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Exploring the Dark Axion Portal in the LUXE-NPOD Experiment

Noam Ness, Barry Cimring

TL;DR

This work studies the dark axion portal within the LUXE–NPOD setup, exploring a multi-particle hidden sector consisting of dark photons (DPs) and axion-like particles (ALPs) and their mutual interactions. Using extended 1D cascade simulations and exact tree-level cross sections, the authors compute primary and secondary production spectra and derive the expected signal yields at the dual interaction points. They show that LUXE–NPOD can probe novel regions of the dark axion parameter space, with ALP masses in the $10$–$500$ MeV range and DP masses in either ${\mathcal{O}({\rm GeV})}$ or ultra-light ${\mathcal{O}(10^{-18}-10^{-13})\ \mathrm{eV}}$ regimes, achieving sensitivities to $\varepsilon$ as small as ${\mathcal{O}(10^{-4}-10^{-2})}$ and to $g_{a\gamma\gamma}$ in ${\mathcal{O}(10^{-4}-10^{-3})\ \mathrm{GeV}^{-1}}$. The dark axion portal enables sensitivity to arbitrarily low DP masses, a feature not typical of DP-only searches, and the paper provides a systematic framework for constraining multi-dimensional parameter spaces in hidden-sector models.

Abstract

The optical dump at the LUXE experiment has the potential to create a large flux of $\mathcal{O}({\rm GeV})$ photons that can be used to look for new physics when directed at a solid material dump. The LUXE-NPOD extension of LUXE, which focuses the hard photons onto a slab of tungsten, offers two interaction points (laser-electron and photon-tungsten), making it well-suited to test theories containing two or more new particles. We examine the dark axion portal, a scenario involving both dark photons (DPs) and axion-like particles (ALPs) and their mutual interactions, and its implications on the phenomenology at LUXE-NPOD. To simulate the spectra of particle populations generated at the electron-laser interaction point, we solve a set of extended 1D cascade equations. We recover a photon spectrum consistent with previous analyses and present previously unconsidered DP and ALP spectra. We derive the overall sensitivity of LUXE-NPOD to various parameters of the new particles, and show that it is capable of probing previously uncharted regions in the dark axion parameter space. For ALPs in the $10$-$500$ MeV mass range and DPs either heavier ($\sim{\rm GeV}$) or significantly lighter $\mathcal{O}(10^{-18}$-$10^{-13})$ eV, we obtain novel constraints on DP kinetic mixing parameters smaller than $10^{-2}$ and on $\mathcal{O}(10^{-4}$-$10^{-3})$ GeV$^{-1}$ ALP-photon couplings. We find that restrictions on $\mathcal{O}\left(10^{-3}\right)$ kinetic mixing can be extracted for arbitrarily small DP masses. Our discussion aims to be systematic and demonstrates a practical method of analyzing constraints on multi-dimensional parameter spaces.

Exploring the Dark Axion Portal in the LUXE-NPOD Experiment

TL;DR

This work studies the dark axion portal within the LUXE–NPOD setup, exploring a multi-particle hidden sector consisting of dark photons (DPs) and axion-like particles (ALPs) and their mutual interactions. Using extended 1D cascade simulations and exact tree-level cross sections, the authors compute primary and secondary production spectra and derive the expected signal yields at the dual interaction points. They show that LUXE–NPOD can probe novel regions of the dark axion parameter space, with ALP masses in the – MeV range and DP masses in either or ultra-light regimes, achieving sensitivities to as small as and to in . The dark axion portal enables sensitivity to arbitrarily low DP masses, a feature not typical of DP-only searches, and the paper provides a systematic framework for constraining multi-dimensional parameter spaces in hidden-sector models.

Abstract

The optical dump at the LUXE experiment has the potential to create a large flux of photons that can be used to look for new physics when directed at a solid material dump. The LUXE-NPOD extension of LUXE, which focuses the hard photons onto a slab of tungsten, offers two interaction points (laser-electron and photon-tungsten), making it well-suited to test theories containing two or more new particles. We examine the dark axion portal, a scenario involving both dark photons (DPs) and axion-like particles (ALPs) and their mutual interactions, and its implications on the phenomenology at LUXE-NPOD. To simulate the spectra of particle populations generated at the electron-laser interaction point, we solve a set of extended 1D cascade equations. We recover a photon spectrum consistent with previous analyses and present previously unconsidered DP and ALP spectra. We derive the overall sensitivity of LUXE-NPOD to various parameters of the new particles, and show that it is capable of probing previously uncharted regions in the dark axion parameter space. For ALPs in the - MeV mass range and DPs either heavier () or significantly lighter - eV, we obtain novel constraints on DP kinetic mixing parameters smaller than and on - GeV ALP-photon couplings. We find that restrictions on kinetic mixing can be extracted for arbitrarily small DP masses. Our discussion aims to be systematic and demonstrates a practical method of analyzing constraints on multi-dimensional parameter spaces.

Paper Structure

This paper contains 14 sections, 35 equations, 9 figures.

Table of Contents

  1. Introduction
  2. Portals to Hidden Sectors
  3. The Dark Axion Portal at LUXE--NPOD
  4. Allowed Processes
  5. Expected Number of Signals
  6. Background Estimation
  7. Existing constraints
  8. Projected Sensitivity
  9. Heavier Dark Photons Mg'>Ma
  10. Ultralight Dark Photons Mg'<<Ma
  11. Conclusions
  12. Acknowledgments
  13. Cascade Equations in 1D
  14. Secondary NP Differential Cross Sections

Figures (9)

  • Figure 1: Schematic of the LUXE configuration and the NPOD extension (inspired by Fig. 2 in Ref. LUXENPOD). Electrons collide with a laser pulse ("optical dump") in the LUXE experiment, generating hard photons which the NPOD extension directs onto solid dump. A forward detector is stationed after the dump.
  • Figure 2: Tree-level Feynman diagrams for secondary NP production of DPs/ALPs at LUXE--NPOD. The processes are facilitated through interactions with electrons $e^-$ or nuclei $N$ in the solid dump. Each case receives contributions from two mediation channels that interfere with one another.
  • Figure 3: Tree-level Feynman diagrams for primary NP production of DPs/ALPs at LUXE--NPOD. The double line represents a dressed Volkov-state electron VolkovStates.
  • Figure 4: Particle spectra generated in electron-laser interaction. Numerically computed spectra of visible and dark photons produced during phase-0 (black and orange, respectively) and phase-1 (green and pink, respectively) of the LUXE experiment after collision with a high-intensity laser. The photon spectra computed using Monte--Carlo methods are also plotted.
  • Figure 5: Current model-independent bounds on the DP mass $m_{\gamma'}$ and kinetic mixing strength $\varepsilon$, inspired by Refs. DPLimitsLight_HandbookCairanOhareGithub. The top panel shows constraints on low-mass DPs, the bottom panel shows constraints on heavier DPs.
  • ...and 4 more figures