Contact Person(s)
Jessie Shelton, David McKeen, and Tao Liu
More details on this mode may be found in Sec. 13 of the Survey of Exotic Higgs Decays, arXiv:1312.4992.
Theoretical Motivation
Here, we consider the decay h→ 2γ+MET. This signature can be realized in several ways. NonResonant:First, consider the nonresonant signature where the photons come from opposite sides of the initial twobody decay, h→ X X, followed by X→ γY on each side of the event with Y a detectorstable, neutral particle.
This can occur in gaugemediated SUSYbreaking models where the lightest neutralino is mainly bino, and decays via χ_{1} ^{0}→ γ~G. Minimal models of gauge mediation make it difficult to obtain a bino with m_{~B} < m_{h}/2 while keeping winos and gluinos sufficiently heavy to avoid constraints. However, more general models of gauge mediation [1] can allow this spectrum to be realized [2].
More generally, this signature may be realized by having two new (Majorana) fermions χ_{1} and χ_{2}, with a dipole coupling
(1)
and a dimension five Higgs portal coupling c_{22}  H  ^{2}( χ_{2}χ_{2} + χ_{2}^{†} χ_{2}^{†}). In this case, both m_{χ1} and m_{χ2} are parameters of the model. It is natural to extend this simple model to include in addition offdiagonal couplings c_{12}  H  ^{2}( χ_{2} χ_{1} + χ_{2}^{†} χ_{1}^{†}) and couplings of the Higgs directly to the lighter of the two new fermions, c_{11} H  ^{2}( χ_{1} χ_{1} + χ_{1}^{†} χ_{1}^{†}). This generic model would then also yield h→ 1 γ+ MET and h→ MET signatures with relative branching fractions uniquely determined by the c_{ij}. Previous study of this topology in the MSSM has been performed in [2] and, for the heavier MSSM Higgses, in [3].  Resonant: Second is the case where the photons reconstruct an intermediate resonance, h→ X X, with X→ γγ on one side and X→ invisible on the other.
This can be simply realized in a bottomup fashion by introducing a renormalizable Higgs portal interaction leading to a coupling of a to h, λH^{2}a^{2}, and also coupling a to photons and to a neutral, detectorstable particle χ via, e.g.,
(2)
M and M′ are the scales of the two dimensionfive operators, and we have assumed that a is a real pseudoscalar and that χ is a Dirac fermion for definiteness. For some regions of parameter space, a→γγ and a→―χχ can have comparable branching fractions, making h→ 2γ+MET an important final state. Unlike the nonresonant case, the resonant signature has the useful additional handle that the two photons should reconstruct m_{a}, improving the search prospects. This simplified model can be trivially generalized to the case that the Higgs decays to two distinct states, a_{1} and a_{2}, with a_{1}→γγ and a_{2}→inv. This can proceed through a dimensionfour Higgs portal interaction, λ_{12}  H  ^{2}a_{1}a_{2}, if a_{1} couples to photons while a_{2} decays invisibly. This decay mode can dominate over h→inv. or h→4γ if λ_{12} >> λ_{11,22} where λ_{11,22} are the coupling constants of the other allowed Higgs portal interactions, λ_{11}  H  ^{2}a_{1}^{2}+λ_{22}  H  ^{2}a_{2}^{2}. While, in this resonant case, we limit our study to the situation m_{a1} ≅ m_{a2} ≡ m_{a}, the two intermediate particles having different masses is a wellmotivated possibility.  Cascade: The last decay topology we consider involves the initial decay h→ XY, followed by X→ YZ, Z→γγ with Y again appearing as missing energy in the detector. A concrete model for this involves neutral (Majorana) fermions χ_{1} and χ_{2} coupled to the Higgs through c_{12}H^{2}(χ_{2}χ_{1}+χ_{2}^{†}χ_{1}^{†}), with χ_{1} stable on detector scales, and a scalar s that can decay to two photons through the dimensionfive operator sF_{μν}F^{μν}.^{1} The decay can proceed through h→χ_{1}χ_{2}, and χ_{2}→ sχ_{1}, s→γγ if there is also a Yukawa interaction between s and χ_{1,2},given by y_{12}s(χ_{2}χ_{1}+χ_{2}^{†}χ_{1}^{†}).
Existing Experimental Searches and Limits
We focus on direct limits on the simplified models described above, ignoring modeldependent indirect limits on searches for e.g., gauginos produced via DrellYan. GMSB searches at the LHC have good prospects for discovering or excluding exotic Higgs decays into 2γ+MET, in both the resonant and nonresonant scenarios. The ATLAS search for 2γ+MET using 7 TeV data [4] has some sensitivity, setting limits of <~15% on the exotic Higgs branching fraction over much of the parameter space. The more recent CMS study using 4.04 fb^{−1} of 8 TeV data [5] sets the current best limits. This search selects events with at least two photons and at least one central jet, and bins events in 5 exclusive MET bins beginning from a minimum of 50 GeV. We show the reach of this search in the resonant and nonresonant cases in Figs. 1 and 2 (left), as a function of m_{χ1} in the nonresonant topology and m_{a} in the resonant topology. In Fig. 2 (right) we show the reach in the case of the cascade topology as a function of m_{s}, setting m_{χ1}=0 and m_{χ2}=60 GeV. We find that the limit obtained in this case is not very sensitive to the value of m_{χ2}=60 GeV chosen. In all three topologies the Br(h→2γ+MET) can be constrained at the level of a few percent over much of the parameter space.Figure 1: Approximate 95% C.L. upper limit on (σ/σ_{SM}) ×Br(h→ χ_{2}χ_{2}→ 2γ+MET) from the results of Ref. [5], for multiple values of m_{χ2} as indicated by the text labeling the different curves. Solid lines correspond to 100% photon efficiency, and dashed lines to a (flat) 80% photon efficiency.
Figure 2: Approximate 95% C.L. upper limit on (σ/σ_{SM})× Br(h→ aa→ 2γ+MET) from the 2γ+MET search in Ref. [5]. The solid line corresponds to 100% photon efficiency, and the dashed line to a (flat) 80% photon efficiency. Left: Resonant case, where h→ aa, one a decays to γγ and the other decays invisibly. Right: Cascade case, where h→χ_{1}χ_{2}, χ_{2}→ sχ_{1}, s→γγ. Here m_{χ1}=0 and m_{χ2}=60 GeV (the limit is insensitive to the particular value of m_{χ2} as long as it is kinematically allowed).
References

