Breakthrough in Nuclear Physics: First Detailed Measurements of Neutron Structure with Advanced Detector

Recent advancements at the Thomas Jefferson National Accelerator Facility enable scientists to study the internal structure of neutrons in great detail. A new detector, developed over a decade, allows researchers to investigate how quarks and gluons influence the spin of nucleons—protons and neutrons.

This breakthrough, published in Physical Review Letters, marks a significant shift in nuclear physics, which has focused mainly on protons. Scientists have now observed the neutron’s structure for the first time. Silvia Niccolai, a director at the French National Centre for Scientific Research (CNRS), highlighted that this finding enriches our understanding of nucleon behavior.

Researchers used the CLAS12 detector to examine deeply virtual Compton scattering (DVCS). This technique has focused on protons, as neutrons are harder to detect due to their scattering patterns. Niccolai sought to address this by proposing the Central Neutron Detector, completed in 2015 and installed in the experimental setup two years later.

From 2019 to 2020, the Central Neutron Detector gathered data, but researchers faced challenges, including proton contamination in the neutron signals. Adam Hobart, a researcher at IJCLab, managed to resolve these issues by utilizing machine learning techniques to differentiate valid neutron signals from noise.

This experiment yields the first DVCS measurements on neutrons, providing essential data. The researchers also accessed generalized parton distributions (GPDs), which describe how quarks and gluons are distributed within nucleons. This work enabled the team to explore the spin structure of nucleons and better understand quark contributions to total nucleon spin.

In the future, researchers plan to collect more data using the Central Neutron Detector to refine their measurements. Niccolai expressed pride in this project, viewing the publication of their findings as a significant personal achievement. This work is a vital step in solving the nucleon spin crisis and advancing our understanding of nuclear physics.