Neutron astonishes physicists – oscillation of electromagnetic features does not apply to theoretical models

Confused oscillation: Physicists have re-measured the properties of neutrons – and noticed surprising things. This is because the electromagnetic shape factors of the core module do not change with increasing energy, but fluctuate from time to time. This oscillation, which is already observed in protons, is not yet theoretically explained, the group explains in “Nature Physics”. However, this refers to the internal structure of the neutron, which is more energetic and complex than expected.

Protons and neutrons, each consisting of three quarks, are the basic building blocks of matter – they together form the nucleus. But despite this basic emphasis, the key elements still remain Mystery On. Even with such basic features Lifespan, Size And Internal structure There are great uncertainties. In addition, physicists repeatedly observe phenomena that do not match theoretical models.

The secret of the form factor

A new understanding of the properties of the neutron has now been achieved by the physicists of the BESIII collaboration. The purpose of the experiment was to more accurately determine the so-called electromagnetic factors of the neutron. They describe the average distribution of electric charge and magnetization within a neutron, thus providing clues for the behavior and arrangement of three quarks connected via gluons within their interior.

Frank Moss from the Helmholtz Institute of Mines (HIM) explains, “The single shape factor, measured at a given energy, does not say much at first. Only knowing the shape factors at different energies allows decisions to be made about the structure of the neutron.” Since there are no measurements, the team has now closed this gap with eradication tests.

To do this, physicists studied the properties of neutrons and anti-neutrons formed when electrons and positrons collide at the BESIII particle accelerator in China. “In a symbolic sense, we have filled an empty area in the map of neutron-shaped factors with new data,” says Mass.

The oscillation patterns are inconsistent

The analysis presented several new findings. One of them: depending on the energy, the shape factor of the neutron does not form a smooth line, but rather shows an oscillating shape. With increasing energy, the deviations become smaller and smaller. As physicists explain, this surprising behavior indicates a clear deviation from the expected behavior. However, a similar oscillation has recently been observed in protons.

“We now observe behavior associated with a similar frequency in neutrons, but with a larger phase change,” the scientists write. “These results suggest that the intrinsic kinetics of the nucleons responsible for these almost orthogonal oscillations are not yet understood.” In other words: something is going on within the key components that the current models have not yet captured.

“Now, in theory, our colleagues are being asked to create models for this extraordinary behavior,” says Mass.

The previous deviation was denied

However, the new measurements also reveal that the discrepancy found in the previous measurements does not seem to be above all. Researchers have demonstrated a stronger affinity for virtual photons for a neutron than for a proton – so the neutron must consistently show a larger shape factor than the proton. But this is contrary to basic principles: “One can expect it to be the other way around because the proton is charged,” says Mass.

The data from the BESIII experiment now contradict the previous conclusion: “Our results show that the photon-proton interaction is stronger than the corresponding photon-neutron interactions – as predicted by most theoretical models,” the group writes. “It clarifies the mystery of more than 20 years of this connection.”

Astronomy is also important for physics

The new measurement data will help solve some of the mysteries about these construction blocks of matter. Although many of the basic properties of neutrons and protons are not fully understood by any means, they provide at least new starting points for research into key building blocks and their behavior.

These discoveries can not only benefit research in particle physics and materials, but also provide new insights into astronomical physics: “By looking at the smallest structural blocks of matter, we can understand events that take place on very large dimensions – for example, the combination of the two. This extreme physics of neutron stars is very attractive, ”says Mass. (Natural Physics, 2021; doi: 10.1038 / s41567-021-01345-6)

Source: University of Mainz

10. November 2021

– Nadja Podbregar