Аннотация
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.
Язык оригинала | английский |
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Страницы (с-по) | 485-492 |
Число страниц | 8 |
Журнал | Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics |
Том | 767 |
DOI | |
Состояние | Опубликовано - 10 апр 2017 |