Motivation and detectability of an invisibly-decaying Higgs boson at the Fermilab Tevatron

TL;DR

This paper argues that a light Higgs with mass below ~150 GeV may decay invisibly in a variety of beyond-Standard-Model scenarios, such as decays to neutralinos, Majorons, KK neutrinos, or singlet-induced channels, potentially leaving only missing energy in detectors. It analyzes two Tevatron search channels—ZH with Z decaying to leptons and Z decaying to bb—to probe invisible decays, showing that a 3σ observation is feasible for $m_H$ around 125 GeV in the dilepton channel with 30 fb$^{-1}$ and that the bb channel offers a complementary reach. The work emphasizes a holistic search strategy that combines visible and invisible final states, given the possible dominance of invisible decays in certain models. It highlights the implications for neutrino-mass generation mechanisms and TeV-scale gravity scenarios, and provides practical guidance for maximizing Tevatron sensitivity to invisibly-decaying Higgs bosons. Overall, the study maps the Tevatron’s potential to discover or constrain invisibly-decaying Higgs bosons in the low-mass region and argues for including such channels in comprehensive Higgs searches.

Abstract

A Higgs boson with mass below 150 GeV has a total decay width of less than 20 MeV into accessible Standard Model states. This narrow width means that the usual branching fractions for such a light Higgs boson are highly susceptible to any new particles to which it has unsuppressed couplings. In particular, there are many reasonable and interesting theoretical ideas that naturally imply an invisibly-decaying Higgs boson. The motivations include models with light supersymmetric neutralinos, spontaneously broken lepton number, radiatively generated neutrino masses, additional singlet scalar(s), or right-handed neutrinos in the extra dimensions of TeV gravity. We discuss these approaches to model building and their implications for Higgs boson phenomenology in future Tevatron runs. We find, for example, that the Tevatron with 30 fb^{-1} integrated luminosity can make a 3σobservation in the l+ l- plus missing transverse energy channel for a 125 GeV Higgs boson that is produced with the same strength as the Standard Model Higgs boson but always decays invisibly. We also analyze the b anti-b plus missing transverse energy final state signal and conclude that it is not as sensitive, but it may assist in excluding the possibility of an invisibly-decaying Higgs boson or enable confirmation of an observed signal in the dilepton channel. We argue that a comprehensive Higgs search at the Tevatron should include the possibility that the Higgs boson decays invisibly.

Figures (4)

• Figure 1: The distribution of the backgrounds for $l^+l^-+\hbox{${\hbox{$E$/}}_T$}\,$ as a function of the dilepton $E_T$, or equivalently, $\hbox{${\hbox{$E$/}}_T$}\,$. This distribution is plotted after all cuts and efficiencies have been applied except the cut on $E_T$.
• Figure 2: The distribution of the background and signal+background for $ZH_{\rm inv}\rightarrow l^+l^-+\hbox{${\hbox{$E$/}}_T$}\,$ as a function of the dilepton $E_T$, or equivalently, $\hbox{${\hbox{$E$/}}_T$}\,$. This distribution is plotted after all cuts and efficiencies have been applied except the cut on $E_T$.
• Figure 3: Calculation of the significance in fb$^{1/2}$, defined as $S/\sqrt{B}$, as a function of the dilepton $E_T$, or, equivalently $\hbox{${\hbox{$E$/}}_T$}\,$. The lines from top to bottom refer to $m_{H_{\rm inv}}=90, 100, 110, 120, 130, 140, 150$ GeV.
• Figure 4: Contours of $95\%$ exclusion, $3\sigma$ observation, and $5\sigma$ discovery in the $m_{H_{\rm inv}}$ vs. luminosity plane. From this plot one can learn, for example, that with $30\hbox{\rm, fb}^{-1}$ a $3\sigma$ observation is possible for $m_{H_{\rm inv}}\hbox{$\;\stackrel{<}{\sim}\;$} 125$ GeV.