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Register a new userLimit on the production of a new vector boson in $mathrm{e^+ e^-}rightarrow {rm U}gamma$, U$rightarrow pi^+pi^-$ with the KLOE experiment
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The recent interest in a light gauge boson in the framework of an extra U(1) symmetry motivates searches in the mass range below 1 GeV. We present a search for such a particle, the dark photon, in ${rm e^+ e^-}rightarrow {rm U}gamma$, U$rightarrow pi^+pi^-$ based on 28 million $mathrm{e^+ e^-} rightarrow pi^+ pi^-gamma$ events collected at DA$Phi$NE by the KLOE experiment. The $pi^+ pi^-$ production by initial-state radiation compensates for a loss of sensitivity of previous KLOE ${rm U} rightarrow mathrm{e^+ e^-}$, $mu^+mu^-$ searches due to the small branching ratios in the $rho-omega$ resonance region. We found no evidence for a signal and set a limit at 90% CL on the mixing strength between the photon and the dark photon, $varepsilon^2$, in the U mass range between $527$ and $987$~MeV. Above 700 MeV this new limit is more stringent than previous ones.
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The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the $mathrm{U}$ boson, with the KLOE detector at the DA$Phi$NE $mathrm{e}^{+}mathrm{e}^{-}$ collider. Using an integrated luminosity of 1.54 fb$^{-1}$, we studied the process $mathrm{e}^{+}mathrm{e}^{-} to mathrm{U}gamma$, with $mathrm{U} to mathrm{e}^{+}mathrm{e}^{-}$, using radiative-return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90%~CL upper limit on the mixing strength between the Standard Model photon and the dark photon, $varepsilon^2$, at $10^{-6}$--$10^{-4}$ in the 5--520~MeV/c$^2$ mass range.
We have searched for a light vector boson $U$, the possible carrier of a dark force, with the KLOE detector at the DA$Phi$NE epm collider, motivated by astrophysical evidence for the presence of dark matter in the universe. Using epm collisions collected with an integrated luminosity of $239.3$~pb$^{-1}$, we look for a dimuon mass peak in the reaction epmto$mu^+ mu^-$gam, corresponding to the decay $Utomu^+mu^-$. We find no evidence for a $U$ vector boson signal. We set a 90% CL upper limit for the mixing parameter squared between the photon and the $U$ boson of 1.6$times$10$^{-5}$ to 8.6$times$10$^{-7}$ for the mass region $520<m_{rm U}<980$ MeV.
Results of a study of the $K^+ rightarrow pi^{0} e^{+} u gamma $ decay at OKA setup are presented. More than 32000 events of this decay are observed. The differential spectra over the photon energy and the photon-electron opening angle in kaon rest frame are presented. The branching ratios, normalized to that of $K_{e3}$ decay are calculated for different cuts in $E^*_gamma$ and $cosTheta^{*}_{egamma}$. In particular, the branching ratio for $E^{*}_{gamma}>30$ MeV and $Theta^{*}_{e gamma}>20^{circ}$ is measured R = $frac{Br(K^+ rightarrow pi^{0} e^{+} u_{e} gamma) } {Br(K^+ rightarrow pi^{0} e^{+} u_{e})} $ = =(0.587$pm$0.010($stat.$)$pm$0.015($syst.$))$times10^{-2}$, which is in a good agreement with ChPT $O(p^{4})$ calculations.
A new measurement of the branching ratio, $R_{e/mu} =Gamma (pi^+ rightarrow mbox{e}^+ u + pi^+ rightarrow mbox{e}^+ u gamma)/ Gamma (pi^+ rightarrow mu^+ u + pi^+ rightarrow mu^+ u gamma)$, resulted in $R_{e/mu}^{exp} = (1.2344 pm 0.0023 (stat) pm 0.0019 (syst)) times 10^{-4}$. This is in agreement with the standard model prediction and improves the test of electron-muon universality to the level of 0.1 %.
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.
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