25 research outputs found
First observation of the reaction gamma gamma -> pi2 -> pi0 pi0 pi0
No full textThe Crystal Ball detector has been used at the DORIS II storage ring at DESY to study the reaction gamma gamma -> pi0 pi0 pi0 in the pi0 pi0 pi0 invariant mass range from 850 MeV/c 2 to 2600 MeV/c 2. An enhancement around 1750 MeV/c 2 is attributed to the pi2(1670) resonance. The observed pi0 pi0 invariant mass distribution and the pi0 angular distributions are consistent with those expected for the decay chain pi2 -> pi0 f2(1270) -> pi0 pi0 pi0. From our measurements we find the following resonance parameters: two photon partial width Gamma(gamma gamma)(pi2) = (1.41+.0.23+.0.28)keV, mass M(pi2)=(1742+-31+-49)MeV/c 2 and total width Gamma(tot)(pi2)=(236+.49+.36)MeV
Measurement of pi0 and eta meson production in e+e- annihilation at sqrt(s) near 10 GeV
No full textWe present a study of inclusive pi0 and eta production in e+e- annihilation at sqrt(s)=(approx) 10 GeV. Our analysis is based on integrated luminosities of 46.2 pb-1 taken at the Y(1S) resonance and 42.1 pb-1 taken in the neighboring continuum. We measure the inclusive pi0 and eta spectra for direct Y(1S) -> 3 g decays and continuum processes e+ e- -> q qbar and obtain the following mean particle multiplicities per event: Continuum:=3.64+-0.21+-0.36, =0.22+-0.04+-0.03Y(1S) -> 3g:=3.39+-0.14+-0.34, =0.35+-0.04+-0.04We compare our results with predictions of different fragmentation models and with other measurements performed in e+e- annihilation at similar center-of-mass energies
Determination of Gamma-ee of the Upsilon(1S) and Upsilon(2S) Resonances, and Measurement of R At W = 9.39 GeV.
No full textUsing the Crystal Ball detector operating at the DORIS II storage ring we have measured the leptonic partial widths Fee of the Y(1S) and Y(2S) resonances. We find Gamma-ee(Y(1S)) = 1.34+-0.03+-0.06 keV andGamma-ee(Y(2S)) = 0.56+-0.04+-0.02 keV.The effect on Gamma-ee of applying different prescriptions for radiative corrections is discussed. W e also measure R, the ratio of non-resonant hadronic cross section to the Born cross section of mu pair production, at c.m. energy W = 9 . 3 9 G e V to beR=3.48+-0.04+-0.16
Search For Exotic Tau-decays
No full textThe Crystal Ball detector at the Doris II storage ring at DESY was used to search for the exotic decay processes tau -> e gamma, tau -> e pi0, tau -> e eta. No signal was observed. We obtained the following 90% CL upper limits on the branching fractions:B(tau -> e gamma)< 2.0x10^(-4),B(tau -> e pi0) < 1.4x10^(-4),B(tau -> e eta) < 2.4x10^(-4)
The Michel Parameter For the Decay Tau -> e nu nubar
No full textThe Crystal Ball detector at the Doris II storage ring at DESY has been used to study the electron energy spectrum of the decay tau -> e nu nubar. In the standard model the Lorentz structure of the decay matrix element is of the well known V-A type, resulting in a Michel parameter of p=0.75. Our spectrum is found to be consistent with this value. A fit yields the value of 0.64+-0.06+-0.07
Formation of the Pseudoscalars pi0, eta, and eta' In the Reaction gamma gamma -> gamma gamma
