PIDCalib2

A set of software tools for estimating LHCb PID efficiencies.

The package includes several user-callable modules:

• make_eff_hists creates histograms that can be used to estimate the PID efficiency of a user's sample
• ref_calib calculates the LHCb PID efficiency of a user reference sample
• merge_trees merges two ROOT files with compatible TTrees
• pklhisto2root converts Pickled boost-histograms to ROOT histograms

Setup

When working on a computer that where the LHCb software stack is available (LXPLUS, some university cluster, etc.), one can setup PIDCalib2 by running

lb-conda pidcalib bash

After this, the following commands will be available

pidcalib2.make_eff_hists
pidcalib2.ref_calib
pidcalib2.merge_trees
pidcalib2.pklhisto2root

To run make_eff_hists, you will need access to CERN EOS. You don't need to do anything special on LXPLUS. On other machines, you will usually need to obtain a Kerberos ticket by running

kinit [username]@CERN.CH

Installing from PyPI

The PIDCalib2 package is available on PyPI. It can be installed on any computer via pip simply by running (preferably in a virtual environment; see venv)

pip install pidcalib2

Note that this will install the xrootd Python bindings. One also has to install XRootD itself for the bindings to work. See this page for XRootD releases and instructions.

make_eff_hists

This module creates histograms that can be used to estimate the PID efficiency of a user's sample.

Reading all the relevant calibration files can take a long time. When running a configuration for the first time, we recommend using the --max-files 1 option. This will limit PIDCalib2 to reading just a single calibration file. Such a test will reveal any problems with, e.g., missing variables quickly. Keep in mind that you might get a warning about empty bins in the total histogram as you are reading a small subset of the calibration data. For the purposes of a quick test, this warning can be safely ignored.

Options

To get a usage message listing all the options, their descriptions, and default values, type

pidcalib2.make_eff_hists --help

The calibration files to be processed are determined by the sample, magnet, and particle options. All the valid combinations can be listed by running

pidcalib2.make_eff_hists --list configs

Aliases for standard variables are defined to simplify the commands. We recommend users use only the aliases when specifying variables. When you use a name that isn't an alias, a warning message like the following will show up in the log. Use with caution.

'probe_PIDK' is not a known PID variable alias, using raw variable

All aliases can be listed by running

pidcalib2.make_eff_hists --list aliases

A file with alternative binnings can be specified using --binning-file. The file must contain valid JSON specifying bin edges. For example, a two-bin binning for particle Pi, variable P can be defined as

{"Pi": {"P": [10000, 15000, 30000]}}

An arbitrary number of binnings can be defined in a single file.

Complex cut expressions can be created by chaining simpler expressions using &. One can also use standard mathematical symbols, like *, /, +, -, (, ). Whitespace does not matter.

Examples

• Create a single efficiency histogram for a single PID cut

  pidcalib2.make_eff_hists --sample Turbo18 --magnet up --particle Pi --pid-cut "DLLK > 4" --bin-var P --bin-var ETA --bin-var nSPDhits --output-dir pidcalib_output
  

• Create multiple histograms in one run (most of the time is spent reading in data, so specifying multiple cuts is much faster than running make_eff_hists sequentially)

  pidcalib2.make_eff_hists --sample Turbo16 --magnet up --particle Pi --pid-cut "DLLK > 0" --pid-cut "DLLK > 4" --pid-cut "DLLK > 6" --bin-var P --bin-var ETA --bin-var nSPDhits --output-dir pidcalib_output
  

• Create a single efficiency histogram for a complex PID cut

  pidcalib2.make_eff_hists --sample Turbo18 --magnet up --particle Pi --pid-cut "MC15TuneV1_ProbNNp*(1-MC15TuneV1_ProbNNpi)*(1-MC15TuneV1_ProbNNk) < 0.5 & DLLK < 3" --cut "isMuon==0" --bin-var P --bin-var ETA --bin-var nSPDhits --output-dir pidcalib_output
  

ref_calib

This module uses the histograms created by make_eff_hists to assign efficiency to events in a reference sample supplied by the user. Adding of efficiency to the user-supplied file requires PyROOT and is optional.

