Search

Neutral kaons provide one of the most sensitive systems to CP and CPT violation. Recent results on neutral kaons obtained by the KLOE experiment operating at the DAΦNE e + e − collider are presented. They include: the first observation of the quantum interference in the channel ϕ → K S K L → π + π − π + π − , the measurements of the main K L branching ratios, lifetime and form factor and the measurement of the semileptonic K S branching ratio. The latter are used for the determination of V u s . A direct search of the CP violating K S → π 0 π 0 π 0 decay, a preliminary study of the K S → π 0 π + π − decay and the measurement of the branching ratio of the CP violating K L → π + π − decay are also presented.

The KLOE experiment at the electron-positron collider DAΦNE uses the radiative return to measure the hadronic cross section σ ( e + e − → π + π − ) . The energy of DAΦNE is fixed at s = M Φ = 1020 MeV , but the emission of one (or more) photons in the initial state (ISR) reduces the collision energy, allowing to cover the two-pion invariant mass M π π in the region from the two pion threshold to m ϕ . The precise measurement of this cross section is used to calculate the hadronic contribution to the muon anomaly a μ . A first measurement, in which the ISR-photon is detected at small polar angles, has already been performed at KLOE. Here we present the status of a complementary analysis at large photon polar angles. This allows to extend the measurement of the two-pion cross section to low masses below 600 MeV.

Recent results on the charged kaons, obtained at the KLOE experiment operating at DAΦNE, the Frascati ϕ -factory, are presented. These are the already published fully inclusive K μ 2 + ( γ ) and the preliminary results on the semileptonic decay K l 3 + and on the charged kaon lifetime τ ± .

The ϕ meson provides through its decay channels a wide range of interesting physics. I review the results obtained at the KLOE experiment, operating at the DAΦNE ϕ factory, including kaon physics, scalar and pseudoscalar mesons physics. I will also discuss the physics program available with a high statistics data sample, provided by a future ϕ factory.

Recent results obtained by the KLOE experiment operating at DAΦNE, the Frascati ϕ-factory, are presented. They mainly concern neutral kaon decays including rare KS decays, KL lifetime, the radiative ϕ→f0γ decay and the measurement of the e+e- hadronic cross section using initial state radiation.

Using a large sample of pure, slow, short lived K0 mesons collected with KLOE detector at DaFne, we have measured the KS lifetime. From a fit to the proper time distribution we find tau = (89.562 +- 0.029_stat +- 0.043_syst) ps. This is the most precise measurement today in good agreement with the world average derived from previous measurements. We observe no dependence of the lifetime on the direction of the Ks., Comment: 5 pages, 7 figures

We have measured the cross section of the radiative process e+e−→π+π−γe+e−→π+π−γ with the KLOE detector at the Frascati ϕ -factory DAΦNE, from events taken at a CM energy W=1 GeVW=1 GeV. Initial state radiation allows us to obtain the cross section for e+e−→π+π−e+e−→π+π−, the pion form factor |Fπ|2|Fπ|2 and the dipion contribution to the muon magnetic moment anomaly, View the MathML sourceΔaμππ=(478.5±2.0stat±5.0syst±4.5th)×10−10 in the range View the MathML source0.1

We present a measurement of the slope parameter α for the decay, with the KLOE experiment at the DAΦNE ϕ-factory, based on a background free sample of ∼17 million η mesons produced in ϕ radiative decays. By fitting the event density in the Dalitz plot we determine . The result is in agreement with recent measurements from hadro- and photo-production experiments.

The KLOE experiment has collected an integrated luminosity of about 2.5 fb−1 at the φ factory DAφNE. φ radiative decays have been used to investigate the properties of the light scalar mesons f0(980)/a0(980), whose structure is still controversial.A direct search of σ(600)→π0π0 decay has been performed with data taken at 1 GeV, where φ decays are suppressed.The whole KLOE data set includes also 100 million η’s produced through the radiative decay φ→ηγ and tagged by means of the monochromatic recoil photon. From this sample we have investigated η decays relevant to test ChPT predictions. We present published and preliminary results achieved from full statistics.

