Abstract
High-energy gamma gamma colliders constitute a potential running mode of future lepton colliders such as the ILC and CLIC. We study the sensitivity of a high-energy gamma gamma collider to the Higgs portal scenario to a hidden sector above the invisible Higgs decay threshold. We show that such gamma gamma collisions could allow to probe the existence of dark sectors through the Higgs portal with precision competitive with other planned collider facilities, profiting from the unique combination of sizable cross-section with clean final state and collider environment. In addition, this search could cover the singlet Higgs portal parameter space yielding a first-order electroweak phase transition in the early Universe.
Highlights
Right: γ γ colliders setup to probe the Higgs portal above the mh/2 threshold, from a combination of reach in energy and clean collision environment
We show that such γ γ collisions could allow to probe the existence of dark sectors through the Higgs portal with precision competitive with other planned collider facilities, profiting from the unique combination of sizable cross-section with clean final state and collider environment
Invisible final states can be investigated at lepton colliders via single photon + E/ T processes, yet for the case of the Higgs portal scenario, since the mediator to the dark sector is the Higgs particle, the corresponding mono-photon rate is generally proportional to the lepton Yukawas,2 and very small
Summary
The possibility of a high-energy γ γ (or γ e) collider based on a linear e+e− collider has been considered since the early. The energy spectrum of the resulting photon beam is peaked at Eγmax, and the number of high energy photons dramatically increases for polarised beams with 2λe Pγ = −1, being λe (|λe| ≤ 1/2) the mean helicity of the initial electron and Pγ that of the laser photon In addition to this high-energy peak there is a factor 5–8 larger (in luminosity) low-energy spectrum which is produced by multiple Compton scattering and beamstrahlung photons. These low-energy collisions have a large longitudinal boost in the detector reference frame. (ii) An analytic high-energy γ γ collider luminosity spectrum for κmax = 4.8 and 2λe Pγ = −1 without multiple Compton scattering and beamstrahlung√effects obtained from [39] and labelled here Lnγcγ (y).
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