= Laboratory evidence for the Hoyle state
In 1953, <David Noel Ferguson Dunbar> and collaborators used accelerated <deuterons> on <nitrogen-14>, populating <carbon-12> through ${}^{14}\mathrm N(d,\alpha){}^{12}\mathrm C$. Magnetic analysis resolved outgoing <alpha particle> groups. At $620\,\mathrm{keV}$ incident <energy> and laboratory angle $90$ degrees, they reported excitation $7.68\pm0.03\,\mathrm{MeV}$, with yield $6\%$ of the $4.43\,\mathrm{MeV}$ group's yield. The stronger group supplied an internal comparison. The paper's opening explicitly relates the search to <Fred Hoyle>'s abundance argument. This is evidence for a nuclear level from a different entrance reaction than stellar fusion.<The 7.68-Mev state in C12 by David Noel Ferguson Dunbar and others>[1953 paper, p. 649, abstract and opening paragraphs]{ref}
The inference uses <energy> and <momentum conservation>: at fixed incident <energy> and observation angle, more <energy> retained as <carbon-12> excitation leaves less outgoing <kinetic energy>. A resolved particle group therefore identifies a nuclear level. This laboratory nuclear line supports an input required by a stellar synthesis model. It does not reproduce <core helium burning>, measure a complete stellar <carbon> yield, or by itself determine the stabilizing decay probability.
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