cross-sections of combined processes
Dear experts,
I am comparing the cross-sections of two processes after generating them first as individual processes and then combining them in a single run.
For eg,
generate p p > t t~
output ttbar
generate p p > w+ w-
output ww
and
generate p p > t t~ @1
add process p p > w+ w- @2
output combined_proc
We compare the cross-sections of these processes for three different number of events, 10,1000 and 10000 keeping the same iseed value. However the cross-sections for ttbar, ww and combined_proc differ by upto 11 % for w+w- pair production whereas upto 0.5% for tt~ pair production in each case. I am unsure as to why this discrepancy occurs especially for ww where it is nearly 11 %.
I was wondering whether for the combined processes, could it be that the number of events for computing the cross-section of the combined process and not the individual process is 1000 events during survey whereas for the processes generated separately, survey uses 1000 events and hence resulting in better accuracy in the results?
Your advice in this regard will be very helpful to understand this issue.
Thanking You,
Best Regards,
Juhi
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