[1] P. Meade, N. Seiberg, and D. Shih, General Gauge Mediation, Prog.Theor.Phys.Suppl. 177 (2009) 143158, [arXiv:0801.3278].

[2] J. D. Mason, D. E. Morrissey, and D. Poland, Higgs Boson Decays to Neutralinos in LowScale Gauge Mediation, Phys.Rev. D80 (2009) 115015, [arXiv:0909.3523].

[3] J. L. DiazCruz, D. K. Ghosh, and S. Moretti, The Diphoton signature of Higgs bosons in GMSB models at the CERN LHC, Phys.Rev. D68 (2003) 014019, [hepph/0303251].

[4] ATLAS Collaboration, G. Aad et. al., Search for diphoton events with large missing transverse momentum in 7 TeV protonproton collision data with the ATLAS detector, Phys.Lett. B718 (2012) 411430, [arXiv:1209.0753].[5] CMS Collaboration, Search for supersymmetry in events with photons and missing energy.
Footnotes:
^{1}The s F_{μν}F^{μν} operator could arise through mixing between s and h, see for example Sec. , although that would lead to a very suppressed h→ 2γ+MET branching ratio compared to final states like bb+MET. For 2γ+MET to be dominant, the s F_{μν}F^{μν} operator would have to be generated by a direct coupling of s to electricallycharged matter, e.g. (heavy) vectorlike leptons. For a similar model, see the γγjj page.File translated from T_{E}X by T_{T}H, version 4.03. On 11 Dec 2013, 15:34.