TauFakeFactors

FakeFactor framework for the estimation of jets misidentified taus with pyROOT.

Setup

The environment can be set up with conda via

conda env create --file environment.yaml

Event preselection

This framework is designed for n-tuples produced with CROWN as input.

All information for the preselection step is defined in a configuration file in the configs/ folder. The preselection config has the following parameters:

• The expected input folder structure is NTUPLE_PATH/ERA/SAMPLE_TAG/CHANNEL/*.root

  parameter	type	description
  ntuple_path	string	absolute path to the folder with the n-tuples on the dcache, a remote path is expected like "root://cmsxrootd-kit.gridka.de//store/user/USER/..."
  era	string	data taking era ("2018, "2017", "2016preVFP", "2016postVFP")
  channel	string	tau pair decay channels ("et", "mt", "tt")
  tree	string	name of the tree in the n-tuple files ("ntuple" in CROWN)
  analysis	string	analysis name, needed to get the output features which are saved/needed for the later steps e.g. "smhtt_ul"

• The output folder structure is OUTPUT_PATH/preselection/ERA/CHANNEL/*.root

  parameter	type	description
  output_path	string	absolute path where the files with the preselected events will be stored, a local path is expected like "/ceph/USER/..."

• In processes all the processes are defined that should be preprocessed.
  The names are also used for the output file naming after the processing.
  Each process needs two specifications:

  parameter	type	description
  tau_gen_modes	list	split of the events corresponding to the origin of the hadronic tau
  samples	list	list of all sample tags corresponding to the specific process

  The tau_gen_modes have following modes:

  parameter	type	description
  T	string	genuine tau
  J	string	jet misidentified as a tau
  L	string	lepton misidentified as a tau
  all	string	if no split should be performed

• In event_selection, parameter for all selections that should be applied are defined.
  This is basically a dictionary of cuts where the key is the name of a cut and the value is the cut itself as a string e.g. had_tau_pt: "pt_2 > 30". The name of a cut is not really important, it is only used as an output information in the terminal. A cut can only use variables which are in the ntuples.

• In mc_weights all weights that should be applied for simulated samples are defined.
  There are two types of weights.

  1. Like for event_selection a weight can directly be specified and is then applied to all samples the same way e.g. lep_id: "id_wgt_mu_1"
  2. Some weights are either sample specific or need additional information. Currently implemented options are:

     parameter	type	description
     generator	string	"" if a normal generator weight should be applied to all samples, if "stitching" for DY+jets and W+jets a special stitching weights is applied
     lumi	string	luminosity scaling, this depends on the era and uses the era parameter of the config to get the correct weight, so basically it's not relevant what is in the string
     Z_pt_reweight	string	reweighting of the Z boson pt, the weight in the ntuple is used and only applied to DY+jets
     Top_pt_reweight	string	reweighting of the top quark pt, the weight in the ntuple is used and only applied to ttbar

• In emb_weights all weights that should be applied for embedded samples are defined.
  Like for event_selection a weight can directly be specified and is then applied to all samples the same way e.g. single_trigger: "trg_wgt_single_mu24ormu27"

Scale factors for b-tagging and tau ID vs jet are applied on the fly during the FF calculation step.

To run the preselection step, execute the python script and specify the config file (relative path possible):

python preselection.py --config-file PATH/CONFIG.yaml

Fake Factor calculation

In this step the fake factors are calculated. This should be run after the preselection step.

All information for the FF calculation step is defined in a configuration file in the configs/ folder.
The FF calculation config has the following parameters:

• The expected input folder structure is FILE_PATH/preselection/ERA/CHANNEL/*.root

  parameter	type	description
  file_path	string	absolute path to the folder with the preselected files
  era	string	data taking era ("2018, "2017", "2016preVFP", "2016postVFP")
  channel	string	tau pair decay channels ("et", "mt", "tt")
  tree	string	name of the tree in the preselected files (same as in preselection e.g. "ntuple")

• The output folder structure is workdir/WORKDIR_NAME/ERA/fake_factors/CHANNEL/outputfiles

  parameter	type	description
  workdir_name	string	relative path where the output files will be stored

• General options for the calculation:

  parameter	type	description
  use_embedding	bool	True if embedded sample should be used, False if only MC sample should be used

