n-p short-range correlations from (p,2p+n) measurements

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Chromodynamics

Background:

• Understanding nucleon-nucleon interactions within atomic nuclei is crucial for nuclear structure and reactions.
• Short-range correlations (SRCs) are a key feature of nuclear matter, influencing nuclear properties.
• Previous studies have explored SRCs, but direct observation in specific reactions remains an active area of research.

Purpose of the Study:

• To investigate the presence and characteristics of short-range neutron-proton (n-p) correlations in carbon-12.
• To analyze the momentum distributions of correlated nucleons following quasielastic scattering.
• To quantify the contribution of correlated pairs to the overall reaction dynamics.

Main Methods:

• Studied the 12C(p,2p+n) reaction using a carbon-12 target and proton beam at momenta of 5.9, 8.0, and 9.0 GeV/c.
• Analyzed quasielastic (proton, 2 protons) events, comparing the momentum of the knocked-out proton (p(f)) with the coincident neutron momentum (p(n)).
• Examined the directional correlation between p(f) and p(n) for nucleons with momentum exceeding the Fermi momentum (k(F)).

Main Results:

• Observed a strong back-to-back directional correlation between p(f) and p(n) for |p(n)| > k(F), indicating short-range n-p correlations.
• Constructed longitudinal center-of-mass and relative motion distributions for correlated n-p pairs.
• Determined that 49±13% of events with |p(f)| > k(F) exhibited directionally correlated neutrons with |p(n)| > k(F).

Conclusions:

• The study provides direct evidence for short-range neutron-proton correlations in carbon-12 nuclei.
• These correlations significantly influence the momentum distributions of nucleons in high-energy scattering reactions.
• The findings contribute to a deeper understanding of nuclear structure and the role of nucleon-nucleon interactions.