add-tupletools.md

layout	title	subtitle	minutes
page	First steps in LHCb	TupleTools and branches	15

Learning Objectives {.objectives}

• Add extra TupleTools to the default DecayTreeTuple
• Configure the extra TupleTools
• Use branches
• Find useful TupleTools
• Learn how to use LoKi functors in a DecayTreeTuple

Usually, the default information stored by DecayTreeTuple as shown in our minimal DaVinci job is not enough for physics analysis. Fortunately, most of the information we need can be added by adding C++ tools (known as TupleTools) to dtt; there is an extensive library of these, some of which will be briefly discussed during the lesson.

Default DecayTreeTuple tools {.callout}

The default tools added in DecayTreeTuple are:

• TupleToolKinematic, which fills the kinematic information of the decay.
• TupleToolPid, which stores DLL and PID information of the particle.
• TupleToolANNPID, which stores the new NeuralNet-based PID information of the particle.
• TupleToolGeometry, which stores the geometrical variables (IP, vertex position, etc) of the particle.
• TupleToolEventInfo, which stores general information (event number, run number, GPS time, etc) of the event.

In order to add TupleTools to dtt, we have to use the addTupleTool method of DecayTreeTuple (only available when we have from DecayTreeTuple.Configuration import * in our script). This method instantiates the tool, adds it to the list of tools to execute and returns it. For example, if we want to fill the tracking information of our particles, we can add the TupleToolTrackInfo tool in the following way:

track_tool = dtt.addTupleTool('TupleToolTrackInfo')

Some tools can be configured. For example, if we wanted further information from the tracks, such as the number of degrees of freedom of the track fit, we would have to turn on the verbose mode of the tool:

track_tool.Verbose = True

If we don't need to configure the tool or we want to use the defaults, there's no need for storing the returned tool in a variable. For example, if we wanted the information of the PV associated to our particle, we could just add the TupleToolPrimaries with no further configuration:

dtt.addTupleTool('TupleToolPrimaries')

The way the DecayTreeTuple.Decay is written in in our minimal DaVinci job,

dtt.Decay = '[D*(2010)+ -> (D0 -> K- pi+) pi+]CC'

means that the configured TupleTools will only run on the head of the decay chain, that is, the D*(2010)+. In order to select the particles for which we want the information stored, we need to mark them with a ^ symbol in the decay descriptor. For example, if we want to fill the information of the D0 and its children, as well as the soft pi+, we would modify the above line to look like this:

dtt.Decay = '[D*(2010)+ -> ^(D0 -> ^K- ^pi+) ^pi+]CC'

This will run all the configured TupleTools on the marked particles, with the caveat that some tools are only run on certain types of particles (eg, tracking tools on particles that have an associated track). This configuration is not optimal, since there may be tools which we only want to run on the D's and some only on the children. Enter Branches, which allow us to specify which tools get applied to which particle in the decay (in addition to the TupleTools configured at the top level).

Branches let you define custom namespaces in your ntuple by means of a dict. Its keys define the name of each branch (and, as a consequence, the prefix of the corresponding leaves in the ntuple), while the corresponding values are decay descriptors that specify which particles you want to include in the branch.

dtt.addBranches({'Dstar' : '[D*(2010)+ -> (D0 -> K- pi+) pi+]CC',
                 'D0'    : '[D*(2010)+ -> ^(D0 -> K- pi+) pi+]CC',
                 'Kminus': '[D*(2010)+ -> (D0 -> ^K- pi+) pi+]CC',
                 'piplus': '[D*(2010)+ -> (D0 -> K- ^pi+) pi+]CC',
                 'pisoft': '[D*(2010)+ -> (D0 -> K- pi+) ^pi+]CC'})

Note that in order to use branches, we have to make sure that all particles we want to use are marked in the main decay descriptor (dtt.Decay). DaVinci will ignore branches for particles that have not been marked in dtt.Decay!

Once the branches have been configured, they can be accessed as dtt.PARTICLENAMEand TupleTools can be added as discussed before. For example, if we want to store the proper time information of the D0, we would do

dtt.D0.addTupleTool('TupleToolPropertime')

Do I really have to type my decay descriptor that many times? {.callout}

No! You can use the (new) dtt.setDescriptorTemplate() method to set up your decay descriptor and branches in just one line! Well, nearly: because this is a new feature it is not available in most released versions of DaVinci, but this snippet will add it to an older version. With that out of the way, you can simply use

dtt.setDescriptorTemplate('${Dstar}[D*(2010)+ -> ${D0}(D0 -> ${Kminus}K- ${piplus}pi+) ${pisoft}pi+]CC')

This will set up both dtt.Decay and Branches for you.

The usage of Branches is very important (and strongly encouraged) to keep the size of your ntuples small, since it prevents us from storing unneeded information (for example trigger information, which will be discussed at a later lesson).

