From LUXE to Future Colliders: Probing Strong-Field QED and Beyond

Strong-field quantum electrodynamics offers a unique window into non-perturbative phenomena such as vacuum pair production, in which electron–positron pairs are created from the vacuum in the presence of intense electromagnetic fields. The LUXE experiment at DESY is designed to probe this regime using collisions between a high-intensity laser and the 16.5 GeV electron beam of the European XFEL. Future accelerator infrastructures, such as linear colliders, could extend these studies to even higher intensity and energy scales. Additionally, high-energy photons produced in such interactions can be used in beam-dump experiments to search for new physics.

💡 Research Summary

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The paper presents a comprehensive overview of strong‑field quantum electrodynamics (SF‑QED) studies centered on the LUXE experiment at DESY and explores how the lessons learned can be extended to future high‑energy accelerator facilities. LUXE is designed to collide the 16.5 GeV electron beam from the European XFEL with an ultra‑intense optical laser, reaching values of the quantum non‑linearity parameter χ close to or exceeding unity. In this regime, two hallmark processes dominate: non‑linear Compton scattering, where an electron absorbs multiple laser photons and emits a high‑energy photon, and non‑linear Breit–Wheeler pair production, in which the emitted photon converts into an electron‑positron pair in the same laser field. By measuring the spectra, harmonic structure, and pair‑production rates as functions of laser intensity and electron energy, LUXE provides a direct probe of the transition from perturbative to non‑perturbative QED.

The experimental layout includes a dipole magnet downstream of the interaction point to separate charged particles from the photon beam, allowing simultaneous detection of electrons, positrons, and photons with dedicated trackers and high‑granularity calorimeters. This configuration enables a stringent benchmark of theoretical predictions (world‑line instanton methods, Volkov‑state calculations) and numerical tools (particle‑in‑cell codes, Monte‑Carlo generators). The staged laser power increase—from tens to several hundred terawatts—offers a systematic scan of the χ‑parameter space, revealing how higher‑order harmonics emerge and how the pair‑production probability deviates from simple power‑law scaling.

Beyond LUXE, the authors argue that future linear colliders (ILC, CLIC) and circular electron‑positron machines (FCC‑ee, CEPC) will naturally encounter strong‑field effects. In linear colliders, beam‑beam interactions generate intense beamstrahlung fields that can push χ well above one, potentially affecting beam dynamics and precision measurements. Current simulation packages (e.g., GUINEA‑PIG, CAIN) lack fully validated models for this regime, underscoring the need for data from LUXE‑type experiments to calibrate and improve them. Circular colliders, with their high repetition rates and possible dedicated laser‑interaction stations, could achieve even larger photon fluxes, while crystal‑channeling techniques provide an alternative method to reach comparable χ values using aligned crystal fields.

A particularly innovative aspect of the paper is the proposal to exploit the intense high‑energy photon beams produced in strong‑field interactions for photon‑beam‑dump (NPOD) searches for new, weakly coupled particles such as axion‑like particles (ALPs). In the LUXE‑NPOD concept, a short tungsten dump (2 m) is followed by a 10 m decay volume and a large‑acceptance electromagnetic calorimeter. Assuming a background‑free environment and an annual running time of 10⁷ s, the expected photon flux (~10¹⁰ photons) yields sensitivity to ALP–photon couplings gₐγ down to ~10⁻⁶ GeV⁻¹, surpassing existing limits from fixed‑target and beam‑dump experiments. Scaling to future colliders, where photon energies and fluxes can be an order of magnitude larger, the reach extends to ALP masses in the MeV–GeV range and couplings an order of magnitude weaker.

In summary, the paper positions LUXE as a dual‑purpose platform: (1) a precision testbed for non‑perturbative QED, providing essential data to validate and refine theoretical and computational frameworks, and (2) a source of high‑energy photons that can be repurposed for novel searches for physics beyond the Standard Model. By linking strong‑field laboratory studies with the physics program of next‑generation colliders, the authors outline a roadmap where advances in laser‑particle interactions directly inform both fundamental quantum field theory and the hunt for new, light, weakly interacting particles.