We update the values of the eta-eta' mixing angle and of the eta' gluonium content by fitting our measurement R_phi = BR(phi to eta' gamma)/ BR(phi to eta gamma) together with several vector meson radiative decays to pseudoscalars (V to P gamma), pseudoscalar mesons radiative decays to vectors (P to V gamma) and the eta' to gamma gamma, pi^0 to gamma gamma widths. From the fit we extract a gluonium fraction of Z^2_G = 0.12 +- 0.04, the pseudoscalar mixing angle psi_P = (40.4 +- 0.6) degree and the phi-omega mixing angle psi_V = (3.32 +- 0.09) degree. Z^2_G and psi_P are fairly consistent with those previously published. We also evaluate the impact on the eta' gluonium content determination of future experimental improvements of the eta' branching ratios and decay width., Comment: 13 pages, 7 figures to submit to JHEP

F. Ambrosino et al. 2009. 8pp. Prepared for 23th Les Rencontres de Physique de La Vallee d'Aoste, La Thuile, Aosta Valley, Italy, 1-7 Mar 2009. Published in Nuovo Cim.C32N5-6:129-136,2009. Also in *La Thuile 2009, Results and

Some experiments have shown evidence for the ?(600) meson as a ?+?- resonance. Here we recall the contribution of the KLOE experiment to the study of light scalar mesons 0+ and present a search for the ? meson production in the reaction e+e- ? e+e-?0?0 based on a data sample of 11 pb-1 integrated luminosity at ?s = 1 GeV.

The KLOE experiment at the DA?NE ?-factory has performed a new precise measurement of the pion form factor using Initial State Radiation events, with photons emitted at small polar angle. Results based on an integrated luminosity of 240 pb-1 and extraction of the ?? contribution to a? in the mass range [0.35,0.95] GeV2 are presented, the systematic uncertainty is reduced with respect to the published KLOE result.

The e + e − hadronic cross section is measured at the Frascati ϕ -factory DAΦNE with the KLOE detector using initial state radiation (ISR). Two different analyses have been developed for the channel e + e − → π + π − γ , which differ by the photon polar angle direction. The so-called small angle analysis, in which the photon is not detected, has been published with a total error on the pion form factor of 1.3%. In a second approach, where the photon is emitted at large polar angles, the mass region below 0.35 GeV 2 becomes accessible. The status and the prospects of these analyses are reported.

We have measured the fully inclusive K + → μ+ν(γ ) absolute branching ratio with the KLOE experiment at DAFNE, the Frascati φ- factory. From some 865 283 K+ →μ+ ν(γ ) decays obtained from a sample of ∼ 5.2 × 108, φ-meson decays, we find BR(K+ →μ+νμ(γ )) = 0.6366 ± 0.0009stat. ± 0.0015syst., corresponding to an overall fractional error of 0.27%. Using recent lattice results on the decay constants of pseudoscalar mesons one can obtain an estimate for the CKM mixing matrix element |Vus| = 0.2223± 0.0026.

We review the present experimental results on Kaon decays needed for the extraction of the CKM matrix element |Vus|.

The KLOE experiment at the DAΦNE ϕ-factory in Frascati performs a measurement of the cross section ee→ππ using Initial State Radiation events, known as radiative return method. Here we present work in progress to improve the published result which used photons emitted at small polar angles without requiring their explicit detection (no photon tagging). In particular, a possibility to normalize the cross section using μμγ events is discussed. The knowledge of the μμγ cross section also allows to test the initial state radiator function.

