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Register a new userCombination of KLOE $sigmabig(e^+e^-rightarrowpi^+pi^-gamma(gamma)big)$ measurements and determination of $a_{mu}^{pi^+pi^-}$ in the energy range $0.10 < s < 0.95$ GeV$^2$
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The three precision measurements of the cross section $sigmabig(e^+e^-rightarrowpi^+pi^-gamma(gamma)big)$ 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 $sigmabig(e^+e^-rightarrowpi^+pi^-gamma(gamma)big)$. We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range $0.10 < s < 0.95$ GeV$^2$ of $a_{mu}^{pi^+pi^-} = (489.8 pm 1.7_{rm stat} pm 4.8_{rm sys} ) times 10^{-10}$.
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We have measured the ratio $sigma(e^+e^-rightarrowpi^+pi^-gamma)/sigma(e^+e^-rightarrow mu^+mu^-gamma)$, with the KLOE detector at DA$Phi$NE for a total integrated luminosity of $sim$ 240 pb$^{-1}$. From this ratio we obtain the cross section $sigma(e^+e^-rightarrowpi^+pi^-)$. From the cross section we determine the pion form factor $|F_pi|^2$ and the two-pion contribution to the muon anomaly $a_mu$ for $0.592<M_{pipi}<0.975$ GeV, $Delta^{pipi} a_mu$= $({rm 385.1pm1.1_{stat}pm2.7_{sys+theo}})times10^{-10}$. This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement of the muon anomaly.
Charge asymmetry in processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi- gamma is measured using 232 fb-1 of data collected with the BABAR detector at center-of-mass energies near 10.58 GeV. An observable is introduced and shown to be very robust against detector asymmetries while keeping a large sensitivity to the physical charge asymmetry that results from the interference between initial and final state radiation. The asymmetry is determined as afunction of the invariant mass of the final-state tracks from production threshold to a few GeV/c2. It is compared to the expectation from QED for e+ e- --> mu+ mu- gamma and from theoretical models for e+ e- --> pi+ pi- gamma. A clear interference pattern is observed in e+ e- --> pi+ pi- gamma, particularly in the vicinity of the f_2(1270) resonance. The inferred rate of lowest order FSR production is consistent with the QED expectation for e+ e- --> mu+ mu- gamma, and is negligibly small for e+ e- --> pi+ pi- gamma.
The process $e^+e^- to pi^+pi^-pi^0eta$ is studied in the center-of-mass energy region below 2 GeV with the SND detector at the VEPP-2000 $e^+e^-$ collider. The four intermediate states contribute to this process: $omegaeta$, $phieta$, $a_0(980)rho$, and a structureless $pi^+pi^-pi^0eta$ state. We measure the total $e^+e^- to pi^+pi^-pi^0eta$ cross section and the cross sections for its components: $omegaeta$, $phieta$, and a sum of $a_0(980)rho$ and the structureless state. Our results are in agreement with previous measurements and have comparable or better accuracies.
We present new results on the related rare KL decay modes KL -> pi+ pi- gamma and KL -> pi+ pi- e+ e-. KTeV has performed the first direct measurement of the form factor for the direct emission component of KL -> pi+ pi- gamma decays, a quantity with ramifications for particular chiral models. In addition, the form factor and direct emission/inner bremsstrahlung branching ratio - also presented here - are important input parameters for the understanding of the planar-angle distribution of KL -> pi+ pi- e+ e- decays. Preliminary results indicating the presence of a T-violating asymmetry in the KL -> pi+ pi- e+ e- angular distribution are presented.
Based on a sample of 225.3 million J/psi events accumulated with the BESIII detector at the BEPCII, the decays of eta to pi+pi-l+l- are studied via J/psi to gammaeta. A clear eta signal is observed in the pi+pi-e+e- mass spectrum, and the branching fraction is measured to be BR(eta to pi+pi-e+e-) = (2.11pm0.12 (stat.)pm0.15 (syst.))times10^{-3}, which is in good agreement with theoretical predictions and the previous measurement, but is determined with much higher precision. No eta signal is found in the pi+ pi- mu+ mu- mass spectrum, and the upper limit is determined to be BR(eta to pi+ pi- mu+ mu-)<2.9times10^{-5} at the 90% confidence level.
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