This image shows beams of lead ions colliding, scattering particles. Their signals are measured by the cylindrical ATLAS detector.This image shows beams of lead ions colliding, scattering particles. Their signals are measured by the cylindrical ATLAS detector. (CERN)

A phase of matter created moments after the Big Bang is thought to have been detected at the Large Hadron Collider in Switzerland.

"Striking" evidence of a quark-gluon plasma has been observed by a team of researchers, including Canadians, at the facility near Geneva, the European Organization for Nuclear Research (CERN) announced Friday.

What is quark-gluon plasma?

Quarks and gluons are very tiny particles that combine into larger particles called protons. Those in turn combine with electrons to form atoms in the world we know today. However, during the initial moments of the Big Bang, this hadn't yet happened. The temperature was likely 100,000 to a million times what it was at the centre of the sun, and quarks moved freely in a "soup" called a plasma. Physicists hypothesize that as the universe cooled, small groups of quarks separated into individual protons, and as it cooled further, small groups of protons combined with electrons to form individual atoms.

"People have been searching for evidence of this for decades," Canadian physicist Richard Teuscher said Friday from CERN's laboratory. "What's exciting is if this is really true … [it's] the first unambiguous measurement of this condition of the early universe."

The results of the experiment by an international collaboration called ATLAS were accepted Friday morning for publication in the scientific journal Physical Review Letters, less than 24 hours after it was submitted, said Teuscher, a research scientist at the Canadian Institute for Particle Physics and a physics professor at the University of Toronto.

Normally, the peer review process takes weeks or months, added Teuscher, a member of ATLAS who did some of the data analysis for the experiment.

Physicists theorize that a few hundred millionths of a second after the Big Bang (about 14 billion years ago), the universe was made of a quark-gluon plasma — an extremely hot soup of very tiny subatomic particles.

Canadian physicist Richard Teuscher, shown inside the tunnel of the Large Hadron Collider during construction a few years ago, said people have been searching for evidence of quark-gluon plasma for decades. Canadian physicist Richard Teuscher, shown inside the tunnel of the Large Hadron Collider during construction a few years ago, said people have been searching for evidence of quark-gluon plasma for decades. (Matthias Haase/CERN)The Large Hadron Collider produces extremely high-energy collisions of larger particles, mimicking the Big Bang and potentially reproducing the types of matter that existed during the early moments of the universe.

In this case, researchers spent three weeks smashing lead ions into one another and measuring the resulting signals. Ions are particles produced by adding or removing electrons from atoms. They are charged and can therefore be propelled by an electromagnetic field inside a particle accelerator or collider.

Teuscher likened the colliding ions to two bean bags crashing at extremely high speed, causing their contents to spray out.

"But it doesn't just spray out randomly all over the place," he added.

Instead, two cones or "jets" of particles spray out in opposite directions.

Plasma fireball

The lead ions are so massive and the energy of their collision is so high that it is expected to produce a "fireball" of quark-gluon plasma — "something like the fireball produced at the time of the Big Bang."

Canadian content

Canadians make up more than 150 of the researchers involved in ATLAS. They have mainly been involved with designing, building and operating detectors called liquid argon calorimeters, including the forward calorimeter, under projects funded by the Natural Sciences and Engineering Research Council. Team members include physicists from the University of Alberta, Carleton University, McGill University, University of Montreal, Simon Fraser University, University of Regina, University of Toronto, University of British Columbia, University of Victoria, York University and TRIUMF, Canada's national laboratory for particle and nuclear physics.

One of the jets of particles must pass through the fireball to get out the other side, melting in the process.

As predicted, the data shows that in half the collisions, only one of the two jets can be observed, Teuscher said: "The other jet has been blown to smithereens."

The researchers used two different methods to confirm their results. Teuscher added that another experiment called CMS, which uses different detectors, is reporting similar results, although those haven't yet been published.

Peter Krieger, an associate professor of physics at the University of Toronto, said a detector called the forward calorimeter built in Canada by researchers at the University of Toronto and at Carleton University in Ottawa was a key component in the recent discovery.

It helped confirm that the evidence was the result of a certain type of ion collision, where the two ions strike each other head on instead of grazing each other. The head-on collision releases more energy, and is therefore the type that is predicted to produce a quark-gluon plasma.

Next, ATLAS researchers will be collecting more data and poring through it for different kinds of evidence of quark-gluon plasma.

A cross-section of the cylindrical ATLAS experimental setup is shown on the left. The lines in the centre are tracks left by the jets of particles produced during the collision. The lighter green and red rings are the detectors, while the dark red and green bars (and the graphs at centre and right) represent the signals they detect. Normally, a collision will generate two signal peaks representing two jets, one on either side of the cylinder. However, in this case, one disappears. A cross-section of the cylindrical ATLAS experimental setup is shown on the left. The lines in the centre are tracks left by the jets of particles produced during the collision. The lighter green and red rings are the detectors, while the dark red and green bars (and the graphs at centre and right) represent the signals they detect. Normally, a collision will generate two signal peaks representing two jets, one on either side of the cylinder. However, in this case, one disappears. (ATLAS experiment/CERN)