The KLOE detector at DAΦNE , the Frascati φ-factory, has collected about 30 pb by the end of year 2000. The φ(1020) meson decays about 34% of the times into a K0L-K 0 S pair; DAΦNE is therefore an exceptional source of almost monochromatic, tagged K0S particles, allowing for detailed studies of their more rare decays. The above mentioned integrated luminosity corresponds to about 30 millions produced K0S. In KLOE the presence of a K0S is easily tagged by the observation of the corresponding K0L impinging onto the electromagnetic calorimeter before decay. Thanks to this technique we have performed a preliminary measurement of the ratio of the partial decay widths of the K0S into two charged and two neutral pions: B(K0S → π π)/B(KS → π π) = 2.23 × (1 ± 0.35× 10 (stat) ± 1.5× 10 (syst) ). We have also observed several hundreths semileptonic decays of the K0S by far the largest sample of this decay mode ever observed by any experiment so far. The preliminary estimate of the corresponding branching ratio is B(K0S → π eν) = (6.8 ± 0.3 (stat))×10; systematic effects are still under study and are presently estimated to be at the few percent level.

The goal of the KLOE-2 experiment operating at the upgraded DANE e + e − collider is to collect an integrated luminosity of about 20 fb −1 over 3-4 years of running. The KLOE-2 apparatus is now equipped with an inner tracker, new scintillation calorimeters and tagging detectors for γγ physics. These will allow measurements to refine and extend the KLOE programme on kaon physics and tests of fundamental symmetries as well as quantum interferometry. Here the latest results from the KLOE data analysis are presented and the perspectives at KLOE-2 outlined.

We report the measurement of the ratio Γ(η→π^+π^-γ)/Γ(η→π^+π^-π^0) analyzing a large sample of ϕ→ηγ decays recorded with the KLOE experiment at the DAΦNE e^+ e^- collider, corresponding to an integrated luminosity of 558 pb^-1. The η→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→π^+ π^- γ)/Γ(η→π^+ π^- π^0)= 0.1838± 0.0005_stat± 0.0030_syst is in agreement with a recent CLEO measurement, which differs by more 3 σ from the average of previous results.

The existence of a light dark force mediator has been tested with the KLOE detector at DA Phi NE. This particle, called U. is searched for using the decay chain phi -> eta U, eta -> pi(+)pi(-)pi(0), U -> e(+)e(-). No evidence is found in 1.5 fb(-1) of data. The resulting exclusion plot covers the mass range 5 < M-U < 470 MeV, setting an upper limit on the ratio between the U boson coupling constant and the One structure constant, alpha'/alpha, of <= 2 x 10(-5) at 90% C.L. for 50 < M-U < 420 MeV. (C) 2011 Elsevier B.V. All rights reserved.

The processes e^+e^-→ e^+e^-X, with X being either the η meson or π^0π^0, are studied at DAΦNE, with e^+e^- beams colliding at √(s)≃1 GeV, below the ϕ resonance peak. The data sample is from an integrated luminosity of 240 pb^-1, collected by the KLOE experiment without tagging of the outgoing e^+e^-. Preliminary results are presented on the observation of the γγ→η process, with both η→π^+π^-π^0 and η→π^0π^0π^0 channels, and the evidence for γγ→π^0π^0 production at low π^0π^0 invariant mass.

In an experiment performed at ITEP TWA heavy ion accelerator, the yields of hydrogen (p,d,t) and helium (from He to He) isotopes at 3.5o from fragmentation of C at T0 = 0.2 3.2 GeV/nucleon on a Be target have been measured. Momentum spectra of the fragments in the projectile rest frame have been obtained in larger momentum intervals than in the previous experiments with heavy ion beams. The main attention was given to the region of high momentum where fragment velocity exceeds the velocity of the projectile nucleus. The obtained data cover about 6 orders of the differential cross section magnitude. It made possible the observation of a transition from the Gaussian shape of the longitudinal momentum spectra in projectile rest frame, expected for the evaporation mechanism, to the exponential shape, typical for the cumulative (pre-equilibrium) processes. The Feynman x distributions for protons are analyzed in the framework of quark-gluon string model. The probabilities of existence of sixand nine-quark clusters are estimated and compared with the results on two(three-) nucleon short range correlations in nuclei measured at Jefferson Laboratory.