No full textThe Crystal Ball detector has been used at the DORIS II storage ring at DESY to study the reaction e+ e- -> e+ e- gamma* gamma* -> e+ e- X -> e+ e- gamma gamma, where X is a narrow resonance with mass between 100 and 3000 MeV. Formation of pi0, eta and eta' mesons is observed, and the following meson partial widths are obtained: Gamma(pi0 -> gamma gamma) = 7.7+-0.5+-0.5 eV, Gamma(eta -> gamma gamma) = 0.514+-0.017+-0.035 keV, and Gamma(eta' -> gamma gamma) = 4.7+-0.5+-0.5 keV. No other narrow resonances are observed, and upper limits are given for the product Gamma(X -> gamma gamma) B(X -> gamma gamma)
Search For Radiative Y(1s) Decays Into Light Mesons
No full textWe have searched for radiative decays of the Y(1S) resonance, Y(1S) -> gamma X, where X is one of the mesons eta, eta', f2(1270), f2(1720), or a narrow resonance with mass less than 3 GeV/c^2 which decays into either pi0 pi0 or eta eta. The mesons are identified in their all-neutral decay modes. Since we do not find any such decays, we calculate upper limits on the corresponding branching ratios. These limits are compared to theoretical predictions and to the orresponding branching ratios measured in radiative J/Psi decays
Observation of a new eta pi0 pi0 resonance at 1900 MeV/c^2 in two-photon scattering
No full textUsing the Crystal Ball detector at the DORIS II e+e- storage ring, we measure the ηπ 0π 0 mass spectrum in the reaction e+e- -> e+e- eta pi0 pi0 -> e+e- 6gamma from the eta pi0 pi0 threshold to about 2500 MeV/c 2. The spectrum is dominated by the eta′, for which we determine Gamma(gamma gamma)(eta') BR(eta' -> 6 gamma)=0. 36+-0.02+-0.03 keV. In addition, we observe an enhancement in the cross section near 1900 MeV/c 2 which we attribute to the two-photon production of a new resonance X(1900). The angular distributions and the invariant mass distribution of the eta pi0 subsystem are consistent with those expected for the hypothetical eta2 meson with J(PC)=2(-+). For this J(P) assignment the resonance parameters are M(X)=1876+-35+-50 MeV/c 2, Gamma-tot(X)=228+-90+-34 MeV/c 2 and Gamma(gamma gamma)(X) BR(X -> eta pi pi)=0.9+-0.2+-0.3 keV
Measurement of the Decay of the Y(1S) and Y(2S) Resonances To Muon Pairs
No full textUsing the Crystal Ball detector at the e+e-storage ring DORIS II, we have measured the branching fraction to muon pairs B(mu-mu) of the UPSILON(1S) and UPSILON(2S) resonances and for the first time the product of the muonic partial width GAMMA(mu-mu) and the branching fraction to electrons B(ee) for both resonances. We obtain B(mu-mu) (1S) = (2.31 +/- 0.12 +/- 0.10)%, GAMMA(mu-mu) (1S) . B(ee) (1S) = (31.2 +/- 1.6 +/- 1.7) eV, and B(mu-mu) (2S) = (1.22 +/- 0.28 +/- 0.19)%, GAMMA(mu-mu) (2S) . B(ee) (2S) = (6.5 +/- 1.5 +/- 1.0) eV. Inserting the present world average value of B(ee) (1S) = (2.52 +/- 0.17)%, we determine the muonic partial width of the UPSILON(1S) as GAMMA(mu-mu) (1S) = (1.24 +/- 0.06 +/- 0.11) keV. In addition, we present the first indication of the expected interference between mu-pair production in the continuum and in UPSILON(1S) decays
Measurement of the Properties of the eta' and Search For Other Resonances In Gamma-gamma -> eta pi0 pi0
No full textThe reaction e+e- -> e+e- eta pi0 pi0 has been observed with the Crystal Ball detector at the DORIS II storage ring at DESY. The eta pi0 pi0 mass spectrum is dominated by the eta', and the two-photon width Gamma(eta' -> gamma gamma) is determined to be 4.6+-0.4+-0.6 keV. Limits on Gamma(X ->gamma gamma) x B(X -> eta pi pi) are given for other possible states