Where to find TupleTools {.callout}

One of the most difficult things is to know which tool we need to add to our DecayTreeTuple in order to get the information we want. For this, it is necessary to know where to find TupleTools and their code. TupleTools are spread in 9 packages under Analysis/Phys (see the head of svn here), all starting with the prefix DecayTreeTuple, according to the type of information they fill in our ntuple:

• DecayTreeTuple for the more general tools.
• DecayTreeTupleANNPID for the NeuralNet-based PID tools.
• DecayTreeTupleDalitz for Dalitz analysis.
• DecayTreeTupleJets for obtaining information on jets.
• DecayTreeTupleMC gives us access to MC-level information.
• DecayTreeTupleMuonCalib for muon calibration tools.
• DecayTreeTupleReco for reconstruction-level information, such as TupleToolTrackInfo.
• DecayTreeTupleTracking for more detailed tools regarding tracking.
• DecayTreeTupleTrigger for accessing to the trigger information of the candidates.

The TupleTools are placed in the src folder within each package and it's usually easy to get what they do just by looking at their name. However, the best way to know what a tool does is check its documentation, either by opening its .h file or be searching for it in the latest doxygen. Most tools are very well documented and will also inform you of their configuration options. As an example, to get the information on the TupleToolTrackInfo we used before we could either check its source code or its web documentation. In case we need more information or need to know exactly what the code does, the fill method is the one we need to look at.

As a shortcut, the list of tupletools can also be found in doxygen at the top of the pages for the IParticleTupleTool and the IEventTupleTool interfaces (depending on whether they fill information about specific particles or the event in general).

The updated options can be found here.

Test your ntuple {.challenge}

Run the options in the same way as in the minimal DaVinci job lesson. You will obtain a DVntuple.root file, which we can open and inspect with ROOT's TBrowser:

$ root DVntuple.root
root [0]
Attaching file DVntuple.root as _file0...
root [1] TBrowser *b = new TBrowser()
root [2]

Try to locate the branches we have added, which are placed in the TupleDstToD0pi_D0ToKpi/DecayTree, and plot some distributions by double-clicking the leaves.

Picking up with the LoKi functors lesson, let's store some specific bits of information discussed there in our ntuple. To add LoKi-based leaves to the tree, we need to use the LoKi::Hybrid::TupleTool, which is configured with 3 arguments:

• Its name, specified in the addTupleTool call after a /. This is very useful (and recommended) if we want to have different LoKi::Hybrid::TupleTool for each of our branches. For instance, we may want to add different information for the D*, the D0 and the soft $\pi$:

  dstar_hybrid = dtt.Dstar.addTupleTool('LoKi::Hybrid::TupleTool/LoKi_Dstar')
  d0_hybrid = dtt.D0.addTupleTool('LoKi::Hybrid::TupleTool/LoKi_D0')
  pisoft_hybrid = dtt.pisoft.addTupleTool('LoKi::Hybrid::TupleTool/LoKi_PiSoft')

• The Preambulo property, which lets us perform preprocessing of the LoKi functors to simplify the code that is used to fill the leaves, for example creating combinations of LoKi functors or performing mathematical operations:

  preamble = [
      'DZ = VFASPF(VZ) - BPV(VZ)',
      'TRACK_MAX_PT = MAXTREE(ISBASIC & HASTRACK, PT, -1)'
  ]
  dstar_hybrid.Preambulo = preamble
  d0_hybrid.Preambulo = preamble

• The Variables property, consisting of a dict of (variable name, LoKi functor) pairs. In here, LoKi functors can be used, as well as any variable we may have defined in the Preambulo:

  dstar_hybrid.Variables = {
      'mass': 'M',
      'mass_D0': 'CHILD(M, 1)',
      'pt': 'PT',
      'dz': 'DZ',
      'dira': 'BPVDIRA',
      'max_pt': 'MAXTREE(ISBASIC & HASTRACK, PT, -1)',
      'max_pt_preambulo': 'TRACK_MAX_PT',
      'sum_pt_pions': 'SUMTREE(211 == ABSID, PT)',
      'n_highpt_tracks': 'NINTREE(ISBASIC & HASTRACK & (PT > 1500*MeV))'
  }
  d0_hybrid.Variables = {
      'mass': 'M',
      'pt': 'PT',
      'dira': 'BPVDIRA',
      'vtx_chi2': 'VFASPF(VCHI2)',
      'dz': 'DZ'
  }
  pisoft_hybrid.Variables = {
      'p': 'P',
      'pt': 'PT'
  }

In the code snippets specified above (available here), you can see that the NINTREE functor counts the number of particles that pass the specified criteria. While this is not very useful for ntuple-building (we can always do it offline), it's a very powerful functor to use when building decay selections.

Getting more practice {.challenge}

In the LoKi::Hybrid::TupleToolwe've used some functors that have not been described previously. Find out what they do in the doxygen. To check SUMTREE and CHILD, run the code above and check that the Dstar_max_pt and Dstar_max_pt_preambulo and the Dstar_mass_D0 and D0_mass branches have exactly the same values.