Heidelberg 2015 – wissenschaftliches Programm

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SYDM: Symposium Dipole Moments - A Tool to Search for New Physics

SYDM 1: Session 1

SYDM 1.4: Gruppenbericht

Dienstag, 24. März 2015, 12:40–13:00, C/gHS

Measurement of the e⁺e⁻→ π⁺π⁻ Cross Section Using Initial State Radiation at BESIII — •Benedikt Kloss and Achim Denig — Institut für Kernphysik Mainz

The cross section σ(e⁺e⁻→ π⁺π⁻) has been measured with ever increasing accuracy at accelerators in Novosibirsk, Orsay and Frascati. More recently the two most accurate measurements have been obtained by the KLOE collaboration in Frascati and the BABAR collaboration at SLAC. Both experiments claim an accuracy of better than 1% in the energy range below 1 GeV in which the ρ resonance is largely dominating the cross section. However a discrepancy of approximately 3% on the peak of the ρ(770) resonance is observed increasing towards higher energies. Unfortunately this discrepancy limits our current knowledge of a_µ≡ (g−2)_µ/2, which is a famous precision observable of the Standard Model (SM) of particle physics. Another comparable experiment is needed. This measurement can be done at the BESIII experiment in Beijing, China. Using the technique of initial state radiation it might be possible to measure this hadronic cross section below 3.0 GeV with a comparable precision to BABAR and KLOE. This talk will give an overview of the current status of this analysis.