Plate Nº 51 · recorded October 10, 2026
PhysicsReported finding
Jet Diffusion Wakes Detected in Quark-Gluon Plasma, 20 Years On
The CMS Collaboration at CERN has measured diffusion wakes behind jets in quark-gluon plasma for the first time, confirming a 20-year-old prediction about the universe's most perfect liquid.
By Priya Raman3 min read665 words
In brief
- CMS Collaboration at CERN measured jet diffusion wakes in quark-gluon plasma for the first time; result appeared in Physical Review Letters on September 30, 2026.
- Quark-gluon plasma existed from about a trillionth of a second to a few microseconds after the Big Bang at temperatures 200,000 times the sun's core.
- The fluid's shear-viscosity-to-entropy-density ratio is 0.08 to 0.20 kelvin-seconds, less than one-tenth that of water at room temperature and about a millionth that of dry air.
- QGP was recognized as a liquid in 2005 at Brookhaven's Relativistic Heavy Ion Collider; the diffusion wake was predicted shortly afterward.
- Each QGP droplet from lead-lead collisions at CERN lasted about 10⁻²² seconds, and the wake signal required statistical analysis of millions of collisions.
The CMS Collaboration at CERN has measured diffusion wakes behind high-energy jets in quark-gluon plasma for the first time, confirming a phenomenon physicists predicted two decades ago. The result appeared in Physical Review Letters on September 30, 2026.
When boats cross smooth water, two thin waves trail behind them at a theoretical angle of 19.5° from the boat's path. Physicists have now spotted the particle-physics analogue of those wakes in quark-gluon plasma (QGP), a state of matter that filled the universe for its first few microseconds after the Big Bang.
What is quark-gluon plasma?
QGP existed from roughly a trillionth of a second to a few microseconds after the Big Bang. It ran 200,000 times hotter than the sun's core. In 2005, experiments at Brookhaven National Laboratory's Relativistic Heavy Ion Collider revealed that this matter behaves as a liquid, not a gas.
Olga Evdokimov, a University of Illinois, Chicago physicist who collaborates on the CMS experiment, calls QGP "the hottest, densest and most perfect fluid in the universe."
The liquid's shear-viscosity-to-entropy-density ratio sits between 0.08 and 0.20 kelvin-seconds. Water at room temperature measures about ten times higher. Dry air clocks in roughly a million times higher.
What are jets, and why do they matter?
When CERN's Large Hadron Collider smashes heavy nuclei together, it briefly recreates the primordial QGP.
Sometimes a single quark or gluon emerges from the collision with enough momentum to travel far. Because the strong force grows stronger with distance — a quirk called asymptotic freedom — that particle cannot escape alone. It drags companions along, forming a conical spray called a jet.
These streams act like probe darts hurled into the primordial soup. How they bend, slow, and shed energy reveals hidden properties of the QGP.
How did researchers spot the wakes?
The CMS team slammed lead nuclei into lead nuclei moving in opposite directions. Each smash produced a hot QGP droplet lasting about 10⁻²² seconds. Most jets shoot out back-to-back at exactly 180° to conserve momentum. Interactions inside the QGP nudge them slightly off-axis.
Researchers analyzed millions of collisions, selecting events whose jets carried momentum above a threshold. They then searched statistically for the wake patterns. The challenge: large-scale ripples, ridges, and valleys in the particle distribution dwarf the tiny wake signatures. Unlike a boat on smooth water, these wakes form inside an extraordinarily messy fluid packed with interacting particles.
Experimenters have spent twenty years learning to subtract those ocean-like waves from their data.
Why has this taken 20 years to find?
The wake signals are too thin to spot in a single collision. Statistically, the team needed enormous datasets and careful analysis.
Earlier attempts, some by Evdokimov's own group, failed to find conclusive evidence.
"The biggest surprise, or rather, excitement for us was being able to finally observe the phenomenon," Evdokimov said. "Many previous searches, including some conducted by my group, did not observe the wake signals or yield conclusive results."
What does the wake reveal about the QGP?
The plasma runs so hot that particles "boil" out of the vacuum itself, Evdokimov explained. The droplet expands at roughly half the speed of light, adding thousands of tracks to a region just a few to ten times the diameter of a proton.
The wake's shape and strength offer a new window on the QGP's transport properties. Together with earlier measurements of how jets lose energy, these results help physicists pin down quantum chromodynamics, the theory describing how quarks and gluons interact.
Why does this matter for cosmology?
For two decades, the diffusion wake stood as a missing piece in the experimental record of quark-gluon plasma. Confirming it gives researchers a second independent probe of the fluid's behavior, alongside jet-quenching measurements. Future analyses with more collision data will sharpen the picture of the exotic liquid that briefly filled all of space.
via Phys.org Physics (Source)
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