A state of matter believed to have existed at the very start of the universe, called quark-gluon plasma, has been produced by University of Kansas researchers working with an international team at the Large Hadron Collider. The material, dubbed by physicists the “littlest liquid,” was found by colliding protons with lead nuclei at high energy inside the supercollider’s Compact Muon Solenoid detector.
Quan Wang, a KU postdoctoral researcher working with the team at CERN, the European Organization for Nuclear Research, said:
“Before the CMS experimental results, it had been thought the medium created in a proton on lead collisions would be too small to create a quark-gluon plasma.
Indeed, these collisions were being studied as a reference for collisions of two lead nuclei to explore the non-quark-gluon-plasma aspects of the collisions. The analysis presented in this paper indicates, contrary to expectations, a quark-gluon plasma can be created in very asymmetric proton on lead collisions.”
Senior scientists associated with the CMS detector said the unexpected discovery has shed new light on high-energy physics.
Yen-Jie Lee, assistant professor of physics at MIT and co-convener of the CMS heavy-ion physics group, said:
“This is the first paper that clearly shows multiple particles are correlated to each other in proton-lead collisions, similar to what is observed in lead-lead collisions where quark gluon plasma is produced. This is probably the first evidence that the smallest droplet of quark gluon plasma is produced in proton-lead collisions.”
Lee described quark-gluon plasma as a very hot and dense state of matter of unbound quarks and gluons, that is, not contained within individual nucleons.
“It’s believed to correspond to the state of the universe shortly after the Big Bang,” Wang said. “The interaction between partons — quarks and gluons — within the quark-gluon plasma is strong, which distinguishes the quark-gluon plasma from a gaseous state where one expects little interaction among the constituent particles.”
Wang said such work may help scientists to better understand cosmic conditions in the instant following the Big Bang.
“While we believe the state of the universe about a microsecond after the Big Bang consisted of a quark-gluon plasma, there is still much that we don’t fully understand about the properties of quark-gluon plasma,” he said. “One of the biggest surprises of the earlier measurements at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory was the fluid-like behavior of the quark-gluon plasma. Being able to form a quark-gluon plasma in proton-lead collisions helps us to better define the conditions needed for its existence.”
Photo: “CERN LHC Tunnel1” by Julian Herzog CC BY-SA 3.0