{"id":504470,"date":"2026-06-17T14:41:10","date_gmt":"2026-06-17T14:41:10","guid":{"rendered":"https:\/\/www.newsbeep.com\/ie\/504470\/"},"modified":"2026-06-17T14:41:10","modified_gmt":"2026-06-17T14:41:10","slug":"improved-quantum-interference-imaging-of-atomic-nuclei","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ie\/504470\/","title":{"rendered":"Improved Quantum Interference Imaging of Atomic Nuclei"},"content":{"rendered":"

Newswise \u2014 UPTON, N.Y. \u2014 Scientists studying particle collisions at the Relativistic Heavy Ion Collider<\/a> (RHIC) usually capture what happens when atomic nuclei smash into one another at nearly the speed of light. But even when the nuclei don\u2019t collide, interesting things can happen. In a new paper just published in Physical Review Letters, members of RHIC\u2019s STAR collaboration describe a new way to use near-miss collisions at RHIC to study what\u2019s going on inside the nucleus. The approach advances the reach of RHIC, a U.S. Department of Energy (DOE) Office of Science user facility at DOE\u2019s Brookhaven National Laboratory, into the next frontier in nuclear physics \u2014 a journey into the inner workings of the building blocks of matter.<\/p>\n

The technique relies on particles of light, known as photons, that surround the nuclei as they speed around the 2.4-mile RHIC racetrack. Acting something like the beam of a giant X-ray machine, the photons around one nucleus can interact with particles called gluons inside a nucleus whizzing by in the opposite direction. By tracking the signals produced by those interactions, scientists can map out the distribution of the gluons \u2014 the gluelike particles that hold the nucleus together.<\/p>\n

\u201cThis as an extension of the many ways people have used light to probe hidden structures in our world \u2014 from using X-rays to see broken bones and reveal the 3D atomic structures of proteins, to capturing signals from the cosmic microwave background to study the evolution of the universe,\u201d said Ashik Ikbal, a STAR collaborator from Kent State University who carried out this work as a major component of his postdoctoral research. \u201cIn this case, we\u2019re using light to map out features at a scale much smaller than atoms to study the gluons that hold quarks together inside the protons and neutrons of atomic nuclei.\u201d<\/p>\n

Nuclear physicists are particularly interested in gluons because they appear to play an outsized role in establishing the fundamental properties of protons and neutrons \u2014 the building blocks of nearly all the visible matter in our universe. Mapping out gluons is one of the central goals of the Electron-Ion Collider<\/a> (EIC), a new nuclear physics research machine under construction at Brookhaven Lab that will build on RHIC\u2019s infrastructure and science.<\/p>\n

At the EIC, virtual photons emitted by electrons will provide the \u201cbeams\u201d that scientists use to reveal gluons\u2019 arrangements and interactions within protons and nuclei. These new results from RHIC provide a preview of this imaging technique and a way to test its assumptions.<\/p>\n

Using light to create particles and map structures<\/p>\n

The particles of light used in this imaging technique at RHIC are something of an artifact. They emerge as a cloud of electromagnetic energy that surrounds the positively charged ions traveling around the circular accelerator at close to the speed of light. When two ions traveling in opposite directions pass very close by one another without colliding, these \u201cshockwaves\u201d of energy can sometimes interact with one another to create new particles<\/a> of matter and antimatter out of pure energy.<\/p>\n

At other times, the photons create new particles by interacting with gluons inside the nuclei. For example, an earlier STAR paper<\/a> traced photon-gluon interactions that generated particles known as rho mesons. STAR scientists detected those particles by looking for pairs of oppositely charged pions \u2014 the \u201cdaughters\u201d into which the rhos decay. By tracking the pions\u2019 speed and the angles at which they struck the detector, the scientists suggested they could use ripples of interference generated by these quantum-entangled particles to map out gluon distributions within the nuclei.<\/p>\n

But because the rho particles decay so quickly, there was uncertainty about the origin of the interference \u2014 specifically whether it was coming from the decay \u201cdaughter\u201d pions or the rho \u201cparents.\u201d In addition, the somewhat lightweight rho particles lack the \u201cfocus\u201d to map detailed gluon features.<\/p>\n

Flipping the interference pattern<\/p>\n

This new paper builds on that previous work by tracking the daughters of heavier mesons known as J\/psi particles, which are also created in photon-gluon interactions.<\/p>\n

\u201cThe heavier yet more compact structure of J\/psi particles should boost their imaging resolution,\u201d said Zebo Tang, a professor from the University of Science and Technology of China (USTC) who is one of the newly appointed deputy spokespersons for the STAR Collaboration. \u201cJ\/psi particles also live longer than rhos before decaying, giving more time for separation between their own interference patterns and that of the particles into which they decay \u2014 in this case, electrons and positrons.\u201d<\/p>\n

Most importantly, these electron and positron daughters have a quantum property called spin, unlike the daughters of rhos. That spin completely \u201cflips\u201d the particles\u2019 interference pattern compared to what the scientists saw when studying the rhos.<\/p>\n

