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---+++ b Tag Analysis with a CMSSW EDAnalyzer in CMSSW 12.0.X

<!--STARTWORKBOOK-->

Most physics analysis will use this method, as it is the most general and flexible way to access and save event information.  One should start by learning how to create a generic EDAnalyzer and configuration files, as described *[[WorkBookWriteFrameworkModule][here]]* in the workbook.

In summary, to access b-tag information in each event, one can edit your EDAnalyzer code in the following ways.  Add the following header file at the beginning of the code:

<verbatim>
#include "DataFormats/BTauReco/interface/JetTag.h"</verbatim>

Add the following line below the include statements:

<verbatim>
using reco::JetTagCollection;</verbatim>

In the EDAnalyzer class definition section, define a token to identify the b-tagging discriminator you want to study:

<verbatim>
edm::EDGetTokenT<JetTagCollection> bTagToken_;</verbatim>

Finally, we access the b-tag information by adding the following lines in the =EDAnalyzer::analyze()= portion of the code:

<verbatim>
// Get b-tag information
edm::Handle<JetTagCollection> bTagHandle = iEvent.getHandle(bTagToken_);
const reco::JetTagCollection &bTags = *(bTagHandle.product());

// Loop over jets and study b-tag info
for(unsigned int i = 0; i != bTags.size(); i++){
     printf("[bTagInfo] (pt, eta, phi) jet = %7.2f %6.3f %6.3f | 
                b-tag descriminator = %6.3f \n",
                bTags[i].first->pt(), bTags[i].first->eta(),
                bTags[i].first->phi(), bTags[i].second() ) ;
}</verbatim>

Next, we need to add the name of the b-tag input tag to the configuration file.  This is done through the variable =bTags= (as defined in the above portion of the code).  Add the following line to the configuration code:

<verbatim>
bTags = cms.untracked.InputTag('myChosenBTag')</verbatim>

where =myChosenBTag= can be the module name of any b-tag discriminator one wants to analyze. Some examples include =pfCombinedSecondaryVertexV2BJetTags=, =pfJetProbabilityBJetTags=, =softPFMuonBJetTags=, and more.  You can find all of the possible tags in a given data file by exploring the output of the command

<verbatim>
edmDumpEventContent /path/to/mySourceDataFile.root</verbatim>

Next, we need to edit the =Build.xml= file associated with the EDAnalyzer.  Add the line

<verbatim>
<user name=DataFormats/BTauReco></verbatim>

The output of your EDAnalyzer should look like this : %TWISTY{mode="div" showlink="show" hidelink="hide" remember="on" 
                showimgleft="%ICONURLPATH{toggleopen-small}%" 
                hideimgleft="%ICONURLPATH{toggleclose-small}%"}%
<verbatim>
04-Feb-2022 22:26:01 CET  Initiating request to open file file:/afs/cern.ch/cms/Tutorials/workbook_twiki2021/MinBias_pythia8_14TeV_100events.root
04-Feb-2022 22:26:07 CET  Successfully opened file file:/afs/cern.ch/cms/Tutorials/workbook_twiki2021/MinBias_pythia8_14TeV_100events.root
Begin processing the 1st record. Run 1, Event 1, LumiSection 1 on stream 0 at 04-Feb-2022 22:26:22.670 CET

...

Begin processing the 34th record. Run 1, Event 32, LumiSection 1 on stream 0 at 04-Feb-2022 22:26:24.932 CET
analyzing event run: 1 lumi: 1 event: 32
[bTagInfo] (pt, eta, phi) jet =   51.85  0.323  2.104 | b-tag descriminator =  0.130 
[bTagInfo] (pt, eta, phi) jet =   43.04 -0.775 -1.651 | b-tag descriminator =  0.080 
[bTagInfo] (pt, eta, phi) jet =   26.93  0.123 -1.657 | b-tag descriminator =  0.250 
[bTagInfo] (pt, eta, phi) jet =   21.11 -1.077  1.221 | b-tag descriminator =  0.361 

...

Begin processing the 99th record. Run 1, Event 99, LumiSection 1 on stream 0 at 04-Feb-2022 22:26:26.543 CET
analyzing event run: 1 lumi: 1 event: 99
Begin processing the 100th record. Run 1, Event 95, LumiSection 1 on stream 0 at 04-Feb-2022 22:26:26.548 CET
analyzing event run: 1 lumi: 1 event: 95
[bTagInfo] (pt, eta, phi) jet =   23.35 -0.934 -0.067 | b-tag descriminator =  0.362 
[bTagInfo] (pt, eta, phi) jet =   21.11 -0.585 -0.919 | b-tag descriminator =  0.144 </verbatim>

%ENDTWISTY%

<!--STOPWORKBOOK-->

-- Main.ClaytonBennett - 2022-02-21

Topic revision: r2 - 2022-05-16 - DylanSheldonRankin

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