How to generate H+ -> W* A (W off-shell)
I am using MG5_aMC_v3_1_0 & Pythia8 to simulate tt-> WbWH+, H+->WA. When the H+ decay is on shell all is well; MG5 simulates up to the H+ and Pythia8 takes over. But for mH+ < mA + mW I cannot persuade Pythia to run. So I try:
generate p p > t t~, (t~ > b~ w-), (t > b h+, (h+ > h1 f f ))
with f any fermion. I need to remove the (H+ taubar nu) coupling, but OK, that gives the Feynman diagram I want.
However, the kinematics is changed. If we compare the two approaches (Pythia v MG5 for the H+ decay) when using masses allowing on-shell decay, the pT of the A produced by Madgraph is considerably more than that from Pythia. This presumably means the ff mass is reduced. But which is correct?
I try to debug by asking MG5 to simulate a process I know the distribution:
generate p p > Z H , ( Z > p p ) , ( H > Z Z , ( Z > l+ l- ) )
but with or without madspin that typically produces masses for both Z bosons of 60 GeV, not 90/30 you expect. [I have trouble running madspin as it sees the "( Z" in the above as a particle name, and I need to delete all the brackets from the process spec in proc_card_mg5 AFTER mg5_aMC has run. But I think thats not relevant]
Am I doing something wrong in these setups? Any hints much appreciated
Bill
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