“We can say that the system definitely flows like a liquid,” says Harris.
One of the first lead-ion collisions in the LHC as recorded by the ATLAS experiment on November 8, 2010. Image courtesy CERN.
Scientists from the ALICE experiment at CERN’s Large Hadron Collider have publicly revealed the first measurements from the world’s highest energy heavy-ion collisions. In two papers posted today to the arXiv.org website, the collaboration describes two characteristics of the collisions: the number of particles produced from the most head-on collisions; and, for more glancing blows, the flow of the system of two colliding nuclei.
Both measurements serve to rule out some theories about how the universe behaves at its most fundamental, despite being based on a relatively small number of collisions collected in the first few days of LHC running with lead-ion beams.
In the first measurement, scientists counted the charged particles that were produced from a few thousand of the most central lead-ion collisions—those where the lead nuclei hit each other head-on. The result showed that about 18,000 particles are produced from collisions of lead ions, which is about 2.2 times more particles than produced in similar collisions of gold ions at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider.