Abstract: High-energy colliders offer a unique sensitivity to dark photons, the mediators of a broken dark U(1) gauge theory that kinetically mixes with the Standard Model (SM) hypercharge. Dark photons can be detected in the exotic decay of the 125 GeV Higgs boson, h→ZZD →4ℓ, and in Drell-Yan events, pp→ZD → ℓℓ. If the dark U(1) is broken by a hidden-sector Higgs mechanism, then mixing between the dark and SM Higgs bosons also allows the exotic decay h → ZDZD → 4ℓ. We show that the 14 TeV LHC and a 100 TeV proton-proton collider provide powerful probes of both exotic Higgs decay channels. In the case of kinetic mixing alone, direct Drell-Yan production offers the best sensitivity to ZD , and can probe ϵ ≳ 9 × 10−4 (4 × 10−4) at the HL-LHC (100 TeV pp collider). The exotic Higgs decay h → ZZD offers slightly weaker sensitivity, but both measurements are necessary to distinguish the kinetically mixed dark photon from other scenarios. If Higgs mixing is also present, then the decay h → ZDZD can allow sensitivity to the ZD for ϵ ≳ 10−9 − 10−6 (10−10 − 10−7) for the mass range 2mμ < mZD < mh/2 by searching for displaced dark photon decays. We also compare the ZD sensitivity at pp colliders to the indirect, but model-independent, sensitivity of global fits to electroweak precision observables. We perform a global electroweak fit of the dark photon model, substantially updating previous work in the literature. Electroweak precision measurements at LEP, Tevatron, and the LHC exclude ϵ as low as 3 × 10−2. Sensitivity can be improved by up to a factor of ∼ 2 with HL-LHC data, and an additional factor of ∼ 4 with ILC/GigaZ data.
- Beyond Standard Model
- Gauge Symmetry
- Higgs Physics
ASJC Scopus subject areas
- Nuclear and High Energy Physics