We have measured the ratio R S = Γ(KS → π π(γ))/Γ(KS → π π) with the KLOE detector at the DAΦNE ee collider. This measurement is fully inclusive with respect to the ππγ final state. The sample of over 10 two-pion decays of tagged KS mesons allows a statistical error as low as ∼ 0.1% to be obtained. The accuracy is limited by systematic uncertainties, which are estimated primarily from data. We find R S =2.236±0.003stat±0.015syst. The most recent measurement of R S = Γ(KS → π π)/Γ(KS → π π) dates back to 1976. The authors quote an accuracy of 4.3% [1]. This and other results of similar accuracy determine the current world-average value of R S, 2.197±0.026, the fractional error on which is 1.2%. Moreover, the averaging of the existing results is somewhat questionable, since the various experiments have not clearly described their procedures for handling radiative ππγ decays. It is currently of interest to improve the accuracy on R S, with particular attention to an accurate determination of what part of the radiative spectrum is included in the quoted result [2]. The validity of the ∆I = 1/2 rule, empirically established in K, Λ, Σ, and Ξ decays, has never been satisfactorily understood. This lack of understanding is closely connected with the difficulty in relating R(ǫ/ǫ) to the CKM matrix elements [3]. The value of R S also enters into the theoretical calculation for the ratio of branching ratios for the decays KL→μ μ and KL→π π [4]. We describe the first measurement of R S to achieve an accuracy below 1%,

KLOE has collected about 30 pb in year 2000 at the DAΦNE collider, which yields the largest population of φ meson radiative decays studied so far. We present the results obtained for φ → ηγ and φ → η′γ : the ratio of these two BR’s has been measured to be (5.3± 0.5 ± 0.3) · 10, leading to a very accurate determination of the mixing angle in the flavor basis φP = (40 +1.7 −1.5) ◦ and to the most accurate determination of BR(φ → η′γ ) to date: (6.8± 0.6 ± 0.5) · 10.

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).

The ϕ-meson leptonic widths, Γee and Γμμ, are obtained, respectively, from the e+e− forward–backward asymmetry and the μ+μ− cross section around the ϕ-mass energy. We find Γee=1.32±0.05±0.03keV and ΓeeΓμμ=1.320±0.018±0.017keV. These results, compatible with Γee=Γμμ, provide a precise test of lepton universality. Combining the two results gives Γℓℓ(ϕ)=1.320±0.023keV.

The KLOE experiment at the DAΦNE e+e− collider and its physics program is presented. The most recent results obtained using the data collected during the year 2000 (about 20 pb−1) are presented, in particular the ratio of branching ratios BR(KS → π+π−)/BR(Ks → π0π0), the branching ratio for the Ke3 decay of the KS, the ratio BR(φ → η′γ)/BR(φ → ηγ) and the pseudoscalar mixing angle ϕP, and the branching ratios for the decays φ → f0γ and φ → a0γ.

KLOE uses the radiative return to measure the hadronic cross section e+e- → π+− at DANE. Theemission of one or more hard photons in the initial state (ISR) reduces the collision energy, otherwise fixed at 1020 MeV, and allows to perform an effective scan of the two pions invariant mass squared, sπ, in the whole sπ, region from threshold to mφ2. An extremely accurate knowledge of experimental systematics, background, luminosity and, on the theoretical side, a precise description of initial state radiation are needed to perform a competitive measurement. We present here the status of the analysis of 140 pb−1 collected in 2001. A preliminary evaluation of the hadronic contribution to aμ in the sπ range between 0.37 GeV2 and 0.93 GeV2 yields aμ = 378.4 ± 0.8stat ± 4.5syst ± 3.0theo ± 3.8FSR, consistent with the CMD-2 result and confirming the present discrepancy between e+e− and τ data.

We describe the status of the analyses in progress on light meson spectroscopy in the KLOE experiment. We present the analyses of phi decays into f0(980)gamma and a0(980)gamma, the Dalitz plot analysis of the eta to pie+ pie- pie0 decay, the branching ratio measurement of eta to pie0 gamma gamma, the upper limits on Br(eta to 3 gamma) and Br(eta to pie^+ pie^-), the measurement of the ratio Br(phi to eta' gamma)/Br(phi to eta gamma) and phi leptonic width measurements.

The measurement of hadronic cross sections, especially at low centre-of-mass energies, is currently attracting a lot of attention due to the role these measurements play in the theoretical evaluation of the anomalous magnetic moment of the muon. The KLOE experiment at the DAPhiNE phi-factory in Frascati aims at a measurement of the cross section of the dominant process e(+)e(-) --> pi(+)pi(-) at energies below 1 GeV exploiting the radiative return from the phi to the rho and omega mesons. This method has systematical errors completely different from previous measurements. The method of the measurement as well as the current status of the analysis axe presented.