WorkBookHLTTutorial < CMSPublic

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---+ 4.6 HLT Tutorial
%COMPLETE4%
%BR% [[#ReviewStatus][Detailed Review status]]

| *Newsbox* |
| This page has been updated for CMSSW 52X and the latest 2012 HLT studies|

---++ Goals of this page:

This page is intended to familiarize you with HLT ideas, software and utilities. In particular, you will learn:
   * how to run various trigger paths,
   * how to analyze HLT related information.

---++ Contents

   * [[#IntroDuction][Introduction]]
   * [[#TrigPath][Producing events with Triggers]]
      * [[#LookCode][A quick look at the code]]
      * [[#RunTrig][Running Trigger paths]]
   * [[#AnaTrig][Analyzing Trigger/Offline information]]
      * [[#LoneInfo][L1 Information]]
      * [[#HltInfo][HLT Information]]
      * [[#OffInfo][Offline-reconstructed Information]]
      * [[#McInfo][MC truth information]]
      * [[#RateEff][Calculate the rate of a new trigger]]
      * [[#IllusTra][Recipes]]
      * [[#BranchTags][Explanation of branch tags]]

   * [[#ReviewStatus][Review Status]]

#IntroDuction
---++ Introduction

Why a trigger ?
   * Most of events/processes produced at a high-energy hadronic collider are not interesting : an early decision, i.e. online selection, has to be made to avoid running the offline code on millions of uninteresting events

High Level Trigger (HLT) :
   * Takes events accepted by the L1, first level of the CMS Trigger
   * Decides, based on more elaborated algorithms, whether the event should be kept
Therefore, it is a crucial part of the CMS data flow since it's the HLT algorithms and filters which will decide whether an event should be kept for an offline analysis : any offline analysis depends on the outcome of HLT, i.e. on the HLT efficiency.

Important benchmark ideas :
   * Rates (at 2E33) :
      * 13 MHz -&gt; L1 -&gt; 50kHz
      * -&gt; HLT -&gt; 150 Hz
   * Conceive and run approx. 200 triggers, as efficient as possible
   * Reconstruction :
      * Seeded by L1
      * As close as possible to offline reconstruction
      * Regional reconstruction : saving CPU
      * HLT level : typically :
         * L2 : Calorimeter and Muon information
         * L3 : Tracking information

Example of HLT reconstruction : Muons :
   * L2 :
      * Uses L1 seeds : Up to 4 muons provided by Global Muon Trigger (GMT), information : (pT, charge, phi, eta)
      * "StandAlone" muons : using muon segments, charge clusters, then Outside-&gt;In fitting
      * Filters : pT, invariant-mass
      * Filters : Calorimeter-based isolation
   * L3 :
      * Uses L2 seeds
      * "Global regional muon reconstruction" : using tracker information in muon window
      * Filters : pT, invariant-mass, Impact-Parameter, track-quality
      * Filters : Tracker-based isolation

---

Please do visit Trigger, HLT pages :
   * CMS Trigger TDR : [[http://cmsdoc.cern.ch/cms/TDR/TRIGGER-public/trigger.html][Trigger TDR]]
   * Trigger Studies Group page : [[https://twiki.cern.ch/twiki/bin/view/CMS/TriggerStudies][Main page of TSG]]
   * Trigger software guide : [[https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideGlobalHLT][Trigger software guide]]

Subscribe to hypernews :
   * hn-cms-online-selection@cern.ch : general trigger discussions
   * hn-cms-hlt@cern.ch : HLT Software

#TrigPath
---++ Producing event with Triggers

Triggers defined as =path= blocks : sequence of modules and operands :
<verbatim>
path MyTrigger = {doL1Reco & doL1Seeding & ApplyPrescale & doHltReco, HltCondition}
</verbatim> Modules :
   * Reconstruction : =doL1Reco=, =doHltReco=, etc...
   * Prescale : =ApplyPrescale=
   * Filter : =HltCondition=
Operands :
   * the "," or dependency operator, the operand to the right is dependent on the operand on the left (i.e. the right accesses data produced by the left)
   * the "&amp;" or sequencing operator, the operand on the left is executed first, followed by the operand on the right, but they are not dependent on each other

Consequences :
   1 The result of each operand is a boolean : the final outcome of =MyTrigger= is "reject" or "accept"
   1 For a given path, the overall answer is the "AND" of all operands : If ever one of the operands on the left fails, reject AND stop processing : Saving CPU time !

