Atom smasher revs up

The Star detector tracks particles after a collision

By BBC News Online science editor Dr David Whitehouse

Deep in the sandy woods of New York's Long Island, physicists are travelling back to the dawn of the Universe.

We have just detected the most spectacular subatomic collisions ever witnessed by humankind

Satoshi Ozaki

They have begun smashing the nuclei of gold atoms together at the Relativistic Heavy Ion Collider (RHIC), the world's newest and biggest particle accelerator built to study the building blocks of matter.

The facility aims to recreate the conditions of the early Universe.

Scientists will use data collected during the experiments to explore the particles known as quarks and gluons that make up protons and neutrons.

The RHIC has gone online after a publicity campaign sought to reassure local people that its work was safe and would not result in the creation black holes that would destroy the Earth, as some had predicted.

'New era of study'

The high temperatures and densities achieved in the collisions should, for a fleeting moment, reveal the quarks and gluons in a soup-like plasma, a state of matter that is believed to have last existed just millionths of a second after the Big Bang.

Physicists at the US Department of Energy's Brookhaven National Laboratory, who run the RHIC, say early work has already revealed amazing images of particles streaming away from a collision point.

The lab reassured local people that the RHIC was safe

"This moment represents the culmination of many years of hard work, and now all the pieces are in place," says Satoshi Ozaki, Associate Laboratory Director for the RHIC. "We have just detected the most spectacular subatomic collisions ever witnessed by humankind, and are launching a new era for the study of nuclear matter."

Previous studies with lower-energy collisions at the Cern laboratory in Switzerland have hinted at the existence of a quark-gluon plasma.

"But RHIC will produce far more definitive results and allow detailed studies of the quark-gluon plasma," says Laboratory Director John Marburger.

Core of the Sun

Detailed studies of the properties of the quark-gluon plasma, such as its temperature, energy, particle densities, and entropy, will help explain the origins of protons, neutrons and other elementary particles. Only then will we truly understand why they form "the dazzling diversity of matter that we see today, including ourselves," says Thomas Kirk, Associate Laboratory Director for High Energy and Nuclear Physics.

The RHIC's capabilities stem from its size and dual-ring design. Inside the underground accelerator tunnel are two accelerator rings, each 3.9 km (2.4 miles) in circumference and composed of 1,740 superconducting magnets.

The ions travel close to the speed of light before colliding in the detectors

These magnets guide ions of gold around each of the circular rings in opposite directions. The ions move at 99.995% of the speed of light and collide at points where the two rings cross.

For a fraction of a second, the colliding ions reach temperatures one hundred thousand times hotter than the core of the Sun - hot enough to "melt" the ions into their component quarks and gluons.

Sophisticated detectors have been constructed at the collision points around the ring to gather and decipher the enormous volumes of data from the experiments. Two large detectors, Phenix and Star, are several stories tall.