\u201cIf you think of a repeating wave with alternating peaks and dips, the rhos and their daughter pions produced interference waves with essentially the exact same pattern \u2014 peaks lined up with peaks, dips lined up with dips. But when we tracked the electron and positron daughters of J\/psi decays, they produced the opposite pattern \u2014 opposite from the rhos, their pion daughters, and even their own J\/psi parents. Wherever there were low points became high points, and the high points became low points,\u201d said Prithwish Tribedy, a Brookhaven Lab\/STAR collaboration physicist.<\/p>\n

The scientists saw the same flipped pattern in data from near-miss collisions using three different types of ions at RHIC \u2014 gold, zirconium, and ruthenium. In fact, the interference pattern became stronger with the smaller nuclei, which is exactly what theorists had predicted would happen if the interference was being driven by the decay daughters.<\/p>\n

\u201cSeeing this flipped pattern and alignment with predictions in data from collisions using three different types of nuclei gives us confidence that the daughters are the true source of the interference,\u201d said Kaiyang Wang, a student at USTC, who worked on this project as part of his PhD thesis.<\/p>\n

What is particularly exciting is that this measurement does more than just confirm a quantum interference effect. It allows scientists to use this information and a bit of backtracking to learn how gluons are distributed within atomic nuclei.<\/p>\n

Mapping out gluons<\/p>\n

In the case of either the rho or J\/psi decay, scientists can use the momentum distribution and angles at which the daughter particles strike the detector to infer spin information about their parent particles. This is easier for J\/psi than rho, but the method works for both particles. The parent spin, in turn, gives them information about the spin alignment of the photon that triggered the initial photon-gluon interaction, the orientation of the nucleus with which it collided, and the exact location of the gluon that created the parent particle. You can think of it as a super high-tech way of \u201cgeolocating\u201d gluons at the subatomic scale.<\/p>\n

\u201cThe parent particles are ultimately what we are using to \u2018see\u2019 inside the nucleus, because they are the ones that are closest to the gluon-triggered action, but knowing that the daughters give us direct access to those interactions is what makes this imaging possible,\u201d said Wangmei Zha, a professor at USTC who is a member of the STAR collaboration.<\/p>\n

The future of gluon imaging<\/p>\n

\u201cThis will be exactly the technique used at the EIC,\u201d said Farid Salazar, a nuclear theorist at Temple University who helped develop the theoretical predictions used for comparison with the RHIC measurements and for the future science program at the EIC.<\/p>\n

At the EIC, the photons will be emitted by electrons interacting with ions and the measurements will rely mainly on J\/psi decays.<\/p>\n

For one thing, the spins of the J\/psi decay daughters make it easy to infer the parents\u2019 spin orientation. In addition, their compact size gives them the ability to see details at a finer scale. They are also easier to describe through mathematical calculations. This makes it much easier to derive the theoretical predictions scientists use when evaluating experimental measurements \u2014 to see if the data match theorists\u2019 predictions of how gluons are expected to behave.<\/p>\n

One of the major mysteries physicists hope to explore at the EIC is whether gluons \u2014 which can split and recombine \u2014 reach a state of \u201csaturation\u201d where these splitting and recombination processes balance one another out within atomic nuclei. Other STAR findings<\/a> have already shown hints of gluon recombination, a necessary step to achieving the steady state of gluon saturation. With J\/psi imaging using virtual photons, the EIC may be the first to reveal definitive evidence of this new state of matter, known as a \u201ccolor glass condensate.\u201d<\/p>\n

\u201cRHIC operations have wrapped up<\/a>, and work is beginning to transform the accelerator infrastructure at Brookhaven Lab into the EIC, but we\u2019ll be conducting deep analyses of RHIC data for many years to come,\u201d Brookhaven\u2019s Tribedy said. \u201cThese analyses will undoubtedly produce many more discoveries \u2014 and help us develop the theoretical and experimental approaches for the EIC.\u201d<\/p>\n

Additional collaborators on this analysis include Declan Keane and Zhangbu Xu from Kent State University, Daniel Brandenburg from Ohio State University, and Shuai Yang from South China Normal University.<\/p>\n

This research was supported by the DOE Office of Science, the U.S. National Science Foundation (NSF), and a range of international agencies and organizations listed in the scientific paper. In addition to using the Open Science Grid, supported directly by NSF, the researchers made use of computing resources in the\u00a0Scientific Data and Computing Facilities<\/a>\u00a0at Brookhaven Lab and the\u00a0National Energy Research Scientific Computing\u00a0Center<\/a>\u00a0(NERSC), which is another DOE Office of Science user facility at DOE\u2019s Lawrence Berkeley National Laboratory.<\/p>\n

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov<\/a>.<\/p>\n

Follow @BrookhavenLab on social media. Find us on Instagram<\/a>, LinkedIn<\/a>, X<\/a>, and Facebook<\/a>.<\/p>\n

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