In a case of the plot thickening as the mystery unfolds, the Higgs boson has just gotten heavier, even though the subatomic particle has yet to be found. In a letter to the scientific journal Nature, published in the June 10, 2004 issue, an international collaboration of scientists working at the Tevatron accelerator of the Fermi National Accelerator Laboratory (Fermilab), report the most precise measurements yet for the mass of the top quark — a subatomic particle that has been found — and this requires an upward revision for the long-postulated but still undetected Higgs boson.