The 3 sigma discrepancy between the two most precise asymmetry measurements, A_LR and A_FB^b, has been an enduring feature of the
LEP/SLC data. Currently at 3.2 sigma, it is responsible for the marginal confidence level of the global fit, CL= 0.13, or CL= 0.02 if
NuTeV is included.
Since both anomalies involve challenging systematic issues, it might appear that the SM could still be valid if both anomalies result from underestimated systematic error. Indeed the CL of the global fit would then increase to 0.78, but that fit predicts a small Higgs boson mass, m_H= 48 GeV, which is only consistent at CL= 0.03 with the 95% CL lower limit, m_H > 114 GeV, established by direct searches.
The data then favor new physics whether the anomalous measurements are excluded from the fit or not, and the Higgs boson mass cannot be predicted until the new physics is understood. Some measure of statistical fluctuation is needed to maintain the validity of the SM, which is unlikely by broad statistical measures.
New physics is favored, but the SM fit is not definitively excluded. While it is important to search for a light Higgs boson, it is also important to be prepared to investigate other options for electroweak symmetry breaking at the LHC.
