arXiv subjects
Publications and source records attributed to The KLOE Collaboration.
We report the first observation of the rare eta->e+e-e+e- decay based on 1.7 fb^{-1} collected by the KLOE experiment at the DAFNE phi-factory. The selection of the e+e-e+e- final state is fully inclusive of radiation. We have identified 362 +- 29 events resulting in a branching ratio of (2.4 +- 0.2_stat+bckg +- 0.1_syst) x 10^{-5}.
We report the measurement of the ratio $Γ(η\to π^+π^-γ)/Γ(η\to π^+π^-π^0)$ analyzing a large sample of $ϕ\to ηγ$ decays recorded with the KLOE experiment at the DA$Φ$NE $e^+ e^-$ collider, corresponding to an integrated luminosity of 558 pb$^{-1}$. The $η\to π^+π^-γ$ process is supposed to proceed both via a resonant contribution, mediated by the $ρ$ meson, and a non resonant direct term, connected to the box anomaly. The presence of the direct term affects the partial width value. Our result $R_η=Γ(η\to π^+ π^- γ)/Γ(η\to π^+ π^- π^0)= 0.1838\pm 0.0005_{stat} \pm 0.0030_{syst}$ is in agreement with a recent CLEO measurement, which differs by more 3 $σ$ from the average of previous results.
We present a precise measurement of the ratio R_K=B(K\to eν(γ))/B(K\to μν(γ)) and a study of the radiative process $K\to eνγ$, performed with the KLOE detector. The results are based on data collected at the Frascati $e^+e^-$ collider DAFNE for an integrated luminosity of 2.2 fb$^{-1}$. We find R_K = (2.493\pm0.025\pm0.019)x10^{-5}$, in agreement with the Standard Model expectation. This result is used to improve constraints on parameters of the Minimal Supersymmetric Standard Model with lepton flavor violation. We also measured the differential decay rate $dΓ(K\to eνγ)/dE_γ$ for photon energies $10<E_γ<250$ MeV. Results are compared with predictions from theory.
We describe the KLOE detector at DAFNE, and its physics program. The impact of our results on flavor and hadron physics to date, as well as an outlook for further improvement in the near future, are discussed.
We have studied the e+e- -> omegapi0 cross section in the sqrt(s) interval 1000-1030 MeV using the pi+pi-pi0pi0 and pi0pi0gamma final states with a sample of ~600 pb^-1 collected with the KLOE detector at DAFNE. By fitting the observed interference pattern around M_phi for both final states, we extract the ratio of the decay widths Gamma(omega->pi0gamma)/Gamma(omega->pi+pi-pi0) = 0.0897 +- 0.0016 and derive the branching fractions BR(omega -> pi+pi-pi0)= (90.24 +- 0.19)%, BR(omega -> pi0gamma) = (8.09 +- 0.14)%. The parameters describing the e+e- -> omegapi0 reaction around M_ϕare also used to extract the branching fraction for the OZI and G-parity violating phi -> omegapi0 decay: BR(phi->omegapi0) = (4.4 +- 0.6)x10^-5.
A preliminary measurement of RK = Gamma(Ke2)/Gamma(Km2) at the KLOE experiment is discussed. The result, RK = (2.55+-0.05+-0.05)x 10^-5, is based on 1.7 fb^-1 of luminosity integrated on the phi-meson peak at the Frascati e^+e^- collider DAFNE, corresponding to ~8000 observed Ke2 events. Perspectives on the methods planned to improve both the statistical and the systematic errors are briefly outlined.
The KLOE Experiment at the $ϕ$ factory DA$Φ$NE, has measured the cross section $σ(e^+e^-\toπ^+π^-γ)$ using two different selection schemes: requiring the photon emission at small polar angle and detecting the photon at large polar angle in the calorimeter. Using a theoretical radiator function we extract the pion form factor and obtain the $ππ$ contribution to the anomalous magnetic moment of the muon. Results presented here come from the analysis of 240 pb^{-1} collected in 2002, with improved systematic uncertainty with respect to the published KLOE analysis. We also include an update of the previous analysis.
We have analyzed 1.62 fb$^{-1}$ of $e^{+}e^{-}$ collisions at a center of mass energy $\sim M_ϕ$ collected by the KLOE experiment at DA$Φ$NE. This sample corresponds to a production of $\sim$ 1.7 billion of $\ks$ $\kl$ pairs which allowed us to search for the rare $K_S\to γγ$ decay. $K_S$ are tagged by the $K_L$ interaction in the calorimeter and the signal is searched for by requiring two additional prompt photons. Strong kinematic requirements reduce the initial 0.5$\times 10^6$ events to 2300 candidates from which we extract a signal of 600 $\pm$ 35 events. By normalizing to the $\ks \to 2 π^0$ decays counted in the same sample, the measured value of BR($\ks \to γγ$) is (2.27 $\pm 0.13(stat.) ^{+0.03}_{-0.04} (syst.)) \times 10^{-6}$, in agreement with $O(P^4)$ Chiral Perturbation Theory predictions.
