StBeamBackMaker Class Reference
Beam background tracker in the TPC. More...
#include <StBeamBackMaker.h>
Public Member Functions | |
| StBeamBackMaker (const char *name="StBeamBackMaker") | |
| Constructor. | |
| Int_t | Make () |
| Run the tracker on the current event. | |
Detailed Description
Beam background tracker in the TPC.The beam background tracker in the TPC is a maker that is meant to run in bfc.C (big full chain) after TPC hits have been created and stored in the TPC hit collection of the StEvent structure and after ITTF, the STAR tracking software, has run. The beam background tracker then scavenges leftover TPC Hits to look for beam background tracks parallel to the z-axis that presumably originate upstream of either the blue or yellow beam scrapping against focussing/steering magnet elements in the beamline and spraying particles that shower into the IR (intersection region). Detectors at forward rapidity, such as the Endcap EMC, are most affected by this type of beam background events and this has been confirmed by several physics analyses.
The tracker algorithm is:
1. Collect all leftover TPC hits into a C++ multiset with their z-coordinate used as a key. This ensures the hits are sorted in ascending z-ccordinate and the insert and delete times are O(logN). 2. Look for track seeds. Start a track seed with the hit with the smallest z-coordinate. Keep adding hits to the track seed so long as the radial distance in xy between the the centroid and the hit is less than MAX_R_DISTANCE (= 5 cm).
3. Weed out track seeds with less than MIN_TRACK_SEED_HITS (= 100) hits.
4. Perform linear fits in the zx and zy-planes. Save only tracks that have absolute slopes in both planes less than MAX_SLOPE (= 0.1). At the same time, add to the track available hits that are within a radial distance of 5 cm of the fitted line.
5. Merge linear tracks if both end points of the first track are within 5 cm of the centroid of the track in the xy-plane.
6. Refit the track and remove hits that are not within a radius of 5 cm in the xy-plane of the refitted line. Pileup tracks are discarded. A non-pileup track has at least 4 hits in each of the following TPC zones along the beamline:
a. -200 <= z < -150 cm (far east) b. -50 <= z < 0 cm (near east) c. 0 <= z < 50 cm (near west) d. 150 <= z < 200 cm (far west)
7. Convert all tracks to StTrack for storage into StEvent:
a. The track key is the highest key from existing tracks in StEvent incremented by 1. b. The track flag is set to 901 (beam background track in TPC). c. The track encoded method is kLine3D. d. The track origin is the point (x-intercept, y-intercept, 0) e. The track momentum is set to (dx/dz, dy/dz, 1), then the magnitude is adjusted to 999 GeV/c. This is a simple measure to prevent unsuspecting folks from accidentally using these beam background tracks as genuine charged particles from collisions in the STAR detector in their physics analysis. f. The first point, last point, hits, number of hits is saved in StTrackDetectorInfo and StTrackFitTraits.
8. In StEvent, trackNodes() and trackDetectorInfo() are updated.
Definition at line 96 of file StBeamBackMaker.h.
Constructor & Destructor Documentation
| StBeamBackMaker::StBeamBackMaker | ( | const char * | name = "StBeamBackMaker" |
) | [inline] |
Constructor.
- Parameters:
-
Name of the instance of StBeamBackMaker
Definition at line 102 of file StBeamBackMaker.h.
The documentation for this class was generated from the following files:
- StBeamBackMaker/StBeamBackMaker.h
- StBeamBackMaker/StBeamBackMaker.cxx
