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:
|
| 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.
Tracks
Extends Trajectory. A collection of state vectors which describe the position, momentum, and charge at various points in the DC.
Program Flowchart
