Double counting in Drell-Yan production
Asked by
Stephanie Baines
Hello,
I am producing Drell-Yan corss sections in Madgraph. It seems when I generate j j > a > e+ e-, madgraph counts twice the cross section I calculate from the Feynman rules analytically because it generates all processes twice
u u~ > a > e+ e-
u~ u > a > e+ e-
d d~ > a > e+ e-
d~ d> a > e+ e-
s s~ > a > e+ e-
s~ s > a > e+ e-
c c~ > a > e+ e-
c~ c > a > e+ e-
I don't understand why this is correct.
If one considers the cross section
e+ e- > a > e+ e- which is identical bar a factor for charge and colour, the total cross section as given by Madgraph is not doubled to include e- e+ > a > e+ e-.
Which is physically correct if I want to know what would be produced by proton-proton collisions?
Thank you!
Best
Stephanie
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