Precise Measurement of thee+e−→π+π−(γ)Cross Section with the Initial State Radiation Method atBABAR

A precise measurement of the cross section of the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}(\ensuremath{\gamma})$ from threshold to an energy of 3 GeV is obtained with the initial state radiation (ISR) method using $232\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected with the BABAR detector at ${e}^{+}{e}^{\ensuremath{-}}$ center-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\gamma}(\ensuremath{\gamma})$. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the $\ensuremath{\pi}\ensuremath{\pi}$ cross section measured from threshold to 1.8 GeV is $\mathbf{(}514.1\ifmmode\pm\else\textpm\fi{}2.2(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}3.1(\mathrm{syst})\mathbf{)}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$.

Precise Measurement of thee+e−→π+π−(γ)Cross Section with the Initial State Radiation Method atBABAR | Litlas