Motivation


Searches for exotic Higgs decays are a particularly rich and fruitful way to seek evidence of new physics.
  • The SM-like Higgs boson has an extremely narrow width, Γh ≅ 4.07 MeV, so that Γh/mh ≅ 3.3 ×10−5. Even a small coupling to another light state can easily open up additional sizable decay modes.
  • There are very good reasons to suspect that new physics couples preferentially to the Higgs boson, since it provides one of only a few "portals" that allow SM matter to interact with hidden-sector matter that is SM-neutral via potentially (super-)renormalizable interactions (see e.g.  [11,12,13,14]). This is the famous Higgs portal, which includes terms like

    or

    for a singlet scalar s or singlet fermion ψ. Exotic branching fractions Br(h→ ss, ψψ)  ∼ 10% only require a coupling ζ ∼ 0.01, or Λ as large as several TeV (for μ ∼ mψ). Thus exotic Higgs decays can indirectly probe new physics scales beyond the kinematic reach of the LHC, and may even provide the only evidence of a new sector at the LHC.
  • Higgs "coupling fits" constrain Br(h→BSM) <~ 20 − 60% at 95% CL, depending on assumptions, see [1,2,3,4,5,6,7] for some recent fits. Future projections suggest an ultimate precision at the LHC on this indirect measurement of Br(h→BSM) of O(5−10%) [8,9,10]. Branching fractions of O(10%) into exotic decay modes are therefore not only still allowed by existing data but will remain reasonable targets for the duration of the physics program of the LHC.
  • The data collected at the LHC7 and LHC8 may easily contain O(50,000) exotic Higgs decays per experiment, assuming  ∼ 10% exotic branching fraction. For those decay modes which pass trigger thresholds with high enough efficiency, dedicated searches represent a tremendous potential for discoveries of new physics.
  • Branching fractions as small as O(10−6) could be detected at the LHC14 with 300  fb−1, if the decay signature is both visible and clean.

References

[1]
G. Belanger, B. Dumont, U. Ellwanger, J. Gunion, and S. Kraml, Status of invisible Higgs decays, [arXiv:1302.5694].
[2]
P. P. Giardino, K. Kannike, I. Masina, M. Raidal, and A. Strumia, The universal Higgs fit, [arXiv:1303.3570].
[3]
J. Ellis and T. You, Updated Global Analysis of Higgs Couplings, [arXiv:1303.3879].
[4]
K. Cheung, J. S. Lee, and P.-Y. Tseng, Higgs Precision (Higgcision) Era begins, [arXiv:1302.3794].
[5]
A. Djouadi and G. Moreau, The couplings of the Higgs boson and its CP properties from fits of the signal strengths and their ratios at the 7+8 TeV LHC, [arXiv:1303.6591].
[6]
CMS Collaboration, Combination of standard model Higgs boson searches and measurements of the properties of the new boson with a mass near 125 GeV.
[7]
ATLAS Collaboration, Combined coupling measurements of the Higgs-like boson with the ATLAS detector using up to 25 fb−1 of proton-proton collision data.
[8]
M. E. Peskin, Comparison of LHC and ILC Capabilities for Higgs Boson Coupling Measurements, [arXiv:1207.2516].
[9]
CMS Collaboration, Projected Performance of an Upgraded CMS Detector at the LHC and HL-LHC: Contribution to the Snowmass Process, [arXiv:1307.7135].
[10]
ATLAS Collaboration, Physics at a High-Luminosity LHC with ATLAS, [arXiv:1307.7292].
[11]
R. E. Shrock and M. Suzuki, Invisible Decays of Higgs Bosons, Phys.Lett. B110 (1982) 250.
[12]
M. J. Strassler and K. M. Zurek, Echoes of a hidden valley at hadron colliders, Phys.Lett. B651 (2007) 374-379, [hep-ph/0604261].
[13]
R. Schabinger and J. D. Wells, A Minimal spontaneously broken hidden sector and its impact on Higgs boson physics at the large hadron collider, Phys.Rev. D72 (2005) 093007, [hep-ph/0509209].
[14]
B. Patt and F. Wilczek, Higgs-field portal into hidden sectors, [hep-ph/0605188].
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