{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"4193feec6eb5a4c5f396fa070974be38ce8dca576842bf3e1ba0820b98792f2e","created":"2026-10-03T07:18:07Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"6637c1d9688722abd0989a3d4cabadd8b8d1b907ba327140e1c8eba60ad79bd2","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"nuc.ab-initio-nuclei.tetraneutron","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Four neutrons alone are not expected to hold together, yet a 2022 experiment saw a short-lived bump in the energy of four outgoing neutrons. Theory disagrees on whether a true resonance (a quasi-bound state that falls apart quickly) can exist.","posed_since":"2002","precise":"Duer et al. (Nature 606, 678, 2022) reported a resonance-like structure in the $4n$ system at $E = 2.37 \\pm 0.38\\,\\text{(stat)} \\pm 0.44\\,\\text{(sys)}\\,\\mathrm{MeV}$ above threshold with width about $1.75\\,\\mathrm{MeV}$, from quasi-elastic alpha knockout on 8He. Determine whether the $4n$ S-matrix with realistic $\\mathrm{NN} + 3\\mathrm{N}$ forces has a pole near this energy, or whether the peak is a final-state correlation effect. Answer: pole position, or a proof that no pole lies within $5\\,\\mathrm{MeV}$ of threshold, with interaction uncertainty.","problem_ref":null,"references":"","settled_by":"Complex-scaling and Faddeev-Yakubovsky calculations of the 4n continuum agreeing across methods, plus a second experiment using a different reaction.","status_note":"Ab initio calculations disagreed; the most recent lattice EFT study (Wu et al., PRL 136, 142502, 2026) found no resonance but a weak dineutron-dineutron attraction giving a confined 4n energy of 1.7 to 3.3 MeV near the observed peak, favoring a correlation effect without a pole.","title":"Does a four-neutron resonance 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