Resonances in 12C+12C fusion inside the carbon-burning Gamow window
In plain words
Carbon burning in massive stars and in exploding white dwarfs starts when two carbon-12 nuclei fuse, and the fusion probability may be boosted by narrow resonances (energies where the two nuclei briefly form a long-lived state). Direct and indirect experiments disagree on whether such resonances exist at the stellar energies.
Precise statement
Determine the total $\mathrm{12C}+\mathrm{12C}$ fusion S*-factor (alpha plus proton channels) for $E_{\mathrm{cm}}=1.5\ \text{to}\ 2.5\,\mathrm{MeV}$, the Gamow window for $T=5e8\ \text{to}\ 1e9\,\mathrm{K}$, including the presence, energies and strengths of any resonances, and hence the reaction rate at $T=5e8\ \text{to}\ 1e9\,\mathrm{K}$ to 20 percent. The answer must reconcile direct particle-gamma coincidence data, which extend down to about $E_{\mathrm{cm}} \sim 2.2\,\mathrm{MeV}$, with indirect Trojan-horse extractions that claim strong resonant enhancement below 2 MeV.
What would settle it
A direct measurement of the $\alpha$ and proton channels down to $E_{\mathrm{cm}} \sim 1.5\ \mathrm{MeV}$ with background low enough to resolve or exclude resonances, cross-checked against the Trojan-horse normalization.
Status in the literature
Unverified note
Direct STELLA data were refined in 2025 and new Trojan-horse data appeared in 2026; direct and indirect rates remain in tension below $E_{\mathrm{cm}} \sim 2.5\,\mathrm{MeV}$.