Speaker
Description
New $BABAR$ results, based on the full $BABAR$ dataset, are presented on the processes $e^+e^-\to \pi^+\pi^-(\gamma)$ and $e^+e^-\to \mu^+\mu^-(\gamma)$ using the Initial State Radiation method at the PEP II collider. To reduce systematic uncertainties the measurement of the $\pi^+\pi^-$ cross section is obtained through the ratio with $\mu^+\mu^-$ and the final state includes additional photons in order to be less sensitive to radiative corrections, a technique pioneered in the 2009 $BABAR$ result. The separation between the pion and muon channels is achieved by fitting the angular distribution in the two-particle system without relying on particle identification, which was the source of the largest systematic uncertainty in the 2009 result. The analysis is performed with multiple blinding factors on the efficiency measurements and in the fits yielding the cross sections. These $BABAR$ results, which are essentially independent from those obtained in 2009, provide an important new precision input for computing the hadron vacuum polarization contribution to the muon $g-2$ anomalous magnetic moment.
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