Measurement of the <math display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>-</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>-</mo></msup></math> cross section from threshold to 1.2 GeV with the CMD-3 detector

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.

Note:

54 pages, 36 figures; as published in Phys. Rev. D 109, 112002

electron positron: annihilation
electron positron: colliding beams
pi: pair production
muon: magnetic moment
magnetic moment: anomaly
energy resolution: high
charge: asymmetry
Novosibirsk VEPP-2000
channel cross section: measured
experimental results

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

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Measurement of the $e^{+} e^{-} \to π^{+} π^{-}$ cross section from threshold to 1.2 GeV with the CMD-3 detector