Based on an integrated luminosity of 1.61 fb$^{-1}$ $e^+e^-$ collision data collected with the KLOE detector at DA$Phi$NE, the Frascati $phi$-factory, a search for the $P$- and $CP$-violating decay $etatopi^{+}pi^{-}$ has been performed. Radiative $p
hitoetagamma$ decay is exploited to access the $eta$ mesons. No signal is observed in the $pi^{+}pi^{-}$ invariant mass spectrum, and the upper limit on the branching fraction at 90% confidence level is determined to be ${mathcal B}(etatopi^{+}pi^{-})<4.9times10^{-6}$, which is approximately three times smaller than the previous KLOE result. From the combination of these two measurements we get ${mathcal B}(etatopi^{+}pi^{-}) < 4.4times10^{-6}$ at 90% confidence level.
Based on a sample of 300 million $K_S$ mesons produced in $phi to K_L K_S$ decays recorded by the KLOE experiment at the DA$Phi$NE $e^+e^-$ collider we have measured the branching fraction for the decay $K_S to pi mu u$. The $K_S$ mesons are identif
ied by the interaction of $K_L$ mesons in the detector. The $K_S to pi mu u$ decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of $K_L to pi mu u$ decays. A fit to the reconstructed muon mass distribution finds $7223 pm 180$ signal events. Normalising to the $K_S to pi^+ pi^-$ decay events the result for the branching fraction is $mathcal{B}(K_S to pi mu u) = (4.56 pm 0.11_{rm stat} pm 0.17_{rm syst})times10^{-4}$.
The last decade witnessed an increasing interest in axions and axion-like particles with many theoretical works published and many new experimental proposals that started a real race towards their discovery. This paper is the Conceptual Design Report
of the KLASH (KLoe magnet for Axion SearcH) experiment at the Laboratori Nazionali di Frascati (LNF). The idea of this experiment has been stimulated by the availability of the large volume superconducting magnet, with a moderate magnetic field of 0.6 T, used in the KLOE detector at the DAFNE collider. The main conclusion we draw from this report is the possibility to build and put in operation at LNF in 2-3 years a large haloscope with the sensitivity to KSVZ axions in the low mass range between 0.2 and 1 $mu$eV, complementary to that of other experiments. Timeline and cost are competitive with respect to other proposals in the same mass region thanks to the availability of most of the infrastructure, in particular the superconducting magnet and the cryogenics plant.
Recently some of the authors proposed a search for galactic axions with mass about 0.2~$mu$eV using a large volume resonant cavity, tens of cubic meters, cooled down to 4~K and immersed in a magnetic field of about 0.6~T generated inside the supercon
ducting magnet of the KLOE experiment located at the National Laboratory of Frascati of INFN. This experiment, called KLASH (KLoe magnet for Axion SearcH), has a potential sensitivity on the axion-to-photon coupling, $g_{agammagamma}$, of about $6times10^{-17}$ $mbox{GeV}^{-1}$, reaching the region predicted by KSVZcite{KSVZ} and DFSZcite{DFSZ} models of QCD axions. We report here the status of the project.
We searched for the $mu^+mu^-$ decay of a light vector gauge boson, also known as dark photon, in the $e^+ e^- to mu^+ mu^- gamma_{rm ISR}$ process by means of the Initial State Radiation (ISR) method. We used 1.93~fb$^{-1}$ of data collected by the
KLOE experiment at the DA$Phi$NE $phi$-factory. No structures have been observed over the irreducible $mu^+ mu^-$ background. A 90% CL limit on the ratio $varepsilon^2=alpha^{prime}/alpha$ between the dark coupling constant and the fine structure constant of $ 3times 10^{-6}-2times 10^{-7}$ has been set in the dark photon mass region between 519 MeV and 973 MeV. This new limit has been combined with the published result obtained investigating the hypothesis of the dark photon decaying into hadrons in $e^+ e^- to pi^+ pi^- gamma_{rm ISR}$ events. The combined 90% CL limit increases the sensitivity especially in the $rho-omega$ interference region and excludes $varepsilon^2$ greater than $(13-2)times 10^{-7}$. For dark photon masses greater than 600 MeV the combined limit is lower than 8~$times, 10^{-7}$ resulting more stringent than present constraints from other experiments.
Using 1.63 fb$^{-1}$ of integrated luminosity collected by the KLOE experiment about $7times 10^4$ $K_S rightarrow pi^{pm}e^{mp} u$ decays have been reconstructed. The measured value of the charge asymmetry for this decay is $A_S = (-4.9 pm 5.7_{stat
} pm 2.6_{syst}) times 10^{-3}$, which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives $A_S = (-3.8 pm 5.0_{stat} pm 2.6_{syst}) times 10^{-3}$ and, together with the asymmetry of the $K_L$ semileptonic decay, provides significant tests of the CPT symmetry. The obtained results are in agreement with CPT invariance.
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 anomal
ous 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 $a_{mu}^{pi^+pi^-} = (489.8 pm 1.7_{rm stat} pm 4.8_{rm sys} ) times 10^{-10}$.
We have measured the running of the effective QED coupling constant $alpha(s)$ in the time-like region $0.6<sqrt s< 0.975$ GeV with the KLOE detector at DA$Phi$NE using the Initial State Radiation process $e^+e^-tomu^+ mu^-gamma$. It represents the f
irst measurement of the running of $alpha(s)$ in this energy region. Our results show a more than 5$sigma$ significance of the hadronic contribution to the running of $alpha(s)$, which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the $e^+e^-topi^+pi^-$ cross section measured by KLOE, the real and imaginary part of the shift $Deltaalpha(s)$ has been extracted. By a fit of the real part of $Deltaalpha(s)$ and assuming the lepton universality the branching ratio $BR(omegatomu^+mu^-) = (6.6pm1.4_{stat}pm1.7_{syst})cdot 10^{-5} $ has been determined.
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.
Using $1.6$ fb$^{-1}$ of $e^+ e^-tophitoetagamma$ data collected with the KLOE detector at DA$Phi$NE, the Dalitz plot distribution for the $eta to pi^+ pi^- pi^0$ decay is studied with the worlds largest sample of $sim 4.7 cdot 10^6$ events. The Dali
tz 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 $gX^2Y$ term. The statistical uncertainty of all parameters is improved by a factor two with respect to earlier measurements.
