Nuclear Physicists Can See Inside the Atomic Nucleus

Nuclear Physicists Can See Inside the Atomic Core
Nuclear Physicists Can See Inside the Atomic Core

The Relativistic Heavy Ion Collider (RHIC) has a new application for nuclear physicists to observe the structure and properties of atomic nuclei. The approach consists of light particles surrounding gold ions racing around the collider and a new type of quantum entanglement never observed before.
Through a series of quantum fluctuations, light particles or photons interact with gluons. As a result of these interactions, a spacer particle is created and this particle rapidly decays into two “pions” with different charges (p).

By analyzing the velocities and angles at which these p+ and p- particles come into contact with RHIC's STAR detector, scientists can gain important information about the photon and use it to map the arrangement of gluons within the nucleus more accurately than ever before.

"This method is similar to how doctors use positron emission tomography to see what's going on inside the brain and other body parts," says James Daniel Brandenburg, a former Brookhaven Laboratory physicist who joined the Ohio State University as an assistant professor in January 2023 and a member of the STAR collaboration. But in this case, we're talking about mapping features the size of a single proton, or a femtometer, or a quadrillionth of a meter.

STAR scientists find it even more surprising that their observation was made possible by the discovery of a whole new kind of quantum interference.

"We're measuring two outgoing particles, and it's clear that their charges are different - they're different particles," says Zhangbu Xu, a Brookhaven physicist and STAR collaborator. "However, we do see interference patterns that indicate that these particles are entangled or synchronized even though they are distinguishable particles."

The implications of this finding could extend far beyond the grand goal of cataloging the components of matter.

For example, many researchers are interested in entanglement, including those who will share the 2022 Nobel Prize in Physics. One of the goals is to create computers and communication tools much more powerful than what we currently have.

Photons or identical electrons have been used in most entanglement observations to date, including the recent demonstration of laser interference at different wavelengths.

Brandenburg claims this is the first experimental observation of entanglement between several particles.

Using RHIC, a user resource provided by the DOE Office of Science, physicists can discover the quarks and gluons that make up protons and neutrons, the most fundamental building blocks of nuclear matter. They do this by bringing together heavy atomic nuclei, such as gold, that pass through the collider at close to the speed of light.

By analyzing the strength of these collisions between nuclei, which can "melt" the boundaries between protons and neutrons, scientists can learn more about the states of quarks and gluons in the early cosmos.

But nuclear physicists are also interested in how quarks and gluons behave inside atomic nuclei as they currently exist, to better understand the force that holds these atomic building blocks together.

A new result suggests there may be a way to use photon "clouds" surrounding ions moving in RHIC to access the nucleus. If two gold ions pass very close to each other without interacting, photons around one can see inside the other ion.

In this previous work, we showed that the polarization of these photons is due to the electric field extending outward from the nucleus of the ion. And right now, we're successfully using this technology to look at high-energy nuclei.

Thanks to the quantum interference seen between p+ and p- in recently processed data, it is possible to predict very precisely the polarization direction of photons. This allows physicists to study the gluon distribution both parallel to and perpendicular to the photon's path.

Two-dimensional imaging turned out to be very important.

According to Brandenburg, the average gluon density was determined as a function of distance from the nucleus in all previous experiments where the direction of polarization was unknown.

The images are so detailed that we can even tell where the protons and neutrons are located inside these huge nuclei.

According to the researchers, both the observations of the electrical charge distribution in the nuclei and the theoretical predictions made using the gluon distribution are qualitatively supported by the new images.

To better understand how physicists make these 2D observations, let's go back to the particle produced by the photon-gluon interaction. This particle is known as rho, and it decomposes into p+ and p- in less than four septillionths of a second. Details on the dispersion of gluons and the blurring of photons, as well as the momentum of the main rho particle, are revealed by adding the momentum of these two pions.

To isolate just the gluon distribution, the researchers measure the angle between the p+ or p- pathway and rho's orbit. The blur caused by the photon probe decreases as the angle approaches 90 degrees. The distribution of gluons across the entire nucleus can be visualized by researchers by tracking the pions produced by rho particles moving at various angles and energies.

Evidence that the p+ and p- particles striking the STAR detector are the result of interference patterns formed by the entanglement of these two oppositely charged particles is the quantum anomaly that makes the measurements possible.

Remember that every particle has wave existence as well as physical existence.

Much like waves on the surface of a pond that propagate outward when hitting a rock, the mathematical "wave functions" that describe the crests and troughs of particle waves can interact to reinforce or cancel each other out.

Photons around two close-racing ions seem to interact with gluons inside the nuclei, producing two rho particles, one in each nucleus. As each rho decays to a p+ and p-, the wavefunction of the negative pion from one rho interacts with the wavefunction of the negative pion from the other. When the amplified wavefunction encounters it, the STAR detector receives a p-. When the wavefunctions of the two positively charged pions behave similarly, the detector receives a p+.

One of the first proponents of this theory, Wangmei Zha, a researcher at the University of Science and Technology of China, claimed that interference is between two wave functions of the same particles, but cannot exist without entanglement between two different particles, p+ and p-. Quantum mechanics is unusual in this way.

Rhos can only be bent. Experts think differently. The origin is 20 times further than the maximum distance rho particle wavefunctions can travel in their short existence, making it impossible for them to interact before transforming into p+ and p-.

The p+ and p- wave functions from each rho decay preserve the quantum information of their parent particles, even though they arrive at the detector several meters apart; their peaks and troughs remain in the same phase, showing that they “know each other”.

If p+ and p- weren't entangled, the two p+ (or p-) wavefunctions would appear randomly without any noticeable interference effects, according to Chi Yang, a STAR colleague at Shandong University in China who led the study that led to this conclusion. would have phase. These precise measurements would not be possible and we would not be able to determine any orientation regarding photon polarization.

Future research at RHIC using heavier particles and other lifetimes, as well as the Electron-Ion Collider (EIC) being built at Brookhaven, will examine the precise distributions of gluons within nuclei and examine various theories of quantum interference.



Günceleme: 21/01/2023 15:14

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