Low-energy hadronic cross sections measurements at BABAR, and implication for the g − 2 of the muon

The BABAR Collaboration has an intensive program studying the cross sections of hadron production in low-energy e+e− annihilation, accessible via initial-state radiation. Our measurements allow a significant improvement in the precision of the predicted value of the muon anomalous magnetic moment. These improvements are necessary for shedding light on the current > 3 sigma difference between the predicted and the experimental values. We have published results on a number of processes with two to six hadrons in the final state, and other final states are currently under investigation. We report here on the most recent results obtained by analysing the entire BABAR dataset. DIS2016, 24th workshop on Deep-Inelastic Scattering and Related Subjects. 11-15 April 2016, DESY Hamburg 1 The muon gyromagnetic factor and “anomalous” moment As a result of more than three decades of intense efforts to validate every corner of the standard model (SM) of elementary particles and their interactions, and to submit it to a redundant metrology with an always increasing precision, the SM has only become more and more “standard”, with some very few exceptions that include the “tension” between the theoretical prediction and the unique precise experimental measurement of the “anomalous” magnetic moment of the muon, aμ, which is the relative deviation of the gyromagnetic factor, gμ, from the value of g = 2 for a pointlike Dirac particle, i.e. aμ ≡ (gμ − 2)/2. 1 ar X iv :1 60 4. 07 64 1v 2 [ he pex ] 2 7 A pr 2 01 6