write nanoAOD trigObj

_episodes/04-TriggerObj.md

@@ -0,0 +1,75 @@
+---
+title: "Accessing trigger objects"
+teaching: 30
+exercises: 0
+objectives:
+- "Learn how to access the trigger information stored in MiniAOD and NanoAOD"
+- "Learn what is trigger objects and how to access them"
+- "Measure trigger efficiency using the tag-and-probe method"
+---
+
+> ## MiniAOD
+{: .solution}
+
+> ## NanoAOD
+> Trigger objects are also stored in NanoAOD. Here are a short example of accessing 
+> ~~~
+> from coffea.nanoevents import NanoAODSchema
+> fpath="root://cmseos.fnal.gov//store/user/cmsdas/2023/short_exercises/Trigger/New_NanoAOD_M1000.root"
+> events = NanoEventsFactory.from_root(fpath,schemaclass=NanoAODSchema).events()
+> ~~~
+> Trigger object is one of the fields of the event
+> ~~~
+> trig = events.TrigObj
+> trig.fields
+> ['pt',
+>  'eta',
+>  'phi',
+>  'l1pt',
+>  'l1pt_2',
+>  'l2pt',
+>  'id',
+>  'l1iso',
+>  'l1charge',
+>  'filterBits']
+> ~~~
+> The trigger objects has an `id` attribute so that you can easily find same type of trigger objects (e.g. trigger muons)
+> ~~~
+> trigMuon = trig[trig.id==15]
+> # ID of the object: 11 = Electron (PixelMatched e/gamma), 22 = Photon (PixelMatch-vetoed e/gamma), 13 = Muon, 15 = Tau, 1 = Jet, 6 = FatJet, 2 = MET, 3 = HT, 4 = MHT
+> # Note that id matches the pdgId of the particles
+> ~~~
+> 
+> ### Filter bits
+> The information of which trigger paths the trigger object has passed is stored compactly in the `filterBits` field.<br>
+> The `filterBits` encoding can be found from the documentations links below. 
+> 
+> For example, for muons, the bits meaning is the following:
+> ~~~
+>   1    = TrkIsoVVL,
+>   2    = Iso, 
+>   4    = OverlapFilter PFTau,
+>   8    = 1mu,
+>   16   = 2mu,
+>   32   = 1mu-1e, 
+>   64   = 1mu-1tau,
+>   128  = 3mu, 
+>   256  = 2mu-1e,
+>   512  = 1mu-2e,
+>   1024 = 1mu (Mu50), 
+>   2048 = 1mu (Mu100)
+> ~~~
+> Therefore, if you want to find trigger muons in `Iso` paths:
+> ~~~
+> filterBit = 2
+> passIso = trigMuon.filterBits &(1<<filterBit)==(1<<filterBit) # mask for each trigMuon
+> IsoTrigMuon = trigMuon[passIso] 
+> ~~~
+>
+> ### References
+> [Documentation of specific version](https://cms-nanoaod-integration.web.cern.ch/autoDoc/). 
+> [Current definitionof  trigger object in CMSSW](https://github.com/cms-sw/cmssw/blob/master/PhysicsTools/NanoAOD/python/triggerObjects_cff.py). 
+{: .solution}
+
+{% include links.md %}
+