CERN’s Large Hadron Collider collides protons most of the year but switches to massive lead nuclei for a month. Collisions of these heavy ions reproduce the quark-gluon plasma that filled the universe millionths of a second after the big bang. Much of the program for quark-gluon plasma studies is shaped by theoretical and experimental contributions from Berkeley Lab’s Nuclear Science Division, as shown by results from ALICE and other experiments during the LHC’s first lead-lead run just concluded.

The Large Hadron Collider has completed many successful months of colliding protons (hydrogen ions) at record-breaking energies and now begins four weeks of colliding much more massive lead ions, giving access to different physical phenomena. Berkeley Lab hosts U.S. participation in the ALICE experiment, designed specifically to study the heavy-ion collisions that give rise to a unique phase of matter, the quark-gluon plasma. Berkeley Lab is also a major participant in the ATLAS experiment, one of the other LHC experiments that will study lead-lead collisions.

Beams of protons were brought together in the first focused collisions on Tuesday, March 30, at CERN’s Large Hadron Collider. The world’s record collisions open a new realm of high-energy physics.

After more than a year of repairs, the Large Hadron Collider located at the CERN laboratory near Geneva, Switzerland is back on track to create high-energy particle collisions that may yield extraordinary insights into the nature of the physical universe.

The ALICE detector at CERN’s Large Hadron Collider will study the fireballs that result when energetic lead ions collide, recreating conditions like those when the universe was just a millionth of a second old. An ALICE instrument called EMCal will signal the most interesting events. Designed by an international collaboration spearheaded by scientists and engineers at Berkeley Lab and other U.S. institutions, EMCal is now on its way to completion.