Universality of nucleon-nucleon short-range correlations: Two-nucleon momentum distributions in few-body systems

Using realistic wave functions, the proton-neutron and proton-proton momentum distributions in 3He and 4He are calculated as a function of the relative, krel, and center of mass, Kc.m., momenta and the angle between them. For large values of krel 2 fm−1 and small values of Kc.m. 1.0 fm−1, both distributions are angle independent and decrease with increasing Kc.m., with the pn distribution factorizing into the deuteron momentum distribution times a rapidly decreasing function of Kc.m., in agreement with the two-nucleon (2N) short-range correlation (SRC) picture. When Kc.m. and krel are both large, the distributions exhibit a strong angle dependence, which is evidence of three-nucleon (3N) SRC. The predicted center of mass and angular dependence of 2N and 3N SRC should be observable in two-nucleon knock-out processes A(e, e pN)X