The bremsstrahlung-like production of the massive spin-2 dark matter mediator

TL;DR

This paper investigates the production of a massive spin-2 mediator linking Standard Model particles and dark matter via bremsstrahlung-like processes in fixed-target experiments, deriving new constraints on its parameter space.

Contribution

It introduces a detailed comparison between the Weizsaker-Williams approximation and exact calculations for spin-2 mediator production, and derives novel experimental constraints from E137 data.

Findings

E137 experiment constrains spin-2 mediator couplings to $8\times10^{-8}$ to $10^{-5}$ GeV$^{-1}$.

Mass range of the mediator constrained between 100 MeV and 800 MeV.

Universal coupling to photons and leptons established from constraints.

Abstract

The link between Standard Model (SM) particles and dark matter (DM) can be introduced via spin-2 massive mediator, G, that couples to photon and charged leptons. Moreover, in a mediator mass range from sub-MeV to sub-GeV, fixed-target facilities such as NA64e, LDMX, NA64$\mu$, M$^3$, and E137, can potentially probe such particle of the hidden sector via the signatures that are described by the bremsstrahlung-like process involving tensor mediator. We compare numerically the Weizsaker-Williams (WW) approximation and the exact tree-level (ETL) approach for the bremsstrahlung-like mediator production cross section by choosing various parameters of the fixed-target experiments. In addition, we derive novel constraints on spin-2 DM mediator parameter space from the data of the E137 fixed-target experiment. In particular, we demonstrate that the E137 experiment has been ruled out the the couplings of the spin-2 mediator at the level of $8\times10^{-8}~\mbox{GeV}^{-1}~\lesssim~c^{\rm G}_{ee}~\lesssim~10^{-5}~\mbox{GeV}^{-1}$ for the typical masses in the range $100~\mbox{MeV}~\lesssim~m_{\rm G}~\lesssim 800~\mbox{MeV}$, that corresponds to the statistics of $1.87\times 10^{20}$ electrons accumulated on target. The latter implies its universal coupling to photons and leptons, $c^{\rm G}_{ee} = c^{\rm G}_{\gamma \gamma}$.