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The inclusive production cross section of Λ, Λ¯ in e+e− annihilation at a c.m. energy of 29 GeV has been measured with the time-projection-chamber detector at PEP. The average Λ, Λ¯ multiplicity has been measured to be 0.197 ± 0.012(stat.) ±0.017(syst.). Λ−Λ¯ pairs have been observed in jets for the first time, and the average number of Λ−Λ¯ pairs per event has been measured to be 0.042 ± 0.017 ± 0.014.
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The distribution of particles in three-jet events is compared with the predictions of three fragmentation models currently in use: the Lund string model, the Webber cluster model, and an independent fragmentation model. The Lund model and, to a certain extent, the Webber model provide reasonable descriptions of the data. The independent fragmentation model does not describe the distribution of particles at large angles with respect to the jet axes. The results provide evidence that the sources of hadrons are Lorentz boosted with respect to the overall c.m.
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Inclusive production cross sections for photons and π0's ine+e− annihilation at a center of mass energy of 29 GeV have been measured. The π0 production spectrum agrees with a corresponding measurement for π±. The ratio of the π0 inclusive rate to the average for π± is 0.92±0.14. The fractions of the total energy carried by photons and π0's are 0.244±0.016 and 0.217±0.033, respectively. The fraction of total energy carried by all stable hadrons, prompt leptons and photons is determined to be 0.938±0.045, leaving 0.062±0.045 for neutrinos.
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The reaction γp→ρfast0pπ+π− has been studied with the linearly polarized 20-GeV monochromatic photon beam at the SLAC Hybrid Facility to test the prediction of s-channel helicity conservation in inelastic diffraction for t’<0.4 (GeV/c)2. In a sample of 1934 events from this reaction, the ρ0 decay-angular distributions and spin-density-matrix elements are consistent with s-channel helicity conservation, the π+π− mass shape displays the same skewing as seen in the reaction γp→pπ+π−, and the pπ+π− mass distribution compares well and scales according to the vector dominance model with that produced in π±p→πfast±pπ+π−.
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SPIN DENSITY MATRIX ELEMENTS FOR THE DIFFRACTIVE RHO0 MESON FROM STUDY OF THE ANGULAR DISTRIBUTIONS. CORRECTION HAS BEEN MADE FOR THE (20 +- 5) PCT NON DIFFRACTIVE BACKGROUND IN THE FINAL DATA SAMPLE, ASSUMING IT TO HAVE AN ISOTOPIC ANGULAR DISTRIBUTION.
Bose-Einstein correlations between like-sign pions have been investigated in e+e− annihilation at √s =29 GeV using the Time Projection Chamber detector at the SLAC e+e− storage ring PEP. The production rate of like-sign pion pairs with small relative momentum is found to be increased by more than 50% over the rate expected for uncorrelated production of pions. From the correlation length, a typical source radius of 0.65 fm is derived. Data are consistent with a spherical shape of the pion source. No dependence of radius or correlation strength on the event multiplicity is observed.
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