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Carleton University physicists have new insight into universe secrets


Ottawa, ON – Carleton physicists are among the first in the world to directly observe “jet quenching” as a partner involved in the European Organization for Nuclear Research (CERN) experiment ATLAS.

After less than three weeks of heavy-ion running at the Large Hadron Collider (LHC) in Geneva, three experiments have already brought new insight into matter as it would have existed in the very first instants of the universe.

The ATLAS experiment is the first ever to observe the direct evidence of jet quenching, where energetic jets of particles produced in LHC collisions lose nearly all their momentum travelling across a hot, dense primordial state of matter which may be the quark-gluon plasma predicted by our theories of strong nuclear interactions.  The absorption of quark particles into the hot dense plasma created during the collision of lead ions is referred to as jet quenching. 

“This breakthrough is a testament to the great success of the Canadian detectors built for ATLAS,” said Robert McPherson from the University of Victoria and Institute of Particle Physics, spokesperson of the ATLAS-Canada collaboration. “The Carleton University and University of Toronto groups who led the forward calorimeter construction effort in Canada are to be particularly congratulated for this great success.”

Carleton’s partnership played a key role as detector components built at the university were vital elements in producing the results in the experiment. Data from the forward calorimeters were used to select events for this analysis.

Carleton’s Gerald Oakham, leader of the Carleton calorimeter team says: “It is gratifying to see that the Canadian-built components have been critical to the production of this physics result.”

An ATLAS paper on the experiment was accepted a few hours after submission by the prestigious journal Physical Review Letters.

One of the primary goals of the lead-ion program at CERN is to create matter as it would have been at the birth of the universe. Early experiments have found that when lead ions collide in the LHC they can concentrate enough energy in a tiny volume to produce tiny droplets of this primordial state of matter. Results have already ruled out some theories about how the primordial universe behaved.

“It is impressive how fast the experiments have arrived at these results, which deal with very complex physics,” said CERN’s Research Director Sergio Bertolucci. “The experiments are competing with each other to publish first, but then working together to assemble the full picture and cross-check their results. It’s a beautiful example of how competition and collaboration is a key feature of this field of research.”

“This is part of a huge experiment to discover more about the origins of the universe by recreating the aftermath of the Big Bang and is one of the most complex and significant experiments in today’s world,” says Dr Oakham.

The ATLAS measurements herald a new era in the use of jets to probe the quark gluon plasma. Future jet quenching and other measurements from experiments will provide powerful insight into the properties of the primordial plasma and the interactions among its quarks and gluons.

With more research to be conducted over the next week, the data generated is expected to greatly contribute to the emergence of a more complete model of quark gluon plasma and the very early universe.