Probing hidden spin-2 mediator of dark matter with NA64e, LDMX, NA64$\mu$ and M$^3$

TL;DR

This paper investigates the potential of fixed-target experiments to detect a hidden spin-2 mediator linking Standard Model particles and dark matter, analyzing missing-energy signatures and experimental sensitivities.

Contribution

It introduces a simplified model with a spin-2 mediator coupling to SM and dark matter via dimension-5 operators and evaluates experimental reach for detection at NA64, LDMX, and M3.

Findings

Derived expected experimental sensitivities for spin-2 mediator detection.

Analyzed the impact of nuclear and atomic form factors on emission spectra.

Estimated the total cross-section and detection prospects for the mediator.

Abstract

The connection between Standard Model (SM) particles and dark matter (DM) can be introduced via hidden spin-2 massive mediator. In the present paper we consider the simplified benchmark link between charged lepton sector of SM and DM particles which are considered to be a hidden Dirac fermions from the dark sector. The regarding couplings are established through the dimension-5 operators involving spin-2 mediator field and the energy-momentum tensors of both SM and DM sectors. We study in detail the implication of this scenario for the lepton fixed-target facilities, such as NA64$e$, LDMX, NA64$\mu$ and M$^3$. In particular, for the specific experiment we discuss in detail the missing-energy signatures of spin-2 boson production followed by its invisible decay into stable DM pairs. Moreover, we derive the expected reaches of these experiments for the projected statistics of the leptons accumulated on the target. We also discuss the implication of both nuclear and atomic form-factor parametrizations for the differential spectra of hidden spin-$2$ boson emission, the total cross-section of its production and the experimental reach of the fixed-fixed target facilities for probing hidden spin-$2$ DM mediator.