Recently it has been demonstrated that particle factories, such as DAPHNE and PEP-II, operating at fixed center-of-mass energies, are able to measure hadronic cross sections as a function of the hadronic system energy using the raditive return. This paper is an experimental overview of the progress in this aera. Preliminary results from KLOE for the process e+e- -> \rho \gamma -> \pi+\pi-\gamma and a fit to the pion form factor are presented. Some first results from the BABAR collaboration are also shown.

The KLOE experiment is currently taking data at the electron‐positron collider DAΦNE, the Frascati φ‐factory. At the end of this run, we expect to have integrated 2.5 fb−1 of collisions at center of mass energy W ∼ M φ. Large samples of light pseudoscalar and scalar mesons are produced through φ radiative decays. A summary of the measurements in progress on the previously collected 450 pb−1 allows us to quote the expectations on the entire sample. KLOE has also proven the feasibility of precise measurement of the hadronic cross‐section σ(e+e− → π+π−) in the region 0.33

The KLOE experiment at the Frascati $\phi$-factory DA$\Phi$NE has collected about 0.5 fb$^{-1}$ of data till the end of the year 2002. These data allow to perform a wide physics program, ranging from the physics of charged and neutral kaons to radiative $\phi$-decays. Results are presented for the $K_L$ lifetime and the semileptonic processes $K_{S,L} \to \pi e \nu$. From the light meson spectroscopy program, results on the decays $\phi \to f_0(980)\gamma, a_0(980)\gamma$ as well as $\phi \to \eta \gamma, \eta' \gamma$ are presented., Comment: 5 pages, 3 figures, Proceedings contribution to the 10th Int. Symposium on "Meson-Nucleon Physics and the Structure of the Nucleon" (MENU04), Beijing, China, Aug. 30 - Sept. 4, 2004

The KLOE experiment at the electron‐positron collider DAPHNE has collected in the 2001–2002 running period an integrated luminosity of 450 pb−1. Through the radiative φ decays, large samples of the light scalar mesons f0(980) and a0(980) are available. The f0 meson is clearly observed in π+π− and π0π0 final states, the a0 in the ηπ0 final states. Invariant mass spectra and Dalitz plot densities are analyzed to investigate the controversial structure of these particles.

The KLOE experiment at the Frascati φ factory, Daφne, has collected ~500 pb -1, i.e. 1.5 × 10^9 φ decays. At the φ factory it is possible to select pure KL and KS beams. Although the integrated luminosity is insufficient for precision tests of the CP, T symmetries in kaon decays, a wide number of topics in kaon and hadronic physics are accessible from the largest sample of φ decays at rest collected so far. The cross section σ(e+e- --> π+π-γ) below 1 GeV, relevant for the precise evaluation of the muon magnetic moment, has been measured with a statistical accuracy better than 1%. For the KS, we obtained the ratio of the branching fractions Γ(KS --> π+π-(γ))/Γ(KS --> π0π0) = (2.239 +/- 0.003stat +/- 0.015syst), fully inclusive of the ππγ final state. The analysis of the ~20,000 KS semileptonic decays KS --> πeν is being finalized providing precise measurements of both, the KS semileptonic branching ratio, and Re x+, i.e. the ΔS = ΔQ rule violation parameter. For the KL, we obtained the ratio Γ(KL --> γγ)/Γ(KL --> π0π0π0) = (2.80 +/- 0.02stat +/- 0.02syst) × 10-3, of interest to Chiral Perturbation Theory (ChPT), as well as preliminary results on the branching ratios to other decay modes. In particular, our measurements of the semileptonic decays of both, neutral, and charged kaons will improve the precision of the CKM matrix element |Vus|, clarifying the present disagreement between different experiments. The φ radiative decays, both in scalar and pseudo-scalar mesons, have been analyzed giving new measurements of the ɛ - ɛ' mixing angle, and of the φ --> a0(980)γ, φ --> f0(980)γ branching ratios.

