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Register a new userMeasurement of the eta mass at KLOE
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The KLOE collaboration
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An integrated luminosity of 410 pb^(-1), corresponding to ~ 17 million of eta events, has been analyzed to measure the eta mass using the decay eta to gamma gamma. The measurement is insensitive to the calorimeter energy calibration and the systematic error on the measurement is dominated by the uniformity of the detector response. As a cross check of the method the pi0 mass from the decay phi to pi0 gamma, pi0 to gamma gamma has been measured and it is in agreement with the most accurate previous determinations. The result obtained is m(eta) = 547.873 +/- 0.007 (stat.) +/- 0.031 (syst.) MeV, that is today best measurement of the eta mass.
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Working at a $phi$-factory, KLOE/KLOE-2 has collected a very large and clean sample of $eta$ decays, which allow to perform a variety of precision measurements. This report presents the recent results on the $eta$-meson decays from KLOE/KLOE-2 experiments, including the search of the $C$-violating decay $etarightarrowgammagammagamma$, the determination of the $CP$ asymmetry in $etarightarrowpi^+pi^-e^+e^-$, the precision measurement of the $etarightarrowpi^+pi^-pi^0$ Dalitz plot distribution, the search for the $CP$-violating decay $etarightarrowpi^+pi^-$ and the precision measurement of ${cal O}(p^6)$ dominated decay $etarightarrowgammagammapi^0$.
Here we present KLOE results on the phi meson decays in pi0 pi0 gamma, pi+ pi- gamma and eta pi0 gamma, the measurement of the ratio Br(phi to eta gamma)/Br(phi to eta gamma) with the estimate of the eta gluonium content and the measurement of the eta mass.
The ratio R_{eta}=Gamma(eta -> pi^+pi^-gamma)/Gamma(eta -> pi^+pi^-pi^0) has been measured by analyzing 22 million phi to eta gamma decays collected by the KLOE experiment at DAPhiNE, corresponding to an integrated luminosity of 558 pb^{-1}. The eta to pi^+pi^-gamma proceeds both via the rho resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, R_{eta}= 0.1856pm 0.0005_{stat} pm 0.0028_{syst}, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the eta -> pi^+pi^-gamma decay could be described in a model-independent approach in terms of a single free parameter, alpha. The determined value of the parameter alpha is alpha = (1.32 pm 0.08_{stat} +0.10/-0.09_{syst}pm 0.02_{theo}) GeV^{-2}
We present a measurement of {eta} meson production in photon-photon interactions produced by electron-positron beams colliding with sqrt{s}=1 GeV. The measurement is done with the KLOE detector at the phi-factory DA{Phi}NE with an integrated luminosity of 0.24 fb^{-1}. The e^+e^- --> e^+e^-{eta} cross section is measured without detecting the outgoing electron and positron, selecting the decays {eta}-->{pi}^+{pi}^-{pi}^0 and {eta}-->{pi}^0{pi}^0{pi}^0. The most relevant background is due to e^+e^- --> {eta}{gamma} when the monochromatic photon escapes detection. The cross section for this process is measured as {sigma}(e^+e^- -->{eta}{gamma}) = (856 pm 8_{stat} pm 16_{syst}) pb. The combined result for the e^+e^- -->e^+e^-{eta} cross section is {sigma}(e^+e^- -->e^+e^-{eta}) = (32.72 pm 1.27_{stat} pm 0.70_{syst}) pb. From this we derive the partial width {Gamma}({eta}-->{gamma}{gamma}) = (520 pm 20_{stat} pm 13_{syst}) eV. This is in agreement with the world average and is the most precise measurement to date.
We measure the mass of the eta meson using psi(2S) --> eta J/psi events acquired with the CLEO-c detector operating at the CESR e+e- collider. Using the four decay modes eta --> gamma gamma, 3pi0, pi+pi-pi0, and pi+pi-gamma, we find M(eta)=547.785 +- 0.017 +- 0.057 MeV, in which the first uncertainty is statistical and the second systematic. This result has an uncertainty comparable to the two most precise previous measurements and is consistent with that of NA48, but is inconsistent at the level of 6.5sigma with the much smaller mass obtained by GEM.
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