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Measurement of the $e^+ e^− \to \pi^+ \pi^−$ cross section between 600 and 900 MeV using initial state radiation

The collaboration
Phys.Lett.B 753 (2016) 629-638, 2016.

Abstract
We extract the $e^+e^-\rightarrow \pi^+\pi^-$ cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fb$^{-1}$ taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor $|F_\pi|^2$ as well as the contribution of the measured cross section to the leading order hadronic vacuum polarization contribution to $(g-2)_\mu$. We find this value to be $a_\mu^{\pi\pi,\rm LO}(600-900\;\rm MeV) = (368.2 \pm 2.5_{\rm stat} \pm 3.3_{\rm sys})\cdot 10^{-10}$.

• Bare Cross Section

10.17182/hepdata.73898.v4/t1

Bare cross section $\sigma^\mathrm{bare}(e^+e^-\to\pi^+\pi^-(\gamma_\mathrm{FSR}))$ of the process $e^+e^-\to\pi^+\pi^-$ measured using the initial state radiation method. The data is corrected concerning...

• Covariance Matrix of the Bare Cross Section

10.17182/hepdata.73898.v4/t2

Statistical covariance matrix of the bare cross section $\sigma^\mathrm{bare}(e^+e^-\to\pi^+\pi^-(\gamma_\mathrm{FSR}))$.

• Pion Form Factor

10.17182/hepdata.73898.v4/t3

Pion form factor $|F_\pi|^2$ measured using the initial state radiation method. The data is corrected concerning vacuum polarization effects.

• Covariance Matrix of the Pion Form Factor

10.17182/hepdata.73898.v4/t4

Statistical covariance matrix of the pion form factor $|F_\pi|^2$.

Version 4 modifications: fix some entries