Physics Letters B (Apr 2017)

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

  • 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

DOI
https://doi.org/10.1016/j.physletb.2016.12.016
Journal volume & issue
Vol. 767, no. C
pp. 485 – 492

Abstract

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We have measured the running of the effective QED coupling constant α(s) in the time-like region 0.6<s<0.975 GeV with the KLOE detector at DAΦNE using the Initial-State Radiation process e+e−→μ+μ−γ. It represents the first measurement of the running of α(s) in this energy region. Our results show a more than 5σ significance of the hadronic contribution to the running of α(s), which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the e+e−→π+π− cross section measured by KLOE, the real and imaginary parts of the shift Δα(s) have been extracted. From a fit of the real part of Δα(s) and assuming the lepton universality the branching ratio BR(ω→μ+μ−)=(6.6±1.4stat±1.7syst)⋅10−5 has been determined.

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