PID in O2

Here are described the PID working principles in O2 as well as how to get PID information (expected values, separation et cetera) in your task.

Introduction

PID is handled in O2 via the reimplementation of base classes found in Analysis/DataModel/include/PIDBase/.

The parametrization of the expected detector response (e.g. signal, resolution, separation) is handled in the classes derived from Analysis/DataModel/include/PIDBase/ParamBase.h. Examples of these derived classes can be found in Analysis/DataModel/include/PID/BetheBloch.h, in this example the base class is specialized to implement BetheBloch parametrization for the expected signals.

The parametrization objects are used in the classed derived from Analysis/DataModel/include/PIDBase/DetectorResponse.h for each detector/device. These are the interface between the user and the parametrization and give expected detector response (signal, resolution, separation) for each particle species index (as defined in DataFormats/Reconstruction/include/ReconstructionDataFormats/PID.h). Examples of these derived classes can be found in Analysis/DataModel/include/PID/PIDTOF.h, in this example the base class is specialized to implement the TOF detector response. In order to ensure the versatility of the PID framework objects derived from DetectorResponse.h are not expected to change significantly as the main physical meaning of the response is contained in the parametrization objects. The parametrization can be loaded from a local file or from CCDB depending on the needs (e.g. different periods, different parametrization et cetera).

The interface between the detector and the Analysis Framework is fully enclosed in Analysis/DataModel/include/PID/PIDResponse.h. Here are defined the tables for the PID.

The filling of the PID tables is delegated to dedicated tasks in Analysis/Tasks/ Examples of these tasks can be found in Analysis/Tasks/pidTOF.cxx and Analysis/Tasks/pidTPC.cxx for TOF and TPC tables respectively.

Usage in tasks

Tables for PID values in O2 are defined in Analysis/DataModel/include/PID/PIDResponse.h. You can include it in your task with:

#include "PID/PIDResponse.h"

In the process functions you can join the table to add the PID information to the track.

For the TOF PID as:

  void process(aod::Collision const& collision, soa::Join<aod::Tracks, aod::TracksExtra, aod::pidRespTOF> const& tracks)
 

For the TPC PID as:

  void process(aod::Collision const& collision, soa::Join<aod::Tracks, aod::TracksExtra, aod::pidRespTPC> const& tracks)
 

For both TPC and TOF PID as:

  void process(aod::Collision const& collision, soa::Join<aod::Tracks, aod::TracksExtra, aod::pidRespTPC, aod::pidRespTOF> const& tracks)
 

Task for PID spectra (and to fill PID tables!)

O2 tasks dedicated to the filling of the PID tables are called with

TOF PID Table
```
  o2-analysis-pid-tof
```
TPC PID Table
```
  o2-analysis-pid-tpc
```

Example of tasks that use the PID tables (and how to run them)

TOF PID task Analysis/Tasks/pidTOF.cxx You can run the TOF spectra task with:

  o2-analysis-spectra-tof --aod-file AO2D.root -b | o2-analysis-pid-tof -b
 

TPC PID task Analysis/Tasks/pidTPC.cxx You can run the TPC spectra task with:

  o2-analysis-spectra-tpc --aod-file AO2D.root -b | o2-analysis-pid-tpc -b
 