A “Little Bang” arrives at the LHC

In November, the Large Hadron Collider (LHC) at CERN began its first heavy-ion run, producing lead-lead collisions with the highest center of mass energy ever achieved. Now, a pair of papers appearing in Physical Review Letters, from the ALICE [1] and ATLAS [2] experiments at the LHC, presents a first glimpse of what new information these high-energy collisions will offer about the quark-gluon plasma—the state of matter believed to have filled the universe at the time of the Big Bang. The ALICE results strongly indicate that the quark-gluon plasma remains a nearly ideal liquid, as seen earlier at the Relativistic Heavy Ion Collider (RHIC), even at significantly higher energies. Complementing this work, the ATLAS team has shown that even very high energy jets of particles emitted from the collision lose a large fraction of their energy into the quark-gluon plasma (and are sometimes completely dissipated), a sign that the quarks and gluons are strongly interacting with the hotter plasma.

Phys. Rev. Lett. 105, 252302 (2010) – Published December 13, 2010