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 portfolio
of QCD calculations of physics processes interfaced to APPLgrid will
be presented.
Primary authors
Mark Sutton
(University of Sussex (GB))
Mark Sutton
