The Brandeis Experimental High-energy physics group contributed to the ATLAS experiment's latest findings regarding a quark-gluon plasma which support certain theories about the earliest stages of the universe, according to Prof. Craig Blocker (PHYS). This plasma is important because there is a theory that predicts that the very early universe went through a stage during which it was a quark-gluon plasma, and all the matter that we know now was condensed into a very small volume at a high temperature, Blocker said. "The fact that [this state of matter] was predicted and we see it is significant."

"In the plasma, sometimes a pair of very high-energy particles is created, and what we see is that one of the particles loses a lot of energy as it travels through the plasma. So we see an imbalance of the two particles, and that is the evidence we have for the plasma," Blocker said.

The members of the group are Physics Profs. Jim Bensinger, Hermann Wellenstein, Larry Kirsch and Blocker; associate research scientist Christoph Amelung, who works in Geneva at the Large Hadron Collider; and Brandeis graduate studentsScott Aefsky, Dan Pomeroy, Serdar Gozpinar,Lou Bianchini and Laurel Coffey.

Blocker said in an interview with the Justice that the Brandeis group did not specifically work on the analysis of the plasma but that "we are part of the collaboration [of the ATLAS experiment], and we built and installed parts of the detector that were used." The ATLAS experiment studies proton-proton collisions, particle physics and heavy ion physics, according to Blocker.

The Brandeis group became part of the ATLAS collaboration after it was involved in building a superconducting supercollider near Dallas, but the construction of that collider was canceled by Congress in 1993, according to an e-mail from Blocker. The Brandeis group looked for another outlet for its efforts and "decided that the LHC had the most promise for providing interesting new particle physics results," Blocker wrote.

The heavy-ion experiment, which was conducted in the LHC in Geneva using lead nuclei, rendered evidence that is significant because it "is probably the first definitive evidence of the creation of a quark-gluon plasma in collisions like this," Blocker said.

He explicated quarks and gluons by explaining that protons and neutrons are made of quarks, while gluons are what bind quarks together. If protons and neutrons collide at very high-energy densities, as in the LHC, the "state of matter [of] the quarks and gluons is different than what is normally found in a proton or neutron," Blocker said.

The LHC, according to the European Organization for Nuclear Research's website, is a circular accelerator 17 miles in circumference that has a beam of protons going in one direction in the circle and a beam of protons traveling in the opposite direction. Those beams collide at very high energies, almost reaching the speed of light, in various places around the circle, and it is from these collisions that the quark-gluon plasma was created.

Blocker further explained how the plasma was created in the LHC. He said that the scientists at ATLAS started colliding lead nuclei, which contain a high number of protons and neutrons, at very high energies, and during the 3 weeks in December 2010 that they ran those experiments, the scientists discovered the presence of the plasma.

High-energy experiments like this one are only conducted at a few places around the world, Blocker said. Thus, the actual experiment is conducted in Geneva, and data is processed there, but then the group at Brandeis uses that data for their analyses of the findings.

"These heavy-ion collisions were done just at the end of running [the experiment] in December, and this data came on very suddenly, which is unusual. We were happy about it, but it was somewhat surprising," Blocker said. He went on to say that once ATLAS starts running again in a few weeks, they will return to proton-proton collisions and "hopefully we'll find some very interesting and new physics" from those collisions.