When I only allow a subset of the Z0 decay channels the cross section for Z0 production is automatically rescaled accordingly. Why is the cross section not rescaled when I study prompt J/Psi production, and only allow it to decay to leptons?

A J/Psi can be produced many different ways. For instance, you could start out with a normal QCD jet process, where the showers give a g -> b bbar branching. After hadronization a B meson is formed that then decays to the J/Psi. Here it is NOT possible to know beforehand that a J/Psi will be produced, and therefore it is not possible to take the choice of allowed J/Psi decay modes into account in cross-secion calculations. Therefore there is a clear dividing line in the program: - all particles up to and including Upsilon systems can occur "at random", and therefore a change of branching ratios is NOT propagated to the process cross section; - all particles above this, i.e. W, Z, top, Higgs, SUSY?, ..., occur only as part of the hard process (with perturbatively calculable branching ratios) and so changes in the choice of allowed channels IS propagated to the process cross section.

For a specific process like g g -> g J/Psi it would still have been possible to let the program rescale the cross section based on allowed J/Psi decay channels, but then one would be faced with the J/Psi having different consequences when produced in different channels. This would be even more confusing than the current rule.

Edit | Attach | Watch | Print version | History: r1 | Backlinks | Raw View | WYSIWYG | More topic actions
Topic revision: r1 - 2007-03-23 - unknown
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    GeneratorServices/Pythia6 All webs login

This site is powered by the TWiki collaboration platform Powered by PerlCopyright & 2008-2023 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
or Ideas, requests, problems regarding TWiki? use Discourse or Send feedback