Diffractive Vector Meson Production at HERA: from soft to hard QCD

Experimental results from HERA on diffractive vector meson production and their theoretical interpretation within microscopic QCD are reviewed with an emphasis on the BFKL color dipole and kt-factorization approaches.Comment: 178 pages including 78 figure

Measurement of the partial width of the Z0 into b anti-b final states using their semileptonic decays

The spectra of prompt electrons and muons from the semi-leptonic decays of heavy hadrons produced inZ 0 decays have been used to measure the coupling of theZ 0 tob quarks weighted by theB hadrons mean semi-leptonic branching fraction, giving a value: BRbsl∗Γbbˉ/ΓH=0.0221±0.0015 . The data has also been used to measure the value of the fragmentation parameter, defined in the context of the LUND PS Model, version 7.2, giving: ε(b)=(8+5−3±2)10−3 . The corresponding value of the mean fraction of the beam energy taken by aB hadron in the fragmentation of ab quark is: XbE−−−=0.69+0.02−0.03±0.01 . If the values of Γbbˉ andΓ H are taken from the Standard Model, the following value is obtained for the mean semi-leptonic braching fraction ofB hadrons: BR sl b =(10.1±0.7)%. Taking the value of Γbbˉ/ΓH from an independent analysis of DELPHI data based on the use of the boosted sphericity product, a value: BR sl b =(10.1±1.3)% is obtained