Prospect of Studying Nonperturbative QED with Beam-Beam Collisions

We demonstrate the experimental feasibility of probing the fully nonperturbative regime of quantum electrodynamics with a 100 GeV-class particle collider. By using tightly compressed and focused electron beams, beamstrahlung radiation losses can be mitigated, allowing the particles to experience extreme electromagnetic fields. Three-dimensional particle-in-cell simulations confirm the viability of this approach. The experimental forefront envisaged has the potential to establish a novel research field and to stimulate the development of a new theoretical methodology for this yet unexplored regime of strong-field quantum electrodynamics.

Figure 1

(a) Illustration of a beam-beam collider for probing the fully nonperturbative QED regime. (b) 3D osiris-qed simulation of the collision of two spherical 10 nm electron beams with 125 GeV energy (blue). The fully nonperturbative QED regime $\alpha {\chi }^{2/3}\ge 1$ is experienced by 38% of the colliding particles (red). The interaction produces two dense gamma-ray beams with 0.2 photons with $E_{\gamma }\ge 2m{c}^2$ per primary electron (yellow).

Figure 2

Dressed loop expansion of the polarization operator $\mathcal{P}$ (top row) and mass operator $\mathcal{M}$ (bottom row). Wiggly lines denote photons and double lines dressed electron or positron propagators [1]. According to the Ritus-Narozhny conjecture, the diagrams shown represent the dominant contribution at $n$ loop and $\alpha {\chi }^{2/3}$ is the true expansion parameter of strong-field QED in the regime $\chi \gg 1$ [25, 26, 27].

Figure 3

Results of 3D simulations with osiris-qed for the parameters of the NPQED collider in Table 1. $f_q$ (solid red line): fraction of beam electrons experiencing $\alpha {\chi }^{2/3}\ge 1$; $f_{\gamma }$ (dashed blue line): number of high-energy photons ($E_{\gamma }\ge 2m{c}^2$) emitted per beam electron; $f_p$ (dotted black line): number of secondary pairs per beam electron (all quantities are shown as a function of the beam crossing time). The shaded areas represent an estimate for the importance of nonperturbative quantum effects ($f_{\gamma }\sim 30\%$, $f_p\sim 25\%$). They were obtained by modifying the photon emission or pair production probabilities in osiris-qed as explained in the main text and the Supplemental Material [30] (upper curves: state-of-the-art simulation, lower curves: modified probabilities).

Figure 4

Relative energy loss and number of secondary pairs $f_p$ (inset plot) for three beam lengths: 10 nm (solid red line, $D={10}^{-3}$), 100 nm (dashed blue line, $D=0.1$), and 500 nm (dotted back line, $D=2.5$). In the latter case electron trajectories are severely modified, leading to strong disruption. The interaction results in a full-featured QED cascade, which multiplies the particle density and completely absorbs the energy of the initial beam.