Quark-gluon plasma behaves collectively as a true liquid, according to particle collision measurements completed by physicists working on the Compact Muon Solenoid detector at the CERN Large Hadron Collider. The researchers identified wakes and swirling patterns trailing individual quarks as they shot through the dense primordial medium.
The finding resolves a long-standing debate over how the primordial soup that filled the newborn universe responds to high-speed particles. Yen-Jie Lee, a professor of physics at the Massachusetts Institute of Technology who led the analysis, stated: “It has been a long debate in our field, on whether the plasma should respond to a quark. Now we see the plasma is incredibly dense, such that it is able to slow down a quark, and produces splashes and swirls like a liquid. So quark-gluon plasma really is a primordial soup.”
Keep reading: Venus atmosphere preserves peptides that create life structures
How did physicists isolate the wake of a single quark?
Previous searches for wakes in quark-gluon plasma struggled because particle collisions routinely generate quarks in pairs with antiquarks traveling in opposite directions. When both particles cut through the medium simultaneously, their opposing disturbance patterns overlapped and washed out the experimental signal. To bypass that barrier, researchers looked for collisions where a single quark traveled alone through the fluid while paired in momentum with a different subatomic particle.
Learn more: Massive gas cloud disguises early black hole as cosmic star
Working alongside a team led by Professor Yi Chen at Vanderbilt University, the physicists identified collision events where a quark formed alongside a Z boson. A Z boson is an uncharged elementary particle associated with the weak nuclear force that traverses the scorching medium without interacting significantly with the surrounding quarks and gluons. Because the neutral particle passes through cleanly without generating a hydrodynamic disturbance, any ripples, wakes, or splashes recorded on the opposite side of the collision could be attributed entirely to the solitary quark.
Collision parameters measured at the Large Hadron Collider
The research group conducted its measurements by sifting through massive datasets collected during high-energy runs at the underground accelerator located near Geneva, Switzerland. The team mapped how energy spread across the surrounding debris, comparing experimental particle trajectories against hydrodynamics work from Daniel Pablos, a professor of physics at the University of Oviedo and specialist in medium response theory.
Learn more: AI drives MIT research into developing antibiotics against superbugs
- 13 billion: total heavy-ion collisions evaluated across the accelerator database
- 5.02 TeV: center-of-mass energy per nucleon utilized during lead-lead collision runs
- 2,000: rare events identified where a clean Z boson emerged in the opposite direction of a high-energy quark
- Less than 1 quadrillionth of a second: lifetime of the microscopic droplet of plasma before cooling into standard matter
Hybrid model predictions match liquid wakes in primordial soup
During the first microseconds following the Big Bang, the universe reached temperatures of trillions of degrees, preventing quarks and gluons from coalescing into protons and neutrons. Matter existed entirely as an intensely hot, nearly frictionless fluid that expanded and cooled rapidly. Theoretical calculations had long suggested that this primordial state would act as a continuous liquid rather than an unorganized cloud of independently scattering particles.
The disturbance patterns registered by the CMS detector aligned directly with predictions established by the hybrid model, a theoretical framework co-created by Krishna Rajagopal, William A. M. Burden Professor of Physics at the Massachusetts Institute of Technology. The framework predicted that energetic quark jets would transfer momentum to the medium and leave trailing hydrodynamic wakes, creating miniature ripples resembling those formed by an object slicing across water. “This is something that many of us have argued must be there for a good many years, and that many experiments have looked for,” Rajagopal stated.
Publication record and research timeline
The analytical techniques and experimental results were cataloged through collaborative contributions across global physics institutions, receiving partial financial backing from the U.S. Department of Energy.
- January 28, 2026: formal announcement by the Massachusetts Institute of Technology outlining the detection of quark wakes
- Physics Letters B: publication of the research paper titled ‘Evidence of medium response to hard probes using correlations of Z bosons with hadrons in heavy ion collisions’
- Volume 874, Article 140120: official bibliographic reference and digital archive placement for the study
- October 6, 2026: distribution of the analyzed collision findings across international research platforms
Next steps for tracking hydrodynamic wakes at CERN
The experimental team plans to apply the Z boson tagging technique to incoming collision datasets to track how wakes propagate, expand, and dissipate inside the dense fluid. By analyzing the time required for disturbances to fade, physicists aim to measure the viscosity and internal transport properties of the primordial fluid under extreme conditions.
See also: Webb telescope reveals hidden black hole glowing like star
“We’ve gained the first direct evidence that the quark indeed drags more plasma with it as it travels. This will enable us to study the properties and behavior of this exotic fluid in unprecedented detail,” Lee stated. Lee added: “Studying how quark wakes bounce back and forth will give us new insights on the quark-gluon plasma’s properties. With this experiment, we are taking a snapshot of this primordial quark soup.”