Exclusive hadronic cross sections measured via ISR from BABAR

Abstract

Measuring the inclusive hadronic cross section in e + e − annihilation is of major interest for the determination of the Standard Model prediction of the anomalous magnetic moment of the muon a μ . The QED and weak contribution to a μ can be calculated with very high precission. At low energies, however, perturbation theory cannot be used to calculate the hadronic contribution a μ had . It therefore has to be derived via a dispersion relation from the sum of measured cross sections of exclusive hadronic reactions. Decreasing the experimental uncertainties on these channels is of utmost importance for an improved Standard Model prediction of a μ . Between 1999 and 2008 a data set of approximately 500 fb−1was recorded with the BABAR detector at the B-Factory PEP-II at SLAC (Stanford, USA), an electron-positron storage ring with fixed Center of Mass energy of 10.58 GeV. Using the technique of Initial State Radiation the energy range from threshold up to 4.5 GeV can be accessed. The measurement of the important process e + e − → π + π − and other channels will be presented.