h → 4j

Contact Person(s)

David Curtin, Rouven Essig, Prerit Jaiswal, Yi-Ming Zhong
More details on this mode may be found in Section 7 of Survey of Exotic Higgs Decays (arXiv:1312.4992).

Theoretical Motivation

Exotic Higgs decays to four jets generally proceed through a cascade decay : h → a a followed by a → j j, where a is a (pseudo-)scalar. A number of well-motivated theoretical models can lead to such Higgs decays and can be broadly classified into two categories :
  • a can mix with another heavier pseudo-scalar if a second Higgs doublet is present, for example in the NMSSM (or 2HDM + S models in general). This scenario allows for the decay of a to gluon jets, when a is light enough so that its decay to heavy SM fermions is kinematically forbidden. Further, in certain regions of the parameter space (see Section 2HDM + S for details), the couplings of a to the down type quarks and charged leptons can be very suppressed. In this case, a dominantly decays to light (mostly charm) jets. A similar situation also occurs in the "charming Higgs" scenario of the Little Higgs [1].
  • If there are new heavy BSM vector-like fermions that couple to a, it can decay into gluons or photons through loop processes [2,3,4]. The scenario can be realized in Little Higgs models and extra dimensional models. For ma above a few GeV up to half the Higgs mass, h→ aa→ gggg dominates over h→ aa → γγgg and h → aa→ γγγγ. In general the signal is hard to find against combinatorial background.

Existing Experimental Constraints


Estimates of Sensitivity

There are a few existing collider studies for the 14 TeV LHC run in the four-jet final state [5,6], which we briefly summarize here. There also exist collider studies which consider more exotic Higgs production modes [7], but we do not consider them here. In reference [5], Higgs production in association with leptonic W boson is considered as the production mode for mh = 120  GeV followed by the Higgs decay, h → a a → j j j j. Analysis is divided into categories depending on the mass of a:
  • ma = 4  GeV : In this case, the opening angle between the two gluons from an a decay are so small that a pair of gluons appears as a single jet, leading to Higgs final state signature of two jets, lepton and missing energy. Readers interested in the details of selection cuts are referred to reference  [5]. The authors show that a discovery at 7σ significance is possible at the LHC14 with 30  fb−1 data assuming BR(h→ aa → gggg)  ∼ 100 %. However, assuming a more realistic branching ratio of BR(h → aa → gggg)  ∼ 10 % in the post Higgs discovery era, 2σ exclusion (3σ evidence) is possible with 300 fb−1 (500 fb−1) of data at LHC14.
  • ma = 8  GeV : The opening angle between the two gluons from an a decay is larger than the previous case, so that simple jet substructure techniques can be used for discovery. Again, interested readers are referred to [5] for details of jet substructure cuts. The authors find that  ∼ 3 σ statistical significance can be reached with 30  fb−1 data assuming BR(h→ aa → gggg)  ∼ 100 %. With BR(h→ aa → gggg)  ∼ 10 %, however, 2σ exclusion (3σ evidence) requires 1000 fb−1 (3000 fb−1) of data at LHC14.
A similar jet substructure analysis on h → aa → jjjj is also presented in [6], with the consideration of the tth production channel besides the V h channel. The authors reach a similar conclusion for discovery prospects as described above. A more recent study [8] explores the ma > 15 GeV regime. It focuses on the substructure of fat-jets that contain an entire boosted Higgs decay, and that could be 2-, 3- or 4-pronged. Here as well, Higgs production in association with vector bosons is considered. The authors include two cases depending on the mass of the scalar, a: (i) light scalar (ma < 30  GeV) and (ii) heavy scalar (30  GeV < ma < mh/2). In the light scalar regime, the h→ aa → jjjj signature can be observed at a significance of 3σ with 100  fb−1 of 14 TeV LHC luminosity while for the heavy scalar case, the significance is too small to observe with the same amount of data. The above techniques can be adopted for h→ aa→ 4 b searches by adding b-tags (see Section h → 4b).

Related Decay Modes

In NMSSM and 2HDM + S models, if a is heavy enough such that decays to heavy fermions are kinematically allowed, then such decays are generally dominant for which we refer the reader to h → 4bh → 4τ and h → 2b 2τ. For light a, the relevant decay modes are h → 4γ and h → 2γ 2j.

Additional Remarks

An interesting scenario occurs when the effective agg vertex coupling is small enough that a decays through displaced vertices which can enhance the discovery potential of the channel [3].


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[3]S. Chang, P. J. Fox, and N. Weiner, Visible Cascade Higgs Decays to Four Photons at Hadron Colliders, Phys.Rev.Lett. 98 (2007) 111802, [hep-ph/0608310].
[4]S. Chang, P. J. Fox, and N. Weiner, Naturalness and Higgs Decays in the MSSM with a Singlet, JHEP 0608 (2006) 068, [hep-ph/0511250].
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[8]D. E. Kaplan and M. McEvoy, Associated Production of Non-Standard Higgs Bosons at the LHC, Phys.Rev. D83 (2011) 115004, [arXiv:1102.0704].

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