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 MotivationExotic 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 .
- 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 ConstraintsNone.
Estimates of SensitivityThere 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 , but we do not consider them here. In reference , 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 . 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  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.
Related Decay ModesIn 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 → 4b , h → 4τ and h → 2b 2τ. For light a, the relevant decay modes are h → 4γ and h → 2γ 2j.
Additional RemarksAn 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 .
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