Measurement of the leptonic decay widths of the φ-meson with the KLOE detector

The φ-meson leptonic widths, $\Gamma_{ee}$ and $Gamma_{μμ}$, are obtained, respectively, from the e+e− forward-backward asymmetry and the μ+μ− cross section around the φ-mass energy. We find $\Gamma_{ee}=1.32±0.05±0.03$ keV and $\sqrt{\Gamma_{ee} \Gamma_{\mu\mu}=1.320±0.018±0.017$ keV. These re- sults, compatible with $\Gamma_{ee}=\Gamma_{\mu \mu}$, provide a precise test of lepton universality. Com- bining the two results gives $\Gamma_{\ell \ell} = 1.320 ± 0.023$ keV