Bottom-quark fragmentation: comparing results from tuned event   generators and resummed calculations
  We study bottom-quark fragmentation in e+e- annihilation, top and Higgs decay H -> b bbar, using Monte Carlo event generators, as well as calculations, based on the formalism of perturbative fragmentation functions, which resum soft- and collinear-radiation effects in the next-to-leading logarithmic approximation. We consider the PYTHIA and HERWIG generators, and implement matrix-element corrections to the parton shower simulation of the H -> b bbar process in HERWIG. We tune the Kartvelishvili, string and cluster models to B-hadron data from LEP and SLD, and present results in both x_B and moment spaces. The B-hadron spectra yielded by HERWIG, PYTHIA and resummed calculations show small discrepancies, which are due to the different approaches and models employed and to the quality of the fits to the e+e- data. 
Gennaro Corcella (CERN), Volker Drollinger (Padua)