min invariant mass of a top-antitop pair

Hello,

We are generating the following process: p p -> t t~ and p p -> t t~ j
matched with pythia parton shower in a BSM model. We are interested
in large invariant mass events. To obtain only 1000 events with
more than 1 TeV of invariant mass we have done 23 runs of 100 000
events; a total of 1 123 000 events if we take into account that the
matching discards roughly a half of the total generated events to
avoid double counting. In order to reduce the computing time, we
wonder if we could generate events with a minimum invariant mass for a
pair of tops as we can do it for jets or b quarks modifying the
run_card.dat.

Thanks in advance,

Juan