Speaker
Mark Sutton
(University of Sussex (GB))
Description
Recent developments in the fast reproduction of the results of QCD calculations
using the APPLgrid project are presented. The calculation of cross-sections at
Next-to-Leading order in QCD involves the integration over the final state phase
space in order to cancel the infra-red divergences. For the calculation of cross
sections for observables at hadron-hadron colliders this integration requires the
Monte Carlo generation of a large number of event weights. These calculations
typically need to be repeated if a different choice of parton densities within
the proton are required or a different choice of factorisation or renormalisation
scales. This makes the full calculation with many of the available parton density
function error sets, and indeed the inclusion of these calculations in iterative
fits to the proton parton densities, computationally prohibitive.
The APPLgrid project allows the {\em a posteriori} inclusion of the parton densities
in the calculation of the cross section by storing the weights from the Monte Carlo integration over the hard-subprocess phase space from the underlying QCD Calculation
code in a look-up table so that the full calculation need be performed only once,
after which the cross section can be recreated with any parton density set using a
fast convolution over the stored weights This reduces the time required to obtain
the cross section from many days, down to a few milliseconds. Detailed examples
from the increasingly large menagery of QCD calculations of physics processes
interfaced to APPLgrid will be presented.
Author
Mark Sutton
(University of Sussex (GB))