The module works in two steps:

1. Calculate the efficiency and save it as a TTree in a separate file.
2. Optionally copy the efficiency TTree to the reference file and make it a friend of the user's TTree. The user must request the step by specifying --merge on the command line.

Be aware that --merge will modify your file. Use with caution.

Options

The sample and magnet options are used solely to select the correct PID efficiency histograms. They should therefore mirror the options used when running make_eff_hists.

bin-vars must be a dictionary that relates the binning variables (or aliases) used to make the efficiency histograms with the variables in the reference sample. We assume that the reference sample branch names have the format [ParticleName]_[VariableName]. E.g., D0_K_calcETA, corresponds to a particle named D0_K and variable calcETA. If the user wants to estimate PID efficiency of their sample using 1D binning, where calcETA corresponds to the ETA binning variable alias of the calibration sample, they should specify --bin-vars '{"ETA": "calcETA"}'.

ref-pars must be a dictionary of particles from the reference sample to apply cuts to. The keys represent the particle branch name prefix (D0_K in the previous example), and the values passed are a list containing particle type and PID cut, e.g. '{"D0_K" : ["K", "DLLK > 4"], "D0_Pi" : ["Pi", "DLLK < 4"]}'.

The --merge option will copy the PID efficiency tree to your input file and make the PID efficiency tree a "Friend" of your input tree. Then you can treat your input tree as if it had the PID efficiency branches itself. E.g., input_tree->Draw("PIDCalibEff") should work. ROOT's "Friend" mechanism is an efficient way to add branches from one tree to another. Take a look here if you would like to know more.

Examples

• Evaluate efficiency of a single PID cut and save it to user_ntuple_PID_eff.root without adding it to user_ntuple.root

  python -m pidcalib2.ref_calib --sample Turbo18 --magnet up --ref-file data/user_ntuple.root --output-dir pidcalib_output --bin-vars '{"P": "mom", "ETA": "Eta", "nSPDHits": "nSPDhits"}' --ref-pars '{"Bach": ["K", "DLLK > 4"]}'
  

• Evaluate efficiency of a single PID cut and add it to the reference file user_ntuple.root

  python -m pidcalib2.ref_calib --sample Turbo18 --magnet up --ref-file data/user_ntuple.root --output-dir pidcalib_output --bin-vars '{"P": "mom", "ETA": "Eta", "nSPDHits": "nSPDhits"}' --ref-pars '{"Bach": ["K", "DLLK > 4"]}' --merge
  

• Evaluate efficiency of multiple PID cuts and add them to the reference file

  python -m pidcalib2.ref_calib --sample Turbo18 --magnet up --ref-file data/user_ntuple.root --output-dir pidcalib_output --bin-vars '{"P": "P", "ETA": "ETA", "nSPDHits": "nSPDHits"}' --ref-pars '{"Bach": ["K", "DLLK > 4"], "SPi": ["Pi", "DLLK < 0"]}' --merge
  

Caveats

You might notice that some of the events in you reference sample are assigned PIDCalibEff, PIDCalibErr, or both of -999.

• PIDCalibEff is -999 when for at least one particle
  • The event is out of range
  • The relevant bin in the efficiency histogram has no events whatsoever
• PIDCalibErr is -999 when for at least one particle
  • The event is out of range
  • The relevant bin in the efficiency histogram has no events whatsoever
  • The relevant bin in the efficiency histogram has no events passing PID cuts

Development

1. Clone the repository from GitLab
2. (Optional) Set up a virtual environment

   python3 -m venv .venv
   source .venv/bin/activate
   

3. Install pinned dependencies

   pip install -r requirements-dev.txt
   

4. Install xrootd (possibly manually; see this issue)
5. Run the tests

   pytest
   

6. Run the modules

   python3 -m src.pidcalib2.make_eff_hists -h
   

Tips

Certain tests can be excluded like this

pytest -m "not xrootd"

See available tags in the src/pidcalib2/tests/test_*.py files.