Bochum 2009 – scientific programme

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HK: Fachverband Hadronen und Kerne

HK 61: Fundamental Symmetries

HK 61.4: Talk

Wednesday, March 18, 2009, 17:30–17:45, H-ZO 70

Measurement of the cross section e⁺e⁻→π⁺π⁻π⁰π⁰ via Radiative Return at BaBar — •Andreas Hafner, Miriam Fritsch, and Achim Denig — Universität Mainz

We present a measurement of the cross section of the exclusive hadronic reaction e⁺e⁻→π⁺π⁻π⁰π⁰ with the Babar detector at PEP-II, an e+e- collider running at the fixed CMS energy of 10.6 GeV. Events with photon emission in the initial state (ISR) are used, lowering the effective CMS energy of the hadronic system and allowing for a measurement of the entire energy range < 4.5 GeV (so-called Radiative Return). The preliminary precision of the measurement has a systematic uncertainty of ca. 8% and will be further reduced in near future. The measurement is also interesting from the hadron spectroscopy point-of-view, we see a dominance of the ωπ⁰ and a1(1260)π intermediate states and we can extract for the first time the branching ratio of the J/Ψ →π⁺π⁻π⁰π⁰ decay. Cross section measurements of this kind are needed as input for a precise theoretical prediction of the anomalous magnetic moment of the muon. A comparison of the theory prediction with the direct measurement of the muon anomaly allows a unique precision test of the Standard Model of particle physics.