Abstract
We extract the e+e−→π+π− 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 |Fπ|2 as well as the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to (g−2)μ. We find this value to be aμππ,LO(600–900MeV)=(368.2±2.5stat±3.3sys)⋅10−10, which is between the corresponding values using the BaBar or KLOE data.
Highlights
IntroductionThe two most precise measurements have been performed by the KLOE Collaboration in Frascati [8] and the BaBar Collaboration at SLAC [9,10]
The cross section σππ = σ (e+e− → π +π −) has been measured in the past with ever increasing precision at accelerators in Novosibirsk [1,2,3], Orsay [4], Frascati [5,6,7,8], and SLAC [9,10]
The accuracy of the Standard Model (SM) prediction of (g − 2)μ is entirely limited by the knowledge of the hadronic vacuum polarization contribution, which is obtained in a dispersive framework by using experimental data on σ (e+e− → hadrons) [11,12,13]
Summary
The two most precise measurements have been performed by the KLOE Collaboration in Frascati [8] and the BaBar Collaboration at SLAC [9,10]. Both experiments claim a precision of better than 1% in the energy range below 1 GeV, in which the ρ(770) resonance with its decay into pions dominates the total hadronic cross section. In the ISR method events are used in which one of the beam particles radiates a high-energy photon In such a way, the available energy to produce a hadronic (or leptonic) final state is reduced, and the hadronic (or leptonic) mass range below the center-of-mass (cms) energy of the e+e− collider becomes available.
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