Scientists achieve higher accuracy between protons, neutrons, weaker force measurements

In a one-of-a-kind experiment at the Department of Energy’s Ak Ridge National Laboratory, atomic physicists have accurately measured the weak interaction between protons and neutrons. The result is a measure of weak force theory, as predicted by the standard M. Dale of Particle Physics.

Observe the team’s weak strength, in detail Physical Review Letters, ORNL’s Spleen Neutron Source or SNS. The accuracy was measured by an experiment called N3H or N-helium-3 running on. Their discovery yielded the smallest uncertainty of any comparatively weak force measurement to date in the nucleus of an atom, establishing an important benchmark.

The standard model describes the basic building blocks of matter in the universe and the fundamental forces acting between them. Calculating and measuring the weak force between protons and neutrons is a very difficult task.

“Because the interactions we are looking for are very weak, the effect we want to accurately detect in nuclear physics experiments is very small and, therefore, extremely difficult to observe,” said David Bowman, author and team leader for Basics. Said. Neutron physics at ORNL.

Weak force, one of the four basic forces in nature, describes the interaction between strong atomic force, with electromagnetism and gravity, and subtomic particles called quakes that make up protons and neutrons. Weak energy is also responsible for the radioactive decay of atoms. Some methods of weak power are one of the least understood aspects of the standard model.

To detect insidious weak interactions, high-precision experiments are required, led by large international teams with state-of-the-art equipment and very high neutron flux-like world class colds like fundamental neutron physics beamline on SNS. SNS The neutrons produced at are ideal for precision experiments that address the role of weak forces in the reaction between neutrons and other nuclei.

Bowman, a leading scientist in the field, has been studying nuclear physics and subatomic interactions since the early 1960s.

“Initially, from the experimental research point of view, exceptional nuclear models were collected. But, in recent years, there has been a great development in the calculation of weak force interactions in the nuclear atmosphere,” he said. “New nuclear technologies have become available with varying degrees of independence, and now the calculations are at a very advanced level.”

Scientists’ latest experiment focuses on helium-3, a light and stationary isotope consisting of two protons and a neutron, the only element in nature that has more protons in its structure than neutrons. “When a neutron and a helium-3 nucleus come together, the reaction produces a stimulated, unstable helium-4 isotope, which decomposes one proton and one triton (consisting of two neutrons and one proton), both of which are smaller. Also generates detectable electricity. “Target cells signal passing through helium gas,” said Michael Garrick, corresponding author and professor of subatomic physics at the University of Manitoba.

The N-helium-3 experiment used neutron beamline, polarization, and diagnostics, similar to its predecessor NPDGama, using a liquid hydrogen target that produces gamma rays from neutron proton interactions. The team found that more gamma rays go down towards the neutron spin direction, leading to successful measurements of the mirror-asymmetric component of the weak force.

Like NPDGama, the N-helium-3 experiment is the culmination of a decade of research, preparation and analysis. The configuration of the experiment created an extremely low background environment where the neutrons could be controlled before entering the helium-3 gas container. Garrick led the group that created the combined helium-3 target and built a detector system to select very small signals and led the subsequent analysis.

In the experiment, S.N.S. A beam of slow moving or cold neutrons enters the helium-3 target. An instrument was built to control the atomic spin direction of helium-3 atoms. When neutrons interact with a magnetic field, another device flips their spin direction either up or down, defining the spin state. When the neutrons reached the target, they interacted with the protons inside the helium-3 atom, sending current signals measured by sensitive electronics.

“Our unique goal was to develop a gas cell that simultaneously served as a position-sensitive detector to measure the subtomic products of the reaction.”

Christopher Crawford, co-author of the university and professor of atomic physics, said, “To accommodate the different conditions of this experiment, we discovered the novelty required to lute the neutron’s spin direction, before they reacted with the helium-3 target,” Kentucky. “This universal spin flipper was capable of operating in a wide neutron velocity range with high efficiency.”

Weak force experiments have to be argued with the strong force that can distort the data and the dominant nature of the background noise. “The N-helium-3 experiment should be sensitive to small effects 100 million times smaller than the background,” Crawford said. “It’s like finding a 1-inch needle in a 40-foot-high barn full of hay.”

For about a year, the team collected and analyzed data to determine the power of the similarity-violation, a specific property of the weak power between neutrons and protons. This phenomenon is unique to the weak force and is not seen in strong force, electromagnetism or gravity.

N-helium-3 exploited the symmetry of the experimental configuration achieved by well-controlled neutron polarization, measuring the combination of neutron spin and outgoing velocity of reaction products for both neutron polarizations. “This has a definite hand,” said Ford. “Since the right and left hands looked opposite in the mirror, this observation was fully sensitive to the influence of the other three forces.”

The results of N-helium-3, along with NPDGama, have changed the way molecular physicists understand the role of weak force in molecular structure. Both help answer the remaining questions in the standard by the ability to make accurate calculations.

“Now what’s going to happen next, we need more criteria – like these very specific criteria found on the SNS,” Bowman said. “Advances in this area require a dialogue between experimenters and theorists. They benchmark theories as soon as the results of experiments like ours are available and allow the theorist to modify models that predict new observations that may then be experimentally accessible.” ”