We have measured the running of the effective QED coupling constant α(s)α(s) in the time-like region View the MathML source0.6<0.975 GeV with the KLOE detector at DAΦNE using the Initial-State Radiation process e+e−→μ+μ−γe+e−→μ+μ−γ. It represents the first measurement of the running of α(s)α(s) in this energy region. Our results show a more than 5σ significance of the hadronic contribution to the running of α(s)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−e+e−→π+π− cross section measured by KLOE, the real and imaginary parts of the shift Δα(s)Δα(s) have been extracted. From a fit of the real part of Δα(s)Δα(s) and assuming the lepton universality the branching ratio BR(ω→μ+μ−)=(6.6±1.4stat±1.7syst)⋅10−5BR(ω→μ+μ−)=(6.6±1.4stat±1.7syst)⋅10−5 has been determined.
Titolo: | Measurement of the running of the fine structure constant below 1 GeV with the KLOE detector |
Autori: | ANASTASI, ANTONIO (Primo) |
Data di pubblicazione: | 2017 |
Rivista: | |
Abstract: | We have measured the running of the effective QED coupling constant α(s)α(s) in the time-like region View the MathML source0.6<0.975 GeV with the KLOE detector at DAΦNE using the Initial-State Radiation process e+e−→μ+μ−γe+e−→μ+μ−γ. It represents the first measurement of the running of α(s)α(s) in this energy region. Our results show a more than 5σ significance of the hadronic contribution to the running of α(s)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−e+e−→π+π− cross section measured by KLOE, the real and imaginary parts of the shift Δα(s)Δα(s) have been extracted. From a fit of the real part of Δα(s)Δα(s) and assuming the lepton universality the branching ratio BR(ω→μ+μ−)=(6.6±1.4stat±1.7syst)⋅10−5BR(ω→μ+μ−)=(6.6±1.4stat±1.7syst)⋅10−5 has been determined. |
Handle: | http://hdl.handle.net/11570/3105935 |
Appare nelle tipologie: | 14.a.1 Articolo su rivista |
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