Tracking Efficiencies
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Intro
Hit patterns obtained from the tracking detectors that are not sufficient for a track reconstruction contribute to tracking inefficiencies. The main sources for these inefficiencies are if either too few wires along a track fire (plane efficiencies) or if too many wires in a single event fire (maxmul cut).
Essentials
Permutated Plane Efficiencies
A small number of hits in the tracking chambers may imply that HRC is unable to reconstruct a track from the hits. Even though it is impossible to calculate directly the fraction of reconstructed tracks from all tracks which should have been reconstructed, it is possible to determine efficiencies for single tracking planes, and then to combine them to the efficiency by which HRC finds a track.
The plane efficiency for tracking plane i is defined as the ratio of the number of tracks with a hit in plane i to the total number of tracks selected for plane i.
ACE
ACE is a program which calculates the plane efficiencies in the various tracking detectors from the tracks previously reconstructed by HRC. Global plane efficiencies (= permutated plane efficiencies) are calculated separately for the front upper half, the front lower half, back upper half, and the back lower half of the spectrometer. The procedure to combine plane efficiencies has to take into account all requirements of HRC made for finding a track. The calculation is performed by ACE by summing up the probabilities for all permutations of firing and not firing planes which would allow a reconstruction by HRC.
Where can I find Permutated Plane Efficiencies in the uDSTs?
The permutated plane efficiency of NOVC tracking is provided in the uDSTs in the table g1TrkEffi. The table contains the permuated plane efficiencies and their errors separately for the front and the back regions in the top and bottom halves. See also the corresponding section on the Standard Cuts page.
The 'maxmul' cut
For events with high multiplicities, not only the CPU time for reconstruction increases drastically, but also the probability increases to find hits in a straight line which do not correspond to a real particle. The track reconstruction code HRC assumes that events for which the maximum number of hits per tracking plane (maxmul) exceeds 22 are mainly caused by showers of particles in the tracking detectors and should not be reconstructed. In the standard configuration, HRC applies a cut of maxmul<=22.
More Info
- The permutated plane efficienies are displayed vs. run number in the offline data quality plots:
uDST example for 06d0
slow production example for 07b0
- The tracking efficienies are not taken into account by default in the BadBurst lists (Data Quality Masks). Only for certain years, one badbit is reserved for the efficiencies:
for example bit 26 in 06d0
- Tracking: Wolfgang Wander's thesis german
- ACE: Machiel Kolstein thesis [1]
- Tracking related effects are relevant for the determination of absolute cross sections, see for example ps pdf (Ph.D. thesis).