Illuminating Dark Photons with High-Energy Colliders (1412.0018v2)

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 -> Z Z_D -> 4l, and in Drell-Yan events, pp -> Z_D -> 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 -> Z_D Z_D -> 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 Z_D, and can probe epsilon >~ 9 x 10^-4 (4 x 10^-4) at the HL-LHC (100 TeV pp collider). The exotic Higgs decay h -> Z Z_D 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 -> Z_D Z_D can allow sensitivity to the Z_D for epsilon >~ 10^-9 - 10^-6 (10^-10 - 10^-7) for the mass range 2 m_mu < m_(Z_D) < m_h/2 by searching for displaced dark photon decays. We also compare the Z_D 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 epsilon as low as 3 x 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.

• The paper demonstrates that exotic Higgs decays, via channels like h → ZZ_D and Z_D Z_D, offer promising pathways for dark photon detection.
• It analyzes Drell-Yan production and collider sensitivity, revealing strong potential at both the 14 TeV LHC and future 100 TeV proton-proton colliders.
• The study integrates findings from direct collider searches with electroweak precision tests, enhancing our understanding of dark sector physics beyond the Standard Model.

Exploring Dark Photon Detection via High-Energy Colliders

The paper "Illuminating Dark Photons with High-Energy Colliders" investigates the potential for high-energy colliders, particularly the Large Hadron Collider (LHC) and a proposed 100 TeV proton-proton collider, to probe dark photons. Dark photons are mediators of a broken dark $U(1)$ gauge symmetry that kinetically mixes with the Standard Model (SM) hypercharge. This paper focuses on their detection through the exotic decays of the Higgs boson and Drell-Yan processes.

Key Findings

1. Exotic Higgs Decays: The paper explores two main channels for the production of dark photons via exotic Higgs decays—$h \to Z Z_D \to 4\ell$ and $h \to Z_D Z_D \to 4 \ell$, where $Z_D$ denotes the dark photon. It shows that both channels provide a potential pathway for detecting dark photons, especially for their masses below the $Z$ boson mass.
2. Drell-Yan Production: The paper notes that the kinetic mixing allows direct production of dark photons through Drell-Yan events, $pp \to Z_D \to \ell\ell$. This method offers the strongest sensitivity for dark photons if Higgs mixing is not present.
3. Collider Sensitivity: The 14 TeV LHC's sensitivity, particularly at the high-luminosity (HL) stage, and future 100 TeV proton-proton colliders are evaluated for their potential to probe dark photons. The calculations show significant potential for both colliders to explore previously inaccessible regions of parameter space.
4. Electroweak Precision Tests (EWPTs): The authors perform a global electroweak fit of the dark photon model to compare collider-based sensitivities with the model-independent sensitivity of historical and prospective electroweak precision observables. It finds that these provide an indirect yet notable sensitivity to dark photons.

Implications

The implications of detecting dark photons through these processes are twofold. Practically, it provides a path for exploring high-impact physics beyond the current SM with significant precision and access to new mass ranges. Theoretically, the paper of dark photons enriches our understanding of dark sector physics, possibly revealing aspects of universe's composition and governing symmetries.

Future Prospects

Future developments in this research area could involve enhanced experimental setups at colliders, allowing more precise measurements and possibly new detection techniques for dark photons. The theoretical understanding and assumptions behind kinetic and Higgs mixing theories may also evolve, refining the predictions and sensitivity analyses.

Conclusion

This paper lays a robust foundation for utilizing high-energy colliders in the search for dark photons, highlighting viable detection channels and setting the stage for future experiments. The proposed searches could bridge existing gaps in particle physics, providing crucial insights into phenomena beyond the SM. The clarity and precision of numerical results and claims offer a compelling case for continued exploration in this promising field.

This research significantly contributes to the ongoing discourse regarding the exploration of hidden sectors and the potential discovery of new particles that could profoundly impact our understanding of fundamental physics. Collectively, the proposed collider probes complement indirect methods like EWPTs, together charting a promising path forward in the quest for dark photons.