Maximal entanglement sheds new light on particle creation

UPTON, N.Y. — Physicists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Stony Brook University (SBU) have shown that particles produced in collimated sprays called jets retain information about their origins in subatomic particle smashups. The study was recently published as an Editor’s Suggestion in the journal Physical Review Letters.

“Despite extensive research, the connection between a jet’s initial conditions and its final particle distribution has remained elusive,” said Charles Joseph Naim, a research associate at the Center for Frontiers in Nuclear Science (CFNS) in SBU’s Department of Physics and Astronomy. “This study, for the first time, establishes a direct connection between the ‘entanglement entropy’ at the earliest stage of jet formation and the particles that emerge as a jet evolves.”

The evidence comes from an analysis of jet particles emerging from proton-proton collisions captured by the ATLAS experiment at the Large Hadron Collider, a 17-mile-circumference circular collider located at CERN, the European Organization for Nuclear Research. In these powerful collisions, the individual building blocks of the colliding protons, known as quarks and gluons, scatter off one another and sometimes get knocked free with enormous amounts of energy. But quarks can’t stay free for long. They and the gluons that normally hold them together immediately begin to split and reconnect through a branching process called fragmentation. The result is the formation of many new composite particles made of pairs or triplicates of quarks — collectively known as hadrons — that spray out of the collision in a coordinated way, that is, as a jet.

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Study co-authors Dmitri Kharzeev, Charles Joseph Naim, Zhoumunding Tu, Jaydeep Datta, and Abhay Deshpande at the Center for Frontiers in Nuclear Science at Stony Brook University. (Rachel Rodriguez/Stony Brook University)

“We wanted to see if the distribution of the hadrons in the jet was influenced by the level of entanglement among the quarks and gluons at the time the jet first formed,” said Abhay Deshpande, a distinguished professor at SBU. Deshpande holds a joint appointment as director of science for the Electron-Ion Collider (EIC), a new nuclear physics research facility under construction at Brookhaven Lab, and he is also currently serving as Brookhaven Lab’s interim associate laboratory director for nuclear and particle physics.

The analysis was motivated in part by earlier research by study co-authors Zhoudunming Tu and Dmitri Kharzeev, both with faculty roles at SBU and appointments at Brookhaven Lab. Their study, published last year, revealed a connection between entanglement among quarks and gluons within protons and the overall distribution of particles emerging from proton-proton and electron-proton smashups. In that work, the higher the entanglement entropy among the quarks and gluons, the greater the entropy, or “messiness,” in the distribution of particles produced.

“This earlier study revealed that there is maximal entanglement among the quarks and gluons within the high-energy proton,” said Tu. “In this work, we extend this approach to the production of jets, which form from the fragmentation of those quarks and gluons. Will there also be maximal entanglement ‘inside’ these fragmenting high-energy quarks and gluons?”

Such a state of maximal entanglement among the jet-forming quarks and gluons predicts a connection between the jet fragmentation function and the entropy, or disorder, of hadrons emerging from the jet. This entropy would be observed as a large number of different types of hadrons — mainly pions, kaons, and protons — striking the detector. Conversely, such an observation of a high degree of disorder among jet particles and its correlation with the initial fragmentation predictions would be evidence of this maximal entanglement in the fragmenting quarks and gluons.

When the scientists looked at the data from the LHC’s proton-proton collisions, the distribution of jet hadrons matched this prediction based on maximal entanglement in the earliest stage of jet formation.

“This new study offers a novel quantum-level perspective on the fragmentation process,” said Kharzeev.

Study co-author Jaydeep Datta, a research scientist at SBU, added, “This study paves the way for further exploration of how quantum entanglement influences hadron formation, including at the upcoming Electron-Ion Collider.”

The EIC will have active participation from many Stony Brook University faculty and students, and it promises unprecedented precision in studying quantum entanglement effects in high-energy collisions. Among other things, the EIC will compare jets emerging from electron-proton collisions with jets emerging from electron-nucleus collisions. These experiments will explore how far the quantum effects extend within nuclei — and potentially modify the microcosm within protons.

This research was funded by the Center for Frontiers in Nuclear Science at Stony Brook University; the DOE Office of Science; the Co-design Center for Quantum Advantage, a Brookhaven-led National Quantum Information Science Research Center also supported by the DOE Office of Science; and by a Laboratory Directed Research and Development project at Brookhaven Lab.

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.

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