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".

-=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||

-=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.

===Double t fRawT[[nWires], fCorT[[nWires], fRefT[[nRefWires], and Int t fTCounter[[nWires]===

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)||

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