Physicists still can’t explain the anomaly in the proton experiment • The Record

Physicists in America have confirmed a strange measurement first discovered by scientists probing the internal structure of protons two decades ago.

This latest experiment – conducted at the Thomas Jefferson National Accelerators Facility by a team of academics primarily from Temple University in Philadelphia – shows that the standard model for the formation of protons is not entirely correct and suggests that scientists still do not fully understand protons. As it is supposed.

Today it is understood that protons and other subatomic particles are generally made up of quarks, which are smaller particles that carry a fractional charge. The Simplified Standard Model asserts that protons contain two positively charged quarks and one negatively charged quark. Seems obvious, doesn’t it?

But more realistically, the proton is a mixed chaos Countless quarks and antiquarks interact with each other by exchanging gluons – a separate type of particle that is the strong force that holds quarks together to form a proton.

However, that’s not the whole picture either. There’s something strange going on inside a subatomic particle and we’re two decades away from figuring out what that is.

In Jefferson’s lab, the team bombarded liquid hydrogen with electrons to study the inner nature of the proton in each hydrogen atom using Virtual Compton scattering. Electrons interact with hydrogen protons, eventually causing the proton’s quarks to release a photon. The detectors measure how the electrons and photons are scattered, to find out the position and momentum of the quarks. The information gives researchers an idea of ​​the proton’s internal structure, and a way to measure a proton’s electric polarization.

“We want to understand the proton’s infrastructure,” said Ruanan Lee, the study’s first author. published in nature and a graduate student at Temple University, in the current situation.

“And we can imagine it as a model with the three balanced quarks in the middle. Now, put the proton in the electric field. The quarks have a positive or negative charge. They will move in opposite directions. So, the electric polarization reflects how easy it is to distort the proton by the electric field.”

The distortion shows how well a proton can expand under an electric field. Under conventional theories, protons should become more rigid as they are distorted by electric fields at higher energies. The graph plotting the electric polarization versus the electric field strength should be smooth — but the researchers noticed a distinct bump.

This bump is a strange analogy confirmed by the Temple team.

“What we actually see is that the electric polarization decreases monotonously at first, but at some point there is a local improvement of this property before it decreases again,” Nikos Sparveris, co-author of the research and associate professor of physics at Temple University, said. record.

It is not clear at this point what could be causing this effect

“It is not clear at this point what could have caused this effect.”

The team believes that the bump shows that an unknown mechanism may influence the strong force in some way.

“The first hint of such an anomaly was reported 20 years ago (that was an experiment at MAMI Microtron in Germany), but the results came with a great deal of uncertainty and have not been independently confirmed in the meantime. In this work we were able to measure more accurately. In our new experiment, we already found evidence of a structure in electric polarization, but we observe half the size compared to what was originally reported.”

Electric polarization gives scientists a way to examine the proton’s internal structure and the strength that holds it together. “Reported measurements indicate the existence of a new, not yet understood dynamic mechanism in the proton and pose notable challenges to nuclear theory,” according to the team’s paper. [Arxiv preprint].

The group plans to conduct more follow-up experiments to study the abnormal protrusion in more detail. “We need to determine the shape of such a structure as accurately as possible (it’s an important input to the theory, in trying to explain the cause of the effect) and we need to rule out any possibility that this effect is an experimental artifact,” concluded Sparveris. ®

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