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  • 1
    ISSN: 1435-3725
    Keywords: 12.38.-t ; 13.85.-t ; 13.87.Ce ; 13.87.Fh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a study of correlations between D and $${\overline D}$$ mesons produced in 500 GeV/cπ−-nucleon interactions, based on data from experiment E791 at Fermilab. We have fully reconstructed 791 ± 44 charm meson pairs to study correlations between the transverse and longitudinal momenta of the two D mesons and the relative production rates for different types of D meson pairs. We see slight correlations between the longitudinal momenta of the D and the $${\bar D}$$ , and significant correlations between the azimuthal angle of the D and the $${\bar D}$$ . The experimental distributions are compared to a next-to-leading-order QCD calculation and to predictions of the PYTHIA/JETSET Monte Carlo event generator. We observe less correlation between transverse momenta and different correlations between longitudinal momenta than these models predict for the default values of the model parameters. Better agreement between data and theory might be achieved by tuning the model parameters or by adding higher order perturbative terms, thus contributing to a better understanding of charm production. The relative production rates for the four sets of charm pairs, $$D^0{{\overline D}^0}, D^0 D^{-}, D^+{{\overline D}^0}, D^+ D^{-}$$ as calculated in the PYTHIA/JETSET event generator with the default parameters, agree with data as far as the relative ordering, but predict too many $$D^+ {{\overline D}^0}$$ pairs and too few $$D^+ D^{-}$$ pairs.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1435-3725
    Keywords: 12.38.-t ; 13.85.-t ; 13.87.Ce ; 13.87.Fh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a study of correlations between D and $${\overline D}$$ mesons produced in 500 GeV/cπ−-nucleon interactions, based on data from experiment E791 at Fermilab. We have fully reconstructed 791 ± 44 charm meson pairs to study correlations between the transverse and longitudinal momenta of the two D mesons and the relative production rates for different types of D meson pairs. We see slight correlations between the longitudinal momenta of the D and the $${\bar D}$$ , and significant correlations between the azimuthal angle of the D and the $${\bar D}$$ . The experimental distributions are compared to a next-to-leading-order QCD calculation and to predictions of the PYTHIA/JETSET Monte Carlo event generator. We observe less correlation between transverse momenta and different correlations between longitudinal momenta than these models predict for the default values of the model parameters. Better agreement between data and theory might be achieved by tuning the model parameters or by adding higher order perturbative terms, thus contributing to a better understanding of charm production. The relative production rates for the four sets of charm pairs, $$D^0{{\overline D}^0}, D^0 D^{-}, D^+{{\overline D}^0}, D^+ D^{-}$$ as calculated in the PYTHIA/JETSET event generator with the default parameters, agree with data as far as the relative ordering, but predict too many $$D^+ {{\overline D}^0}$$ pairs and too few $$D^+ D^{-}$$ pairs.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 3
    ISSN: 1432-2242
    Keywords: Aegilops ; Allotetraploid ; Diploidization ; Pairing control ; Synaptonemal complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Allotetraploid Aegilops species sharing the U genome, Ae. columnaris (UUMM), Ae. ovata (UUMM), Ae. triaristata (UUMM), Ae. triuncialis (UUCC) and Ae. variabilis (UUSS), regularly form bivalents at metaphase I of meiosis. The pattern of zygotene and pachytene pairing was analyzed by whole-mount surface-spreading of synaptonemal complexes under the electron microscope. The data indicated that at the zygotene stage the chromosomes were almost exclusively associated as bivalents; only a few multivalents (7%) were observed. These observations are discussed in relation to mechanisms of diploidization of polyploid meiosis.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2242
    Keywords: Aegilops ; Allotetraploid ; Diploidization ; Pairing control ; Synaptonemal complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chromosome pairing behaviour of the allotetraploid Aegilops species sharing the D genome, Ae. crassa (DDMM), Ae. cylindrica (DDCC) and Ae. ventricosa (DDNN), was analyzed by electron microscopy in surfacespread prophase-I nuclei. Synaptonemal-complex analysis at zygotene and pachytene revealed that synapsis in the allotetraploids was mostly between homologous chromosomes, although a few multivalents were also formed. Only homologous bivalents were observed at metaphase-I. It is concluded that the mechanism controlling bivalent formation in these species acts mainly at zygotene by restricting pairing to homologous chromosomes, but also acts at pachytene by preventing chiasma formation in homoeologous associations. These observations are discussed in relation to mechanisms of diploidization of polyploid meiosis.
    Type of Medium: Electronic Resource
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