Measurement of additional radiation in the initial-state-radiation processes $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}\gamma$ and $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\gamma$ at BABAR

Abstract

A dedicated measurement of additional radiation in $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}\gamma$ and $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\gamma$ initial-state-radiation events is presented using the full BABAR data sample. For the first time results are presented at next-to- and next-to-next-to-leading order, with one and two additional photons, respectively, for radiation from the initial and final states. Comparison with predictions from Phokhara and AfkQed Monte Carlo generators is performed, revealing discrepancies in the one-photon rates and angular distributions for the former. This disagreement has a negligible effect on the BABAR measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}(\gamma )$ cross section, but could affect other measurements significantly. This study sheds a new light on the longstanding discrepancy in this channel that affects the theoretical prediction of hadronic vacuum polarization contributions to the muon magnetic moment anomaly.

arXiv comment9 pages, 8 figures and 1 table, v2 corresponds to the published version

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Cited by in corpus (8)

• Tensions in $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}(\gamma )$ measurements: the new landscape of data-driven hadronic vacuum polarization predictions for the muon $g-2$
• Model Independent Tests of the Hadronic Vacuum Polarization Contribution to the Muon $g$$-$$2$
• Complete dispersive evaluation of the hadronic light-by-light contribution to muon $g-2$
• Precision evaluation of the $\eta$- and ${\eta }^{\prime }$-pole contributions to hadronic light-by-light scattering in the anomalous magnetic moment of the muon
• Hybrid calculation of hadronic vacuum polarization in muon g-2 to 0.48\%
• Improved evaluation of the electroweak contribution to muon $g-2$
• The Muon Magnetic Moment and Physics Beyond the Standard Model
• Measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\pi }^0$ cross section in the energy range 0.62-3.50 GeV at Belle II