GAMMA-RAY SPECTRAL CLUES TO FLEETING PARTNERS INSIDE NUCLEI

Nuclei are not bags of static balls. Most protons and neutrons move under the overall nuclear environment, but a small fraction can form fleeting close-range partners and carry unusually large momenta. These short-range correlations cannot be photographed directly. Instead, they leave statistical clues in the high-energy gamma-ray spectrum emitted at the earliest stage of a heavy-ion collision: faster neutron-proton encounters are more likely to produce energetic gamma rays, hardening the spectral tail. A recent ¹²⁴Sn+¹²⁴Sn experiment at 25MeV per nucleon used this idea, together with transport-model comparisons, detector calibration, and background checks, to infer that about 20% of nucleons in ¹²⁴Sn belong to short-range-correlation-related high-momentum components. The result provides a complementary gamma-ray route for studying short-distance motion inside nuclei.