{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"7cf868479ac11624e05064056d8bc317e6243cd566e20a9b5f62f1cf3bbf2a84","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["34e8ffef844ab12d1ea9768a811995a0e2aa6fbc6d46e3cf56d69735447a1912","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"cdbd2e63a8c67740eb2689e9637a303e2a6ea3dc127c76a661815861b389b0b2","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"plasma.vacuum-birefringence-schwinger.tunneling-breit-wheeler","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"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.","posed_since":"","precise":"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.","problem_ref":"34e8ffef844ab12d1ea9768a811995a0e2aa6fbc6d46e3cf56d69735447a1912","references":"","settled_by":"A positron-yield scan versus laser intensity with calibrated gamma spectrum showing the $\\exp(-8/(3\\chi_{\\gamma}))$ dependence.","status_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.","title":"Observation of tunneling pair creation in gamma-ray laser 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