Measurement of the e+e- →π+π- cross section from threshold to 1.2 GeV with the CMD-3 detector

Abstract

The cross section of the process e+e-→π+π- has been measured in the center of mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The measurement is based on a full dataset collected below 1 GeV during three data taking seasons, corresponding to an integrated luminosity of about 62 pb-1. In the dominant ρ-resonance region, a systematic uncertainty of 0.7% has been reached. At energies around φ-resonance the π+π- production cross section was measured for the first time with high beam energy resolution. The forward-backward charge asymmetry in the π+π- production has also been measured. It shows a strong deviation from the theoretical prediction based on the conventional scalar quantum electrodynamics framework, and it is in good agreement with the generalized vector-meson-dominance and dispersive-based predictions. The impact of the presented results on the evaluation of the hadronic contribution to the anomalous magnetic moment of muon is discussed.