A long-awaited particle accelerator powered up last week and began smashing the nuclei of atoms in the highest energy collisions ever achieved in a laboratory. Physicists hope such collisions will yield a bizarre type of matter that blinked out of existence a millionth of a second after the universe was born.
Particle physicists would like to recreate the early universe in miniature by cooking up a soupy, exceedingly hot mix of fundamental particles called quark-gluon plasma. Earlier this year, researchers at CERN, the European accelerator laboratory in Geneva, claimed to have glimpsed the plasma (ScienceNOW, 10 February). Now, scientists working with the Relativistic Heavy Ion Collider (RHIC) in Upton, New York, hope to confirm that tentative claim and to study in detail the properties of the weird stuff.
Ordinary matter resembles a ballroom filled with waltzing couples, while quark-gluon plasma looks more like teenagers slam-dancing at a rock concert. Within the matter around us, particles called quarks clump together in twos or threes, each group cloaked in a cloud of particles called gluons. As with ballroom dancers, no quark or gluon dares dance by itself. But in quark-gluon plasma, free-flying quarks and gluons bounce off one another willy-nilly, each grooving to its own beat. Astrophysicists believe that the piping hot, newborn universe was one big quark-gluon plasma until it cooled below roughly a trillion degrees Celsius.
To reproduce such staggering temperatures, RHIC scientists smash gold nuclei together at near light-speed. Nine years in the making, RHIC consists of two circular accelerators, nearly 4 kilometers in circumference, in which the nuclei race in opposite directions. The two rings cross and the ions collide in the hearts of four enormous detectors, which collect the thousands of particles that blast out of the collisions. Researchers will analyze the different types of particles to infer whether the plasma flashed into existence.
On 12 June, 2 days after RHIC fired up, researchers watching a monitor revealing activity inside one of the detectors saw evidence of the first gold-gold collision. "All of a sudden there was this explosion of particles and there was no mistaking that two heavy ions had collided. People did jump and cheer!" says Brookhaven physicist Tom Ludlam.
RHIC will allow physicists to peer far deeper into nuclear matter than any previous machine, says theoretical physicist Miklos Gyulassy of Columbia University. "To me," he says, "RHIC is the Hubble Space Telescope of nuclear physics."