Burkhardt, Hans

Pietrzyk, B.

Hal - Université Grenoble Alpes

Low energy hadronic contribution to the QED vacuum polarization

HAL Université de Savoie

Low energy hadronic contribution to the QED vacuumpolarizationB. Pietrzyk, H. BurkhardtTo cite this version:B. Pietrzyk, H. Burkhardt. Low energy hadronic contribution to the QED vacuum polarization.International Europhysics Conference on High Energy Physics EPS 2003, Jul 2003, Aachen,Germany. 2003. <in2p3-00013950>HAL Id: in2p3-00013950http://hal.in2p3.fr/in2p3-00013950Submitted on 21 Aug 2003HAL 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.Abstract ID-126LAPP-EXP 2003-07July 15, 2003Low energy hadronic contributionto the QED vacuum polarizationB. PietrzykLaboratoire de Physique des Particules LAPP, IN2P3-CNRS,F-74941 Annecy-le-Vieux Cedex, Franceand H. BurkhardtCERN, AB Division, CH-1211 Geneva 23, SwitzerlandAbstractRecent improvements in the low energy e+e− annihilation data and their inﬂuence onthe determination of the hadronic contribution to the determination of the QED ﬁnestructure constant at mZ are discussed.Contribution to the International Europhysics Conference on High Energy Physics,July 17th - 23rd, 2003 in Aachen, GermanyContact 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 contributionto the running of the QED ﬁne structure constant [1]. It was obtained from a dispersionintegral over a parametrization of the measured cross section of e+e− → hadrons. Weobtained a hadronic contribution 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 pion form factor factor results obtained with the CMD-2 detector at the VEPP-2Mcollider [2]. The overall uncertainty of the ρ region integral, including the statistical un-certainty, is 2.3% (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 just become available [4]. In this contribution, we evaluatedthe impact of these improvements on our result at s = m2Z .The changes in the result of ∆α(5)had(m2Z) are illustrated in Fig. 1. Going from thepreprint [2] to the published version [3] of the CMD-2 results lowers the value of ∆α(5)had(s)by about 10% of the total uncertainty of 0.00036.Going from the published to the recent revised CMD-2 results [4] moves ∆α(5)had(s) inthe opposite direction by about 28%, which is about 18% of the total uncertainty of ourpublished analysis.We conclude that the most recent CMD-2 results imply a small change in the estimateof the hadronic contribution which becomes ∆α(5)had(s) = 0.02768 ± 0.00036 at s = m2Z .We would like to encourage eﬀorts to further clarify and improve the knowledge of thelow energy hadronic cross sections, using independent information from measurementsof the ”radiative return” to the rho resonance (see, for example, talk [5] at this confer-ence), measurements of BABAR and BELLE using similar techniques, and further directmeasurements in an enlarged energy range which extends into the 1.2 GeV region.References[1] H. Burkhardt and B. Pietrzyk, Phys. Lett. B513 (2001)46.[2] R.R. Akhmetshin et al., CMD-2 Collaboration, hep-ex/9904027.[3] R.R. Akhmetshin et al., CMD-2 Collaboration, Phys. Lett. B527 (2002)161.[4] CMD-2 Collaboration, July 2003, preliminary reanalysed numbers.[5] M. Incagli, talk in the ’Test of the Standard Model’ session at this conference.1Burkhardt, Pietrzyk2001 published 2003 preliminary0.02761±0.00036 0.02768±0.00036∆αhad19992001 2003prelimarypublished revised-10% +18%of total uncertainty on ∆αhadCMD2Figure 1: Changes of the value of ∆α(5)had(s) caused by improvements in calculations of radiativecorrections by the CMD-2 Collaboration in units of the total uncertainty of ∆α(5)had(s).2

Low energy hadronic contribution to the QED vacuum polarization

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