Backport of pythia 8 EGun code from CMSSW_11_1 to CMSSW_9_2_8

[pasmuss]

if this PR is a backport please specify the original PR and why you need to backport that PR:

Backport for PR #29000 to CMSSW_9_2_8 for MC production. #29000 already approved and merged.

PR description (from original request):

Changes for proper treatment of color (conservation and codes):

• Increasing color index after generating one particle (anti particle obtains the same color, just on the anticolor column)
• Adding a check that if only colored particles are generated, the AddAntiParticle option is used to make sure that all colors are balanced
• Only affecting pythia8 EGun

PR validation (from original request):

Ran some tests locally with a core CMSSW script:

• not set AddAntiParticle at all (does not start, option must be set)
• set option to False (runs but does not generate anything and throws errors)
• set option to True (as expected: anti particle gets same anti color as particle gets color, index is not the same for two different particles)

[cmsbuild]

A new Pull Request was created by @pasmuss for CMSSW_9_2_X.

It involves the following packages:

GeneratorInterface/Pythia8Interface

@SiewYan, @efeyazgan, @mkirsano, @cmsbuild, @agrohsje, @alberto-sanchez, @qliphy can you please review it and eventually sign? Thanks.
@alberto-sanchez, @agrohsje, @mkirsano this is something you requested to watch as well.
@davidlange6, @silviodonato, @fabiocos you are the release manager for this.

cms-bot commands are listed here

[qliphy]

please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

-1
Tested at: UNKNOWN
I was not able to find a release to test this PR. See the Jenkins logs for more details.

[qliphy]

@smuzaffar @mrodozov Can you have a look at above message? Thanks!

[smuzaffar]

@silviodonato @qliphy , we are not building IBs for 92X release cycle since May 2018. If we really need to include this in 9.2.X then we have to re-enable 92X IBs first.

[qliphy]

@pasmuss Do you wants to backport to 9_2_X or 9_3_X?

[pasmuss]

MC Request was created in Summer17GS (9_2_8). Can most likely go in Fall17 (9_3_17), if that is easier. Do I need to recreate this pull request then?

[mrodozov]

We have 9.3 IB . Please recreate it with base branch https://github.com/cms-sw/cmssw/tree/CMSSW_9_3_X . Changing the base branch here will bring many differences

[pasmuss]

Created new PR to CMSSW_9_3_X, #29153