Number 286 (Story #2), September 13, 1996 by Phillip F. Schewe and Ben Stein THE STANDARD MODEL OF PARTICLE PHYSICS seems more irreproachable than ever. In numerous experiments physicists have sought to find a discrepancy between experimental findings and predictions based on the model in which the quarks and leptons interact via the exchange of photons, gluons, and the W and Z bosons. (Gravity is usually left out of these studies.) A crack in this model was seemingly uncovered recently at an experiment at CERN in which the decay of Z bosons into particles containing a bottom quark was unexpectedly high. But at the International Conference on High Energy Physics in Warsaw in July, CERN scientists reported that the reanalyzed data was now back in line with theory. (Nature, 22 August 1996.) Another experimental result, the observation earlier this year of an excess of high-energy particle jets in proton-antiproton collisions at Fermilab's Tevatron, was interpreted by some to be possible evidence for the existence of structure inside quarks, and as such to represent a departure from the orthodox standard model. But here again, a further look at the data has made it more compatible with the consensus theory. One of the cornerstones of this theory is the Higgs boson, the particle that supposedly endows the Z and W bosons with a heavy mass and which plays a role in making the weak force (responsible for radioactivity) and the electromagnetic force very different in the way that they act in the universe. Scientists would like actually to detect the Higgs, but they don't know its mass. To get an approximate mass value, and to determine whether present or future accelerators would be able to find the Higgs, theorists need first to pin down the masses of the top quark and the W boson. At a divisional meeting of the APS in Minneapolis in August the two big Tevatron collaborations helped out: the CDF group announced (on the basis of an inventory of 100 top-quark events, from CDF and D0) a new top mass of 176.8 (with an uncertainty of 6.5) GeV; meanwhile the D0 group reported a new W mass of 80.35 (uncertainty of 0.15) GeV, based on data from D0 and CDF. (Science, 23 August 1996.)