When protons and neutrons (nucleons) are bound into atomic nuclei, they are close enough together to feel significant attraction, or repulsion, from the strong, short-distance part of the nucleon-nucleon interaction. These strong interactions lead to hard collisions between nucleons, generating pairs of highly-energetic nucleons referred to as short-range correlations (SRCs). SRCs are an important but relatively poorly understood part of nuclear structure 1-3 and mapping out the strength and isospin structure (neutron-proton vs proton-proton pairs) of these virtual excitations is thus critical input for modeling a range of nuclear, particle, and astrophysics measurements [3][4][5] . Hitherto measurements used two-nucleon knockout or "triple-coincidence" reactions to measure the relative contribution of np-and pp-SRCs by knocking out a proton from the SRC and detecting its partner nucleon (proton or neutron). These measurements [6][7][8] show that SRCs are almost exclusively np pairs, but had limited statistics and required large model-dependent final-state interaction (FSI) corrections. We report on the first measurement using inclusive scattering from the mirror nuclei 3 H and 3 He to extract the np/pp ratio of SRCs in the A=3 system. We obtain a measure of the np/pp SRC ratio that is an order of magnitude more precise than previous experiments, and find a dramatic deviation from the near-total np dominance observed in heavy nuclei. This result implies an unexpected structure in the high-momentum wavefunction for 3 He and 3 H. Understanding these results will improve our understanding of the short-range part of the N-N interaction.

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Background: The Island of Inversion near the N = 20 shell gap is home to nuclei with reordered single-particle energy levels compared to the spherical shell model. Studies of 31 Ne have revealed that its ground state has a halo component, characterized by a valence neutron orbiting a deformed 30 Ne core. This lightly-bound nucleus with a separation energy of only Sn = 170 keV is expected to have excited states that are neutron unbound.Purpose: The purpose of this experiment was to investigate the low-lying excited states in 31 Ne that decay by the emission of a single neutron.Methods: An 89 MeV/nucleon 33 Mg beam impinged on a segmented Be reaction target. Neutron-unbound states in 31 Ne were populated via a two-proton knockout reaction. The 30 Ne fragment and associated neutron from the decay of 31 Ne were detected by the MoNA-LISA-Sweeper experimental setup at the National Superconducting Cyclotron Laboratory. Invariant mass spectroscopy was used to reconstruct the two-body decay energy ( 30 Ne + n).Results: The two-body decay energy spectrum exhibits two features: a low-lying peak at 0.30 ± 0.17 MeV and a broad enhancement at 1.50 ± 0.33 MeV, each fit with an energy-dependent asymmetric Breit-Wigner line shape representing a resonance in the continuum. Accompanying shell model calculations using the FSU interaction within NuShellX, combined with cross-section calculations using the eikonal reaction theory, indicate that these peaks in the decay energy spectrum are caused by multiple resonant states in 31 Ne.Conclusions: Excited states in 31 Ne were observed for the first time. Transitions from calculated shell model final states in 31 Ne to bound states in 30 Ne are in good agreement with the measured decay energy spectrum. Cross-section calculations for the two-proton knockout populating 31 Ne states as well as spectroscopic factors pertaining to the decay of 31 Ne into 30 Ne are used to examine the results within the context of the shell model expectations.