• In target_processes the processes for which FFs should be calculated (normally for QCD, Wjets, ttbar) are defined.
  Each target process needs some specifications:

  parameter	type	description
  split_categories	dict	names of variables for the fake factor measurement in different phase space regions the FF measurement can be split based on variables in 1D or 2D (1 or 2 variables) each category/variable has a list of orthogonal cuts (e.g. "njets" with "==1", ">=2") implemented split variables are "njets", "nbtag" or "deltaR_ditaupair" at least one inclusive category needs to be specified
  split_categories_binedges	dict	bin edge values for each split_categories variable number of bin edges should always be N(variable cuts)+1
  SRlike_cuts	dict	event selections for the signal-like region of the target process
  ARlike_cuts	dict	event selections for the application-like region of the target process
  SR_cuts	dict	event selections for the signal region (normally only needed for ttbar)
  AR_cuts	dict	event selections for the application region (normally only needed for ttbar)
  var_dependence	string	variable the FF measurement should depend on (normally pt of the hadronic tau e.g. "pt_2")
  var_bins	list	bin edges for the variable specified in var_dependence

  Event selections can be defined the same way as in the preselection step event_selection. Only the tau vs jet ID cut is special because the name should always be had_tau_id_vs_jet (or had_tau_id_vs_jet_* in tt channel), this is needed to read out the working points from the cut string and apply the correct tau vs jet ID weights.

• In process_fractions specifications for the calculation of the process fractions are defined.

  parameter	type	description
  processes	list	sample names (from the preprocessing step) of the processes for which the fractions should be stored in the correctionlib json, the sum of fractions of the specified samples is 1.
  split_categories	dict	see target_processes (only in 1D)
  AR_cuts	list	see target_processes
  SR_cuts	list	see target_processes, (optional) not needed for the fraction calculation

To run the FF calculation step, execute the python script and specify the config file (relative path possible):

python ff_calculation.py --config-file PATH/CONFIG.yaml

Fake Factor corrections

In this step the corrections for the fake factors are calculated. This should be run after the FF calculation step.

Currently two different correction types are implemented:

1. non closure correction depending on a specific variable
2. DR to SR interpolation correction depending on a specific variable

All information for the FF correction calculation step is defined in a configuration file in the configs/ folder. Additional information is loaded from the used config in the previous FF calculation step (this is done automatically).
The FF correction config has the following parameters:

• The expected input folder structure is workdir/WORKDIR_NAME/ERA/fake_factors/CHANNEL/*

  parameter	type	description
  workdir_name	string	the name of the work directory for which the corrections should be calculated (normally the same as in the FF calculation step)
  era	string	data taking era ("2018, "2017", "2016preVFP", "2016postVFP")
  channel	string	tau pair decay channels ("et", "mt", "tt")

• In target_processes the processes for which FF corrections should be calculated (normally for QCD, Wjets, ttbar) are defined.
  Each target process needs some specifications:

  parameter	type	description
  non_closure	dict	one or two non closure corrections can be specified indicated by the variable the correction should be calculated for (e.g. leading_lep_pt), if more than one correction is specified, leading_lep_pt should come first (due to code specifics) because the second corrections is calculated with the first already applied
  DR_SR	dict	this correction should be specified only once per process in target_processes

  Each correction has following specifications:

  parameter	type	description
  var_dependence	string	variable the FF correction measurement should depend on (e.g. "pt_1" for "leading_lep_pt")
  var_bins	list	bin edges for the variable specified in var_dependence
  SRlike_cuts	dict	event selections for the signal-like region of the target process that should be replaced compared to the selection used in the previous FF calculation step
  ARlike_cuts	dict	event selections for the application-like region of the target process that should be replaced compared to the selection used in the previous FF calculation step
  AR_SR_cuts	dict	event selections for a switch from the determination region to the signal/application region, this is only relevant for DR_SR corrections
  non_closure	dict	this is only relevant for DR_SR corrections, since for this corrections additional fake factors are calculated it's possible to calculated and apply non closure corrections to these fake factors before calculating the actual DR to SR correction

To run the FF correction step, execute the python script and specify the config file (relative path possible):

python ff_corrections.py --config-file PATH/CONFIG.yaml 

An optional parameter is --only-main-corrections. By using this parameter the precalculation step for the DR to SR corrections is skipped. This is helpful is the precalculations step is already done.

Hints

• check out configs/general_definitions.py, this file has many relevant definition for preselection, plotting or correctionlib output information
• check ntuple_path and output_path (preselection) or file_path and workdir_name (fake factors, corrections) in the used config files to avoid wrong inputs or outputs