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

Abstract

Using realistic wave functions, the proton-neutron and proton-proton momentum distributions in ${}^{3}He$ and ${}^{4}He$ are calculated as a function of the relative, $k_{rel}$, and center of mass, $K_{CM}$, momenta, and the angle between them. For large values of $k_{rel}\gtrsim 2f{m}^{-1}$ and small values of $K_{CM}\lesssim 1.0f{m}^{-1}$, both distributions are angle independent and decrease with increasing $K_{CM}$, with the $pn$ distribution factorizing into the deuteron momentum distribution times a rapidly decreasing function of $K_{CM}$, in agreement with the two-nucleon (2N) short range correlation (SRC) picture. When $K_{CM}$ and $k_{rel}$ 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 $A(e,e^{\prime }pN)X$.

Comments: 5 pages, 5 figures