Matching for top-quark FCNC decay
We are currently studying potential interference effects in top-quark FCNC processes and are facing a problem regarding matching. We are producing samples at LO using the TopFCNC UFO model. Specifically we are generating
a) the "FCNC production process" with "generate p p > t z $$ t~" and "add process p p > t z j $$ t~" (+ antiparticle processes)
including the extra jet in the final state leads to possible interference with the decay process
b) the "FCNC decay process" with "generate p p > t t~ > w+ b u~ z" (+ antiparticle process)
these two are compared with
c) a sample containing both processes with "generate p p > t z" and "add process p p > t z j" (+ antiparticle processes)
The samples a) and c) have matching turned on.
Sample b) shouldn't need matching but we switched matching on and off to see the effect.
As it turns out there are quite some differences in the kinematic properties.
The spectrum of the pT of the Z Boson and the leading Jet pT for instance are softer in case matching is turned on.
The main question is weather matching should be turned on or off in case of the decay process when it is not necessary but shows to have a visible impact. Or if maybe there is additional information to be considered.
The setting for the matching used in the run_card.dat:
#******
# Matching parameter (MLM only)
#******
1 = ickkw ! 0 no matching, 1 MLM
1.0 = alpsfact ! scale factor for QCD emission vx
False = chcluster ! cluster only according to channel diag
5 = asrwgtflavor ! highest quark flavor for a_s reweight
False = auto_ptj_mjj ! Automatic setting of ptj and mjj if xqcut >0
30.0 = xqcut ! minimum kt jet measure between partons
#******
#
#******
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