations, the study shows that this channel enables discovery of heavy Higgs bosons in the 230–450 GeV mass range for low to intermediate $\tan\beta$, provided neutralinos and sleptons are light enough, with backgrounds sufficiently suppressed by kinematic and topological cuts.

ABSTRACT

We discuss the possibilities to observe the decays of heavy SUSY Higgs bosons into supersymmetric particles at the LHC. Such an observation would be of interest either in a discovery search if sparticle modes are the dominant ones, or in a study of additional decay modes, bringing information on the SUSY scenario potentially at work. We will focus on the most promising channel where the heavy neutral Higgses decay into a pair of next-to-lightest neutralinos, followed by their decay into two leptons and the LSP, thus leading to four isolated leptons + missing E_T as the main final state signature. A study with the CMS detector shows that the background (SM + SUSY) can be sufficiently suppressed and that in the mass region between m_A = 230 and 450 GeV, for low and intermediate values of tan beta, the signal would be visible provided neutralinos and sleptons are light enough.

Motivation & Objective

• To assess the discovery potential of heavy MSSM Higgs bosons ($A^0$, $H^0$) when decaying into supersymmetric particles rather than Standard Model particles.
• To evaluate whether the $A^0,H^0 \to \chi^0_2\chi^0_2 \to 4l + E_T^{miss}$ channel provides a viable alternative to SM decay modes in low-$\tan\beta$ regions where $\tau\tau$ decay is suppressed.
• To identify and suppress dominant SM and SUSY backgrounds (e.g., $ZZ$, sneutrino pair production, sparticle cascade decays) using kinematic and topological selection criteria.
• To determine the parameter space (in $m_A$, $\tan\beta$, $M_2$, $\mu$, $m_{\tilde{l}}$) where this signal remains observable despite competing decay modes and background contributions.

Proposed method

• The study uses the CMS detector simulation framework to model signal and background events for the $A^0,H^0 \to \chi^0_2\chi^0_2 \to 4l + E_T^{miss}$ decay chain.
• Signal events are generated with the MSSM framework, varying key parameters: $m_A$, $\tan\beta$, $\mu$, $M_1$, $M_2$, $m_{\tilde{l}}$, and $m_{\tilde{q},\tilde{g}}$.
• Background suppression relies on multiple selection criteria: requiring four isolated leptons, $E_T^{miss} > 40$ GeV, $Z$-boson veto to reject $Z\to ll$ decays, and limiting jet activity to two jets with $E_T < 50$ GeV.
• The $ZZ$ background is the dominant SM background, but it is suppressed by the four-lepton and $Z$-veto requirements.
• Sparticle-induced backgrounds (e.g., sneutrino pair production, squark/gluino cascade decays) are mitigated by requiring low jet multiplicity and $E_T^{miss}$ cuts.
• Discovery potential is evaluated at 100 $fb^{-1}$ integrated luminosity, with signal significance assessed via event counting after successive cuts.

Experimental results

Research questions

• RQ1 Can the $A^0,H^0 \to \chi^0_2\chi^0_2 \to 4l + E_T^{miss}$ decay channel provide a detectable signal for heavy MSSM Higgs bosons in the low-$\tan\beta$ regime where SM decay modes fail?
• RQ2 How effective are kinematic and topological cuts in suppressing dominant SM ($ZZ$) and SUSY ($\tilde{\nu}\tilde{\nu}$, $\tilde{q}/\tilde{g}$ cascade) backgrounds in this channel?
• RQ3 What is the impact of varying $M_2$, $\mu$, $m_{\tilde{l}}$, and $m_{\tilde{q},\tilde{g}}$ on the signal visibility and discovery reach in the $m_A$–$\tan\beta$ plane?
• RQ4 To what extent do light squarks and gluinos compromise the signal significance, and can this be mitigated with additional cuts?
• RQ5 How does the branching ratio of $\chi^0_2 \to l^+l^-\chi^0_1$ depend on $\mu$, $M_1$, $M_2$, and $m_{\tilde{l}}$, and how does this affect the overall signal rate?

Key findings

• The $A^0,H^0 \to \chi^0_2\chi^0_2 \to 4l + E_T^{miss}$ channel provides a clean and detectable signature in the mass range $m_A \sim 230$–450 GeV for $\tan\beta \lesssim 40$ at 100 $fb^{-1}$.
• With $M_2 \approx 120$ GeV, $\mu \approx -500$ GeV, and $m_{\tilde{l}} \approx 250$ GeV, the signal remains observable despite background suppression.
• The $ZZ$ background is the dominant SM background but is effectively suppressed by the four-lepton and $Z$-veto requirements.
• Sparticle backgrounds from sneutrino pair production and squark/gluino cascade decays are suppressed by requiring at most two jets with $E_T < 50$ GeV and limiting $E_T^{miss}$.
• For $m_{\tilde{q},\tilde{g}} \lesssim 500$ GeV, the squark/gluino background becomes comparable to sneutrino production, reducing the discovery reach, but remains manageable with additional cuts.
• The signal discovery reach is strongly dependent on $|\mu|$ and $m_{\tilde{l}}$: larger $|\mu|$ and smaller $m_{\tilde{l}}$ enhance the $\chi^0_2 \to l^+l^-\chi^0_1$ branching ratio, improving signal visibility.