Ionization at a point of the TPC sensitive volume. More...

#include "SimChannel.h"

Public Types
typedef int	TrackID_t
	Type of track ID (the value comes from Geant4) More...

Public Member Functions
	IDE ()
	Default constructor (sets "bogus" values) More...

	IDE (IDE const &ide, int offset)
	Constructor: copies an IDE, and applies the specified offset to track ID. More...

	IDE (TrackID_t tid, float nel, float e, float xpos, float ypos, float zpos, TrackID_t gid=util::kBogusI)
	Constructor: sets all data members. More...

Public Attributes
TrackID_t	trackID
	Geant4 supplied track ID. More...

float	numElectrons
	number of electrons at the readout for this track ID and time More...

float	energy
	energy deposited by ionization by this track ID and time [MeV] More...

float	x
	x position of ionization [cm] More...

float	y
	y position of ionization [cm] More...

float	z
	z position of ionization [cm] More...

TrackID_t	origTrackID
	Geant4 supplied track ID (remains true trackID even for shower secondaries/tertiaries etc) More...

Detailed Description

Ionization at a point of the TPC sensitive volume.

This class stores information about the ionization from the simulation of a small step of a track through the TPC active volume.

Ionization information consists of both energy and number of electrons. It is of paramount importance to understand what each field stores:

position: where the ionization occurred (from Geant4 simulation)
track ID: Geant4 track ID of the ionizing particle
energy: amount of energy released by ionization (from Geant4 simulation)
electrons: amount of electrons reaching the readout channel

Note the different definition of the electrons respect to the rest: it describes the electrons at the anode after the drifting occurred, while all the other quantities can be related to the moment the ionization happened.

The number of electrons typically includes inefficiencies and physics effects that reduce and spread the electrons. In the simulation, this yields a fractional number of electrons.

Each IDE is also typically associated with a time (TDC) count, that is the time at which the ionized electrons reached the readout channel, in electronic ticks, as opposed as the time when ionization occurred. The latter is not stored.

At the time of writing this documentation (LArSoft 6.4.0), IDEs are computed in larg4::LArVoxelReadout. The energy and track ID come directly from Geant4 simulation. The position is the mid point of the Geant4 step that produced ionization. The electrons are

converted from that same energy (using a fundamental conversion factor stored in larcoreobj/SimpleTypesAndConstants/PhysicalConstants.h)
applied recombination effect by larg4::IonizationAndScintillation::Reset()
applied attenuation and diffusion in larg4::LArVoxelReadout::DriftIonizationElectrons()

The latter also assembles the sim::IDE objects to be stored into sim::SimChannel.

Definition at line 85 of file SimChannel.h.

Member Typedef Documentation

typedef int sim::IDE::TrackID_t

Type of track ID (the value comes from Geant4)

Definition at line 88 of file SimChannel.h.

Constructor & Destructor Documentation

sim::IDE::IDE ( )

Default constructor (sets "bogus" values)

Definition at line 23 of file SimChannel.cxx.

     : trackID(util::kBogusI)
     , numElectrons(util::kBogusD)
     , energy(util::kBogusD)
     , x(util::kBogusD)
     , y(util::kBogusD)
     , z(util::kBogusD)
     , origTrackID(util::kBogusI)
   {}

sim::IDE::IDE	(	sim::IDE const &	ide,
		int	offset
	)

Constructor: copies an IDE, and applies the specified offset to track ID.

Definition at line 34 of file SimChannel.cxx.

References origTrackID, and trackID.

                                         : IDE(ide)
   {
 
     trackID = trackID >= 0 ? trackID + offset : trackID - offset;
     origTrackID = origTrackID >= 0 ? origTrackID + offset : origTrackID - offset;
   }