Image: A computer graphic tracks jets of particles
CMS Collaboration / CERN
A computer graphic tracks jets of particles emerging from a heavy-ion collision in the Compact Muon Solenoid, a detector that is part of the Large Hadron Collider.
updated 11/30/2010 4:35:06 PM ET 2010-11-30T21:35:06

Just weeks after the world's largest particle accelerator began smashing together heavy lead ions to create little Big Bangs, the experiment has produced a primordial state of matter akin to what existed at the dawn of the universe.

The Large Hadron Collider, a 17-mile-long underground ring near Geneva run by the European Organization for Nuclear Research (known by the French acronym CERN), began colliding lead ions together Nov. 8. These atomic nuclei contain 82 protons, and are thus much heavier than the lone protons the accelerator was previously colliding.

Now two experiments at the LHC — called ATLAS and CMS, respectively — have reported a phenomenon called "jet quenching" that scientists say could reveal secrets about the nature of matter and the evolution of the universe.

Jet quenching
After two ions crash into each other, detectors measure jets of particles that emerge from the high-energy collision. Jets are formed as the basic constituents of nuclear matter, called quarks and gluons, fly away from the collision point.

In proton collisions, jets usually appear in pairs, emerging back to back. However, in the tumultuous conditions created by heavy-ion collisions such as those made by lead nuclei, the jets interact with a hot dense medium created when temperatures are so high that the basic constituents of matter break apart.

This leads to a characteristic signal, known as jet quenching, in which the energy of the jets can be severely degraded, signaling interactions with the medium more intense than ever seen before.

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"ATLAS is the first experiment to report direct observation of jet quenching," ATLAS spokesperson Fabiola Gianotti said in a statement. "The excellent capabilities of ATLAS to determine jet energies enabled us to observe a striking imbalance in energies of pairs of jets, where one jet is almost completely absorbed by the medium."

Probing very early universe
Jet quenching is a powerful tool for studying nature, especially the behavior of the medium of broken-down particles, called quark-gluon plasma. This plasma is created when super-high temperatures break apart protons into their constituent quarks and gluons. The quarks and gluons then float around in a kind of primordial soup that resembles the universe shortly after the Big Bang.

"It is truly amazing to be looking, albeit on a microscopic scale, at the conditions and state of matter that existed at the dawn of time," said CMS spokesperson Guido Tonelli. "Since the very first days of lead-ion collisions, the quenching of jets appeared in our data while other striking features, like the observation of Z particles, never seen before in heavy-ion collisions, are under investigation. The challenge is now to put together all possible studies that could lead us to a much better understanding of the properties of this new, extraordinary state of matter." (A Z particle is nearly identical to a massless photon yet is very massive.)

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The quark-gluon plasma was created for the first time ever at a smaller particle accelerator called the Relativistic Heavy Ion Collider at Brookhaven National Laboratory in Batavia, Ill. That finding was announced in February.

The ATLAS and CMS measurements offer a new possibility to use jets, which interact with the primordial soup, to probe this unique state of matter, scientists said. Future jet quenching and other measurements from the LHC experiments will provide powerful insight into the properties of the primordial plasma and the interactions among its quarks and gluons, they said.

Preliminary results from the experiments will be presented at a seminar on Dec. 2 at CERN.

For the complete story behind the Large Hadron Collider, check out's special section on "The Big Bang Machine."

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Interactive: Inside the big bang machine

Photos: How the biggest collider was built

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  1. Heart of the machine

    A worker stands inside the ATLAS detector, surrounded by its eight toroidal magnets, just before the installation of the machine's calorimeter. ATLAS, the largest particle detector at Europe's Large Hadron Collider, sits inside an underground cavern as big as a cathedral. (Maximilien Brice / CERN) Back to slideshow navigation
  2. Mission control

    Members of the ATLAS detector team monitor operations at their control room on the campus of Europe's CERN particle-physics research center. A cutaway view of the particle detector can be seen on the computer screen at far right. (Claudia Marcelloni / CERN) Back to slideshow navigation
  3. Down the hole

    The last of 1,746 superconducting magnets is lowered into the Large Hadron Collider's beamline tunnel via a specially constructed pit in April 2007, as seen in this fish-eye view. Dipole magnets like this one produce a magnetic field that is 100,000 times stronger than Earth's, to bend beams of subatomic particles around the circular accelerator. (Claudia Marcelloni / CERN) Back to slideshow navigation
  4. Making the connection

    A welder works on the interconnection between two of the Large Hadron Collider's superconducting magnet systems in the collider tunnel. (Maximilien Brice  / CERN) Back to slideshow navigation
  5. Wheel of fortune

    One of the wheel-shaped slices of the ATLAS muon detector is lowered into a cavern for assembly into a giant device designed to look for evidence of exotic subatomic particles such as the Higgs boson. The Higgs particle is thought to play a key role in producing the property of mass in the universe. (Claudia Marcelloni & J. Pequenao / CERN) Back to slideshow navigation
  6. The theorist and the experiment

    World-famous theoretical physicist Stephen Hawking takes a look at the Large Hadron Collider's underground beamline during a visit in September 2006. (CERN) Back to slideshow navigation
  7. Pulling the trigger

    Each experiment at the Large Hadron Collider requires a "trigger," a combination of hardware and software that decides which collisions are significant enough to pass along for further analysis. This is a fish-eye view inside the trigger chambers for the ALICE detector's muon spectrometer. (Aurelien Muller / CERN) Back to slideshow navigation
  8. Inside the big bang

    A technician from the ALICE installation team works on gas pipes for the detector. ALICE is designed to study lead-ion collisions so intense that they re-create the conditions that existed just after the big bang. (A. Saba & Mona Schweizer / CERN) Back to slideshow navigation
  9. Cycles within cycles

    Technicians often use bicycles to get around the Large Hadron Collider's 17-mile-round tunnel. (Maximilien Brice / CERN) Back to slideshow navigation
  10. Dwarfed by science

    The LHCb detector is designed to study why matter dominates over antimatter in the universe. The worker peeking out from the concrete barriers at left is dwarfed by the detector's lip-shaped magnet assembly at right. (CERN) Back to slideshow navigation
  11. The PC farm

    CERN's Computer Center stores the quadrillions of bytes of data generated by experiments at the Large Hadron Collider and distribute the information to thousands of researchers around the world, using a network known as the LHC Computing Grid. (Maximilien Brice / CERN) Back to slideshow navigation
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