History: BigBite Tracking and Drift Chamber Global Variables

This document describes the variables that are stored as Hall A Global Variables and are available for output to the Root Tree. They can also be examined in the analyzer using the gHaVars->Print() and gHaVars->PrintFull() commands. The subset of Global Variables that are actually written to the Root Tree is determined by a file described in the Hall A C++ Analyzer Documentation topic "Defining the Output".

{maketoc}

!Coordinate Systems

There are three ((coordinate systems)) used:

__Lab Coordinates__ - Hall coordinate system where y goes against gravity, z is in the direction of the beam, and x is to the left when looking down the beam

__Target Coordinates__ - Origin at the center of the target. x goes with gravity, z is parallel to the ground in the direction towards the center of the BigBite drift chambers. y is to the left looking down z

__Detector Coordinates__ - Origin specified by center of the first
plane of the drift chambers. x is "down" in the dispersion direction, z is in the nominal direction of particles such that z = 0 is defined by the first plane of the chamber. y is defined so we have a right handed coordinate system.

!General Global Variables
Global variables defined that are not specifically associated with the BigBite or Neutron Spectrometer arms.

!!Run and Event Information
||__tag__|__description__
g.runnum|Run Number
g.runtype|CODA run type
g.runtime|CODA run time
g.evnum|Event Number
g.evtyp|Event Type
g.evlen|Event Length
g.helicity|Beam Helicity
g.timestamp|Time Stamp||

!Drift Chamber Specific Variables

||__tag__|__description__
B.dc.trackskipped|Bit 0 too busy, no tracking attempted
|Bit 1 tracking was done but reached soft max, skipped some groups
|Bit 2 tracking was done but reached hard max, skipped some groups
B.dc.ncall|Number of calls to THaMWDC::AllCombos()
B.dc.ngrp|Number of tracking groups considered
B.dc.estncall|Estimation of calls to THaMWDC::AllCombos()
B.dc.estngrp|Estimated number of groups
B.dc.cproctime|Amount of time spent in coarse processing (s)
B.dc.fproctime|Amount of time spent in fine processing (s)
||
!MWDC Plane Variables

Global variables associated with the individual chamber planes have labels of the form B.dc..tag. For example, the number of hits in plane v2 can be accessed using the label B.dc.v2.nhit.

!!(THaMWDCHit) TClonesArray* fHits

An fHits array is created for each chamber plane and contains the wire hit information for that plane.

||__tag__| __size__| __default__| __note__| __defining function__| __description__
nhit| [[1] | NULL| 1| THaMWDCPlane::Decode| Number of hits
wire| [[nhit]| NA| |THaMWDCPlane::Decode| wire
rawtime| [[nhit]| NA| |THaMWDCPlane::Decode| Raw TDC time of hit
time| [[nhit]| NA| 2 |THaMWDCPlane::Decode| Drift time (nsec)
offset| [[nhit]| 0.0| | THaMWDCPlane::Decode| TDC offset parameter (nsec)
myref|[[nhit]| 0.0| | THaMWDCPlane::Decode| Time of reference chan (nsec)
dist|[[nhit]| 0.0| | | ?
track| [[nhit]| -1| | |?
showercut|[[nhit]|FALSE| |THaMWDC::ConstructTracks | Boolean value if hit passed shower cuts||

Note 1: To be added into the fHits array, the wire number must be valid. If the no neg ativ e flag is TRUE, the time must be between fMinTime and fMaxTime

Note 2: The driftime is computed as time = rawtime(T DC calibration)-T DC Of f set-Ref erenceC hannelT ime If the reference channel time is not valid, it is not subtracted off, but the hit is stored and fRefOkay is set to FALSE.

!!Parallel Drift Chamber Arrays

Array sizes set to be the number of wires in the plane and map to the wire number. The index of the array is the wire number.

||__tag__| __size__| __default__| __note__| __defining function__| __description__
rawtimeof|[[nWires]| -1e35| | THaMWDCPlane::Decode| Raw TDC Time
cortimeof|[[nWires]| -1e35 | |THaMWDCPlane::Decode| Drift time (nsec)
NumHitsof|[[nWires]| 0| |THaMWDCPlane::Decode| Number of hits on this wire
reftimeof|[[nRefWires]| -2e35| |THaMWDCPlane::Decode| Time of reference channel (nsec)
chi2 |[[nWires]| 0| |THaMWDCGroup::CalcChi2 | Chi squared contribution in track
cchi2 |[[nWires]| 0| |THaMWDCGroup::CalcChi2 | Chi squared contribution in coarse track||

!!Additional Plane Data

||__tag__| __size__| __default__| __note__| __defining function__| __description__
refchokay|[[1]| true| | THaMWDCPlane::Decode| All reference channels in plane are OK||

!BigBite Variables

Global variables associated with the BigBIte tracks are of the form B.tag.

