Densest matter created

Physicists study the debris from high-speed collisions

Scientists have produced the densest matter ever created in a laboratory. The success came at the Brookhaven National Laboratory in New York, US, where physicists smashed together gold nuclei moving at near-light speed.

The experiments were undertaken in the new Relativistic Heavy Ion Collider (RHIC), the biggest and most powerful particle collider yet built.

The researchers who studied the debris streaming from several collision events said that densities more than 20 times higher than those within the nuclei of ordinary matter had been produced. Temperatures in the compressed matter topped one trillion degrees, they added.

The scientists think that large amounts of matter so dense and so hot last existed a few millionths of a second after the Big Bang, the explosion thought to have created the Universe.

Details of the experiments were presented to 700 delegates at the Quark Matter 2001 Conference at Stony Brook University, New York.

The RHIC came on stream last year. It aims to recreate the conditions of the early Universe to help scientists understand the fundamental nature of matter.

By smashing together heavy ions - atoms stripped of their electrons - physicists can explore particles known as quarks and gluons, the component particles of protons and neutrons.

The high temperatures and densities achieved in the collisions allow, for fleeting moments only, the quarks and gluons to exist "freely" in a soup-like plasma.

Although the measurements reported by RHIC researchers could not determine whether a quark-gluon soup had been achieved, they strongly suggested that further collisions would produce the plasma.

"There is some tantalising evidence I would say, but I think that we need to get some better statistics," said John Harris, a physicist at Yale University.

Last year, the Cern European particle physics laboratory near Geneva, Switzerland, saw glimpses of the quark-gluon plasma. But the RHIC is a much more powerful machine and should be capable of producing more definitive results.