We have measured the cross section sigma(e(+)e(-) -> pi(+)pi(-gamma)) at an energy W = m(phi) = 1.02 GeV with the KLOE detector at the electron-positron collider DA Phi NE. From the dependence of the cross section on the invariant mass of the two-pion system, we extract sigma(e(+)e(-) -> pi(+)pi(-)) for the mass range 0.35 < s < 0.95 GeV2. From this result, we calculate the hadronic contribution to the muon anomaly a(mu).

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}., Comment: 12 pages, 3 figures, to be published on PLB

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}., 12 pages, 3 figures, to be published on PLB

We report the measurement of the ratio $��(��\to ��^+��^-��)/��(��\to ��^+��^-��^0)$ analyzing a large sample of $��\to ����$ decays recorded with the KLOE experiment at the DA$��$NE $e^+ e^-$ collider, corresponding to an integrated luminosity of 558 pb$^{-1}$. The $��\to ��^+��^-��$ process is supposed to proceed both via a resonant contribution, mediated by the $��$ 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 $R_��=��(��\to ��^+ ��^- ��)/��(��\to ��^+ ��^- ��^0)= 0.1838\pm 0.0005_{stat} \pm 0.0030_{syst}$ is in agreement with a recent CLEO measurement, which differs by more 3 $��$ from the average of previous results.

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., Comment: 17 pages, 11 figures, revised treatment of FSR uncertainty, version to appear on Physics Letters B

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., 17 pages, 11 figures, revised treatment of FSR uncertainty, version to appear on Physics Letters B

We present a precise measurement of the ratio R_K = \Gamma(Ke2(\gamma))/\Gamma(K\mu2(\gamma)) 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_{stat}\pm0.019_{syst})\times 10^{-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., Comment: 6 pages, prepared for KAON09 Conference, Tsukuba 9-12 June 2009

We present a precise measurement of the ratio R_K=B(K\to e\nu(\gamma))/B(K\to \mu\nu(\gamma)) and a study of the radiative process $K\to e\nu\gamma$, 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 $d\Gamma(K\to e\nu\gamma)/dE_\gamma$ for photon energies $10, Comment: Submitted to European Physics Journal C

We have studied the phi->a_0(980) gamma process with the KLOE detector at the Frascati phi-factory DAPhNE by detecting the phi->eta pi^0 gamma decays in the final states with eta->gamma gamma and eta->pi^+ pi^- pi^0. We have measured the branching ratios for both final states: Br(phi->eta pi^0 gamma)=(7.01 +/- 0.10 +/- 0.20)x10^-5 and (7.12 +/- 0.13 +/- 0.22)x10^-5 respectively. We have also extracted the a_0(980) mass and its couplings to eta pi^0, K^+ K^-, and to the phi meson from the fit of the eta pi^0 invariant mass distributions using different phenomenological models., Comment: 17 pages, 6 figures, submitted to Physics Letters B. Corrected typos in eq.9

We have searched for the decay phi -> K0 K0bar gamma, by detecting K_s pairs plus a photon and with the K_s-mesons decaying to pi^+ pi^-, in a sample of about 1.5x 10^9 phi-decays collected by the KLOE experiment at DAFNE. The reaction proceeds through the intermediate states f_0(980) gamma, a_0(980) gamma. We find five events with 3.2 events expected from background processes. We obtain the upper limit: BR (phi -> K0 K0bar gamma) < 1.9x10^-8 at 90% C.L. ., Comment: 11 pages, 8 figures, submitted to Physics Letters B

We have searched for the decay phi -> K0 K0bar gamma, by detecting K_s pairs plus a photon and with the K_s-mesons decaying to pi^+ pi^-, in a sample of about 1.5x 10^9 phi-decays collected by the KLOE experiment at DAFNE. The reaction proceeds through the intermediate states f_0(980) gamma, a_0(980) gamma. We find five events with 3.2 events expected from background processes. We obtain the upper limit: BR (phi -> K0 K0bar gamma) < 1.9x10^-8 at 90% C.L. ., 11 pages, 8 figures, submitted to Physics Letters B