Recommended reading : [[https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideEDMPathsAndTriggerBits][PathTriggerBits]]

The HLT configuration in CMS is stored in a dedicated database system, [[CMS.EvfConfDBDesign][ConfDB]]. Use the dedicated [[CMS.EvfConfDBGUI][GUI]] to create, manipulate and store trigger path configurations. Use the [[http://www.cern.ch/confdb/browser/][ConfDB web browser]] to browse the content of the configuration database and inspect available HLT menus. The command-line tool [[CMS.EdmConfigFromDB][edmConfigFromDB]] allows you to retrieve (complete or partial) configurations as either ascii or python configuration files to be fed to =cmsRun=.

#LookCode
---+++ A quick look at the code

Please visit :
   * Trigger software guide : [[https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideTriggerStudiesHowTo][TriggerStudySW]]
   * L1-HLT software guide : [[https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideL1Extra][L1Extra]]

HLT code in [[https://github.com/cms-sw/cmssw/tree/CMSSW_5_3_X/HLTrigger][HLTrigger]]

#RunTrig
---+++ Running Trigger paths

Follow instructions from [[https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideGlobalHLT][HLTtable]]

For input files : go on the Data Aggregation System page [[https://cmsweb.cern.ch/das/][DAS]]

#AnaTrig
---++ Analyzing Trigger/Offline information

Motivation : Get in one place, on event-by-event basis :
   * L1-, HLT-related information
   * Offline reconstructed information
   * HLT information without filters: "Open HLT" mode
Enables to :
   1 Study Trigger efficiencies, as function of offline reconstructed quantities...
   1 Get Trigger rejections, overlaps, rates...
   1 ...for L1, HLT conditions

Code :
   * Package : =HLTrigger/HLTanalyzers= : [[https://github.com/cms-sw/cmssw/tree/CMSSW_5_3_X/HLTrigger/HLTanalyzers][HLTanalyzers]]
   * Driving code : =HLTAnalyzer .h .cc= : an EDAnalyzer
   * Configuration file to run : =HLTrigger/HLTanalyzers/test/HLTAnalysis.cfg=

More details in [[https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideHLTAnalyzer][HLTAnaManual]]

#LoneInfo
---+++ Getting the L1 information
Motivation : Have the information of HLT seeds at disposal

Using =L1Extra= objects, from MCTruth or from the L1 Emulator : In the =HLTAnalysis.cfg= file :
<verbatim>
module HLTAnalyzer = {
   ...   
   string l1extramc = l1extraParticles
   ...
}
</verbatim>

| *Physics objects* | *Variables stored* | *L1Extra Class* | *Instances* |
| Muons | E, pT, phi, eta, isolation, mip | <nop>L1MuonParticle |   |
| EM particles | E, ET, phi, eta | <nop>L1EmParticle |  &#8220;Isolated&#8221; and &#8220;NonIsolated&#8221; |
| Jets | E, ET, phi, eta | <nop>L1JetParticle |  "Forward" and "Central" |
| Taus | E, ET, phi, eta | <nop>L1JetParticle | "Tau"  |
| MET | ET, ET(tot), ET(had), phi | <nop>L1EtMissParticle |   |

Branches of variables created per instance.

Code in : =HLTInfo .h .cc=

#HltInfo
---+++ Getting the HLT information

How do I get information about Trigger Results ?
   * From the =TriggerResults= class : Associate Trigger Path to Decision. HLTAnalyzer dynamically creates as many branches as Triggers present, and fill them with corresponding Trigger decision. Trigger branches pop up in form of "TRIGG_".

Code in : =HLTInfo .h .cc=

If you want to get the names of the paths (e.g. for accessing them by
path name rather than by bit number), see the example code in [[https://github.com/cms-sw/cmssw/blob/CMSSW_5_3_X/HLTrigger/HLTanalyzers/src/HLTrigReport.cc][HLTrigger/HLTanalyzers/src/HLTrigReport.cc]].

See also the hypernews discussion [[https://hypernews.cern.ch/HyperNews/CMS/get/csa07/58/2/1/1/1.html][here]].


