B. Cao

Measurement of the φ→π0e+e- transition form factor with the KLOE detector

Abstract A measurement of the vector to pseudoscalar conversion decay ϕ → π 0 e + e − with the KLOE experiment is presented. A sample of ∼9500 signal events was selected from a data set of 1.7 fb −1 of e + e − collisions at s ∼ m ϕ collected at the DAΦNE e + e − collider. These events were used to perform the first measurement of the transition form factor | F ϕ π 0 ( q 2 ) | and a new measurement of the branching ratio of the decay: BR ( ϕ → π 0 e + e − ) = ( 1.35 ± 0.05 − 0.10 + 0.05 ) × 10 − 5 . The result improves significantly on previous measurements and is in agreement with theoretical predictions.

Precision measurement of the η → π + π − π 0 Dalitz plot distribution with the KLOE detector

A bstractUsing 1.6 fb−1 of e+e− → ϕ → ηγ data collected with the KLOE detector at DAΦNE, the Dalitz plot distribution for the η → π+π−π0 decay is studied with the world’s largest sample of ∼ 4.7 · 106 events. The Dalitz plot density is parametrized as a polynomial expansion up to cubic terms in the normalized dimensionless variables X and Y . The experiment is sensitive to all charge conjugation conserving terms of the expansion, including a gX2Y term. The statistical uncertainty of all parameters is improved by a factor two with respect to earlier measurements.

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

Abstract 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 5 σ 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 Δ α ( s ) have been extracted. From a fit of the real part of Δ α ( s ) and assuming the lepton universality the branching ratio B R ( ω → μ + μ − ) = ( 6.6 ± 1.4 s t a t ± 1.7 s y s t ) ⋅ 10 − 5 has been determined.

Combination of KLOE

The three precision measurements of the cross section

\sigma\big(e^+e^-\rightarrow\pi^+\pi^-\gamma(\gamma)\big)

\sigma\big(e^+e^-\rightarrow\pi^+\pi^-\gamma(\gamma)\big)

measurements and determination of

using initial state radiation by the KLOE collaboration provide an important input for the prediction of the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations. We present the construction of these covariance matrices and use them to determine a combined KLOE measurement for

a_{\mu}^{\pi^+\pi^-}

\sigma\big(e^+e^-\rightarrow\pi^+\pi^-\gamma(\gamma)\big)

in the energy range

. We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range

0.10 < s < 0.95

0.10 < s < 0.95

GeV

GeV