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Register a new userMeasurement of $sigma(e^+e^-topi^+pi^-gamma(gamma))$ and the dipion contribution to the muon anomaly with the KLOE detector
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KLOE Collaboration
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We have measured the cross section $sigma(e^+e^-topi^+pi^-gamma(gamma))$ at DA$Phi$NE, the Frascati phi-factory, using events with initial state radiation photons emitted at small angle and inclusive of final state radiation. We present the analysis of a new data set corresponding to an integrated luminosity of 240 pb$^{-1}$. We have achieved a reduced systematic uncertainty with respect to previously published KLOE results. From the cross section we obtain the pion form factor and the contribution to the muon magnetic anomaly from two pion states in the mass range $0.592 < M_{pipi} < 0.975$ GeV. For the latter we find $Delta a^{pipi}_mu = (387.2pm0.5_{rm stat}pm2.4_{rm exp}pm2.3_{rm th})times 10^{-10}$
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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.
We have measured the cross section of the radiative process e+e- -> pi+pi-gamma with the KLOE detector at the Frascati phi-factory DAPHNE, from events taken at a CM energy W=1 GeV. Initial state radiation allows us to obtain the cross section for e+e- -> pi+pi-, the pion form factor |F_pi|^2 and the dipion contribution to the muon magnetic moment anomaly, Delta a_mu^{pipi} = (478.5+-2.0_{stat}+-5.0_{syst}+-4.5_{th}) x 10^{-10} in the range 0.1 < M_{pipi}^2 < 0.85 GeV^2, where the theoretical error includes a SU(3) ChPT estimate of the uncertainty on photon radiation from the final pions. The discrepancy between the Standard Model evaluation of a_mu and the value measured by the Muon g-2 collaboration at BNL is confirmed.
A measurement of the vector to pseudoscalar conversion decay $phi to pi^0 e^+e^-$ with the KLOE experiment is presented. A sample of $sim 9500$ signal events was selected from a data set of 1.7 fb$^{-1}$ of $e^+e^-$ collisions at $sqrt{s} sim m_{phi}$ collected at the DA$Phi$NE $e^+e^-$ collider. These events were used to obtain the first measurement of the transition form factor $| F_{phi pi^0}(q^2) |$ and a new measurement of the branching ratio of the decay: $rm{BR},(phi to pi^0 e^+e^-) = (,1.35 pm 0.05^{,,+0.05}_{,,-0.10},) times 10 ^{-5}$. The result improves significantly on previous measurements and is in agreement with theoretical predictions.
The ratio R_{eta}=Gamma(eta -> pi^+pi^-gamma)/Gamma(eta -> pi^+pi^-pi^0) has been measured by analyzing 22 million phi to eta gamma decays collected by the KLOE experiment at DAPhiNE, corresponding to an integrated luminosity of 558 pb^{-1}. The eta to pi^+pi^-gamma proceeds both via the rho resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, R_{eta}= 0.1856pm 0.0005_{stat} pm 0.0028_{syst}, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the eta -> pi^+pi^-gamma decay could be described in a model-independent approach in terms of a single free parameter, alpha. The determined value of the parameter alpha is alpha = (1.32 pm 0.08_{stat} +0.10/-0.09_{syst}pm 0.02_{theo}) GeV^{-2}
By studying the invariant-mass distribution of the $e^+e^-$ in conversion decays, it is possible to learn more about mesons structure and underlying quark dynamics. At KLOE, the study of the $phi to pi^0 e^+e^-$ process is currently going to be finalized. At present, about 9000 events have been selected from a data sample of 1.7 fb$^{-1}$ from 2004/2005 data taking campaign. A very good agreement between data and Monte Carlo distributions has been achieved for all interesting kinematical variables. A preliminary invariant-mass spectrum of $e^{+}e^{-}$ is presented.
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