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Publications and source records attributed to The KLOE Collaboration.
The KLOE experiment at DA$Φ$NE collected about 450 pb$^-1$ of data in 2001--2002. Much of this data set has been analyzed and has yielded definitive results on $K_S$ and radiative $ϕ$ decays, as well as studies concerning a wide range of topics in kaon and hadronic physics.
We have measured the cross section $σ(e^+e^-\toπ^+π^-γ)$ with the KLOE detector at DA$Φ$NE, at an energy $W=M_ϕ=1.02$ GeV. From the dependence of the cross section on $m(π^+π^-)=\sqrt{W^2-2WE_γ}$, where $E_γ$ is the energy of the photon radiated from the initial state, we extract $σ(e^+e^-\toπ^+π^-)$ for the mass range $0.35<m^2(π^+π^-)<0.95$ GeV$^2$. From our result we extract the pion form factor and the hadronic contribution to the muon anomaly, $a_μ$.
Data collected by the KLOE experiment in years 2001/2002 for a total integrated luminosity of 410 pb$^{-1}$, corresponding to 17 million of produced $η$'s from the $Φ\to ηγ$ radiative decay, have been analyzed to look for the C-violating decay $η\toγγγ$. The signal is searched in events with 4 photons in the final state by using the spectrum of the most energetic photon. The background is evaluated from the data themself, doing a fifth degree polynomial fit outside the signal region, and extrapolating inside it. No signal has been observed and taking into account a selection efficiency $ε= 20.3 %$ we get from a likelihood fit Br$(η\toγγγ) \le 1.6\times10^{-5}$ at 95% CL. The procedure has a systematic ambiguity at the 35 % level.
The KLOE experiment has been running since April 1999 at the DAFNE e+e- collider at a center of mass energy centered around the phi meson mass. The luminosity integrated up to September 2002 is about 500 pb-1 . Here we present the perspectives on the measurement of the V_{us} CKM-matrix element with the KLOE detector, using both charged and neutral kaon semileptonic decays.
Recent results from the KLOE experiment at the DAPHNE e+e- collider are presented. KLOE has collected about 500 pb^-1 of data in the years from 2000 to 2002. Preliminary results are obtained using wide samples of the full statistics and include: the BR of the Ke3 decay of the K_S and the first measurement of its charge asymmetry, the ratio BR(K_S-->pi+pi-(gamma))/BR(K_S-->pi^0pi^0), the ratio BR(K_L-->gammagamma)/BR(K_L-->3pi^0), a detailed study of the decay phi-->pi+pi-pi^0, the ratio BR(phi-->eta' gamma)/BR(phi-->eta gamma) and the pseudoscalar mixing angle phi_P, the phi-->f_0 gamma and the phi-->a_0 gamma BR's.
We have measured the ratio R=Gamma(K_L -> gamma gamma)/ Γ(K_L -> 3 pi^0) using the KLOE detector. From a sample of ~ 10^9 phi-mesons produced at DAFNE, the Frascati phi-factory, we select ~ 1.6 10^8 K_L-mesons tagged by observing K_S -> pi^+ pi^- following the reaction e^+ e^- -> phi -> K_L K_S. From this sample we select 27,375 K_L -> gamma gamma events and obtain R = (2.79 \pm 0.02_{stat} \pm 0.02_{syst}) \times 10^{-3}. Using the world average value for BR(K_{L} -> 3 pi^0), we obtain BR(K_{L} -> gamma gamma) = (5.89 \pm 0.07 \pm 0.08) \times 10^{-4} where the second error is due to the uncertainty on the 3 pi^0 branching fraction.
In the fixed energy environment of the $e^{+}e^{-}$ collider DA$Φ$NE, KLOE can measure the cross section of the process $e^{+}e^{-} \to$ hadrons as a function of the hadronic system energy using the radiative return. At energies below 1 GeV, $e^{+}e^{-} \to ρ\to π^{+}π^{-}$ is the dominating hadronic process. We report here on the status of the analysis for the $e^{+}e^{-} \to \ppg$ channel, which allows to obtain a preliminary measurement of the pion form factor using an integrated luminosity of $\sim73 pb^{-1}$.
We have measured the radiative decays phi -> eta gamma, phi ->etaprime gamma selecting pi+ pi- gamma gamma gamma final state in a sample of about 5 times 10^7 phi mesons produced at the Frascati phi factory DAFNE. We obtain Gamma(phi -> etaprime gamma)/Gamma(phi -> eta gamma)=(4.70 +- 0.47 +- 0.31) times 10^-3. From this result we derive new accurate values for the branching ratio BR(phi ->etaprime gamma) = (6.10 +- 0.61 +- 0.43) times 10^-5, and the mixing angle of pseudoscalar mesons in the flavour basis phi_P=(41.8 +1.9 -1.6) degrees.
