Matching with both b and light jet in 5 flavor scheme

Asked by Siddharth on 2019-05-09

      I am trying to generate the following process in 5 flavor scheme :

define bp = b b~
define p = p b b~
define jl = g u c d s u~ c~ d~ s~
generate p p > bp mu+ mu- QED=99
add process p p > bp mu+ mu- jl QED=99

To generate the above process I use sm-no_b_mass model (MadGraph version 2_6_5).

When I try to do matching upto 1 jet with "JetMatching:nJetMax = 1 " in pythia card, it generates the following error message:

"PY8_parallelization/ 0 launch ends with non zero status: 139. Stop all computation
Please report this bug on"

But when I use the default option "JetMatching:nJetMax = -1" the run is executed.

Could you please help me understand the reason for the error and why the default setting allows the execution.

Thanks and regards

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Solved by:
Olivier Mattelaer
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I do not know the meaning of "JetMatching:nJetMax = -1" (you should check the PY8 manual for that)

Now your syntax (independently of the PY8 parameter) does not make sense.

If you are running in 5 flavor scheme, the "b" jet is a light jet
so your definition of jl is wrong.

Indeed pythia is going to generate soft b jet since this your are in a 5 flavor scheme.
But since you have not include that contribution within your matrix-element at 1 jet, your matching can not work correctly.

In top of that you have a single out "b" in your process definition. This does not make sense either for the matching procedure.
This is likely why you need to have JetMatching:nJetMax = 2 in this case (and likely what -1 assumes if I'm correct).
However this requires that you also add the 0j contribution:
generate p p > mu+ mu-

So I believe that what you want is actually to do a computation in 4 flavor and not in 5.



Siddharth (dwivedi-siddharth) said : #2

Thanks Olivier Mattelaer, that solved my question.