- 3302 - ATOMS - is there a fifth force? NIST, which is America’s Standards Lab has revealed previously unrecognized properties of technologically crucial silicon crystals and uncovered new information about an important subatomic particle and a long-theorized “fifth force of nature“.
--------------------- 3302 - ATOMS - is there a fifth force?
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- Some extensions to the “Standard Model of Particle Physics” posit the existence of a fifth force to complement the existing four fundamental forces. To set bounds on the strength of such an interaction, experiments on vastly different length scales have been performed.
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- Physicists used an unusual method called “Pendellösung interferometry” to measure the neutron structure factors of silicon. The momentum dependence of the structure factors enabled the researchers to put more stringent bounds on the strength of a type of fifth force as well as measure the charge radius of the neutron.
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- By aiming subatomic particles, neutrons at silicon crystals, and monitoring the outcome with exquisite sensitivity, the scientists were able to obtain three extraordinary results:
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--------------------- The first measurement of a key neutron property in 20 years using a unique method;
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--------------------- The highest-precision measurements of the effects of heat-related vibrations in a silicon crystal;
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--------------------- The limits on the strength of a possible "fifth force" beyond standard physics theories.
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- We have four forces in Nature: the Nuclear Strong Force, the Nuclear Weak force, the Electromagnetic Force , and the Force pf Gravity. Is there a Fifth Force?
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- To obtain information about crystalline materials at the atomic scale, scientists typically aim a beam of particles, such as X-rays, electrons or neutrons, at the crystal and detect the beam's angles, intensities and patterns as it passes through or ricochets off planes in the crystal's lattice-like atomic geometry.
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- The information detected is critically important for characterizing the electronic, mechanical and magnetic properties of microchip components and various novel nano-materials for next-generation applications including quantum computing.
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- A vastly improved understanding of the crystal structure of silicon, the 'universal' substrate or foundation material on which everything is built, will be crucial in understanding the nature of components operating near the point at which the accuracy of measurements is limited by quantum effects.
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- Like all quantum particles, neutrons have both point-like particle and wave properties. As a neutron travels through the crystal, it forms standing waves both in between and on top of rows or sheets of atoms called “Bragg planes“.
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- When waves from each of the two routes combine, or "interfere", they create faint patterns called “pendellösung oscillations” that provide insights into the forces that neutrons experience inside the crystal.
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- Neutrons are electrically neutral. But, they are composite objects made up of three elementary charged particles called “quarks” with different electrical properties that are not exactly uniformly distributed.
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- A quark is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called “hadrons“, the most stable of which are protons and neutrons, the components of atomic nuclei.
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- All commonly observable matter is composed of up quarks, down quarks and electrons. Owing to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons such as protons and neutrons and mesons, or in quark–gluon plasmas.
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- For this reason, much of what is known about quarks has been drawn from observations of hadrons
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- As a result, predominantly negative charge from one kind of quark tends to be located toward the outer part of the neutron, whereas net positive charge is located toward the center. The distance between those two concentrations is the "charge radius."
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- Measuring the pendellösung oscillations in an electrically charged environment provides a unique way to gauge the charge radius. When the neutron is in the crystal, it is well within the atomic electric cloud.
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- Because the distances between charges are so small, the inter-atomic electric fields are enormous, on the order of a hundred million volts per centimeter. Because of that very, very large field, the technique is sensitive to the fact that the neutron behaves like a spherical composite particle with a slightly positive core and a slightly negative surrounding shell.
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- The results provide valuable complementary information for both x-ray and neutron scattering. Neutrons interact almost entirely with the protons and neutrons at the centers, or nuclei, of the atoms, and x-rays reveal how the electrons are arranged between the nuclei.
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- One reason these measurements are so sensitive is that neutrons penetrate much deeper into the crystal than x-rays, a centimeter or more, and thus measures a much larger assembly of nuclei. The evidence is that the nuclei and electrons may not vibrate rigidly, as is commonly assumed. That shifts our understanding on the how silicon atoms interact with one another inside a crystal lattice.
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- The Standard Model is the current, widely accepted theory of how particles and forces interact at the smallest scales. But it's an incomplete explanation of how nature works, and scientists suspect there is more to the universe than the current theory describes.
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- The Standard Model describes three fundamental forces in nature: electromagnetic, strong and weak. Each force operates through the action of "carrier particles“. The photon is the force carrier for the electromagnetic force. But the Standard Model has yet to incorporate gravity in its description of nature. Some experiments and theories suggest the possible presence of a “fifth force“.
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- Generally, if there's a force carrier, the length scale over which it acts is inversely proportional to its mass, meaning it can only influence other particles over a limited range. But the photon, which has no mass, can act over an unlimited range.
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- If we can bracket the range over which it might act, we can limit its strength. The results improve constraints on the strength of a potential fifth force by tenfold over a length scale between 0.02 nanometer and 10 nm, giving fifth-force hunters a narrowed range over which to look. A nanometer is one billionth of a meter, 10^-9 meters.
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- The researchers are already planning more expansive pendellösung measurements using both silicon and germanium. They expect a possible factor of five reduction in their measurement uncertainties, which could produce the most precise measurement of the neutron charge radius to date and further constrain, or discover ,a fifth force.
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- They also plan to perform a cryogenic version of the experiment, which would lend insight into how the crystal atoms behave in their so-called "quantum ground state," which accounts for the fact that quantum objects are never perfectly still, even at temperatures approaching absolute zero.
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- Stay tuned, there is much more to learn.
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- October 11, 2021 ATOMS - is there a fifth force? 3302
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