Observation of tunneling pair creation in gamma-ray laser collisions
In plain words
A $\gamma$ ray colliding with a strong laser can turn into an electron-positron pair by quantum tunneling, the same process as Schwinger pair creation but in a moving frame. A 1997 experiment saw pair creation only in the weak-field regime, and the tunneling regime is still unobserved.
Precise statement
Nonlinear Breit-Wheeler pair creation $\gamma + n\,\omega_L \to e+\,e-$ in the regime $a0 >> 1$, $\chi_\gamma < 1$ has a rate proportional to $\exp(-8/(3\chi_\gamma))$, the Schwinger-type tunneling exponent, where $\chi_\gamma \sim 2\left(\hbar\omega_\gamma/(m c^2)\right)\left(E/E_S\right)$ for head-on collisions. SLAC E144 (1997) observed only the multiphoton regime at $a0 \sim 0.3$, where the yield scales as $a0^{2n}$. Determine whether experiments with $a0 >\sim 1$ (LUXE at DESY, E-320 at SLAC FACET-II, or all-optical setups) measure the positron yield versus $a0\text{ and }\chi_\gamma$ showing the transition from power-law to tunneling dependence, with absolute yields matching strong-field QED within stated uncertainties.
What would settle it
A positron-yield scan versus laser intensity with calibrated gamma spectrum showing the $\operatorname{exp}(-8/(3\chi_{\gamma}))$ dependence.
Status in the literature
Unverified note
No tunneling-regime pair data from LUXE (DESY) or E-320 (SLAC FACET-II) are known to this compilation as of 2026; E-320 status should be checked.