LHC experiments shed light on early universe
Washington: Physicists at CERN are not just investigating the recently discovered Higgs-like boson, but they are coming closer to unravelling the properties of the primordial state of the universe.
The ALICE, ATLAS and CMS collaborations have made new measurements of the kind of matter that probably existed in the first instants of the universe, with experiments using heavy ions at CERN’s Large Hadron Collider (LHC).
The new findings are based mainly on the four-week LHC run with lead ions in 2011, during which the experiments collected 20 times more data than in 2010.
Just after the Big Bang, quarks and gluons -- basic building blocks of matter -- were not confined inside composite particles such as protons and neutrons, as they are today. Instead, they moved freely in a state of matter known as ‘quark-gluon plasma’.
Collisions of lead ions in the LHC, the world’s most powerful particle accelerator, recreate for a fleeting moment conditions similar to those of the early universe. By examining a billion or so of these collisions, the experiments have been able to make more precise measurements of the properties of matter under these extreme conditions.
“The field of heavy-ion physics is crucial for probing the properties of matter in the primordial universe, one of the key questions of fundamental physics that the LHC and its experiments are designed to address. It illustrates how in addition to the investigation of the recently discovered Higgs-like boson, physicists at the LHC are studying many other important phenomena in both proton-proton and lead-lead collisions,” said CERN Director General Rolf Heuer.
They will present their latest results at the 2012 Quark Matter conference, which starts today in Washington, DC.
At the conference, the ALICE, ATLAS and CMS collaborations will present more refined characterizations of the densest and hottest matter ever studied in the laboratory -- 100,000 times hotter than the interior of the Sun and denser than a neutron star.
ALICE will present a wealth of new results on all aspects of the evolution in both space and time of high-density strongly interacting matter. Important studies deal with “charmed particles”, which contain a charm or anti-charm quark. Charm quarks, 100 times heavier than the up and down quarks that form normal matter, are significantly decelerated by their passage through quark-gluon plasma, offering scientists a unique tool to probe its properties.
ALICE physicists will report indications that the flow in the plasma is so strong that the heavy charmed particles are dragged along by it. The experiment has also observed indications of a thermalization phenomenon, which involves the recombination of charm and anti-charm quarks to form “charmonium”.
“This is only one leading example of the scientific opportunities in reach of the ALICE experiment,” said Paolo Giubellino, spokesperson of the ALICE collaboration.
“With more data still being analyzed and further data-taking scheduled for next February, we are closer than ever to unravelling the properties of the primordial state of the universe: the quark-gluon plasma,” he added.