!!(THaTrack) TClonesArray* fTracks

An fTracks array is created in the THaSpectrometer class. The tracks are defined in the BigBite detectorframe coordinate system with x towards higher momentum (downwards) z perpendicular to the wire chamber planes in the direction of the particle's momentum and y determined by a right-handed coordinate system. The x- and y- intercepts are defined at z=0. (The first chamber plane.)

!!!Basic Tracking Variables
||__tag__| __size__| __default__| __note__| __defining function__| __description__
tr.n |[[1]| NULL| |THaMWDC::ConstructTracks| Number of tracks found
tr.x |[[tr.n]| NA| | THaMWDC::ConstructTracks| Track X in detector coords at z=0 in meters
tr.y |[[tr.n]| NA| |THaMWDC::ConstructTracks|Track Y in detector coords at z=0 in meters
tr.xp|[[tr.n]| NA| | THaMWDC::ConstructTracks| Track slope dx/dz (tangent theta) in detector coords
tr.yp |[[tr.n]| NA| | THaMWDC::ConstructTracks|Track slope dy/dz (tanget phi) in detector coords
tr.chi2|[[tr.n]| NA| | THaMWDC::ConstructTracks| Chi squared (not reduced)
tr.ndof|[[tr.n]| NA| |THaMWDC::ConstructTracks| Number of degrees of freedom||

!!!Extended Tracking Variables
||__tag__| __size__| __default__| __note__| __defining function__| __description__
tr.p|tr.n|NA| |THaMWDC::FindVertices |Track momentum magnitude (GeV/c)
tr.px|tr.n|NA| | THaMWDC::FindVertices |Track momentum magnitude (GeV/c) times directional cosine in x direction in Lab Coordinates
tr.py|tr.n|NA| | THaMWDC::FindVertices |Track momentum magnitude (GeV/c) times directional cosine in y direction in Lab Coordinates
tr.pz|tr.n|NA| | THaMWDC::FindVertices |Track momentum magnitude (GeV/c) times directional cosine in y direction in Lab Coordinates
tr.vx|tr.n|NA| | THaMWDC::FindVertices |Track vertex x coord in lab coordinates (meters)
tr.vy|tr.n|NA| |THaMWDC::FindVertices |Track vertex y coord in lab coordinates (meters)
tr.vz|tr.n|NA| | THaMWDC::FindVertices |Track vertex z coord in lab coordinates (meters)
tr.fT.x|tr.n|NA| | THaMWDC::FindVertices |Front track (before magnet interaction) x coordinate at z=0 in target coordinates (meters)
tr.fT.y|tr.n|NA| | THaMWDC::FindVertices |Front track y coordinate at z=0 in target coordinates (meters)
tr.fT.xp|tr.n|NA| | THaMWDC::FindVertices |Front track slope dx/dz (tangent theta) in target coords
tr.fT.yp|tr.n|NA| | THaMWDC::FindVertices |Front track slope dy/dz (tangent phi) in target coords
tr.defang|tr.n|NA| |THaMWDC::FindVertices |Deflection angle (radians)
tr.beam.x|tr.n|NA| |THaMWDC::FindVertices |Track x coordinate at beam z in detector coords (meters)
tr.beam.y|tr.n|NA| |THaMWDC::FindVertices |Track y coordinate at beam z in detector coords (meters)
tr.beam.z|tr.n|NA| |THaMWDC::FindVertices |Track z coordinate at beam z in detector coords (meters)||

!!!Coarse Tracking Variables

B.ctr.*

These variables are identical to those above for B.tr.*, however, they are calculated using the coarse tracks. They are available when the SaveCoarseTracks() function is called in the THaBBe class.

See also:
[http://hallaweb.jlab.org/experiment/E02-013/offline/GlobalVars.pdf|BigBite Global and Drift Chamber Variables]
[http://hallaweb.jlab.org/experiment/E02-013/offline/BBextendedvars.txt|BigBite Tracking and extended Drift Chamber Variables]