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

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

doi:10.1016/j.physletb.2016.12.016

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<s<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.

Measurement of the running of the fine structure constant below 1 GeV with the KLOE detector / Anastasi, A., Babusci, D., Bencivenni, G., Berlowski, M., Bloise, C., Bossi, F., Branchini, P., Budano, A., Caldeira Balkeståhl, L., Cao, B., Ceradini, F., Ciambrone, P., Curciarello, F., Czerwiński, E., D'Agostini, G., Dané, E., De Leo, V., De Lucia, E., De Santis, A., De Simone, P., et al.. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - STAMPA. - 767:(2017), pp. 485-492. [10.1016/j.physletb.2016.12.016]