We have measured the ratio $R_ϕ=BR(ϕ\to η^{\prime} γ)/BR(ϕ\to ηγ)$ by looking for the radiative decays $ϕ\to η^{\prime} γ$ and $ϕ\to ηγ$ in the final states $π^+π^-$ 7 $γ$'s and 7 $γ$'s respectively, in a sample of $\sim 1.3\cdot 10^{9}$ $ϕ$ mesons produced at the Frascati $ϕ$-factory. We obtain $R_ϕ=(4.77\pm0.09_{stat}\pm0.19_{sys})\cdot 10^{-3}$ from which we derive $BR(ϕ\to η^{\prime} γ)=(6.20\pm0.11_{stat}\pm0.25_{sys})\cdot 10^{-5}$. In the hypothesis of no gluonium content we extract the pseudoscalar mixing angle in the quark-flavor basis $ϕ_P=(41.4\pm0.3_{stat}\pm0.7_{sys}\pm0.6_{th})^{\circ}$. Combining the value of $R_ϕ$ with other constraints, we estimate the gluonium fractional content of $η^{\prime}$ meson as $Z^2 = 0.14\pm0.04$ and the mixing angle $ϕ_P = (39.7\pm0.7)^{\circ}$.
We present results of a direct search for the decay KS --> e+e- with the KLOE detector, obtained with a sample of e+e- --> phi --> KSKL events produced at DAFNE, the Frascati phi-factory, for an integrated luminosity of 1.3fb-1. The Standard Model prediction for this decay is BR(KS --> e+e-) = 1.6*10^-15. The search has been performed tagging the KS decays by simultaneous detection of a KL interaction in the calorimeter. Background rejection has been optimized by using both kinematic cuts and particle identification. At the end of the analysis chain we find BR(KS --> e+e-) < 2.1*10^-8 at 90% CL, which improves by a factor of ~7 on the previous best result, obtained by CPLEAR experiment.
This paper is devoted to the measurement of the fully inclusive absolute branching ratios of the charged kaon semileptonic decays, $K^{\pm}\toπ^0e^\pmν(γ)$ and $K^\pm \to π^0μ^\pmν(γ)$. The measurements have been done using a tag technique, employing the two-body decays, $K^\pm \to μ^\pmν$ and $K^\pm \to π^\pmπ^0$, and using a sample of about 410 pb$^{-1}$ collected during the 2001 and 2002 data taking of the KLOE experiment at Daphne, the Frascati $ϕ$-factory. The results obtained are BR(K$^\pm_{e3}$) = $0.04965 (38)_{Stat} (37)_{Syst}$ and BR(K$^\pm_{\mu3}$) = $0.03233 (29)_{Stat} (26)_{Syst}$.
We present an improved determination of the CP and CPT violation parameters Re(epsilon) and Im(delta) based on the unitarity condition (Bell-Steinberger relation) and on recent results from the KLOE experiment. We find Re(epsilon) = (159.6 \pm 1.3)10^-5 and Im(delta) = (0.4 \pm 2.1)10^-5, consistent with no CPT violation.
Using a sample of over 400 million phi->KsKl decays produced during the years 2001 and 2002 at the DAFNE e+e- collider, the ratio R=Gamma(Ks->pi+pi-(g))/Gamma(Ks->pi0pi0) has been measured with the KLOE detector. The result is R=2.2555+-0.0012(stat)+-0.0021(syst-stat)+-0.0050(syst), which is in good agreement with the previously published result based on the KLOE data sample from the year 2000. The average of the KLOE results is R=2.2549+-0.0054, reducing the total error by a factor of three, to 0.25%.
Among some 400 million KsKl pairs produced in e+e- annihilations at DAFNE, about 6500 each of Ks->pi+e-nubar and Ks->pi-e+nu decays have been observed with the KLOE detector. From these, the ratio G(Ks->pienu)/G(Ks->p+p-(g))=(10.19+-0.13)10-4 is obtained, improving the accuracy on BR(Ks->pienu) by a factor of four and providing the most precise test of the DeltaS=DeltaQ rule. From the partial width Gamma(Ks->pienu), a value for f+(K0)Vus is obtained that is in agreement with unitarity of the quark-mixing matrix. The lepton charge asymmetry AS=(1.5+-9.6stat+-2.9syst)10-3 is compatible with the requirements of CPT invariance. The form-factor slope agrees with recent results from semileptonic Kl and K+ decays. These are the first measurements of the charge asymmetry and form-factor slope for semileptonic Ks decays.
Recent results obtained by the KLOE experiment operating at DA$Φ$NE, the Frascati $ϕ$-factory, are presented. They mainly concern neutral kaon decays including the $K_L$ dominant branching ratios, the $K_L$ lifetime and the extraction of the $CKM$ parameter $V_{us}$ from the $K_L$ semileptonic decays and lifetime. The best world upper limit on $K_S \to \pppo$ channel is also presented
We have measured the cross section $σ(e^+e^-\to π^+π^- γ)$ at an energy $W=m_ϕ=1.02$ GeV with the KLOE detector at the electron-positron collider DA$Φ$NE. From the dependence of the cross section on the invariant mass of the two-pion system, we extract $σ(e^+e^-\to π^+π^-)$ for the mass range $0.35<s<0.95$ GeV$^2$. From this result, we calculate the pion form factor and the hadronic contribution to the muon anomaly, $a_μ$.
A new measurement of the absolute branching ratio BR($K^\pm \to π^\pm π^0 π^0$) with the KLOE detector at the DA$Φ$NE $e^+e^-$ collider is presented, based on a sample of $\sim 3.3\times 10^7$ charged kaons tagged events, produced in the reaction $e^+e^-\toϕ\to K^+K^-$.The value BR($K^\pm \to π^\pm π^0 π^0$) $= (1.781\pm 0.013_{stat}\pm 0.016_{syst})%$ has been obtained.
We have searched for the C-violating decay eta to gamma gamma gamma in a sample of ~ 18 million eta mesons produced in phi to eta gamma decays, collected with the KLOE detector at the Frascati phi-factory DAFNE. No signal is observed and we obtain the upper limit BR(eta to gamma gamma gamma) less equal than 1.6x10^(-5) at 90 % C.L.