A comparison of forward and backward pp pair knockout in 3He(e,e'pp)n

TL;DR

This study compares forward and backward proton knockout configurations in the $^3$He$(e,e'pp)n$ reaction to identify the optimal setup for measuring nucleon-nucleon short-range correlations and their momentum distributions.

Contribution

It demonstrates that the backward-forward proton emission configuration best reflects the initial-state $pp$ relative momentum distribution, aiding future SRC measurements.

Findings

Backward-forward configuration closely matches initial $pp$ momentum distribution

Forward-forward configuration shows less agreement with initial state

Results guide optimal experimental setup for SRC studies

Abstract

Measuring nucleon-nucleon Short Range Correlations (SRC) has been a goal of the nuclear physics community for many years. They are an important part of the nuclear wavefunction, accounting for almost all of the high-momentum strength. They are closely related to the EMC effect. While their overall probability has been measured, measuring their momentum distributions is more difficult. In order to determine the best configuration for studying SRC momentum distributions, we measured the $^3$He$(e,e'pp)n$ reaction, looking at events with high momentum protons ($p_p > 0.35$ GeV/c) and a low momentum neutron ($p_n< 0.2$ GeV/c). We examined two angular configurations: either both protons emitted forward or one proton emitted forward and one backward (with respect to the momentum transfer, $\vec q$). The measured relative momentum distribution of the events with one forward and one backward proton was much closer to the calculated initial-state $pp$ relative momentum distribution, indicating that this is the preferred configuration for measuring SRC.