The novel method, developed by nuclear physicists at the STAR detector of the Relativistic Heavy Ion Collider (RHIC), relies on particles of light that surround gold ions as they speed around the collider and a new type of quantum entanglement that’s never been seen before.
The STAR detector at the Relativistic Heavy Ion Collider (RHIC) acts like a giant 3D digital camera to track particles emerging from particle collisions at the center of the detector. Image credit: Brookhaven National Laboratory.
Through a series of quantum fluctuations, photons interact with gluons — gluelike particles that hold quarks together within the protons and neutrons of nuclei.
Those interactions produce an intermediate particle that quickly decays into two differently charged pions (π).
By measuring the velocity and angles at which these π+ and π– particles strike RHIC’s STAR detector, the nuclear physicists from the STAR Collaboration can backtrack to get crucial information about the photon — and use that to map out the arrangement of gluons within the nucleus with higher precision than ever before.
“This technique is similar to the way doctors use positron emission tomography (PET scans) to see what’s happening inside the brain and other body parts,” said Dr. James Daniel Brandenburg, a member of the STAR Collaboration and a physicist at the Brookhaven National Laboratory and the Ohio State University.
“But in this case, we’re talking about mapping out features on the scale of femtometers — quadrillionths of a meter — the size of an individual proton.”
Even more amazing is the observation of an entirely new kind of quantum interference that makes their measurements possible.
“We measure two outgoing particles and clearly their charges are different — they are different particles — but we see interference patterns that indicate these particles are entangled, or in sync with one another, even though they are distinguishable particles,” said Dr. Zhangbu Xu, a member of the STAR Collaboration and a physicist at the Brookhaven National Laboratory.
That discovery may have applications well beyond the lofty goal of mapping out the building blocks of matter.
For example, many physicists are seeking to harness entanglement — a kind of ‘awareness’ and interaction of physically separated particles.
One goal is to create significantly more powerful communication tools and computers than exist today.
But most other observations of entanglement to date, including a recent demonstration of interference of lasers with different wavelengths, have been between photons or identical electrons.
“This is the first-ever experimental observation of entanglement between dissimilar particles,” Dr. Brandenburg said.
The team’s work appears today in the journal Science Advances.
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M.S. Abdallah et al. (STAR Collaboration). 2023. Tomography of ultra-relativistic nuclei with polarized photon-gluon collisions. Science Advances, in press; arXiv: 2204.01625
