jet multiplicity and settings in pythia6/8

Asked by Gang Li on 2018-04-21

Dear Madgraph Team,

I want to decay W boson in pythia without any effect of ISR, FSR, hadronization being included.

(1) In pythia6, I change the pythia card as follows:

 !...Parton showering on or off
      MSTP(61)=0
      MSTP(71)=0

!...Fragmentation/hadronization on or off
      MSTJ(1)=0

!...Multiple interactions on or off
      MSTP(81)=0

Is it correct?

(2) For the process

p p > w+ with pythia6 and the above settings, I found exactly 1 or 3 jets in the final state
p p > w+, w+ > j j with pythia6 and the above settings, I found exactly 3 jets in the final state

Here what I mean "jet" is quark after pythia, which is identified by its particle ID. But I expect that there should be exactly 2 jets since I have turned off ISR, FSR and hadronization.
Is there anything I have missed?

Some of particle ID of the final state jets for the process p p > w+, w+ > j j are displayed below. In each parentheses, three numbers denote the PID of three jets in an event.

(4 -3 2) (4 -3 2) (2 -1 2) (2 -1 2) (2 -1 2) (4 -3 2) (2 -1 1) (4 -3 2) (2 -1 2) (2 -1 2) (4 -3 1)...

(3) How to turn off ISR, FSR and hadronization in pythia8 for the same process?

Thanks a lot.

Gang Li

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Gang Li
Solved:
2018-04-22
Last query:
2018-04-22
Last reply:
2018-04-21
Gang Li (ligangpku) said : #1

Some more information added:

For (2), I want to decay W in pythia but I also checked my settings with p p > w+, w+ > j j.

For (3), I want to ask whether it is possible to turn off ISR, FSR and hadronization easily when generating events by adding some sentences in pythia8_card.dat.

Hi,

Pythia6 is actually not supported anymore by their author (since at least 5 year)
and the MG-pythia interface is also not supported anymore.
In any case, this sounds a question for the pythia author.

(3) How to turn off ISR, FSR and hadronization in pythia8 for the same process?

according to http://home.thep.lu.se/Pythia/pythia82html/MasterSwitches.html
you should put the following flag in the pythia8_card.dat

flag PartonLevel:MPI (default = on)
Master switch for multiparton interactions; on/off = true/false. Further options are found here<http://home.thep.lu.se/Pythia/pythia82html/MultipartonInteractions.html>.

flag PartonLevel:ISR (default = on)
Master switch for initial-state radiation; on/off = true/false. Further options are found here<http://home.thep.lu.se/Pythia/pythia82html/SpacelikeShowers.html>.

For (3), I want to ask whether it is possible to turn off ISR, FSR and
hadronization easily when generating events by adding some sentences in
pythia8_card.dat.

All the switch of pythia8 should be supported.

Cheers,

Olivier

On 21 Apr 2018, at 18:32, Gang Li <<email address hidden><mailto:<email address hidden>>> wrote:

Question #668160 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/668160

Gang Li gave more information on the question:
Some more information added:

For (2), I want to decay W in pythia but I also checked my settings with
p p > w+, w+ > j j.

For (3), I want to ask whether it is possible to turn off ISR, FSR and
hadronization easily when generating events by adding some sentences in
pythia8_card.dat.

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Gang Li (ligangpku) said : #3

Dear Olivier,

thanks a lot. Your answer helps.

I have solved the problem with pythia6 events: I used the PID mother particle to reject the incorrect jet.

Best,
Gang Li