Scientists leading the work of the ALICE collaboration have been awarded the European Physical Society's Lise Meitner Prize 2014. Johanna Stachel of Heidelberg University in Germany, Peter Braun-Munzinger of GSI in Germany, Paolo Giubellino of INFN Torino and CERN, and Jürgen Schukraft of CERN shared the award, which is given every two years for outstanding work in the fields of experimental, theoretical or applied nuclear science.
The prize was awarded specifically "for their outstanding contributions to the experimental exploration of the quark-gluon plasma using ultra-relativistic nucleus-nucleus collisions, in particular to the design and construction of ALICE and shaping its physics programme and scientific results bringing to light unique and unexpected features of a deconfined state of strongly-interacting matter at the highest temperatures ever produced in the laboratory."
Quark-gluon plasma is a state of matter thought to have existed in the first moments after the big bang. For a few millionths of a second, the universe was filled with an astonishingly hot, dense soup made of all kinds of particles moving at near light speed. This mixture was dominated by quarks – fundamental bits of matter – and by gluons, carriers of the strong force that normally “glue” quarks together into familiar protons and neutrons and other species. In those first moments of extreme temperature, however, quarks and gluons free to move on their own in what’s called quark-gluon plasma. The ALICE experiment at CERN is specialized to study quark-gluon plasma recreated in high-energy collisions of heavy ions in the Large Hadron Collider (LHC).
"The study of the quark-gluon plasma is a truly fascinating journey," says Giubellino, "leading us to the production in the laboratory of the droplet of the densest and hottest matter ever observed by humans."
High temperature is not the only surprising property of the plasma. The discovery that quark-gluon plasma behaves like a 'strongly coupled perfect liquid' was a surprise finding from the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory. "Now at the LHC we have seen 'quark-gluon-plasma mini-bubbles' in proton-lead and even in some proton-proton reactions, to everybody's great surprise," says Giubellino. "It turned out that the quark-gluon plasma is much more amazing than anyone would have dared to predict."
For Schukraft, the EPS prize is not primarily a reward for personal achievements, but rather recognition of the effort of a community more than 1000 strong working on heavy-ion physics at the LHC. "The LHC heavy-ion programme does very well indeed in terms of scientific returns, and certainly much more than could have reasonably been expected in terms of surprises and discoveries," he says.