Implement stop decay polariation and three-body neutralino decay kinematics in Pythia8

For the pMSSM summary papers, the event generation of a complex mix of SUSY states and decays are done in MadGraph+Pythia8. Due to the complexity, MadSpin cannot be used to produce the correct decay kinematics of stop and neutralino decays. Instead there are implemented as a UserHooks in Pythia for the most common cases. This is targeted to release 21 as the pMSSM paper is reinterpreting Run 2 searches and therefore need to generate samples in MC21.

More details can be found at: https://indico.cern.ch/event/1315516/contributions/5533323/attachments/2697331/4681318/DecayImprovements.pdf

Build area was cleaned as per request posted in the DB. The full software build will be performed

This merge request affects 1 package:

• Generators/Pythia8_i

This merge request affects 3 files:

• Generators/Pythia8_i/CMakeLists.txt
• Generators/Pythia8_i/src/UserHooks/NeutralinoDecay.cxx
• Generators/Pythia8_i/src/UserHooks/StopPolarization.cxx

added 21.6 Generators review-pending-level-1 labels

The system determined that CI tests (with names matching "^CITest_Trigger.*$") are not needed for this code change. They are not run. This is not an indicator to restart the job.

CI Result SUCCESS (hash fa98547a)

	AthGeneration
externals
cmake
make
tests

Full details available on this CI monitor view. Check the JIRA CI status board for known problems
AthGeneration: number of compilation errors 0, warnings 4
For experts only: Jenkins output [CI-MERGE-REQUEST-GCC62-CC7 2282]

I have some minor comments on code, passing for additional review to expert in Generators because of significant code addition.

Dmitriy (L1)

added review-pending-expert label and removed review-pending-level-1 label

added 1 commit

• 46aa9ec3 - use sqr() function

Compare with previous version

resolved all threads

This merge request affects 1 package:

• Generators/Pythia8_i

This merge request affects 3 files:

• Generators/Pythia8_i/CMakeLists.txt
• Generators/Pythia8_i/src/UserHooks/NeutralinoDecay.cxx
• Generators/Pythia8_i/src/UserHooks/StopPolarization.cxx

added review-pending-level-1 label and removed review-pending-expert label

Build area was cleaned as per request posted in the DB. The full software build will be performed

There were multiple CI triggers for this MR and commit. The system ignored duplicates but the GitLab pipeline status may incorrectly show the job as failed. Once the remaining job finished running, the CI results will be posted as usual.

The system determined that CI tests (with names matching "^CITest_Trigger.*$") are not needed for this code change. They are not run. This is not an indicator to restart the job.

CI Result SUCCESS (hash 46aa9ec3)

	AthGeneration
externals
cmake
make
tests

Full details available on this CI monitor view. Check the JIRA CI status board for known problems
AthGeneration: number of compilation errors 0, warnings 4
For experts only: Jenkins output [CI-MERGE-REQUEST-GCC62-CC7 2284]

Hi, compilation warnings do not come from modified files. However, as previous L1 shifter said, passing it for expert review.

Cheers, Francisco Sili (L1)

added review-pending-expert label and removed review-pending-level-1 label

Hi Matthew ( @mgignac ), Dominic ( @dhirsch ) and Ewelina ( @ewelina ),

please have a look on this MR as an experts in generators software.

Dmitriy

Hi @dmaximov since this request aims only for 21.6 I will accept it, but if you decide to submit a similar one for main branch, please make sure that functions from https://gitlab.cern.ch/atlas/athena/-/blob/main/Generators/TruthUtils/TruthUtils/AtlasPID.h are used i.e.your isLepton -> isSMLepton && isCharged isNeutralino will have to be added to TruthUtils/AtlasPID.h Please let me know if/when you plan to go for the main branch.

Thanks, ewelinA

resolved all threads

mentioned in commit c68f6eea

merged

and let me know if you need a new 21.6 release build with this change

Hi Ewelina,

thank you for your reply and review, but I'm not an author of this MR. Author is Brian Petersen, I was an MR review shifter last week.

Dmitriy

added review-approved label and removed review-pending-expert label

Thanks @ewelina,

as this might be useful in the future as well, I'll make a separate request with the suggested changes, but probably only next week. In the mean time, it would be great if a new 21.6 release could be build, so we can start using this for real in the pMSSM.

Cheers, Brian