Resonant Probing Spin-0 and Spin-2 Dark Matter Mediators in Electron Fixed Target Experiments - NA64 and LDMX

Aug 27, 2026

The paper investigates how electron fixed target experiments such as NA64 and LDMX can produce electron-specific dark matter mediators with spin-0 and spin-2. Secondary positrons from electromagnetic showers enable mediator production through annihilation on atomic electrons in addition to bremsstrahlunglike emission. For selected kinematics, this yields enhanced sensitivity in dedicated regions of parameter space. The work derives mediator production and decay expressions and computes the corresponding experimental reach for both NA64 and LDMX.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages12

Reading Time30 min

AccessFree to download

Introduction

Benchmark scenarios for electron-specific dark matter mediators

Cross sections in the Weizsacker-Williams approach

Positron track length and missing-energy signals

Resonant enhancement regions for mediator mass

Experimental reach for NA64 and LDMX

Resonant probing spin-0 and spin-2 dark matter mediators with fixed target experiments I. V. Voronchikhin 1, ∗ and D. V. Kirpichnikov2,† 1 Tomsk Polytechnic University, 634050 Tomsk, Russia 2 Institute for Nuclear Research, 117312 Moscow, Russia (Dated: July 4, 2023) We discuss the mechanism to produce electron-specific dark matter mediators of spin-0 and spin-2 in the electron fixed target experiments such as NA64 and LDMX. The secondary positrons induced by the electromagnetic shower can produce the mediators via annihilation on atomic electrons. That mechanism, for some selected kinematics, results in the enhanced sensitivity with respect to the bounds derived by the bremsstrahlunglike emission of the mediator in the specific parameter space. We derive the corresponding experimental reach of the NA64 and LDMX. arXiv :2304 . 14052v2 [hep-ph] 3 Jul 2023 I. INTRODUCTION The fundamental particle content of the Dark Matter (DM) can not be explained by the Standard Model (SM) even though it is associated with nearly ≃ 85% matter of the Universe [1, 2] . The indirect manifestations of the DM are related mainly to the galaxy rotation velocities, large-scale structures, the cosmic microwave background anisotropy, the gravitational lensing, etc [3–5] . However, the direct detection of the DM particles remains one of the most significant challenges of fundamental physics. One can assume the thermal origin of the DM, implying the equilibrium between the DM and visible matter in the early Universe [6] . In order to avoid the DM overproduction through thermal freeze-out, an idea of existence of the light massive mediator (MED) of DM has been introduced [7–12] . For instance, the typical scenarios with dark boson mediators include spin-0, spin-1 and spin-2 particles such as the hidden Higgs boson [13–19], the dark photon [20–32], and dark graviton [33–45] respectively. Note that, the fermion DM portals have also recently been discussed in the literature [46–51] . The various mechanisms of DM thermalization involving mediators were studied by the authors of Refs. [52–57] . For recent review of the probing these scenarios with acceleratorbased experiments, see the Refs. [58–66] and references therein. In this paper we focus on resonant probing the electron-specific spin-0 (spin-2) DM mediator, denoted by ϕ (G), with electron fixed target experiments, such as NA64 [67–89] and LDMX [12, 90–97] . The typical production mechanisms of spin-0 (spin-2) DM mediator in the reaction of high-energy electrons on a fixed target are associated with ϕ (G)-strahlung in nucleus scattering, e − N → e − Nϕ (G), and resonant annihilation of secondary positrons on atomic electrons, e+ e − → ϕ (G) . In the present paper we consider mostly the invisible decay channels of mediators into pairs of specific DM particles,ϕ (G) → DM + DM. ∗ Corresponding author; e-mail: [i.v.voronchikhin@gmail.com](i.v.voronchikhin@gmail.com) † e-mail: [dmbrick@gmail.com](dmbrick@gmail.com) It is worth mentioning that all DM benchmark scenarios of the present paper imply the light mDM to be in the range 1MeV − 1GeV, such that these masses could be well within experimental reach of the current and forthcoming accelerator-based facilities. Furthermore, these direct DM production limits are complementary to the DM relic-density parameter space [12, 34] . In addition, we note that for both NA64 and LDMX experimental facilities, the resonant production of A′ spin-1 DM mediator, e+ e − → A′ → DM + DM, has been studied explicitly in Refs. [83, 84 , 96–100] . It was shown that including the annihilation channel can provide the improved bounds on thermal DM parameter space. Therefore, the resonant probing spin-0 and spin- 2 DM mediators can extend the experimental reach of NA64e and LDMX, filling a gap in the existing literature [12, 80 , 87] . This paper is organized as follows. In Sec. II we discuss the benchmark scenarios for the electron-specific DM mediators o

FAQs

What production mechanism for spin-0 and spin-2 mediators is emphasized in electron fixed target experiments?

The study emphasizes resonant production via annihilation of secondary positrons on atomic electrons, alongside comparison to bremsstrahlunglike emission in relevant parameter space.

Which experiments are used to evaluate the sensitivity and experimental reach?

The paper derives the experimental reach for NA64 and LDMX, both in the context of electron fixed target setups.

What spin assignments for dark matter mediators are considered?

The work focuses on electron-specific dark matter mediators with spin-0 and spin-2, denoted by ϕ and G in the text.

Aug 27, 2026

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