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The Physics
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We will be studying the reconstruction of the Higgs decaying to a pair of b quarks.
The dijet invariant mass (m(jj)) is the key observable.
The code we will be using is not intended for a full-fledged analysis.
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Setting up the ATLAS Environment
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A software release (e.g. AnalysisBase) is necessary to analyze ATLAS data.
You will learn much more about the details of an ATLAS release on Tuesday!
The UChicago Analysis facility will serve for all ATLAS work throughout this tutorial.
Docker serves as a “portal” for all ATLAS work, that is to say we can do the same work as in the facility. It can be thought of a “virtual machine”.
You will learn much more about Docker on Wednesday!
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Obtaining The Test Files
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An AOD and DAOD file are the same thing, but a DAOD has “what you want”.
The input file container name gives you a lot of nice information about how the file was produced.
You can inspect a file using native ROOT, and looking at CollectionTree or using the checkxAOD.py executable within the release.
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Running the Basic Analysis
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The directory where your source code lives and where you build the code are two separate directories.
When in doubt, you can always remove the entire contents of your build directory.
Information within the (D)AOD is organized in what is called the EDM.
Compiling/linking ATLAS code “by hand” is super long. Thank goodness we have CMake.
Judiciously choose when to parameterize your ignorance. It is a powerful approach, but remember you are a smart human, not a robot.
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Building With CMake
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CMake is easier … when it works.
You will learn all the ins and outs of CMake on Tuesday. For now, it can function as little more than a tool to circumvent the long g++ commands.
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Your First Plot
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The m(jj) spectrum is peaked near the Higgs mass of ~125 GeV.
There seems to be a long tail on the high mass side.
Important Tool 1 - We examine data via a “projection” onto histograms (TH1 in ROOT).
Important Tool 2 - Much of what we study in analysis is the behavior of four-momenta (TLorentzVector in ROOT).
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Extra Exercises
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Writing good code requires care, especially when it gets complicated.
Using configuration files allows us to compile our code less frequently.
The search for VH(bb) is hard!
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