Hidden Higgs Decaying to Lepton Jets

TL;DR

The paper investigates the possibility that a SM-like Higgs, potentially around $m_h\sim 100$ GeV, decays predominantly into a GeV-scale hidden sector, producing lepton jets through cascades. It develops three channels—neutralino, sneutrino, and singlet—for the Higgs to couple to the hidden sector, using a minimal $U(1)_d$ hidden sector with kinetic mixing. Using Monte Carlo simulations to map Higgs-to-hidden-sector decays onto existing LEP-1, LEP-2, and Tevatron searches, the authors identify viable regions in observable space and construct benchmark models. They conclude that the Higgs could have been hidden in current data and advocate dedicated searches leveraging lepton-jet topology, jet shapes, and invariant-mass peaks to discover or constrain such scenarios, with implications for LHC prospects and broader hidden-sector phenomenology.

Abstract

The Higgs and some of the Standard Model superpartners may have been copiously produced at LEP and the Tevatron without being detected. We study a novel scenario of this type in which the Higgs decays predominantly into a light hidden sector either directly or through light SUSY states. Subsequent cascades increase the multiplicity of hidden sector particles which, after decaying back into the Standard Model, appear in the detector as clusters of collimated leptons known as lepton jets. We identify the relevant collider observables that characterize this scenario, and study a wide range of LEP and Tevatron searches to recover the viable regions in the space of observables. We find that the Higgs decaying to lepton jets can be hidden when the event topology mimics that of hadronic backgrounds. Thus, as many as 10^4 leptonic Higgs and SUSY decays may be hiding in the LEP and Tevatron data. We present benchmark models with a 100 GeV Higgs that are consistent with all available collider constraints. We end with a short discussion of strategies for dedicated searches at LEP, the Tevatron and the LHC, that allow for a discovery of the Higgs or SUSY particles decaying to lepton jets.

Figures (10)

• Figure 1: An example of a Higgs decay to lepton jets, through the neutralino production portal of Section \ref{['sec:neutralino-channel']}. The hidden sector cascades can lead to many leptons per Higgs decay, in this case 18. This example uses the particle content and vertices of the minimal $U(1)_d$ hidden sector described in section \ref{['sec:minimal-model']}. A larger hidden sector can lead to even larger multiplicities. If the neutralinos are heavy enough to be produced close to rest, their decay products will be well-separated, and the leptons will partition into 4 distinct lepton jets. Alternatively, if the neutralinos are light and boosted, the event will consist of two groups of collimated leptons, neutralino jets.
• Figure 2: Interactions that follow from kinetic mixing between the hidden photon and hypercharge. The hidden photon couples to the electromagnetic current, including lepton pairs, as in the diagram on the left. The cross on the diagram indicates the $\epsilon$ suppression. The right two diagrams show possible decays of the SM bino to the hidden sector, which follow from gaugino kinetic mixing. The SM LSP is no longer stable, and all SUSY cascades can end in the hidden sector.
• Figure 3: Higgs and $Z$ decays to neutralinos. The neutralinos then decay into the hidden sector as in figure \ref{['f.KMcoup']}. We consider the region of the MSSM parameter space where the Higgs dominantly decays to neutralinos while the charginos are above the LEP bound of $\sim100$ GeV. In this region, we find $m_{\tilde{N}_1} < m_Z/2$, such that the $Z$ can also decay to neutralinos, as in the right diagram. This is consistent with LEP-1 constraints when $\mathrm{BR} \, (Z \rightarrow 2 \,\tilde{N}_1) \lesssim 10^{-3}$.
• Figure 4: Higgs branching ratios for the neutralino and sneutrino channels. Each plot shows the total Higgs branching ratios to the SM and hidden sector, as functions of the Higgs mass. The SM width is dominated by the branching fractions to $b \bar{b}$ and $W^+ W^-$, which are also shown separately. The parameters are fixed according to the benchmark models of Section \ref{['subsec:benchmarks']}. For each model, the Higgs decays dominantly to the hidden sector below the $W^+ W^-$ threshold, and a 100 GeV Higgs satisfies the LEP constraint $\mathrm{BR}~(h\rightarrow~b \bar{b})~<~0.2$. The Higgs widths to SM states are taken from HDECAYDjouadi:1997yw.
• Figure 5: Diagrams relevant for Higgs cascade decays into the hidden sector via the sneutrino channel. The left diagram shows the Higgs decaying into a sneutrino pair. The right two diagrams are examples of two and three body decays of the sneutrino into hidden particles plus a SM neutrino. The neutrino production implies an irreducible missing energy component for this channel, which is constrained by LEP $h \rightarrow E\!\!\!/_T$ searches, as discussed in Section \ref{['subsec:ConstrainObservables']}.