Progress on R Measurement through ISR with BABAR

High-luminosity ee storage rings designed for the study of CP violation, such as KEK-B, PEP-B, and DAΦNE, have opened a new possibility to measure ee annihilation using initialstate radiation (ISR) [1,2,3]. A large mass range becomes accessible in a single experiment, especially at B factories, contrary to the case with fixed energy machines which are optimized only in a limited region. The broad-band coveragemay result into a better understanding of systematic effects since only one experimental set-up is involved. Apart from their own physics interest, ranging from hadronic spectroscopy to tests of QCD, measurements of the ratio R = σ(ee → hadrons)/σpt provide the necessary input to dispersion integrals for computing hadronic vacuum polarization contributions. This is indeed the case when calculating the theoretical prediction for the muon magnetic anomaly aμ and the running of the electromagnetic coupling to the Z mass, α(M Z), one of several ingredients in precision tests of the electroweak theory bearing on such fundamental issues as the structure of the Higgs sector. The cross section for the ISR process ee → fγ with a particular final state f is related to the cross section σf (s) for the direct annihilation ee → f through