Root Output

G4E output data structure

• The g4e output is made out of so called aligned arrays.

• Each array holds values of a single entity e.g. trk_mom - hold momentums for each track in the event.

• Arrays are grouped by name prefixes, e.g tracks (trk_…), hits (hit_…), generator particles (gen_prt_…), etc.

• All arrays with the same name prefix have the same length. e.g. all trk_… has the same length, the length is defined in trk_count variable (while can be retrieved with size() method - trk_mom.size())

• Arrays reference each other with id. This is close to relational DBs. In recent G4E versions (API v3) there is also *_index which reference directly an index in an array:

• All dimensions - mm. All energies and momentums - GeV

If event hierarchy is described like this:

event 1
    track 1 - electron 10GeV
        hit_11
        hit_12
        hit_13
    track 2 - proton   100GeV
        hit_21
        hit_22

In g4e output will be written like this:

event_id  = 1

trk_count = 2
trk_id    = [1,  2]
trk_pdg   = [11, 2112]
trk_mom   = [10, 100]
trk_...   = [...    ]  - all arrays will be of 2 elements

hit_count     = 5
hit_...       = [...] - all arrays are of 5 elements
hit_id        = [1,  2,   3,    4,  5]
hit_trk_id    = [1,  1,   1,    2,  2] - link to tracks
hit_trk_index = [0,  0,   0,    1,  1] - index in track array
hit_z         = [10, 100, 200, -1, -5]

IDs vs Indexes

(Only works with newer G4E)

There are two different fields hit_trk_id and hit_trk_index:

• hit_trk_id - represents a track id issued by Geant4 (unique inside an event). hit_trk_id-s may not correspond to the order of how they are written in trk_… arrays and not all tracks are written

• hit_trk_index - points to track index in trk_… array. So it is safe to use like this:

  for(int i=0; i < hit_count; i++) {
     // Get parent track momentum
     double momentum = trk_mom[hit_trk_index[i]];
  }
  

Controlling what is written

saveSecondaryLevel

To control how many generation of secondaries (tracks and their hits) to save, there is a configuration:

/rootOutput/saveSecondaryLevel <ancestry-level>

<ancestry-level> sets 0-n levels of ancestry which are saved in root file.

Example:

• -1 - save everything

• 0 - save only primary particles

• 1 - save primaries and their daughters

• 2 - save primaries, daughters and daughters’ daughters

• n - save n generations of secondaries

(primaries - particles that came from a generator/input file)

The default level is 3, which corresponds to:

/rootOutput/saveSecondaryLevel 3

API v3

To check the version of api one can use TTree title (events->GetTitle()). For API v3 it should be

 > events = (TTree*) tfile->Get("events")
 > events->GetTitle()
g4e_api_v3

Next are the tables with all values written to the tree:

Event

Event level information

type	name	description
uint64	event_id	Event number
double	evt_true_q2	Values of q2, x, etc. from generator
double	evt_true_x
double	evt_true_y
double	evt_true_w2
double	evt_true_nu
double	evt_true_t_hat
bool	evt_has_dis_info	If true - generator provided q2 and other event info
double	evt_weight	Generator provided event weight

evt_has_dis_info - Some generators (beagle) provide values like x, q2, etc. Some - don’t this flag indicates that this event has this information. If false any value evt_true_* doesn’t make sense

Hits

type	name	description
uint	hit_count	Hits count
uint[]	hit_id	Geant4 id
uint[]	hit_trk_id	Parent tack Geant4 id
uint[]	hit_trk_index	Index in parent track array
int[]	hit_pdg
string[]	hit_vol_name	Name of the volume
double[]	hit_x
double[]	hit_y
double[]	hit_z
double[]	hit_e_loss
uint[]	hit_type	0-sensitive, 1-vol. enter, 2-vol. leave

hit_type - indicates entity that saved the hit.

(defined in g4e::HitTypes structure) - 0 - hit is saved from one of the sensitive detectors - 1 - hit is saved because it is the first step in a volume - 2 - hit is saved because it is the last step in a volume

Hits entering or exiting a volume are saved only for volumes marked in detector construction.

Tracks

type	name	description
uint	trk_count	Tracks in events
uint[]	trk_id	Geant4 id
uint[]	trk_parent_id	Parent track G4 id
uint[]	trk_parent_index	Parent track index in this array
int[]	trk_pdg	PDG code
uint[]	trk_create_proc	Geant4 code of created process
uint[]	trk_level	0 - generated prt, 1 - daughter, 2 - d
double[]	trk_vtx_x
double[]	trk_vtx_y
double[]	trk_vtx_z
double[]	trk_vtx_dir_x	Unit vector pointing track momentum at vtx
double[]	trk_vtx_dir_y
double[]	trk_vtx_dir_z
double[]	trk_mom	Track momentum

Tracks are dynamic objects in Geant4 (changing on each step). Trk momentum is snapshot when track is created, the momentum direction at this point is stored at trk_vtx_dir_[xyz]

trk_level - Is the level of ancestry from generated particle: 0 - generated particles, 1 - daughters of generated particles, 2 - daughters of daughters, etc.

Generated particles

Particle information from generator or particle gun whichever is used.

type	name	description
uint	gen_prt_count	Generated particles count
uint[]	gen_prt_id	Unique ID (from generator)
uint[]	gen_prt_vtx_id	ID of the origin vertex in vertex array
uint[]	gen_prt_vtx_index	Index of a vertex in vertex array
int[]	gen_prt_pdg	PDG code
uint[]	gen_prt_trk_id	Correspoinding track Geant4 ID
uint[]	gen_prt_trk_index	Corresponding track index in trk… arays
double[]	gen_prt_charge	Particle charge
double[]	gen_prt_dir_x	Unit vector pointing particle direction at origin
double[]	gen_prt_dir_y
double[]	gen_prt_dir_z
double[]	gen_prt_tot_mom	Total momentum
double[]	gen_prt_tot_e	Total energy
double[]	gen_prt_time
double[]	gen_prt_polariz_x
double[]	gen_prt_polariz_y
double[]	gen_prt_polariz_z

Generated vertexes

type	name	description
uint	gen_vtx_count	Generated vertexes count
uint[]	gen_vtx_id	Unique ID
uint[]	gen_vtx_part_count	Particles count
double[]	gen_vtx_x
double[]	gen_vtx_y
double[]	gen_vtx_z
double[]	gen_vtx_time
double[]	gen_vtx_weight

CE Emcal

Information of non empty central electron emcal cells

type	name	description
uint	ce_emcal_count	emcal non embpy modules count
string[]	ce_emcal_name	Volume name of the module
uint[]	ce_emcal_id	Module id (1000*row + col)
double[]	ce_emcal_etot_dep	Total energy deposit
uint[]	ce_emcal_npe
double[]	ce_emcal_adc
double[]	ce_emcal_tdc
double[]	ce_emcal_xcrs	X, Y Z of a cell center
double[]	ce_emcal_ycrs
double[]	ce_emcal_zcrs
uint[]	ce_emcal_row
uint[]	ce_emcal_col
uint[]	ce_emcal_section	0 PWO, 1 Glass