In a recent paper cite{benayoun} M.Benayoun {it et al.} use a specific model to compare results on the existing data for the cross section of the process $e^+e^-rightarrow pi^+pi^-$ and state conclusions about the inconsistency of the BABAR results w
ith those from the other experiments. We show that a direct model-independent comparison of the data at hand contradicts this claim. Clear discrepancies with the results of Ref. cite{benayoun} are pointed out. As a consequence we do not believe that the lower value and the smaller uncertainty obtained for the prediction of the muon magnetic anomaly are reliable results.
The BABAR collaboration has nearly completed a program of precise measurements of the cross sections for the dominant channels of e+e- --> hadrons from threshold to an energy of 3-5 GeV using the initial-state radiation (ISR) method, i.e. the measure
ment of the cross sections e+e- --> gamma hadrons with the energetic photon detected at large angle to the beams. These data are used as input to vacuum polarization dispersion integrals, in particular the hadronic contribution to the muon g-2 anomaly. In addition to the recently measured pi+pi- cross section, giving the dominant contibution, many multihadronic channels have been investigated, with some recent examples presented here. We give preliminary results for the process e+e- --> K+K-(gamma) using 232 fb-1 of data collected with the BABAR detector at e+e- center-of-mass energies near 10.6 GeV. The lowest-order contribution to the hadronic vacuum polarization term in the muon magnetic anomaly is obtained for this channel: amu-KK-LO=(22.95 +-0.14(stat) +-0.22(syst)) 10^-10, which is about a factor of three more precise than the previous world average value.
A precise measurement of the cross section of the process $e^+e^-topi^+pi^-(gamma)$ from threshold to an energy of 3GeV is obtained with the initial-state radiation (ISR) method using 232fb$^{-1}$ of data collected with the BaBar detector at $e^+e^-$
center-of-mass energies near 10.6GeV. The ISR luminosity is determined from a study of the leptonic process $e^+e^-tomu^+mu^-(gamma)gamma_{rm ISR}$, which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process $e^+e^-topi^+pi^-(gamma)$ is obtained with a systematic uncertainty of 0.5% in the dominant $rho$ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured $pipi$ cross section from threshold to 1.8GeV is $(514.1 pm 2.2({rm stat}) pm 3.1({rm syst}))times 10^{-10}$.
Results on the lowest-order hadronic vacuum polarization contribution to the muon magnetic anomaly are presented. They are based on the latest published experimental data used as input to the dispersion integral. Thus recent results on tau to nutau p
i pi0 decays from Belle and on e+ e- annihilation to pi+ pi- from BABAR and KLOE are included. The new data, together with improved isospin-breaking corrections for tau decays, result into a much better consistency among the different results. A discrepancy between the Standard Model prediction and the direct g-2 measurement is found at the level of 3 sigma.
A precise measurement of the cross section of the process e+ e- to pi+ pi- (gamma) from threshold to an energy of 3 GeV is obtained with the initial state radiation (ISR) method using 232 fb^-1 of data collected with the BABAR detector at e+ e- cente
r-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process e+ e- to mu+ mu- gamma (gamma). The leading-order hadronic contribution to the muon magnetic anomaly calculated using the pi pi cross section measured from threshold to 1.8 GeV is (514.1 +-2.2(stat} +-3.1(syst}) x 10^{-10}.
