KEK Preprint 2023-51 Belle II Preprint 2024-004 BELLE2-PUB-DRAFT-2023-016 BELLE2-NOTE-PH-2022-038 BELLE2-PUB-PH-2024-002

Measurement of the $e^+e^- \to \pi^+\pi^-\pi^0$ cross section in the energy range 0.62-3.50 GeV at Belle II

Belle II Collaboration

07 April 2024

Abstract: We report a measurement of the $e^+e^- \to \pi^+\pi^-\pi^0$ cross section in the energy range from 0.62 to 3.50 GeV using an initial-state radiation technique. We use an $e^+e^-$ data sample corresponding to 191 $\text{fb}^{-1}$ of integrated luminosity, collected at a center-of-mass energy at or near the $\Upsilon{(4S)}$ resonance with the Belle II detector at the SuperKEKB collider. Signal yields are extracted by fitting the two-photon mass distribution in $e^+e^- \to \pi^+\pi^-\pi^0\gamma$ events, which involve a $\pi^0 \to \gamma\gamma$ decay and an energetic photon radiated from the initial state. Signal efficiency corrections with an accuracy of 1.6% are obtained from several control data samples. The uncertainty on the cross section at the $\omega$ and $\phi$ resonances is dominated by the systematic uncertainty of 2.2%. The resulting cross sections in the 0.62-1.80 GeV energy range yield $ a_\mu^{3\pi} = [48.91 \pm 0.23~(\mathrm{stat}) \pm 1.07~(\mathrm{syst})] \times 10^{-10} $ for the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. This result differs by $2.5$ standard deviations from the most precise current determination.

The record appears in these collections:
Belle II Notes (Internal) > Belle II Notes : Physics
Papers > Paper Drafts (Internal)
Papers > Papers : Physics

 Record created 2024-04-09, last modified 2024-04-09

Download fulltext

Rate this document:

Rate this document:
(Not yet reviewed)