According to researchers, firing neutron beams at silicon samples could lead us to an elusive and unknown “fifth force” in nature.
Using a technique called pendellösung interferellometry, a team of physicists led by Benjamin Heacock of the National Institute of Standards and Technology has used neutron beams to probe the crystal structure of silicon with the highest accuracy achieved so far. obtaining more detailed results than X-ray techniques.
This has revealed previously unrecognized properties of silicon, a crucial material for the technology; more detailed information on the properties of the neutron; and placed significant restrictions on the fifth force, if any.
“Even though silicon is ubiquitous, we are still learning its most basic properties,” says physicist Albert Young of North Carolina State University.
“The neutron, because it has no charge, is excellent for use as a probe because it does not interact strongly with the electrons in the material. X-rays have some drawbacks in measuring the atomic forces of a material due to the its interaction with electrons. “
Neutrons, which are found in atomic nuclei, are released during nuclear fission. These can be focused on beams that penetrate materials to much higher depths than can be achieved with X-rays, and are scattered by atomic nuclei, rather than atomic electrons, meaning they can be used to probe materials. complementary to X-ray measurements.
“One of the reasons our measurements are so sensitive is that neutrons penetrate much more into the crystal than X-rays (an inch or more) and therefore measure a much larger set of nuclei,” says the physicist Michael Huber of NIST.
“We have found evidence that nuclei and electrons may not vibrate rigidly, as is usually assumed. This changes our understanding of how silicon atoms interact with each other within a crystal lattice.”
To do this, the particle beam is aimed at a material. Once the beam penetrates the material, neutrons bounce and disperse through the structural network of atoms.
In a perfect silicon crystal, the lattice sheets of the lattice are arranged in planes that are repeated in spacing and orientation. Bouncing the beam accurately in these planes can cause neutrons to deviate in their paths through the lattice, generating weak interference patterns called pendellösung oscillations that reveal the structural properties of the crystal.
“Imagine two identical guitars,” Huber said.
“Drag them in the same way and, as the strings vibrate, drive them along a road with speed bumps, that is, along the atomic planes of the lattice, and drive the other through a road of the same length without speed bumps.analogue to movement between lattice planes.
“A comparison of the sounds of both guitars tells us something about speed strokes: how big are they, how smooth, and have interesting shapes?”
This technique resulted in a new measurement of the neutron charge radius. Although neutrons are neutral in charge, the three quark particles inside them are not. The ascending quark has a charge of +2/3 and each of the two descending quarks has a charge of -1/3, which means that they generally cancel each other out.
But within the neutron, the charge is not evenly distributed. The positive charge is concentrated in the center and the negative around the edges; the distance between the two is called the load radius.
Pendellösung interferometry is not subject to factors that have led to discrepancies between previous measurements using different techniques, which means, according to the team, that its result could be a key to reducing the size of this radius.
The technique is also able to provide more restrictions on the short-range theoretical force yet to be discovered. In nature, according to the standard model of physics, there are three forces, strong, weak and electromagnetic. Gravity, not included in the standard model, is believed to be the fourth force.
To paraphrase Hamlet, however, there are almost certainly more things in heaven and on Earth than we have described, and some physicists have proposed that there is a fifth unknown force that could explain anomalous observations. If it exists, it can have a force carrier, just as photons are the force carrier for electromagnetism.
The length scale on which a force carrier can act is inversely proportional to its mass. The photon, without mass, has an unlimited range. Pendellösung interferometry can provide restrictions within the reach of the fifth carrier force, which in turn can put limits on its force.
The team’s results have reduced the range of the fifth carrier force tenfold, meaning future searches of the fifth force have a smaller range to look at.
“The most important thing about this work is not only accuracy (we can delve into specific crystal observables), but also that we can do it with a desktop experiment, not with a large collider,” Young said.
“Taking these small-scale, accurate measurements could advance some of the most difficult issues in fundamental physics.”
The research has been published in Science.