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arXiv · 1609.06631

Measurement of the running of the fine structure constant below 1 GeV with the KLOE Detector

2 Collaboration·A. Anastasi·D. Babusci·G. Bencivenni·M. Berlowski·C. Bloise·F. Bossi·P. Branchini·A. Budano·L. Caldeira Balkeståhl·B. Cao·F. Ceradini·P. Ciambrone·F. Curciarello·E. Czerwiński·G. D'Agostini·E. Dané·V. De Leo·E. De Lucia·A. De Santis·P. De Simone·A. Di Cicco·A. Di Domenico·R. Di Salvo·D. Domenici·A. D'Uffizi·A. Fantini·G. Felici·S. Fiore·A. Gajos·P. Gauzzi·G. Giardina·S. Giovannella·E. Graziani·F. Happacher·L. Heijkenskjöld·T. Johansson·D. Kamińska·W. Krzemien·A. Kupsc·S. Loffredo·P. A. Lukin·G. Mandaglio·M. Martini·M. Mascolo·R. Messi·S. Miscetti·G. Morello·D. Moricciani·P. Moskal·M. Papenbrock·A. Passeri·V. Patera·E. Perez del Rio·A. Ranieri·P. Santangelo·I. Sarra·M. Schioppa·A. Selce·M. Silarski·F. Sirghi·L. Tortora·G. Venanzoni·W. Wiślicki·M. Wolke·F. Jegerlehner
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Abstract

We have measured the running of the effective QED coupling constant $\alpha(s)$ in the time-like region $0.6<\sqrt s< 0.975$ GeV with the KLOE detector at DA$\Phi$NE using the Initial State Radiation process $e^+e^-\to\mu^+ \mu^-\gamma$. It represents the first measurement of the running of $\alpha(s)$ in this energy region. Our results show a more than 5$\sigma$ significance of the hadronic contribution to the running of $\alpha(s)$, which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the $e^+e^-\to\pi^+\pi^-$ cross section measured by KLOE, the real and imaginary part of the shift $\Delta\alpha(s)$ has been extracted. By a fit of the real part of $\Delta\alpha(s)$ and assuming the lepton universality the branching ratio $BR(\omega\to\mu^+\mu^-) = (6.6\pm1.4_{stat}\pm1.7_{syst})\cdot 10^{-5} $ has been determined.

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2 Collaboration, A. Anastasi, D. Babusci, G. Bencivenni, M. Berlowski, C. Bloise, F. Bossi, P. Branchini, A. Budano, L. Caldeira Balkeståhl, B. Cao, F. Ceradini, P. Ciambrone, F. Curciarello, E. Czerwiński, G. D'Agostini, E. Dané, V. De Leo, E. De Lucia, A. De Santis, P. De Simone, A. Di Cicco, A. Di Domenico, R. Di Salvo, D. Domenici, A. D'Uffizi, A. Fantini, G. Felici, S. Fiore, A. Gajos, P. Gauzzi, G. Giardina, S. Giovannella, E. Graziani, F. Happacher, L. Heijkenskjöld, T. Johansson, D. Kamińska, W. Krzemien, A. Kupsc, S. Loffredo, P. A. Lukin, G. Mandaglio, M. Martini, M. Mascolo, R. Messi, S. Miscetti, G. Morello, D. Moricciani, P. Moskal, M. Papenbrock, A. Passeri, V. Patera, E. Perez del Rio, A. Ranieri, P. Santangelo, I. Sarra, M. Schioppa, A. Selce, M. Silarski, F. Sirghi, L. Tortora, G. Venanzoni, W. Wiślicki, M. Wolke, F. Jegerlehner. 2016-09-21. Measurement of the running of the fine structure constant below 1 GeV with the KLOE Detector. https://doi.org/10.1016/j.physletb.2016.12.016

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