In the fixed energy environment of the $e^{+}e^{-}$ collider DA$Φ$NE, KLOE can measure the cross section of the process $e^{+}e^{-} \to hadrons$ as a function of the hadronic system energy using the radiative return method. At energies below 1 GeV, $e^{+}e^{-} \to ρ\to π^{+}π^{-}$ is the dominating hadronic process. We report here on the status of the analysis of the process $e^{+}e^{-} \to π^{+}π^{-}γ$. Some preliminary results on the invariant mass spectrum of the two pion system, obtained from the analysis of 22.6 pb$^{-1}$, are presented.
In a sample of 5.3x10^7 phi-decays observed with the KLOE detector at the Frascati phi-factory Dafne we find 605 eta pi0 gamma events with eta --> gammaγand 197 eta pi0 gamma events with eta --> pi+ pi- pi0. The decay phi --> eta pi0 gamma is dominated by the process phi --> a0 gamma. From a fit to the eta pi0 mass spectrum we find BR(phi --> ao(980) gamma)= (7.4 +- 0.7)x10^-5.
We have measured the ratio R=Gamma(Ks -> pi+pi-gamma)/Gamma(Ks -> pi0pi0) with the KLOE detector at the DAFNE e+e- collider. This measurement is fully inclusive with respect to the pi+pi-gamma final state. The sample of over 10^6 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=2.236 +/- 0.003(stat) +/- 0.015(syst).
We present a measurement of the branching ratio BR(KS --> pi e nu) performed using the KLOE detector. KS mesons are produced in the reaction e+ e- --> phi --> KS KL at the DAFNE collider. In a sample of about 5 million KS-tagged events we find 624 +- 30 semileptonic KS decays. Normalizing to the KS --> pi+ pi- count in the same data sample, we obtain BR(KS --> pi e nu) = (6.91 +- 0.37) 10^-4, in agreement with the Standard Model expectation.
The KLOE detector at DAFNE has collected about 30 pb-1 by the end of year 2000,' allowing, among other things, accurate measurements on several decay channels of the K0S meson. With data acquired in the year 2000 run we have measured the ratio of the branching ratios of the K0S to two charged and neutral pions to 1.5 percent accuracy. The branching ratio of the semileptonic decay of the K0S is also measured to 5 percent accuracy, the best measurement of this BR to date.
KLOE has collected about 30 pb^-1 in year 2000 at the DAFNE collider, which yields the largest population of phi meson radiative decays studied so far. We present the result obtained for phi-->eta photon and phi -->eta' photon: the ratio of these two BR's has been measured to be (5.3 +- 0.5 +- 0.3) times 10^-3, leading to a very accurate determination of the mixing angle in the flavor basis (40 +1.7 -1.5 degrees) and to the most accurate determination of BR(phi -->eta' photon) to date: (6.8 +- 0.6 +-0.5) times 10^-5.
We present a study of the reaction e+e- \to pi+pi-gamma at the phi peak with the KLOE detector at the phi-factory DAPHNE. This reaction allows us to obtain the cross section for \e+e- \to pi+pi- from the e+e- center-of-mass energy W = m_ϕ= 1019 MeV down to threshold, i.e. 2m_pi < M_(pipi) < m_phi. This is called radiative return. The status of the analysis and preliminary results on the invariant mass spectrum of the two-pion-state are presented.
The KLOE detector at DAFNE, the Frascati phi-factory, has collected about 30 pb^-1 by the end of 2000, corresponding to about 90 millions of phi(1020) mesons produced. The five photon final state has been exploited to study the rare decays of phi into f0(980) photon and a0(980) photon, with statistical accuracy never reached before. The preliminary results for these branching ratios, from a data sample of 17 pb^-1, are the following: BR(phi-->f0(980) photon)=(23.7 +- 0.6 (stat.) times 10^-5, BR(phi--> a0(980) photon)=(5.8 +- 0.5 (stat.)) times 10^-5. The systematic error is expected to be less than 10%, a precise evaluation is going on. For the ratio of the branching ratios of phi--> f0 photon to phi--> a0 photon we find 4.1 +- 0.4 (stat.).
KLOE, a new state of the art detector recently commissioned for physics operation at DAFNE, has many innovative interesting features, especially in the DAQ and Trigger areas. Custom electronics assert a trigger in a 2 microseconds decision time and distributes it to the FEE with a 50 ps time resolution. Data are read out using 10 front-end data acquisition chains and sent to a farm of online servers through a FDDI Gigaswitch. This design of the KLOE DAQ system allows us to manage an input data rate as high as 50 Mbyte/s, and is completely scalable by extending the number of computers connected to the switch.
The KLOE experiment has collected 2.4 1/pb of integrated luminosity during the commissioning of the DAFNE phi-factory in 1999. The performance of the detector has been studied using phi -> KL KS decays collected during this period, yielding also first measurements of relevant K parameters such as masses and lifetimes. A clean Kshort -> pi+ pi- sample is used to select Klong -> 2pi CP-violating decays and Klong -> Kshort regeneration events in the detector material. Results on the regeneration probability in beryllium-alluminum alloy and carbon-fiber plus aluminum composite are presented.