Particle mass predicted

Particle mass predicted with lattice quantum chromodynamics, then confirmed at Fermilab. Lattice QCD has come far in recent years (for a primer, see the article by Carleton DeTar and Steven Gottlieb, Physics Today, February 2004, page 45 ), and it has now joined other theoretical methods of predicting the mass of a hadron—in this case the charmed B meson, B _c. A reliable treatment of the heavy quarks allowed a team of theoretical physicists to capitalize on earlier improvements in lattice QCD. Those earlier developments provided a realistic treatment of the light “sea quarks,” the virtual quarks whose ephemeral presence influences the “valence” quarks—the anti-bottom and charmed quarks for the B _c —that are considered the nominal constituents of a hadron. The remarkably precise predicted value was 6304 ± 20 MeV. Shortly after the theorists submitted their paper for publication, the first good experimental measurement of the same particle was announced: 6287 ± 5 MeV. The confirmation bolsters confidence that lattice QCD can be used to calculate many other properties of hadrons. (I. F. Allison et al., Phys. Rev. Lett. 94, 172001, 2005; CDF collaboration, http://dx.doi.org/10.1103/PhysRevLett.94.172001 .)