DF Definitions of Tracking Elements

Below are definitions of the structures used in the clas12 dc reconstructions.

Hits

Hit.java

The basic building block of the other structures used in the reconstruction, Hits are simply a representation of a drift chamber wire interaction. It stores all of the relevant information for identifying a wire:

Sector	Which of the six radial sectors the hit is in.
Superlayer	Which of the six superlayers the hit is in.
Layer	Which of the six wire plane layers within the superlayer the hit is in.
Wire	The wire within the layer the hit is in.
TDC	The Time-to-Digital Converter which processed the hit

And some information about the interaction itself:

ID	The hit index in the Evio column.
Cell Size	The size of the wire cell. The wires are arranged in hexagonal cells, but different layers have different sizes of hexagons.
DoCA Error	Uncertainty in the distance of closest approach time.

It should be noted that this implements the Comparable interface; that is to say the the function compareTo() has been implemented such that hits can be absolutely ordered. The ordering appears to be exactly as you would expect: Sector > SuperLayer > Layer > Wire. This allows you to call the built in sort function of ArrayLists of Hits (such as Clusters).

FittedHit.java

An extension of Hit.java which is meant to be used in fitted clusters, this includes additional information:

X	X at Z in local coordinate system
XMP	X at the midplane in the sector coordinate system
Z	Z in the Sector Coordinate System
lX	X in the local coordinate system; used in hit-based fit to cluster.
lY	Y in the local coordinate system; used in hit-based fit to cluster.
Residual	Cluster line to the wire position residual
Time Residual	Cluster line to wire position time residual
Left-Right Ambiguity	Gives a value to handle the left-right ambiguity:
Quality Fac	?
Tracking Status	A flag which denotes the tracking status: -1 => not fit 0 => hit-based tracking fit 1 => time-based tracking fit.
Cluster Fit DoCA	?
Track Fit DoCA	?
Time to Distance	?
Beta	?
Associated State Vector	?
DoCA	?
B	?
lr	?
Associated Cluster ID	?
Remove Flag	?
Associated HB Track ID	?
Associated TB Track ID	?
CrossDirIntersWire	?
SignalPropagAlongWire	?
SignalPropagTimeAlongWire	?
T0	?
tFlight	?
tProp	?
tStart	?
Time	?

Clusters

Clusters are groups of hits within each superlayer.

Segments

A type of FittedCluster that has been pruned of bad hits. Note that in the code this isn't reflected via inheritance, it is simply comment this way.

Crosses

Crosses are used to find tracks. They are implemented as an ArrayList of Segments. The cross "object" is simply a point in 3D space and a direction unit vector.

Program Flowchart