Experiments At LHC Offer Better Understanding Of Primordial Universe
Lawrence LeBlond for redOrbit.com – Your Universe Online
Scientists working at CERN’s Large Hadron Collider are gaining a better understanding of the primordial universe through experimentation involving the use of heavy ions.
The collaborations between the ALICE, ATLAS and CMS projects have made new measurements of the kind of matter that most likely existed during the creation of the universe more than 13 billion years ago.
Results of their experiments will be presented at the Quark Matter 2012 conference in Washington DC, which begins today.
The findings are based on a four-week LHC experiment using the heavy lead ions in 2011, during which the scientists collected 20 times more data than in all of 2010.
To gain an understanding of their findings, it is important to also understand what occurred in the moments just after the creation of the universe (the Big Bang). During the incident, quarks and gluons — the 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.”
Through collisions of lead ions at the LHC, the teams recreated, although for a brief fleeting moment, the conditions similar to those of the universe when it was formed. And through examinations of these billion-plus collisions, scientists 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,” said Rolf Heuer, Director-General at CERN. “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.”
At the meeting, the three teams will present more refined characterizations of the densest and hottest matter ever studied in a lab — 100,000 times hotter than the interior of the Sun and denser than a neutron star.
Each team will present unique findings from the experiments.
ALICE is set to present results on aspects of the evolution of high-density, strongly interacting matter in both space and time. Their studies deal with “charmed particles” that contain a charm or anticharm 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 anticharm quarks to form “charmonium.”
Paolo Giubellino, spokesperson for ALICE, said this is just one example of the scientific opportunities ALICE is involved with. “With more data still being analyzed and further data-taking scheduled for next February, we are closer than ever to unraveling the properties of the primordial state of the universe: the quark–gluon plasma.”
Initial dissociation of charmonium was proposed as a direct signature for the formation of quark-gluon plasma during the 1980s, and first experimental indications of the dissociation were reported from fixed-target experiments at CERN’s Super Proton Synchrotron in 2000. But the much higher energy output from the LHC makes it possible for scientists to study similar tightly-bound states of the heavier beauty quarks for the first time.
CMS experiments now observe clear signs of the expected sequential suppression of the “quarkonium” (quark–antiquark) states.
“CMS will present important new heavy-ion results not only on quarkonium suppression, but also on bulk properties of the medium and on a variety of studies of jet quenching,” said CMS spokesperson Joseph Incandela. “We are entering an exciting new era of high-precision research on strongly interacting matter at the highest energies produced in the laboratory.”
ATLAS will report new findings on jet quenching — the phenomenon in which highly energetic sprays of particles break up in the dense quark–gluon plasma — including a high-precision study of how the jets fragment in matter, and on the correlations between jets and electroweak bosons.
“We have entered a new phase in which we not only observe the phenomenon of quark–gluon plasma, but where we can also make high-precision measurements using a variety of probes,” said ATLAS spokesperson Fabiola Gianotti. “The studies will contribute significantly to our understanding of the early universe.”