Survey return zero cross section in process

[朱鸣迪]

Hi,

  I'm generating events for g g > t t~ h h , ( h > w+ w- , w+ > j j , w- > j j ), ( t > w+ b , w+ > j j ) , ( t~ > w- b~ , w- > j j ) , but when I start my calculations this error happened:
Survey return zero cross section.
   Typical reasons are the following:
   1) A massive s-channel particle has a width set to zero.
   2) The pdf are zero for at least one of the initial state particles
      or you are using maxjetflavor=4 for initial state b:s.
   3) The cuts are too strong.
   Please check/correct your param_card and/or your run_card.
Zero result detected: See https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-14

I dont know how to solve this problem QAQ, Any help would be appreciated!

Thanks.

[Olivier Mattelaer (olivier-mattelaer)]

The first problem is your syntax:
The part h > w+ w-
ask for an ONSHELL higgs to decay to two ONSHELL W, this is not possible since m_h< 2*MW
You should replace
( h > w+ w- , w+ > j j , w- > j j )
by
( h > w+ w- > 4j )

For the rest difficult to comment whithout knowing what your cut are (did you remove them all?).
Do you also have a zero survey if you only ask the production (and no decay)?

Cheers,

Olivier