A Proposal for the Lohengrin Experiment to Search for Dark Sector Particles at the ELSA Accelerator

TL;DR

The paper proposes the Lohengrin experiment at ELSA to search for dark sector particles, especially dark photons, using a fixed-target missing momentum technique with high-intensity electron beams.

Contribution

It introduces a novel experimental setup, Lohengrin, designed to detect feebly interacting dark photons in the 1-100 MeV mass range at the ELSA accelerator.

Findings

Projected sensitivity to dark photon couplings capable of explaining dark matter relic abundance.

Potential to explore new parameter space for dark photons in the 1-100 MeV mass range.

Feasibility of using fixed-target missing momentum technique for dark sector searches.

Abstract

We present a proposal for a future light dark matter search experiment at the Electron Stretcher Accelerator ELSA in Bonn: Lohengrin. It employs the fixed-target missing momentum based technique for searching for dark-sector particles. The Lohengrin experiment uses a high intensity electron beam that is shot onto a thin target to produce mainly SM bremsstrahlung and - in rare occasions - possibly new particles coupling feebly to the electron. A well motivated candidate for such a new particle is the dark photon, a new massive gauge boson arising from a new gauge interaction in a dark sector and mixing kinetically with the standard model photon. The Lohengrin experiment is estimated to reach sensitivity to couplings small enough to explain the relic abundance of dark matter in various models for dark photon masses between approximately 1 MeV and approximately 100 MeV.