#OffInfo
---+++ Getting the Offline-reconstructed and other information

Specify in =HLTAnalysis.cfg= the instances of reconstructed objects that you want :
<verbatim>
module HLTAnalyzer = 
    ...
    string muon = "muons"
    string Electron = "pixelMatchGsfElectrons"
    string Photon = "correctedPhotons"
    string recjets = "iterativeCone5CMS.CaloJets"
    string genjets = "iterativeCone5GenJets"
    string recmet = met
    string genmet = genMet
    string calotowers = towerMaker
    ...
}
</verbatim>

| *Physics objects* | *Variables stored* | *Instances* |
| Muon |  E, ET, pT, eta, phi | muons |
| Electron | E, ET, pT, eta, phi | pixelMatchGsfElectrons |
| Gamma | E, ET, pT, eta, phi | correctedPhotons |
| Jet | E, ET, pT, eta, phi |  iterativeCone5CMS.CaloJets, iterativeCone5GenJets |
| MET |  pT, phi, ET(sum) |  met, genMet |
| Calo Towers | E, ET, E(em), E(had), E(out), eta, phi | towerMaker |
| MC truth | Id, Vtx(X,Y,Z), pT |   |

Code in : =HLTEgamma=, =HLTMuon=, =HLTJets= (deals with MET as well)

   * Getting also information about the MC truth information about generated particles : pT, Identity, Vertex... Code in =HLTMCtruth=

Offline collections can be accessed when running simultaneously and RAW+RECO samples. This can be achieved using crab with use_parent=1 option. Running on a RECO dataset will then allow to access its parent dataset, namely the corresponding RAW dataset.

#McInfo
---+++ Getting the MC truth information

Motivation : Have the generator level information at disposal
| *Object* | *Variables stored* | *Instances* |
| Generated particle | PDG-Identity, particle status, [x,y,z]-component of primary vertex  | genParticles  |
| Generated particle | pT, phi, eta | genParticles  |
|   | Event pT-hat, i.e. scale | genEventScale |


#RateEff
---++++ Calculate the rate of a new trigger:

Please have a look at:
[[https://twiki.cern.ch/twiki/bin/view/CMS/NewOpenHLT][How to run OpenHLT]]

You may also want to take a look at the [[https://twiki.cern.ch/twiki/bin/view/CMS/StrategyforTriggerEvolutionAndMonitoring][recipes from the STEAM group]] 

#IllusTra
---+++ Recipes for producing ntuples

These versions of the analyzer have the !OpenHLT capability included.

For additional tags needed to run on real data consistent with online releases, consult [[https://twiki.cern.ch/twiki/bin/view/CMS/HowToInstallONLINErelease][this page]].

For the correct GlobalTag to use in a given release consult [[https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideFrontierConditions][this page]].

#ReviewStatus
---++ Review status

<!-- Add your review status in this table structure with 2 columns delineated by three vertical bars. Add comments for editing, reviewing, etc -->

| *Reviewer/Editor and Date* | *Comments* |
| <nop>Pedrame Bargassa - 1 Dec 2007 | Author |
| Main.XuanChen - 31 Jul 2014 | changed links from cvs to github, replaced dbs by das |

<!-- Here the "responsible" is the contact person for maintena!!!Show my HLTtable.cfg!!!nce of the page - often initially the page author --> <!-- The "review" person is the most recent person to carry out a full review of the page  - on this field please include the date in the format shown -->
%RESPONSIBLE% <nop>Pedrame Bargassa %BR% 
%REVIEW% Main.ChristosLeonidopoulos - 22 Feb 2008

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
cfg	HLTtable.cfg	r3 r2 r1	manage	5.6 K	2007-04-18 - 17:18	UnknownUser	File to run CMSSW_1_3_0 trigger table on 1_2_0 MC
jpg	hltana_root.jpg	r2 r1	manage	272.5 K	2007-10-26 - 18:30	UnknownUser

Topic revision: r201 - 2014-10-29 - unknown

CMSPublic

ESSENTIALS

Preface
1. Accounts & Registration
2. Basics of Offline
3. Getting Started with Data Analysis
- 3.1 Overview
- 3.2 Which release
- 3.3 Exploring Data
  - -3.3.2 EDM Tools
- 3.4 Fireworks Visualization
  - -3.4.7 Archive
- 3.5 FW Lite
  - -3.5.4 FW Lite in Python
4. CMSSW in Data Analysis
- 4.1 Introduction
  - -4.1.4 Config Editor
- 4.2 PAT
  - -4.2.6 PAT Glossary
- 4.3 Candidate Utilities
- 4.4 Gen Evts in AOD
- 4.5 MC Truth Matching
- 4.6 Access Trigger Info
- 4.7 MiniAOD Data-Tier
- 4.8 NanoAOD Analysis Documentation
5. Distributed Data Analysis
Appendices

ADVANCED TOPICS

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