I will be shocked and disappointed if we don't have at least one major discovery.

Joseph Lykken, Fermilab scientist

Possible hints of the Higgs particle were obtained last year at the Large Electron Positron (Lep) particle collider at Cern, Geneva, shortly before it was closed down.

Like Lep, the Tevatron takes beams of sub-atomic particles, protons and antiprotons, and fires them in opposite directions around a circular track.

After they have built up enough energy, the beams collide head-on in an intense but tiny explosion at the centre of two huge detectors, called CDF and D0, which examine the debris of the impact.

This is the first series of Tevatron experiments since 1997. In the intervening time, a completely new accelerator, called the Main Injector, has been built to feed the protons and antiprotons into the Tevatron for their final acceleration.

New physics

Fermilab's Director Michael Witherell said he was pleased with the culmination of the laboratory's decade-long preparations and anticipated its discoveries.

Data from the first collisions have been obtained

"We can look forward to the excitement of seeing new physics results. We can't predict what nature has in store for us. All we can guarantee is the opportunity for discovery."

According to the researchers, the new series of experiments has the potential for revealing much new physics, including:

• Evidence for a theoretical model known as supersymmetry that unites all of nature's fundamental building blocks.
• Suggestions of possible extra dimensions in the Universe.
• New insight into the difference between matter and antimatter.
• Better understanding of the top quark, discovered at Fermilab in 1995.

Calibrating the detector

"Besides the approximately seven miles (11 km) of particle beam enclosures, the accelerator complex includes 44,000 controllable devices. Millions of components, circuits and parts all have to work together. The Tevatron is one of the most complex devices on Earth."

The current experimental effort will continue, with a mid-course interruption for further upgrades and improvements to accelerators and detectors, until 2007.

At about that time, results will begin to emerge from a new accelerator, the Large Hadron Collider at Cern, which will have seven times the Tevatron's energy and will overtake the Tevatron at the high-energy frontier of modern physics.

The Tevatron's rings where the particles are accelerated