Speaker
Leif Lönnblad
(Lund University (SE))
Description
During the last years, much effort has gone into increasing the
precision of event generators by carefully matching or merging parton
shower programs with exact fixed-order matrix elements. The merging of
tree-level matrix elements has now become the standard for multi-jet
events, but these leading order procedures lack in precision, and also
suffer from a dependence on an unphysical merging scale. For many
processes the matching of Next-to-Leading Order (NLO) matrix elements
with parton showers has become state-of-the-art, but the standard
programs can typically only handle the lowest possible
jet-multiplicities.
In this talk I will present a new algorithm where multi-jet NLO matrix
elements are correctly merged with parton showers. The new
algorithm is based on an improvement of the so-called CKKW-L scheme
for tree-level merging where the combination of different
multiplicities is treated in a unitary way. The algorithm has been
implemented in the Pythia8 event generator and will in principle be
able to handle any process where multi-jet partonic states can be
produced to NLO precision, however, in this talk I will only present
results for W+jets and Higgs+jets observables.
Author
Leif Lönnblad
(Lund University (SE))
