Physicists have just learned something key about the proton

Physics at the smallest scales is challenging to observe: particles are often transient, and the forces that govern their behavior are almost imperceptible. But now, by exploiting decades-old data and a 50-year-old prediction about the effect of gravity on subatomic particles, a team of physicists has derived a measure of a second mechanical property of the proton.

Let's slow down for a moment. A proton is a particle that forms an atom with neutrons and electrons. Protons themselves are made of smaller particles called quarks. These quarks are held together by the strong force, which is one of the… Four fundamental forces. (The other three are gravity, the weak force, and electromagnetism.) The latter team succeeded in measuring the distribution of the strong force inside the proton, and revealed shear stress on the proton's quarks.

“At its peak, this is a force greater than four tons that one would have to apply to a quark to pull it away from a proton,” said Volker Burkert, principal scientist at Jefferson Laboratory and lead author of the study. laboratory launch.

published In Reviews of Modern Physics, the work continues by A Qiyas 2018 From the internal pressure of the proton. The data the team studied came from experiments conducted at Jefferson Laboratory's Continuous Electron Beam Accelerator Facility, or CEBAF, and the researchers used something called “deep virtual Compton scattering” (DVCS) to take the measurement. In DVCS, a high-energy electron is sent to the target hydrogen proton. The quark inside the proton emits a photon that carries information about the quark's properties. DVCS also provides information about the effects of gravity on matter The idea was developed in the early 2000s By physicist Maxim Polyakov.

“This theoretical breakthrough has proven the relationship between the measurement of hypothetical deep Compton scattering and the gravitational shape factor. “We have been able to use that for the first time and extract the pressure, which we did in the Nature paper in 2018, and now the normal force and the shear force,” Burkert added.

Data collection was an accident. The team was trying to perform 3D imaging of the scattering, but in doing so, they collected data that revealed how the strong force affects the proton's interior.

“In my view, this is just the beginning of something much bigger to come,” study co-author Latifa Ouadriri, a researcher at Jefferson Lab, said in the same release. “It really changed the way we think about the structure of the proton.”

The scattering method can guide researchers to the properties of protons “encoded in gravitational form factors,” as the researchers describe them. 2023 Long-Term Plan for Nuclear Science. In other words, DVCS could be a way to discover new physics. Next, the team plans to take new measurements of the proton's size.

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