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. It eventually points to the TriggerInfoTool repository on Github. This is a place where you can find a few examples and explore the way the code is used for extracting trigger information.

Getting 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 (except for a couple of changes):

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

Compile:

scram b

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

nano 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).

The wildcards follow traditional convention: “?” will match any single character, while “*” will match any string after.

As in the last section, make absolutely sure you have access to the conditions database information needed for 2012, which is different than that for 2011. Here is where there is a key difference between using the Virtual Machine or the Docker container. When using the Virtual Machine, you have to replace the three lines that have GlobalTag in them with:

#needed to access the conditions data from the Virtual Machine
process.load('Configuration.StandardSequences.FrontierConditions_GlobalTag_cff')
process.GlobalTag.connect = cms.string('sqlite_file:/cvmfs/cms-opendata-conddb.cern.ch/FT53_V21A_AN6_FULL.db')
process.GlobalTag.globaltag = 'FT53_V21A_AN6::All'

On the other hand, if you are using the Docker container replace them with:

#needed to access the conditions data from the Docker container
process.load('Configuration.StandardSequences.FrontierConditions_GlobalTag_cff')
process.GlobalTag.connect = cms.string('sqlite_file:/opt/cms-opendata-conddb/FT53_V21A_AN6_FULL_data_stripped.db')
process.GlobalTag.globaltag = 'FT53_V21A_AN6_FULL::All'

Remember: These lines, with the GlobaTag string in them, have to do with being able to read CMS database information. We call this the conditions data as we may find values for calibration, alignment, trigger prescales, etc., in there . One can think of the GlobalTag as a label that contains a set of database snapshots that need to be adequate for a point in time in the history of the CMS detector. For the 2012 open data release, the global tag is FT53_V21A_AN6 or FT53_V21A_AN6_FULL (the ::All string is a flag that tells the frameworks to read All the information associated with the tag). You can find more information in this CODP guide. The connect variable in one of those lines just modifies they way in which the framework is going to access these snapshots. For the VM we access them through the shared files system area at CERN (cvmfs). Read in this way, the conditions will be cached locally in your virtual machine the first time you run and so the CMSSW job will be slow. Fortunately, we already did this while setting up our VM, so our jobs will run much faster. In addition, those soft links he had to make are simply pointers to these areas. On the other hand, in the Docker container, these database snapshots live locally in your /opt/cms-opendata-conddb directory. Running over them is much quicker. Feel free to just replace the whole config file with the final version below (if using the VM, uncomment and comment out the section in question appropriately).

Take a look at the full 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'
    )
)

#uncomment to access the conditions data from the Virtual Machine (and comment out the Docker container set below)
#process.load('Configuration.StandardSequences.FrontierConditions_GlobalTag_cff')
#process.GlobalTag.connect = cms.string('sqlite_file:/cvmfs/cms-opendata-conddb.cern.ch/FT53_V21A_AN6_FULL.db')
#process.GlobalTag.globaltag = 'FT53_V21A_AN6::All'

#needed to access the conditions data from the Docker container
process.load('Configuration.StandardSequences.FrontierConditions_GlobalTag_cff')
process.GlobalTag.connect = cms.string('sqlite_file:/opt/cms-opendata-conddb/FT53_V21A_AN6_FULL_data_stripped.db')
process.GlobalTag.globaltag = 'FT53_V21A_AN6_FULL::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 07-Jul-2021 01:36:43.256 CEST
Currently analyzing trigger HLT_Mu12_v16
analyzeSimplePrescales: path HLT_Mu12_v16 [121] prescales L1T,HLT: 400,30
 Trigger path status: WasRun=1 Accept=0 Error =0
Begin processing the 2nd record. Run 194075, Event 14844046, LumiSection 48 at 07-Jul-2021 01:36:43.269 CEST
Currently analyzing trigger HLT_Mu12_v16
analyzeSimplePrescales: path HLT_Mu12_v16 [121] prescales L1T,HLT: 400,30
 Trigger path status: WasRun=1 Accept=0 Error =0
...

Note that the L1 prescale was 400 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 and work assignment

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. You will get an error message. Please copy this error message and paste it into the corresponding section in our assignment form; remember you must sign in and click on the submit button in order to save your work. You can go back to edit the form at any time.

Fortunately, there is a backup solution for us to check on the prescales. Details will not be covered here, but you can find more information in this guide of the CODP.

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/or from the brilcalc tool (not covered here).