The center of mass motion of short-range correlated nucleon pairs studied via the A(e,e'pp) reaction

TL;DR

This paper measures the center-of-mass motion of short-range correlated nucleon pairs in various nuclei, revealing that they are formed from mean-field nucleons and characterized by a narrow Gaussian momentum distribution.

Contribution

First extraction of the center-of-mass momentum distribution of SRC pairs in multiple nuclei, showing they originate from specific quantum states of mean-field nucleons.

Findings

Center-of-mass motion described by a narrow Gaussian distribution (140-170 MeV/c)

SRC pairs are formed from mean-field nucleons in specific quantum states

Results consistent across different nuclei, including heavy and asymmetric ones

Abstract

Short-Range Correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum (kF). A fundamental characteristic of SRC pairs is having large relative momenta as compared to kF, and smaller center-of-mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton (pp) SRC pairs in Carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the A(e,e'pp) reaction. We find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to 170 MeV/c, approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states.