Burkhardt, Hans

Pietrzyk, B.

HAL Université de Savoie

KLOE measurements and the QED vacuum polarizationB. Pietrzyk, H. BurkhardtTo cite this version:B. Pietrzyk, H. Burkhardt. KLOE measurements and the QED vacuum polarization. 2004,pp.1-3. <in2p3-00022161>HAL Id: in2p3-00022161http://hal.in2p3.fr/in2p3-00022161Submitted on 24 Aug 2004HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.LAPP-EXP 2004-4August 3, 2004KLOE measurementsand the QED vacuum polarizationB. PietrzykLaboratoire de Physique des Particules LAPP, IN2P3-CNRS,F-74941 Annecy-le-Vieux Cedex, Franceand H. BurkhardtCERN, AB Departement, CH-1211 Geneva 23, SwitzerlandAbstractRecent KLOE measurements in the low energy e+e− annihilation data and their in-ﬂuence on the determination of the hadronic contribution to the determination of theQED ﬁne structure constant at mZ are discussed.Contribution to the 2004 summer conferencesContact persons: B. Pietrzyk (pietrzyk@lapp.in2p3.fr)and H. Burkhardt (Helmut.Burkhardt@cern.ch)In the year 2001, we published an updated evaluation of the hadronic contribution tothe running of the QED ﬁne structure constant [1], based on a dispersion integral using aparametrization of the measured cross section of e+e− → hadrons. We obtained a hadroniccontribution of ∆α(5)had(s) = 0.02761 ± 0.00036 at s = m2Z .Our parametrization in the c.m.s. energy region between 0.61 and 0.96GeV was basedon form factor results obtained with the CMD-2 detector at the VEPP-2M collider [2].The overall uncertainty of the ρ region integral, including the statistical uncertainty, is2.3% (that of Γee in [2]) in our analysis.Since then, the CMD-2 collaboration improved the treatment of radiative correctionstwice. An intermediate improvement has appeared in the published document [3] and anadditional improvement has become available in 2003 [4]. We have concluded that themost recent CMD-2 results imply only a small change in the estimate of the hadroniccontribution [5].Recently, the KLOE collaboration [6] has measured the cross section of e+e− →hadrons with high statistical accuracy in small energy bins using the ”radiative return”from the φ resonance to the ρ. The c.m.s. energy region covered by KLOE is very similarto that of the published CMD2 data.In our 2001 analysis, we used the parametrization of the pion form factor as publishedby the CMD2 collaboration. There is no consistent set of ρ−ω parameters yet from KLOE.To estimate the eﬀect of the new results on ∆α(5)had(m2Z), we compared the dispersionintegral results using directly the CMD2 and KLOE data points. Outside the measuredregions, we used the parametrization scaled by the change of normalization between theresults given in Ref. [2] and in Ref. [4]. We treated the systematic uncertainties as fullycorrelated between measurements at diﬀerent c.m.s. energies.Similarly, we have directly integrated the KLOE measurements. Outside the measuredregion, the same parametrization from CMD2 is applied. Finally the results of the inte-gration of KLOE and CMD2 results have been combined and introduced in the analysis ofthe hadronic contribution to the determination of the QED ﬁne structure constant at m2Z .The small increase in α(mZ2) due to the recent updates from CMD2, that we reportedin the 2003 summer conference [4] is about cancelled when we include the KLOE data,conﬁrming our published result from the year 2001 [1]. We therefore recommend to useour published 2001 results as a basis of up-to-date electroweak analyses.We would like to strongly encourage eﬀorts to further clarify and improve the knowl-edge of the low energy hadronic cross section, with a consistent ﬁt of the π-form factorbased on all data in an extended energy range, possibly by including also BABAR andBELLE measurements.References[1] H. Burkhardt and B. Pietrzyk, Phys. Lett. B513 (2001)46.[2] R.R. Akhmetshin et al., CMD-2 Collaboration, hep-ex/9904027.1[3] R.R. Akhmetshin et al., CMD-2 Collaboration, Phys. Lett. B527 (2002)161.[4] R.R. Akhmetshin et al., CMD-2 Collaboration, Phys. Lett. B578 (2004)285.[5] B. Pietrzyk and H. Burkhardt, LAPP preprint LAPP-EXP 2003-07.[6] KLOE Note n.192, July 2004.2

KLOE measurements and the QED vacuum polarization

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