A=3(e,e′) xB≥1 cross-section ratios and the isospin structure of short-range correlations

We study the relation between measured high-xB, high-Q2, helium-3 to tritium, (e,e′) inclusive-scattering cross-section ratios and the relative abundance of high-momentum neutron-proton (np) and proton-proton (pp) short-range correlated nucleon pairs in three-body (A=3) nuclei. Analysis of these data using a simple pair-counting cross-section model suggested a much smaller np/pp ratio than previously measured in heavier nuclei, questioning our understanding of A=3 nuclei and, by extension, all other nuclei. Here, we examine this finding using spectral-function-based cross-section calculations, with both an ab initio A=3 spectral function and effective generalized contact formalism spectral functions using different nucleon-nucleon interaction models. The ab initio calculation agrees with the data, showing good understanding of the structure of A=3 nuclei. An 8% uncertainty on the simple pair-counting model, as implied by the difference between it and the ab initio calculation, gives a factor of 5 uncertainty in the extracted np/pp ratio. Thus we see no evidence for the claimed "unexpected structure in the high-momentum wave function for hydrogen-3 and helium-3".