h → MET

Contact Person(s)

Jessie Shelton, Stefania Gori
More details on this mode may be found in Section 5 of Survey of Exotic Higgs Decays (arXiv:1312.4992).

1  Theoretical Motivation

The possibility of Higgs decaying invisibly was first noted by Suzuki and Shrock [1].
A well motivated scenario for such a decay mode is Higgs decaying to dark matter [2,3]. The more minimal models of thermal dark matter annihilating via the Higgs boson are excluded by direct detection (see e.g. [4]), but more involved models do allow for such coupling [5,6].
In SUSY, the Higgs may decay to neutralinos in principle. This is typically not the case in the CMSSM [7], but it may occur in non-minimal scenarios, such as NMSSM [8,9,10] or multiple SUSY breaking sectors (goldstini) [11].
Other theoretical framework with an invisibly decaying Higgs are majorons [1,12] as well as more general pNGBs [13]; hidden sectors [14,15]; fourth-generation neutrinos [16,17]; and right-handed neutrinos [18] and their K-K excitations [7] or superpartners [19].

2  Existing Collider Studies

Invisible decays are difficult experimentally and have an irreducible background from Z→νν production. A Higgs decaying invisibly must be produced in association with another object in order to be observed. In order of production cross-section, the reasonable candidates are then:
  • gg→ h + jets
  • VBF production of h+2j
  • Wh, W→ lν
  • Zh, Z→ l+l, (bb).
tt h production generally suffer from a suppressed cross-section and a complex final state, but has been considered in [20,21].
The gg→ h + jets cross section is the largest, but suffers from a Z+j background [22], making VBF the best mode to look for invisible Higgs decays (see [23,24] for 14 TeV and [22] for 7 and 8 TeV
Ref. [22] estimates that 20 fb−1 at 8 TeV can allow limits to be placed for Br(h→ MET) >~0.4, while Ref. [25] estimates the sensitivity Br(h→ MET) >~0.25 with 300 fb−1 at 14 TeV. Meanwhile Ref. [26] estimates sensitivity for Br(h→ MET) >~0.50 with 30 fb−1 at 14 TeV. Assumptions about systematic errors are critical in obtaining these estimates.
Associated Zh production with a leptonically decaying Z boson can nearly approach the reach of VBF at LHC14 for mh=125 GeV [26], despite its much lower cross-section [27,28,29]. Including Z→ bb as well as Z→ l+l decays can incrementally improve the reach, at both the Tevatron [7] and the LHC [25].

3  Existing Experimental Searches and Limits

The best existing constraints come from ATLAS measurements targeting Zh associated production with Z→ll, which limit the invisible branching fraction to be

Screen Shot 2013-12-18 at 3.15.39 AM

at 95% CL [30] with 4.7 fb −1 at 7 TeV and 13.0 fb−1 at 8 TeV. The measurement by CMS in the same channel with the full 7 and 8 TeV data sets places a 95% CL upper bound on the invisible branching fraction of Br(h→ invisible) < 0.75(0.91) [31]. CMS also has a measurement in the VBF channel, with a 95% CL upper limit [32]

Screen Shot 2013-12-18 at 3.19.10 AM

with 19.6 fb−1 of 8 TeV data. Much weaker limits come from reinterpretation of monojet + MET measurements [33].


Here we list new experimental results pertinent to this exotic higgs decay channel.


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