The experiment, which lasted more than 10 years, provided the first look at a whirlwind of whirling subatomic particles called neutrons and laid the groundwork for uncovering a deep mystery at the heart of matter. Data from the Central Neutron Detector at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility (TJNAF) is already playing a key role in defining the quantum map of the neutron engine.

“This is a very important result for the study of nucleons,” says Sylvia Niccolai, head of research at the French National Center for Scientific Research.

What we think of as the nucleus of an atom is a hive of even smaller particles called quarks, fighting against the viscous exchange of gluons. You will find a proton where two up-flavored quarks bond with a down-flavored quark. If you make these two down quarks and one up quark, you get a neutron.

When we describe a trio of quarks this way, they sound neatly arranged like eggs in a box. In reality their existence is not properly organized at all, with a chaotic storm of particles and anti-particles existing and not existing in quantum competition.

To understand the distribution and movement of quark swarms in gluon chains, physicists traditionally shot nuclear particles with electrons and watched the tiny balls bounce. To make it easier to explain the results of these experiments, theorists call the units of quarks and gluons that move in different quantum frames partons.

In recent years, experiments at high-energy particle accelerators using the CEBAF Large Acceptance Spectrometer and improvements at TJNAF have solved the parton puzzle of the proton, revealing mysteries involving the puzzling discrepancy between nucleon mass and size. Neutrons have proven to be a tougher nut to crack, launching electron shrapnel at angles beyond the reach of the spectrometer’s detector.

“In the standard configuration it was impossible to detect neutrons at these angles,” says Niccolai.

Construction of the new detector started in 2011 in collaboration with CNRS, which was installed in 2017, followed by the first experimental studies in 2019 and 2020.

The design of the experiment was far from smooth, allowing random protons to sneak in and contaminate the results. Only after some refinement with a specially designed machine learning filter could these numbers finally be applied to theoretical models of neutron activity.

The first study to use these data placed much-needed constraints on one of the least understood neutron parton distributions, known as the generalized parton distribution (GPD) E. The researchers exploited the differences in quarks by comparing the experimental results with previous data on protons. Distinguishing an important mathematical feature of GPD E from a similar model.

“GPD E is very important because it can give us information about the spin structure of nucleons,” says Niccolai.

In its quantum sense, spin encompasses a quality similar to the angular momentum in our daily lives. Previous measurements of the spins of the quarks that make up protons and neutrons had shown that these properties account for no more than about 30 percent of a nucleon’s total spin, leading to a spin crisis.

The question of where the remaining bit comes from, whether it is interaction with gluons or some other poorly understood behavior, is a question that future experiments may eventually resolve. Having the opportunity to precisely compare the twin engines burning at the heart of atoms will almost certainly lead to exciting new insights into quantum mechanics. This study was published on: Physical Examination Letters.