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Trigger Manipulation

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Getting trigger prescales

Overview

Teaching: 0 min
Exercises: 25 min
Questions

  • How do I get the prescales for my triggers?

Objectives

  • Learn how to extract the prescales for you triggers

The TriggerInfoTool

The CERN Open Data portal maintains some records that explain how to use certain tools for analysis. One of those is the record about the TriggerInfoTool. You immediately see that it points to the TriggerInfoTool repository on Github. This a place where you can find a few examples and explore the way the code is used for extracting trigger information.

Get the Prescales and the acceptance bit

Let’s work on one of the examples stored in the repository above. In particular, we are going to look at the TriggerSimplePrescalesAnalyzer example (package). The following directions can also be found in that repository.

First make sure you are at the top of your CMSSW_5_3_32/src area and that you have issued the cmsenv command.

Now let’s clone the 2011 branch of this repository, which will be good for the 2012 data we are working with:

git clone -b 2011 git://github.com/cms-legacydata-analyses/TriggerInfoTool.git

Compile:

scram b

Edit the config file to choose the triggers we are interested in (you can use vi or other editor). Remember, we will exercise the TriggerSimplePrescalesAnalyzer example:

vi TriggerInfoTool/TriggerSimplePrescalesAnalyzer/python/simpleprescalesinfoanalyzer_cfg.py

Replace the PoolSource files with the ones we used in our last episode, replace the triggerPatterns parameter with a simpler trigger, like "HLT_Mu12_v??" (note the wildcard at the end ??, so we can get the prescales for all versions of this trigger).

Take a loot at the config file

The config file should look like:

import FWCore.ParameterSet.Config as cms

process = cms.Process("TriggerInfo")

process.load("FWCore.MessageService.MessageLogger_cfi")
#if more events are activated, choose to print every 1000:
#process.MessageLogger.cerr.FwkReport.reportEvery = 1000

process.maxEvents = cms.untracked.PSet( input = cms.untracked.int32(100) )

process.source = cms.Source("PoolSource",
    fileNames = cms.untracked.vstring(
        'root://eospublic.cern.ch//eos/opendata/cms/Run2012B/TauPlusX/AOD/22Jan2013-v1/20000/0040CF04-8E74-E211-AD0C-00266CFFA344.root',
        'root://eospublic.cern.ch//eos/opendata/cms/Run2012C/TauPlusX/AOD/22Jan2013-v1/310001/0EF85C5C-A787-E211-AFC9-003048C6942A.root'
    )
)

#needed to get the actual prescale values used from the global tag
process.load('Configuration.StandardSequences.FrontierConditions_GlobalTag_cff')
process.GlobalTag.connect = cms.string('sqlite_file:/cvmfs/cms-opendata-conddb.cern.ch/FT_53_LV5_AN1_RUNA.db')
process.GlobalTag.globaltag = 'FT_53_LV5_AN1::All'

#configure the analyzer
#inspired by https://github.com/cms-sw/cmssw/blob/CMSSW_5_3_X/HLTrigger/HLTfilters/interface/HLTHighLevel.h
process.gettriggerinfo = cms.EDAnalyzer('TriggerSimplePrescalesAnalyzer',
                              processName = cms.string("HLT"),
                             triggerPatterns = cms.vstring("HLT_Mu12_v??"), #if left empty, all triggers will run
                              triggerResults = cms.InputTag("TriggerResults","","HLT"),
                              triggerEvent   = cms.InputTag("hltTriggerSummaryAOD","","HLT")
                              )


process.triggerinfo = cms.Path(process.gettriggerinfo)
process.schedule = cms.Schedule(process.triggerinfo)

Let’s run:

cmsRun TriggerInfoTool/TriggerSimplePrescalesAnalyzer/python/simpleprescalesinfoanalyzer_cfg.py  > full_prescales.log 2>&1 &

Let’s check the output

HLTConfig has changed . . .
Begin processing the 1st record. Run 194075, Event 14880766, LumiSection 48 at 29-Sep-2020 03:11:45.700 CEST
Currently analyzing trigger HLT_Mu12_v16
analyzeSimplePrescales: path HLT_Mu12_v16 [121] prescales L1T,HLT: 50,30
 Trigger path status: WasRun=1 Accept=0 Error =0
Begin processing the 2nd record. Run 194075, Event 14844046, LumiSection 48 at 29-Sep-2020 03:11:45.712 CEST
Currently analyzing trigger HLT_Mu12_v16
analyzeSimplePrescales: path HLT_Mu12_v16 [121] prescales L1T,HLT: 50,30
 Trigger path status: WasRun=1 Accept=0 Error =0
...

