First Observation of Large Missing-Momentum (e,e'p) Cross-Section Scaling and the onset of Correlated-Pair Dominance in Nuclei

TL;DR

This study presents the first observation of scaling in (e,e'p) cross-section ratios at large missing momentum, indicating the dominance of short-range correlated nucleon pairs in nuclei above the Fermi momentum.

Contribution

It provides the first measurement of $x_B$-scaling in (e,e'p) cross-section ratios at high missing momentum, extending the kinematic range and confirming the onset of correlated-pair dominance.

Findings

Scaling observed over a wide $x_B$ range ($0.7$ to $1.8$).

Good agreement with theoretical models for high missing momentum.

SRCs dominate the cross-section ratios at $p_{miss} oughly 350$ MeV/c.

Abstract

We report the first measurement of $x_B$-scaling in $(e,e'p)$ cross-section ratios off nuclei relative to deuterium at large missing-momentum of $350 \leq p_{miss} \leq 600$ MeV/c. The observed scaling extends over a kinematic range of $0.7 \leq x_B \leq 1.8$, which is significantly wider than $1.4 \leq x_B \leq 1.8$ previously observed for inclusive $(e,e')$ cross-section ratios. The $x_B$-integrated cross-section ratios become constant (i.e., scale) beginning at $p_{miss}\approx k_F$, the nuclear Fermi momentum. Comparing with theoretical calculations we find good agreement with Generalized Contact Formalism calculations for high missing-momentum ($> 375$ MeV/c), suggesting the observed scaling results from interacting with nucleons in short-range correlated (SRC) pairs. For low missing-momenta, mean-field calculations show good agreement with the data for $p_{miss}\le k_F$, and suggest that contributions to the measured cross-section ratios from scattering off single, un-correlated, nucleons are non-negligible up to $p_{miss}\approx 350$ MeV/c. Therefore, SRCs become dominant in nuclei at $p_{miss}\approx 350$ MeV/c, well above the nuclear Fermi Surface of $k_F \approx 250$ MeV/c.