A new determination of the QED coupling α ( M 2 Z ) lets the Higgs off the hook

We use the available data on e+e− → hadrons to determine the value of the QED coupling at the Z pole. The inclusion of recent preliminary BES-II data in the analysis is found to reduce the ambiguity in the determination of the coupling, particularly that arising from the use of either exclusive or inclusive data in the energy region √ s ∼ 2 GeV, in favour of a larger value of α(M2 Z) −1 = 128.978±0.027. As a consequence the predicted value of the mass of the (Standard Model) Higgs boson is increased, so that the preferred value is close to the LEP2 bound. The value of the QED coupling at the Z pole, α(M Z), is the poorest known of the three parameters (GF ,MZ , α(M 2 Z)) which define the standard electroweak model. Indeed it is the precision to which we know α(M Z) which limits the accuracy of the indirect prediction of the mass MH of the (Standard Model) Higgs boson [1, 2]. In fact the predicted allowed domain of MH appears to be not too far from being in conflict with the direct LEP2 bound on the mass. However the quoted mass range for the Higgs does not allow for uncertainty in the value of α(M Z) itself, and so the conflict is less severe than implied by the χ 2 profiles versus MH [1, 2]. Clearly a more precise determination of α(M Z) is especially important. The value of α(M Z) is obtained from α ≡ α(0) = 137.03599976(50) (1) using the relation α(s) = ( 1−∆αlep(s)−∆α had(s)−∆αtop(s) )