Notice that the L1 prescale was 50 for that particular run, whereas the HLT prescale was 30. We would have to run on many more events to see an Accept=1, which would mean the event was accepted by this trigger.

Challenge!

How about now you run with the triggers we were interested in, i.e., the HLT_IsoMu17_eta2p1_LooseIsoPFTau20_v? ones. What do you get?

solution

You will see an output like this:

HLTConfig has changed . . .
Begin processing the 1st record. Run 194075, Event 14880766, LumiSection 48 at 29-Sep-2020 02:26:23.553 CEST
Currently analyzing trigger HLT_IsoMu17_eta2p1_LooseIsoPFTau20_v2
%MSG-e HLTConfigData:  TriggerSimplePrescalesAnalyzer:gettriggerinfo  29-Sep-2020 02:26:23 CEST Run: 194075 Event: 14880766
 Error in determining L1T prescale for HLT path: 'HLT_IsoMu17_eta2p1_LooseIsoPFTau20_v2' with L1T seed: 'L1_SingleMu14er OR L1_SingleMu16er' using L1GtUtils: error code: 210001. > > (Note: only a single L1T name, not a bit number, is allowed as seed for a proper determination of the L1T prescale!)
%MSG
analyzeSimplePrescales: path HLT_IsoMu17_eta2p1_LooseIsoPFTau20_v2 [394] prescales L1T,HLT: -1,1
 Trigger path status: WasRun=1 Accept=0 Error =0
Begin processing the 2nd record. Run 194075, Event 14844046, LumiSection 48 at 29-Sep-2020 02:26:23.584 CEST
Currently analyzing trigger HLT_IsoMu17_eta2p1_LooseIsoPFTau20_v2
%MSG-e HLTConfigData:  TriggerSimplePrescalesAnalyzer:gettriggerinfo  29-Sep-2020 02:26:23 CEST Run: 194075 Event: 14844046
 Error in determining L1T prescale for HLT path: 'HLT_IsoMu17_eta2p1_LooseIsoPFTau20_v2' with L1T seed: 'L1_SingleMu14er OR L1_SingleMu16er' using L1GtUtils: error code: 210001. > > (Note: only a single L1T name, not a bit number, is allowed as seed for a proper determination of the L1T prescale!)
%MSG

Life is not so easy sometimes. While there was no problem getting the HLT prescale (it seems to be 1), i.e., the trigger is unprescaled at the HLT, we can’t say anything about the L1 because there is a limitation in our software. Can you understand why we are getting this error?

 Error in determining L1T prescale for HLT path: 'HLT_IsoMu17_eta2p1_LooseIsoPFTau20_v2' with L1T seed: 'L1_SingleMu14er OR L1_SingleMu16er' using L1GtUtils: error code: 210001. > > (Note: only a single L1T name, not a bit number, is allowed as seed for a proper determination of the L1T prescale!)

Fortunately, there is a backup solution for us to check on the prescales. In a later lesson you will learn about the Brilcalc tool. Once you are setup for using it, you could try this line to check on the L1 prescales for this particular run:

brilcalc trg --prescale -r 194075 --hltpath "HLT_IsoMu17_eta2p1_LooseIsoPFTau20_v?"

Explore the TriggerSimplePrescalesAnalyzer!

On overtime, you could explore the implementation of the code we just used. Play around with it, what else can you learn?

Key Points

  • Prescales can be extracted using the trigger tools in CMSSW and from the brilcalc tool.

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