CERN1's first beams of lead ions - the highest energy beams ever produced by an accelerator - are now ready for experimentation. The new heavy ions facility also opens up a fresh period of research for the Laboratory in this field. This development is an important step towards understanding the matter of the Universe at less than a millionth of a second after its birth.
For some years now, scientists at CERN have been trying to create quark-gluon plasma - the stuff of the early Universe. To do this, they accelerated sulphur and oxygen ions to very high energies and smashed them into stationary targets. Lead, with an atomic weight of 208 compared to sulphur's 32, is by far the heaviest nucleus to be accelerated to date and so it carries much more energy: an astounding 35 TeV. In the collision - which creates a concentration of matter with the highest energy density since the Big Bang - this huge amount of energy is squeezed into a very small space where quark-gluon plasma may be formed. According to theory, this particle soup existed before the Universe cooled down enough for everyday matter to condense out.
To the best of our knowledge, quarks in today's world only exist in clusters which form hadrons - strongly interacting particles such as protons and neutrons. However, at the extremely high energy densities created in lead ion collisions, the idea that a particular quark belongs to a particular hadron becomes meaningless. The quarks are on their own, and since gluons mediate strong interactions, the mix of particles is a quark-gluon plasma. Helmut Haseroth, leader of the project to accelerate lead ions says, "The nicest present for our enthusiasm and effort would be from physics: the discovery at CERN of quark-gluon plasma..."
CERN's new heavy ions facility consists of several specially built systems and the pre-existing, interconnected accelerators, which were themselves upgraded. A new linear accelerator, the Booster synchrotron, the Proton Synchrotron and the Super Proton Synchrotron all accelerate lead ions. However, the Proton Synchrotron also accelerates protons, antiprotons, electrons and positrons, and the injection of the lead ions has to be fitted into this programme. A complicated timing device ensures that all these particles can be accelerated in turn, making CERN's Proton Synchrotron the world's most versatile particle accelerator.
CERN's facility represents scientists' best chance of seeing quark-gluon plasma this millenium.