Search for Light Dark Sectors Using Electron-Photon Collisions

Abstract

The dark photon is a new gauge boson that naturally arises in many beyond the Standard Model theoretical models, featuring interactions that resemble quantum electrodynamics. Due to this feature, it is often considered the portal between dark and visible sectors. For this reason, it has become the target of many experimental searches worldwide. In this work, we propose a search for dark photons based on the Inverse Compton scattering, $γe^- \rightarrow A^\prime e^-$, to be conducted at electron accelerators. In this setup, photons from a laser source would impinge on the accelerated electron beam, producing a dark photon in the final state. We propose an experimental setup to take advantage of the photon counting technique, and we derive the projected sensitivity by considering the energy of the incident photon to be about 1 eV and an electron beam of 3 GeV. We show that this experimental setup could cover an unexplored region of parameter space and constitute a promising probe for dark sectors in the future.

Figures (10)

• Figure 1: Upper exclusion limits in the parameter space of the dark photon mass $m_{A^{\prime}}$ (x-axis) and the kinetic mixing parameter $\varepsilon$ (y-axis). This figure shows only current experimental bounds, excluding those that assume the dark photon is a dark matter candidate, which is not considered in this work.
• Figure 2: Feynman diagrams of the inverse Compton scattering production of dark photons.
• Figure 3: Cross section for $e^-\gamma \to e^- A'$ as a function of the dark photon mass $m_{A'}$ for different collision angles $\theta$. The plotted cross section is normalized by $\varepsilon^2$, allowing the results to be rescaled for any choice of the kinetic mixing parameter $\varepsilon$.
• Figure 4: Cross section $\sigma(e^-\gamma \to e^- A')$ normalized by $\varepsilon^2$ as a function of the laser wavelength $\lambda$ for different collision angles $\theta$, with fixed dark photon mass $m_{A'} = 1~\mathrm{keV}$. The vertical gray dashed lines indicate the optimal sensitivity region, $400~\mathrm{nm} \leq \lambda \leq 4000~\mathrm{nm}$, and the black dashed line shows the wavelength used in this work ($\lambda \simeq 1~\mathrm{eV}$), corresponding to a 1 eV laser beam. This figure is shown for illustrative purposes to highlight the variation of the cross section with wavelength and incidence angle.
• Figure 5: Proposed experimental setup of the experiment illustrating an electron beam (green) with an energy of 3 GeV colliding with a laser of $\mathcal{O}(\mathrm{eV})$ positioned at a certain angle to produce dark photons. The X-ray detectors (and/or calorimeters for high energy photons) detect predominantly background photons.