New physics and recent high precision electroweak measurements

We analyze LEP and SLC data from the 1995 Winter Conferences for signals of new physics. We compare the data with the Standard Model (SM) as well as a number of test hypotheses concerning the nature of new physics: (i) nonstandard Zbb couplings, (ii) nonstandard Zff couplings for the entire third generation, (iii) nonstandard oblique corrections, (iv) nonstandard lepton couplings, (v) general nonstandard W and Z couplings to all fermions, as well as combinations of the above. In most of our analyses, we leave the SM variables αs and mt as free parameters to see how the various types of new physics can affect their inferred values. We find that the best fit (χ2d.o.f. = 8.410) is obtained for the nonstandard Zbb couplings, which also give a ‘low’ value (0.112) for αs. The SM also gives a good description of the Z data, having χ2d.o.f. = 12.412. If αs is held fixed to the low-energy value 0.112, then we find that a combination of the nonstandard Zbb couplings is fit to lie more than four standard deviations away from zero.