Measurement of the e+e- -> pi+pi- cross section using initial state radiation at BESIII

TL;DR

This paper reports a precise measurement of the e+e- to pi+pi- cross section using initial state radiation at BESIII, covering 600-900 MeV, and evaluates its impact on the muon g-2 anomaly.

Contribution

First measurement of the e+e- to pi+pi- cross section in this energy range using initial state radiation at BESIII with high precision.

Findings

Systematic uncertainty of 0.9% achieved.

Cross section data contributes to muon g-2 calculations.

Provides pion form factor measurements in 600-900 MeV range.

Abstract

Using 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, we extract the $e^+e^-\rightarrow \pi^+\pi^-$ cross section and the pion form factor $|F_\pi|^2$ in the energy range between 600 and 900 MeV. We exploit the method of initial state radiation for this measurement, yielding a systematic uncertainty of 0.9%. We calculate the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to $(g-2)_\mu$.