A carbon-target photon experiment found a lower-tail excess in low-momentum η′→γγ events and inferred a possible 57.5 MeV/c² mass reduction at normal nuclear density, with an uncertainty of +5.7/−27.8 MeV/c².
The computational comparison found different modeled rare-earth abundance patterns across six nuclear level-density models and three simulated outflow scenarios, with the strongest contrast in the cold case.