Speaker
Description
New BABAR results are presented on the processes e+e- to pi+pi-(gamma) and mu+mu-(gamma) using the ISR method at PEP II. 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 new analysis does not rely on particle identification (PID) to separate the pion and muon channels, which was the source of the largest systematic uncertainty in the 2009 BABAR result. The data sample uses the full BABAR dataset, and together with releasing the requirements on PID, an overall factor of 6 is gained in statistics. The pi+pi-/mu+mu- separation is achieved by fitting the angular distribution in the 2-particle system with templates built from the individual distributions known from first principles. The analysis is performed with multiple blinding factors on the efficiency measurements and in the fits yielding the cross sections. After unblinding, the muon results are compared to QED predictions and the pion cross section is obtained. 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.
| Tracks | Flavour Beyond the Standard Model |
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