Physicists at Fermilab, the most powerful particle accelerator in the United States, are closing in on one of the universe’s best-kept secrets: what is known as the Holy Grail of physics or the reason why everything has mass. With the Tevatron, an underground particle accelerator buried deep beneath the Illinois prairie, Fermilab scientists smash matter together, accelerating protons and antiprotons in a four-mile-long ring at nearly the speed of light.